INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
UNIT-1 (PART-I)
Introduction to transportation engineering
Overview
Mobility is a basic human need. From the times immemorial, everyone
travels either for food or leisure. A closely associated need is the transport
of raw materials to a manufacturing unit or finished goods for consumption.
Transportation fulfils these basic needs of humanity. Transportation plays a
major role in the development of the human civilization. For instance, one
could easily observe the strong correlation between the evolution of human
settlement and the proximity of transport facilities. Also, there is a strong
correlation between the quality of transport facilities and standard of living,
because of which society places a great expectation from transportation
facilities. In other words, the solution to transportation problems must be
analytically based, economically sound, socially credible, environmentally
sensitive, practically acceptable and sustainable. Alternatively, the
transportation solution should be safe, rapid, comfortable, convenient,
economical, and eco-friendly for both men and material.
1 Transportation system
In the last couple of decades transportation systems analysis has
emerged as a recognized profession. More and more government
organizations, universities, researchers, consultants, and private
industrial groups around the world are becoming truly multi-modal in their
orientation and are opting a systematic approach to transportation
problems.
1.1 Diverse characteristics
The characteristics of transportation system that makes it diverse and
complex are listed below:
1. Multi-modal: Covering all modes of transport; air, land, and sea for
both passenger and freight.
2. Multi-sector: Encompassing the problems and viewpoints of
government, private industry, and public.
3. Multi-problem: Ranging across a spectrum of issues that includes
national and international policy, planning of regional system, the
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
location and design of specific facilities, carrier management issues,
regulatory, institutional and financial policies.
4. Multi-objective: Aiming at national and regional economic
development, urban development, environment quality, and social
quality, as well as service to users and financial and economic
feasibility.
5. Multi-disciplinary: Drawing on the theories and methods of
engineering, economics, operations research, political science,
psychology, other natural, and social sciences, management and
law.
1.2 Study context
The context in which transportation system is studied is also very diverse
and are mentioned below:
1. Planning range: Urban transportation planning, producing long
range plans for 5-25 years for multi-modal transportation systems in
urban areas as well as short range programs of action for less than
five years.
2. Passenger transport: Regional passenger transportation, dealing
with inter-city passenger transport by air, rail, and highway and
possible with new modes.
3. Freight transport: Routing and management, choice of different
modes of rail and truck.
4. International transport: Issues such as containerization, inter-modal
co-ordination.
1.3 Background: A changing world
The strong interrelationship and the interaction between transportation
and the rest of the society especially in a rapidly changing world is
significant to a transportation planner. Among them four critical
dimensions of change in transportation system can be identified; which
form the background to develop a right perspective.
1. Change in the demand: When the population, income, and landuse pattern changes, the pattern of demand changes; both in the
amount and spatial distribution of that demand.
2. Changes in the technology: As an example, earlier, only two
alternatives (bus transit and rail transit) were considered for urban
transportation. But, now new systems like LRT, MRTS, etc offer a
variety of alternatives.
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
3. Change in operational policy: Variety of policy options designed
to improve the efficiency, such as incentive for car-pooling, bus fare,
road tolls etc.
4. Change in values of the public: Earlier all beneficiaries of a
system was monolithically considered as users. Now, not one
system can be beneficial to all, instead one must identify the target
groups like rich, poor, young, work trip, leisure etc.
2 Role of transportation engineer
In spite of the diversity of problem types, institutional contexts and
technical perspectives there is an underlying unity: a body of theory and
set of basic principles to be utilized in every analysis of transportation
systems. The core of this is the transportation system analysis approach.
The focus of this is the interaction between the transportation and activity
systems of region. This approach is to intervene, delicately and
deliberately in the complex fabric of society to use transport effectively in
coordination with other public and private actions to achieve the goals of
that society. For this the analyst must have substantial understanding of
the transportation systems and their interaction with activity systems;
which requires understanding of the basic theoretical concepts and
available empirical knowledge.
2.1 Basic premise of a transportation system
The first step in formulation of a system analysis of transportation system
is to examine the scope of analytical work. The basic premise is the
explicit treatment of the total transportation system of region and the
interrelations between the transportation and socioeconomic context.
They can be stated as:
P1
The total transportation system must be viewed as a single multimodal system.
P2
Considerations of transportation system cannot be separated from
considerations of social, economic, and political system of the
region.
This follows the following steps for the analysis of transportation system:
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
•
•
•
•
S1 Consider all modes of transportation
S2 Consider all elements of transportation like persons, goods,
carriers (vehicles), paths in the network facilities in which vehicles are
going, the terminal, etc.
S3 Consider all movements of passengers and goods for every O-D
pair.
S4 Consider the total trip for every flows for every O-D over all modes
and facilities.
As an example, consider the study of intra-city passenger transport in metro
cities.
•
•
•
•
Consider all modes: i.e. rail, road, buses, private automobiles, trucks,
new modes like LRT, MRTS, etc.
Consider all elements like direct and indirect links, vehicles that can
operate, terminals, transfer points, intra-city transit like taxis, autos,
urban transit.
Consider diverse pattern of O-D of passenger and goods.
Consider service provided for access, egress, transfer points and midblock travel etc.
Once all these components are identified, the planner can focus on elements
that are of real concern.
3 Major disciplines of transportation
Transportation engineering can be broadly consisting of the four major
parts:
•
•
•
•
Transportation Planning
Geometric Design
Pavement Design
Traffic Engineering
A brief overview of the topics is given below: Transportation planning deals
with the development of a comprehensive set of action plan for the design,
construction and operation of transportation facilities.
3.1 Transportation planning
Transportation planning essentially involves the development of a transport
model which will accurately represent both the current as well as future
transportation system.
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
3.2 Geometric design
Geometric design deals with physical proportioning of other transportation
facilities, in contrast with the structural design of the facilities. The topics
include the cross-sectional features, horizontal alignment, vertical
alignment and intersections. Although there are several modes of travel like
road, rail, air, etc. the underlying principles are common to a great extent.
Therefore, emphasis will be normally given for the geometric design of
roads.
3.3 Pavement analysis and design
Pavement design deals with the structural design of roads, both
(bituminous and concrete), commonly known as (flexible pavements and
rigid pavements) respectively. It deals with the design of paving materials,
determination of the layer thickness, and construction and maintenance
procedures. The design mainly covers structural aspects, functional
aspects, drainage. Structural design ensures the pavement has enough
strength to withstand the impact of loads, functional design emphasizes on
the riding quality, and the drainage design protects the pavement from
damage due to water infiltration.
3.4 Traffic engineering
Traffic engineering covers a broad range of engineering applications with a
focus on the safety of the public, the efficient use of transportation resources,
and the mobility of people and goods. Traffic engineering involves a variety
of engineering and management skills, including design, operation, and
system optimization. In order to address the above requirement, the traffic
engineer must first understand the traffic flow behavior and characteristics
by extensive collection of traffic flow data and analysis. Based on this
analysis, traffic flow is controlled so that the transport infrastructure is used
optimally as well as with good service quality. In short, the role of traffic
engineer is to protect the environment while providing mobility , to preserve
scarce resources while assuring economic activity, and to assure safety and
security to people and vehicles, through both acceptable practices and hightech communications.
4 Other important disciplines
In addition to the four major disciplines of transportation, there are several
other important disciplines that are being evolved in the past few decades.
Although it is difficult to categorize them into separate well defined
disciplines because of the significant overlap, it may be worth the effort to
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
highlight the importance given by the transportation community. They can
be enumerated as below:
4.1
4.2
4.3
4.4
4.5
Public transportation: Public transportation or mass
transportation deals with study of the transportation system that
meets the travel need of several people by sharing a vehicle.
Generally, this focuses on the urban travel by bus and rail transit.
The major topics include characteristics of various modes;
planning, management and operations; and policies for promoting
public transportation.
Financial and economic analysis Transportation facilities
require large capital investments. Therefore, it is imperative that
whoever invests money should get the returns. When government
invests in transportation, its objective is not often monetary
returns; but social benefits. The economic analysis of
transportation project tries to quantify the economic benefit which
includes saving in travel time, fuel consumption, etc. This will help
the planner in evaluating various projects and to optimally allocate
funds. On the contrary, private sector investments require
monetary profits from the projects. Financial evaluation tries to
quantify the return from a project.
Environmental impact assessment The depletion of fossil fuels
and the degradation of the environment has been a severe
concern of the planners in the past few decades. Transportation;
in spite of its benefits to the society is a major contributor to the
above concern. The environmental impact assessment attempts in
quantifying the environmental impacts and tries to evolve
strategies for the mitigation and reduction of the impact due to
both construction and operation. The primary impacts are fuel
consumption, air pollution, and noise pollution.
Accident analysis and reduction One of the silent killers of
humanity is transportation. Several statistics evaluates that more
people are killed due to transportation than great wars and natural
disasters. This discipline of transportation looks at the causes of
accidents, from the perspective of human, road, and vehicle and
formulate plans for the reduction.
Intelligent transport system with advent to computers,
communication, and vehicle technology, it is possible in these
days to operate transportation system much effectively with
significant reduction in the adverse impacts of transportation.
Intelligent transportation system offers better mobility, efficiency,
and safety with the help of the state-of-the-art-technology.
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
In addition, disciplines specific to various modes are also common. This
includes railway engineering, port and harbour engineering, and airport
engineering.
Summary
Transportation engineering is a very diverse and multidisciplinary field, which
deals with the planning, design, operation and maintenance of transportation
systems. Good transportation is that which provides safe, rapid, comfortable,
convenient, economical, and environmentally compatible movement of both
goods and people. This profession carries a distinct societal responsibility.
Transportation planners and engineers recognize the fact that transportation
systems constitute a potent force in shaping the course of regional
development. Planning and development of transportation facilities generally
raises living standards and enhances the aggregate of community values.
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
Introduction to Highway Engineering
Overview
Road transport is one of the most common mode of transport. Roads in the
form of trackways, human pathways etc. were used even from the prehistoric times. Since then many experiments were going on to make the
riding safe and comfort. Thus road construction became an inseparable part
of many civilizations and empires. In this chapter we will see the different
generations of road and their characteristic features. Also we will discuss
about the highway planning in India.
1 History of highway engineering
The history of highway engineering gives us an idea about the roads of
ancient times. Roads in Rome were constructed in a large scale and it
radiated in many directions helping them in military operations. Thus, they
are considered to be pioneers in road construction. In this section we will see
in detail about Ancient roads, Roman roads, British roads, French roads etc.
1.1 Ancient Roads
The first mode of transport was by foot. These human pathways would have
been developed for specific purposes leading to camp sites, food, streams
for drinking water etc. The next major mode of transport was the use of
animals for transporting both men and materials. Since these loaded animals
required more horizontal and vertical clearances than the walking man, track
ways emerged. The invention of wheel in Mesopotamian civilization led to
the development of animal drawn vehicles. Then it became necessary that
the road surface should be capable of carrying greater loads. Thus roads
with harder surfaces emerged. To provide adequate strength to carry the
wheels, the new ways tended to follow the sunny drier side of a path. These
have led to the development of foot-paths. After the invention of wheel,
animal drawn vehicles were developed and the need for hard surface road
emerged. Traces of such hard roads were obtained from various ancient
civilization dated as old as 3500 BC. The earliest authentic record of road
was found from Assyrian empire constructed about 1900 BC.
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
1.2 Roman roads
The earliest large-scale road construction is attributed to Romans who
constructed an extensive system of roads radiating in many directions from
Rome. They were a remarkable achievement and provided travel times
across Europe, Asia minor, and north Africa. Romans recognized that the
fundamentals of good road construction were to provide good drainage,
good material and good workmanship. Their roads were very durable, and
some are still existing. Roman roads were always constructed on a firm formed subgrade strengthened where necessary with wooden piles. The
roads were bordered on both sides by longitudinal drains. The next step was
the construction of the agger. This was a raised formation up to a 1 meter
high and 15 m wide and was constructed with materials excavated during
the side drain construction. This was then topped with a sand leveling
course. The agger contributed greatly to moisture control in the pavement.
The pavement structure on the top of the agger varied greatly. In the case of
heavy traffic, a surface course of large 250 mm thick hexagonal flag stones
were provided. A typical cross section of roman road is given in Figure 1 The
main features of the Roman roads are that they were built straight regardless
of gradient and used heavy foundation stones at the bottom. They mixed
lime and volcanic pozzolana to make mortar and they added gravel to this
mortar to make concrete. Thus, concrete was a major Roman road making
innovation
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
1.3 French roads
Figure 2: French roads
The next major development in the road construction occurred during the
regime of Napoleon. The significant contributions were given by Tresaguet
in 1764 and a typical cross section of this road is given in Figure 1. He
developed a cheaper method of construction than the lavish and locally
unsuccessful revival of Roman practice. The pavement used 200 mm pieces
of quarried stone of a more compact form and shaped such that they had at
least one flat side which was placed on a compact formation. Smaller pieces
of broken stones were then compacted into the spaces between larger
stones to provide a level surface. Finally the running layer was made with a
layer of 25 mm sized broken stone. All this structure was placed in a trench
in order to keep the running surface level with the surrounding country side.
This created major drainage problems which were counteracted by making
the surface as impervious as possible, cambering the surface and providing
deep side ditches. He gave much importance for drainage. He also
enunciated the necessity for continuous organized maintenance, instead of
intermittent repairs if the roads were to be kept usable all times. For this he
divided the roads between villages into sections of such length that an entire
road could be covered by maintenance men living nearby.
1.4 British roads
Figure 3: British roads
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
The British government also gave importance to road construction. The
British engineer John Macadam introduced what can be considered as the
first scientific road construction method. Stone size was an important
element of Macadam recipe. By empirical observation of many roads, he
came to realize that 250 mm layers of well compacted broken angular
stone would provide the same strength and stiffness and a better running
surface than an expensive pavement founded on large stone blocks. Thus,
he introduced an economical method of road construction.
The mechanical interlock between the individual stone pieces provided
strength and stiffness to the course. But the inter particle friction abraded
the sharp interlocking faces and partly destroy the effectiveness of the
course. This effect was overcome by introducing good quality interstitial
finer material to produce a well-graded mix. Such mixes also proved less
permeable and easier to compact. A typical cross section of British roads is
given in Figure 3.
1.5 Modern roads
The modern roads by and large follow Macadam's construction method. Use
of bituminous concrete and cement concrete are the most important
developments. Various advanced and cost-effective construction
technologies are used. Development of new equipment’s help in the faster
construction of roads. Many easily and locally available materials are tested
in the laboratories and then implemented on roads for making economical
and durable pavements.
Scope of transportation system has developed very largely. Population of the
country is increasing day by day. The life style of people began to change.
The need for travel to various places at faster speeds also increased. This
increasing demand led to the emergence of other modes of transportation
like railways and travel by air. While the above development in public
transport sector was taking place, the development in private transport was
at a much faster rate mainly because of its advantages like accessibility,
privacy, flexibility, convenience and comfort. This led to the increase in
vehicular traffic especially in private transport network. Thus, road space
available was becoming insufficient to meet the growing demand of traffic
and congestion started. In addition, chances for accidents also increased.
This has led to the increased attention towards control of vehicles so that the
transport infrastructure was optimally used. Various control measures like
traffic signals, providing roundabouts and medians, limiting the speed of
vehicle at specific zones etc. were implemented.
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
With the advancement of better roads and efficient control, more and more
investments were made in the road sector especially after the World wars.
These were large projects requiring large investment. For optimal utilization
of funds, one should know the travel pattern and travel behaviour. This has
led to the emergence of transportation planning and demand management.
2 Highway planning in India
Excavations in the sites of Indus valley, Mohenjo-dero and Harappan
civilizations revealed the existence of planned roads in India as old as 25003500 BC. The Mauryan kings also built very good roads. Ancient books
like Arthashastra written by Kautilya, a great administrator of the Mauryan
times, contained rules for regulating traffic, depths of roads for various
purposes, and punishments for obstructing traffic.
During the time of Mughal period, roads in India were greatly improved.
Roads linking North-West and the Eastern areas through gang etic plains
were built during this time.
After the fall of the Mughals and at the beginning of British rule, many existing
roads were improved. The construction of Grand-Trunk road connecting
North and South is a major contribution of the British. However, the focus
was later shifted to railways, except for feeder roads to important stations.
3 Modern developments
The first World war period and that immediately following it found a rapid
growth in motor transport. So need for better roads became a necessity. For
that, the Government of India appointed a committee called Road
development Committee with Mr.M.R. Jayakar as the chairman. This
committee came to be known as Jayakar committee.
3.1 Jayakar Committee
In 1927 Jayakar committee for Indian road development was appointed. The
major recommendations and the resulting implementations were:
•
Committee found that the road development of the country has
become beyond the capacity of local governments and suggested that
Central government should take the proper charge considering it as a
matter of national interest.
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
•
•
•
•
They gave more stress on long term planning programme, for a period
of 20 years (hence called twenty-year plan) that is to formulate plans
and implement those plans with in the next 20 years.
One of the recommendations was the holding of periodic road
conferences to discuss about road construction and development. This
paved the way for the establishment of a semi-official technical body
called Indian Road Congress (IRC) in 1934
The committee suggested imposition of additional taxation on motor
transport which includes duty on motor spirit, vehicle taxation, license
fees for vehicles plying for hire. This led to the introduction of a
development fund called Central road fund in 1929. This fund was
intended for road development.
A dedicated research organization should be constituted to carry out
research and development work. This resulted in the formation of
Central Road Research Institute (CRRI) in 1950.
3.2 Nagpur road congress 1943
The second World War saw a rapid growth in road traffic and this led to the
deterioration in the condition of roads. To discuss about improving the
condition of roads, the government convened a conference of chief
engineers of provinces at Nagpur in 1943. The result of the conference is
famous as the Nagpur plan.
•
•
•
•
•
A twenty-year development programme for the period (1943-1963)
was finalized. It was the first attempt to prepare a co-ordinated road
development programme in a planned manner.
The roads were divided into four classes:
o National highways which would pass through states, and
places having national importance for strategic, administrative
and other purposes.
o State highways which would be the other main roads of a state.
o District roads which would take traffic from the main roads to
the interior of the district. According to the importance, some
are considered as major district roads and the remaining
as other district roads.
o Village roads which would link the villages to the road system.
The committee planned to construct 2 lakh kms of road across the
country within 20 years.
They recommended the construction of star and grid pattern of roads
throughout the country.
One of the objectives was that the road length should be increased
so as to give a road density of 16kms per 100 sq.km
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
3.3 Bombay road congress 1961
The length of roads envisaged under the Nagpur plan was achieved by
the end of it, but the road system was deficient in many respects. The
changed economic, industrial and agricultural conditions in the country
warranted a review of the Nagpur plan. Accordingly, a 20-year plan was
drafted by the Roads wing of Government of India, which is popularly
known as the Bombay plan. The highlights of the plan were:
•
•
•
•
•
It was the second 20-year road plan (1961-1981)
The total road length targeted to construct was about 10 lakhs.
Rural roads were given specific attention. Scientific methods of
construction were proposed for the rural roads. The necessary
technical advice to the Panchayaths should be given by State
PWD's.
They suggested that the length of the road should be increased so
as to give a road density of 32kms/100 sq.km
The construction of 1600 km of expressways was also then included
in the plan.
3.4 Lucknow road congress 1984
This plan has been prepared keeping in view the growth pattern
envisaged in various fields by the turn of the century. Some of the salient
features of this plan are as given below:
•
•
•
•
•
•
This was the third 20-year road plan (1981-2001). It is also
called Lucknow road plan.
It aimed at constructing a road length of 12 lakh kilometres by the
year 1981 resulting in a road density of 82kms/100 sq.km
The plan has set the target length of NH to be completed by the end
of seventh, eighth and ninth five-year plan periods.
It aims at improving the transportation facilities in villages, towns etc.
such that no part of country is farther than 50 km from NH.
One of the goals contained in the plan was that expressways should
be constructed on major traffic corridors to provide speedy travel.
Energy conservation, environmental quality of roads and road safety
measures were also given due importance in this plan.
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
Summary
This lecture covers a brief history of highway engineering, highlighting
the developments of road construction. Significant among them are
Roman, French, and British roads. British road construction practice
developed by Macadam is the most scientific and the present-day
roads follows this pattern. The highway development and classification
of Indian roads are also discussed. The major classes of roads include
National Highway, State highway, District roads, and Village roads.
Finally, issues in highway alignment are discussed.
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
HIGHWAY PLANNING
1 Objects of highway planning:
Planning is considered as a pre-requisite before attempting any
development programme in the present era. This is particularly true for
any engineering project, as planning is the basic requirement for any
new project or an expansion programme. Thus there is a need for
planned development of the road network and the links. Highway
planning is of great importance when the funds available are limited
whereas the total requirement is much higher. In developing countries
like India it is important to utilize the available funds in the best possible
manner by resorting to best planning principles.
1.1 The objects of highway planning are briefly given below:
(a) To plan overall road network for efficient and safe traffic operation,
but at minimum cost. Here the costs of construction, maintenance and
resurfacing or strengthening of pavement layers and the vehicle
operation cost are to be given due consideration
(b) To arrive at the road system and the lengths of different categories
of roads which could provide maximum utility and could be constructed
within the available resources during the plan period under
consideration
(c) To divide the overall plan into phases and to decide priorities
(d) To fix up date-wise priorities for development of each road link
based on utility as the main criterion for phasing the road development
programme
(e) To plan for future requirements and improvements of roads in view
of anticipated developments
(f) To work out suitable financing system Phases of highway planning
Highway planning includes the following phases:
(a) Assessment of road length requirement for an area (it may be a
district, state or the whole country)
(b) Preparation of master plan showing the phasing of plan in five year
plans or annual plans In order to plan the road system in the selected
region, state or country, different studies and surveys are to be carried
out to collect the data required. The data collected are to be processed
and analysed to arrive at the best possible road network and to arrive
at the optimum length of the road system.
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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(Prepared By: Mr. Saurabh, Assistant Professor, CE)
1.2 Classification of Roads
Different approaches
Types of roads
The roads are generally classified into two categories, depending on whether
they can be used during different seasons of the year:
(i) All-weather roads and
(ii) Fair-weather roads
All-weather roads are those which are negotiable during all seasons of
the year, except at major river crossings where some interruption to
traffic is permissible up to a certain extent, but the road pavement
should be negotiable during all weathers. On 'fair weather roads' the
traffic may be interrupted during monsoon season at causeways where
streams may overflow across the road.
Based on the type of the carriageway or the road pavement, the roads are
classified as `paved roads' and `un-paved roads'. The roads with a hard
pavement surface on the carriageway are called 'paved roads'. The roads
without a hard pavement surface on the carriageway are called 'unpaved
roads'. Earth roads and gravel roads may be called unpaved roads.
Based on the type of pavement surfacing provided, the roads may be
classified as `surfaced roads' and `un-surfaced roads. Road pavements with
any type of bituminous surface or cement concrete are called surfaced roads.
The roads which are not provided with a bituminous or cement concrete
surfacing are called un-surfaced roads.
1.3 Methods of classification of roads
The roads are generally classified based on the following:
(a) Traffic volume
(b) Load transported or tonnage
(c) Location and function
The classification based on traffic volume or tonnage has been
arbitrarily fixed by different agencies and there may not be a common
agreement regarding the limits for each of classification group. Based
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
on the traffic volume or flow, the roads are classified as heavy, medium
and low volume roads. These terms are relative and so the limits under
each class should be clearly defined and expressed as vehicles per
day or 'annual average daily traffic', etc. Likewise, the classification
based on load or tonnage is also relative and the roads may be
classified as class L II etc. or class A, B etc. and the limits may be
expressed in terms of tones per day.
The classification based on location and function should therefore be a more
acceptable classification method for a country as they may be defined
clearly.
2 Road classification based on location and function
2.1 Road classification as per Nagpur road plan:
The Nagpur Road Plan classified the roads in India based on location and
function into following five categories and described below:
(i) National Highways (NH)
(ii) State Highways (SH)
(iii)Major District Roads (MDR)
(iv) Other District Roads (ODR) and
(v) Village Roads (VR)
National Highways (NH) are main highways running through the length and
breadth of India, connecting major ports, foreign highways, capitals of large
states and large industrial and tourist centres including roads required for
strategic movements for the defence of India.
All the national highways are assigned the respective numbers. For example,
NHI is the national highway connecting Delhi, Ambala, Jalandhar and
Amritsar (up to Pakistan border); NH-4 connects Thane, Pune, Belgaum,
Hubli, Bangalore, Chittoor and Chennai.
State Highways (SH) are arterial roads of a state, connecting the national
highways of adjacent state, district headquarters and important cities within
the state and serve as the main arteries for traffic to and from district roads.
These highways are considered as main arteries of commerce by road within
a state or a similar geographical unit.
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
Major District Roads (MDR) are important roads within a district serving
areas of production and markets and connecting with other major roads or
main highways of a district.
The MDR has lower speed and geometric design specifications than NH/SH.
Other District Roads (ODR) are roads serving rural areas of production and
providing them with outlet to market centres, taluk headquarters, block
development headquarters or other main roads. These are of lower design
specifications than MDR Village Roads (VR) are roads connecting villages
or groups of villages with each other to the nearest road of a higher category.
It was specified that these village roads should be in essence farm tracks,
but it was desired that the prevalent practice of leaving such tracks to
develop and maintain by themselves should be replaced by a plan for a
designed and regulated system.
Road classification as per third 20-year road development plan, 1981 2001
The road classification system was modified in the third 20-year road
development plan. The roads in the country are now classified into three
classes, for the purpose of transport planning, functional identification,
earmarking administrative jurisdictions and assigning priorities on a road
network.
(i) Primary system
(ii) Secondary system and
(iii) Tertiary system or rural roads Primary system consists of two categories
of highways:
(a) Expressways and
(b) National Highways (NH)
Expressways are a separate class of highways with. Superior facilities and
design standards and are meant as through routes having very high volume
of traffic. The expressways are to be provided with divided carriageways,
controlled access, grade separations at cross roads and fencing. These
highways should permit only fast-moving vehicles. Expressways may be
owned by the Central Government or a State Government, depending on
whether the route is a
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
National Highway or State Highway. The National Highways form the other
main category of primary system in the country.
The Secondary system consists of two categories of roads:
(a) State Highways (SH) and
(b) Major District Roads (MDR)
The Tertiary systems are rural roads and these consist of two categories of
roads:
(a) Other District Road (ODR)
(b) Village Roads (VR)
The definitions of NH, SH, MDR, ODR and VR are the same as given under
classification of roads by Nagpur Road Plan.
3 Road Patterns:
The various road Patterns may be classified as follows:
(a) Rectangular or block pattern
(b) Hexagonal pattern
(c) Radial or star and block pattern
(d) Radial or star and circular pattern
(e) Radial or star and grid pattern
The above types of road patterns have been shown in Fig. a, b, c, d & e.
Each of these patterns has its own advantages and limitations. There can be
a number of other geometric patterns also. The choice of the pattern very
much depends on the locality, the layout of different towns, villages, industrial
and production centres and on the choice of the planning engineer.
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
PLANNING SURVEYS AND INTERPRETATION
1 Planning Surveys
The studies for collecting the factual data for highway planning are known
as 'fact finding studies' or 'planning surveys. The fact - finding studies point
to an intelligent approach for planning and these studies should be carried
out if the highway programme is to be protected from inconsistent and
short-sighted policies. Planning based on the factual data and analysis
may be considered scientific and sound. The planning surveys consist of
the following studies:
(a) Economic studies
(b) Financial studies
(c) Traffic or road use studies
(d) Engineering studies
Economic studies
The details to be collected during economic studies are useful in
estimating the requirements, cost involved for the proposed highway
improvement programme and the economic justification.
Hence it is desirable to find the service given by each road system to the
population and various types of products (such as different types of
agricultural produce and industrial products) of the area. It is essential to
first collect all details of the existing facilities, the deficiencies, future
trends additional requirements and the estimated cost of improvements.
These particulars are useful to work out economic justification of each
plan. The details to be collected include the following:
(a) Total population and classified distribution of the different population
groups based on occupation, income, etc. in each village, town or other
locality and the area of settlement of each classified in group
(b) Trend of population growth of various population groups
(c) Agricultural and industrial products and their listing in classified groups,
area wise
(d) Industrial and agricultural development, diversifications if any and
future trends
(e) Existing facilities with regard to communication, education, banks,
hospitals, post office, recreation facilities, etc
(f) Per capita income
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
HIGHWAY ALINGMENT:
1. Alignment: is an arrangement in a straight line or in correct relative
positions
The position or the layout of the central line of the highway on the ground is
called the alignment.
Horizontal alignment includes straight and curved paths.
Vertical alignment includes level and gradients.
Alignment decision is important because a bad alignment will enhance the
construction, maintenance and vehicle operating cost. Once an alignment is
fixed and constructed, it is not easy to change it due to increase in cost of
adjoining land and construction of costly structures by the roadside.
A new road should be aligned very carefully as improper alignment would
result in increase in one or more of the following:
(a)Construction cost
(b)Maintenance cost
(c)Vehicle operation cost
(d)Accident rate
FIG-1
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
1.1 Types of alignment:
A. Horizontal Alignment: Horizontal alignment in road design consists
of straight sections of road, known as tangents, connected by circular
horizontal curves.
It is the design of the road in the horizontal plane.
Consists of a series of tangents (straight lines), circular curves and
transition curves.
Should provide safe travel at a uniform design speed.
Horizontal Alignment: FIG-2
B. Vertical Alignment: Vertical alignment is the longitudinal section
(shown on the y-axis of a road, it consists of straight grades joined by
vertical curves.
Vertical alignment specifies the elevations of points along the roadway.
Road Shoulders:
Shoulders are provided along the road edge to serve as an emergency
lane for vehicles.
As per IRC, the min. width of shoulder should be 2.5m.
Uses:
Repair of broken-down vehicles
Overtaking operations
To act as an emergency lane
For future widening of road
For temp. diversion of traffic during road repair etc
Formation width:
Formation width is the top width of the highway embankment or the
bottom width of cutting excluding the side drain.
Formation width = Width of Carry. Way + Width of shoulder
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
FIG-3 FORMATION WIDTH
Right of way:
Right of way is the area of land acquired for the land, along its
alignment.
It is the distance between boundary stones of road on either side of
road.
FIG -4A
FIG -4-B RIGHT OF WAY
Side slope:
The slope of earthwork in Filling(embankment) or cutting is called side
slope.
Berm:
The distance between the road toe and inner edge of borrow pit is called
berm.
It prevents the erosion of embankment soil.
Side drain:
For the drainage of rain water, drains are provided on either side of the
road.
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
Normally, Side drain are required for road in cutting. For road in
embankment side drain is not necessary.
Building line:
The distance from the centre line of road on either side, within which
construction of building is not permitted is called building line.
Purposes:
For future widening of road
To reduce the chance of accidents
To relieve residents from noise pollution
To prevent disturbance to the traffic by nearby residents
Borrow pits:
The pits dug along the road alignment for using excavated earth in
construction of embankment are known as borrow pits.
Borrow pit should be dug at least 5m from toe of embankment.
The small portion left undug in a borrow pit to measure the
depth of excavation is called Deadman
FIG-5
KERBS-The boundaries between pavement and shoulders or footpath
are known as kerbs.
FIG-6
Mountable kerbs:
These kerbs are indicator between the boundary of a road and shoulder.
The height of the kerb is such that driver find no difficulty in crossing these
kerbs and use the shoulder in-case of emergency. Its height is kept on
10cm above the pavement edge.
Semi-barrier kerbs:
It prevents encroachment of slow speed or parking vehicles to the footpath
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
But at emergency vehicle can climb over and can be parked on footpath
or shoulder. Its height is 15 to 20cm
Barrier kerbs:
They are mainly provided to cause obstruction to the vehicles leaving the
carriage way under emergency. Its height is 23 to 45cm Generally, such
kerbs are provided on hills bridges etc.
FIG-7 TYPES OF KERBS
Once the road is aligned and constructed, it is not easy to change the
alignment due to increase in cost of adjoining land and construction of
costly structures by the road side, as the land value increases manifolds
once the road is opened to traffic. Hence the importance of car eful
considerations while finalizing the alignment of a new road need not be
over-emphasized.
1.2 Requirements:
The basic requirements of an ideal alignment between two terminal
stations
are that it should be:
(a)Short
(b)Easy
(c)Safe and
(d)Economical
Short: It is desirable to have a short (or shortest) alignment between two
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
terminal stations. A straight alignment would be the shortest, though there
may be several practical considerations which would cause deviations
from the shortest path.
Easy: The alignment should be such that it is easy to construct and
maintain the road with minimum problems. Also, the alignment should be
easy for the operation of vehicles with easy gradients and curves.
Safe: The alignment should be safe enough for construction and
maintenance from the view point of stability of natural hill slopes,
embankment and cut slopes, foundation of embankments. Also, it should
be safe for the traffic operation with safe geometric features.
Economical: The road alignment could be considered economical only if
the total life cycle cost considering the initial cost, maintenance cost and
vehicle operation cost is lowest.
1.3 Factors Controlling Alignment:
For an alignment to be shortest, it should be straight between the two
terminal stations. This is not always possible due to various practical
difficulties such as intermediate obstructions and topography. A shortest
route may have very steep gradients and hence not easy for vehicle
operation. Similarly, there may be construction and maintenance
problems along a route which may otherwise be short and easy. Roads
are often deviated from the shortest route in order to cater for intermediate
places of importance or obligatory points.
A road which is economical with lowest initial construction cost, need not
necessarily be the most economical in maintenance or in vehicle
operation cost. It may also happen that the shortest and easiest route for
vehicle operation may work out to be the costliest of the different
alternatives from construction view point. Thus, it may be seen that an
alignment can seldom fulfil all the requirements simultaneously; hence a
judicial choice is made considering all the factors.
The various factors which control the highway alignment in general are:
(a)Obligatory points
(b)Traffic
(c)Geometric design
(d)Economics
(e)Other considerations
Obligatory points:
These are control points governing the alignment of the highways. These
control points may be divided broadly into two categories.
(i)Points through which the alignment is to pass
(ii)Points through which the alignment should not pass
Points through which the alignment has to pass
Obligatory points through which the road alignment has to pass are
generally due to the topographic and other site conditions including
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
natural obstructions. Some of the examples of this category include
location of a mountain pass, suitable location of bridge to cross a river,
presence of quarry or an intermediate town to be connected. These
obligatory points necessitate deviation of the road alignment from the
straight alignment with
shortest or easiest path.
Points through which the alignment should not pass
There are obligatory points through which the road should not pass and
these locations may make it necessary to deviate from the proposed
shortest alignment. The obligatory points which should be avoided while
aligning a road include religious places, very costly structures, unsuitable
land etc.
Religious places like temple, mosque, church, grave or tomb have been
protected by the law from being acquired for any purpose. Acquiring costly
structures would mean heavy compensation resulting in increased cost.
Marshy, peaty and water logged areas are generally unsuitable for road
construction and should be avoided as far as possible. If a marshy land
with peaty soil falls on the path of a straight alignment, it may be necessary
to deviate the road alignment from the straight path and go around the
unsuitable land or pond. The other alternative method is to resort to very
expensive construction techniques.
2 Traffic
The road alignment should be decided based on the requirements of road
traffic. Origin and Destination study should be carried out in the area and
the desire lines be drawn showing the trend of traffic flow. The new road
to be aligned should keep in view the desire lines, anticipated traffic flow,
classified traffic volume, their growth and future trends.
Geometric design
Geometric design factors such as gradient, radius of curve and sight
distances also would govern the final alignment of the highway. If straight
alignment is aimed at, often it may be necessary to provide very steep
gradients. As far as possible while aligning a new road, the gradient
should be flat and less than the ruling or design gradient. Thus, it may be
necessary to change the alignment considering the design speed,
maximum allowable super elevation and coefficient of lateral friction. It
may be necessary to make adjustment in the horizontal alignment of roads
keeping in view the minimum radius of curve and the transition curves.
The absolute minimum sight distance, which should invariably be made
available in every section of the road, is the safe stopping distance for the
fast moving vehicles. Also, there should be enough distance visible ahead
for safe overtaking manoeuvres of vehicles moving at design speed on
the road. Hence the alignment should be finalized in such a way that the
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
obstructions to visibility do not cause restrictions to the sight distance
requirements.
Economics
The alignment finalized based on the above factors should also be
economical. While working out the economics, the factors to be
considered are, (I) initial construction cost of the road, (ii) regular and
periodic maintenance cost of the road and (iii) vehicle operation cost in
future years. While trying to decrease the initial construction cost, either
the future road maintenance cost or vehicle operation cost or both of these
may increase considerably. Therefore, while carrying out economic
analysis, it is essential to work out overall economics based on life cycle
cost' of the road project and not consider the initial cost of the road project
only.
Other considerations
Various other factors which may govern either the horizontal or vertical
alignment of the road are drainage considerations, hydrological factors,
political considerations and monotony. The vertical alignment is often
guided by drainage considerations. The sub-surface water level, seepage
flow and high flood level are the factors to be kept in view, while deciding
the highway alignment.
Special Considerations while Aligning Roads on Hilly Areas
During alignment of hill roads, special care should be taken on the
following points which pertain to the hill roads:
(a)Stability of hill side slopes
(b)Drainage of surface and subsurface water flowing from the hill side
(c)Special geometric standards for hill roads, and
(d)Resisting length
Stability
While aligning hill roads, special care should be taken to align the road
along the side of the hill which is stable. A common problem in hill roads
is that of landslides. The cutting and filling of earth to construct roads on
hill-side causes steepening of existing slopes and this affect its stability of
the hill slopes.
Drainage
Numerous hill-side drains should be provided for adequate drainage
facility across the road. But the cross-drainage structure being costly,
attempts should be made to align the road in such a way that the number
of very expensive cross drainage structures is kept minimum.
Geometric standard of hill roads
Different sets of geometric design standards are followed on hill roads with
reference to gradient, curves and speed and they consequently influence
the sight distance, radius of curve and other related features. The route
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
should enable the ruling gradient to be attained in most of the length,
minimizing steep gradients, hair pin bands and needless rise and fall.
Resisting length
The resisting length of a road may be calculated from the total work to be
done to move the loads along the route taking the horizontal length, the
actual difference in levels between the two stations and the sum of
ineffective rise and fall in excess of floating gradient. In brief, the resisting
length of the alignment should kept as low as possible. Thus, the
ineffective rise and excessive fall should be kept minimum.
Engineering surveys for highway alignment
3 Stages of Engineering Surveys
Before a highway alignment is finalized in a new highway project, enearring surveys are to be carried out. These engineering surveys may be
completed in the following four stages: (a)Map study
(b)Reconnaissance survey
(c)Preliminary surveys and
(d)Final location and details -surveys.
3.1 Map Study
If the topographic map of the area is available, it is possible to suggest the
likely routes of the road. In India; topographic maps are available from the
Survey of India with 15- or 30-meter contour intervals. The main features
like rivers, hills valleys, etc. are also shown on these maps. By careful
study of such maps, it is. possible to have an idea of several possible
alternate routes so that further details of these may be studies. Later at
the site. The probable alignment can be located on the map from the
following details available on the map.
(a)Alignment avoiding valleys, ponds or lakes
(b)When the road has to cross a row of hills or mountains, possibility of
crossing through a mountain pass
(c)Approximate location of bridge site for crossing rivers, avoiding bend of
the river, if any
(d)when a road is to be connected between two stations, one of the top
and the other on the foot of the hill, then alternate routes can be suggested
keeping in view the design or ruling gradient and the maximum
permissible gradient
3.2 Reconnaissance
The second stage of engineering surveys for highway alignment is the
reconnaissance survey. During the reconnaissance, the engineer visits
the site and examines the general characteristics of the area before
deciding the most feasible routes for detailed studies A field survey party
-may inspect a fairly broad stretch of land along the proposed alternative
routes of the map in the field. Only very simple survey instruments are
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
used by the reconnaissance party to collect additional details rapidly, but
not accurately. All relevant details which are not available in the map are
collected and noted down. Some of the details to be collected during
reconnaissance are given below:
(i)Valleys, ponds, lakes, marshy land, ridge, hills, permanent structures
and other obstructions along the route which are not available in the map
(ii)approximate values of gradient, length of gradients and radius of curves
of alternate alignments.
(iii)Number and type of cross drainage structures, maximum flood level
and natural ground water level along the probable routes
(iv)Soil type along the routes from field identification tests and observation
of geological features
(v)Sources of construction materials, water and location of stone quarries
(vi)When the road passes through hilly or mountainous terrain, additional
data regarding the geological formation, type of rocks, dip of strata,
seepage flow etc. may be observed so as to decide the stable and
unstable sides of the hill for highway alignment
3.3 Preliminary Survey
The main objectives of the preliminary survey are:
(i) To survey the various alternate alignments proposed after the
reconnaissance and to collect all the necessary physical information and
details of topography, drainage and soil
(ii) To compare the different proposals in view of the requirements of a
good alignment
(iii) To estimate quantity of earth work materials and other construction
aspects and to work out the cost of alternate proposals
(iv) To finalize the best alignment from all considerations the preliminary
survey is carried out to collect all the physical information which ire
necessary in connection with the proposed highway alignment.
The preliminary survey may be carried out by any one of the following
methods:
3.3.1 Soil survey
Soil survey is an essential part of the preliminary survey as the suitability
of the proposed location is to be finally decided based on the soil survey
data. The soil survey conducted at this stage also helps in working out
details of earth work, slopes, suitability of materials, subsoil and surface
drainage requirements and pavement type and the approximate thickness
requirements. All these details are required to make a comparative study
of alternate proposals.
3.3.2 Material survey
The survey for naturally occurring materials likes stone aggregates, soft
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
aggregates, etc. and identification of suitable quarries should be made.
Also, availability of manufactured materials like cement, lime, brick, etc.
and their locations may be ascertained.
3.3.3 Traffic survey
Traffic surveys conducted in the region form the basis for deciding the
number of traffic lanes and roadway width, pavement design and
economic analysis of the highway project. Traffic volume counts of the
classified vehicles are to be carried out on all the existing roads in the
region, preferably for 24 hours per day for seven days. Origin and
destination surveys are very useful for deciding the alignment of the roads.
This study may be carried out on a suitable sample of vehicle users or
drivers. In addition, the required traffic data may also be collected so that
the traffic forecast could be made for 10 to 20-year periods.
3.3.4 Determination of final centre line
After completing the preliminary surveys and conducting the comparative
studies of alternative alignments, the final centre line of the road is to be
decided in the office before the final location survey. For this, the
preliminary survey maps consisting of contour plans, longitudinal profile
and cross sections of the alternate alignments should be prepared and
carefully studied to decide the best alignment satisfying engineering,
aesthetic and economical requirements. After selecting the final
alignment, the grade lines are drawn and the geometric elements of the
horizontal and vertical alignments of the road are designed.
3.3.5 Rapid method using aerial survey and modern technique using
GPS
Aerial photographic surveys and photogrammetric methods are very
much suited for preliminary surveys, especially when the distance and
area to be covered are vast.
The survey may be divided into the following steps:
Taking aerial photographs of the strips of land to be surveyed with the
required longitudinal and lateral overlaps. Vertical photographs are
necessary for the preparation of mosaics.
(a)The photographs are examined under stereoscopes and control points
are selected for establishing the traverses of the alternate proposals. The
control points are located on the maps
(b)Using stereo-pair observations, the spot levels and subsequently
contour details may be noted down on the maps
(c)Photo-interpretation methods are used to assess the geological
features, soil conditions, drainage requirements etc.
3.4 Final Location and Detailed Survey
The alignment finalized at the design office after the preliminary survey is
to be first located on the field by establishing the centre line. Next detailed
survey should be carried out for collecting the information necessary for
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
the preparation of plans and construction details for the highway project.
3.4.1 Location
The centre line of the road finalized in drawings is to be transferred on the
ground during the location survey. This is done using a transit theodolite
and by staking of the centre line. The location of the centre line should
follow, as closely as practicable, the alignment finalized after the
preliminary surveys. Major and minor control points are established on the
ground and centre pegs are driven, checking the geometric design
requirements. However, modifications in the final location may be made
in the field, if found essential. The centre line stakes are driven at suitable
intervals, say at 50 metre intervals in plain and rolling terrains and at 20
metre in hilly terrain.
3.4.2 Detailed survey
Temporary bench marks are fixed at intervals of about 250 m and at all
drainage and under pass structures. Levels along the final centre line
should be taken at all staked points. Levelling work is of great importance
as the vertical alignment, earth work calculations and drainage details are
to be worked out from the level notes. The cross-section levels are taken
up to the desired width, at intervals of 50 to 100 m in plain terrain, 50 to
75 m in rolling terrain, 50 m in built -up areas and 20 m in hilly terrain. The
cross sections may be taken at closer intervals at horizontal curves and
where there is abrupt change in cross slopes. All river crossing, valleys
etc. should be surveyed in detail up to considerable distances on either
side. All topographical details are noted down and also plotted using
conventional signs. Adequate hydrological detail s is also collected and
recorded.
4 DRAWINGS AND REPORT
4.1 Drawings
The following drawings are usually prepared in a highway project:
(i)Key map
(ii)Index map
(iii)Preliminary survey plans
(iv)Detailed plan and longitudinal section
(v)Detailed cross section
(vi)Land acquisition plans
(vii)Drawings of cross drainage and other retaining structures
(viii)Drawings of road intersections
(ix)Land plans showing quarries, etc.
4.2 Key map should show the proposed and existing roads, and important
places to be connected. The size of the plan generally should not exceed
22 x 20 cm. The scale of the map is chosen suitably depending upon the
length of road.
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
4.3 Index map should show the general topography of the area. The
details are symbolically represented. The index map should also be of
suitable scale, the size being 32 x 20 cm.
4.4 Preliminary survey plans showing details of the various alternate
alignments and all information collected should be normally drawn to scale
of 10 cm = 1 km to 25 cm =1 km.
4.5 Detailed plans show the ground plan with alignment and the
boundaries,
contours at intervals of 1 to 2 m in plain terrain and 3 to 6 m in hills,
showing all details including existing structures. A scale of 1/2400 in close
country and a scale of 1/1200 may be adopted for detailed plans. The size
of the drawing may be A-2 size or 60 x 42 cm approximately.
4.6 Longitudinal sections should be drawn to the same horizontal scale
of the ground as in detailed plan. Vertical scale may be enlarged 10 times
of the longitudinal scale. The longitudinal section should show the details
such as datum line, existing ground surface, vertical profile of the
proposed road and position of drainage crossings.
4.7 Detailed cross sections are generally drawn to natural scale of 1 cm
= 2.0 to 2.5 m. Cross section should be drawn every 100 m or where there
are abrupt changes in level. In hill roads the cross sections should be
drawn at closer intervals. The cross-section drawings should extend at
least up to the proposed right of way. The cross-section number, the
reduced distances and the area of filling and/or cutting should be shown- on cross section drawings.
4.8 Land acquisition plans and schedules are usually prepared from the
survey drawings for land acquisition details. These plans show all general
de tails such as buildings, wells, nature of gradients and other details
required for assessing the values. The scale adopted may be 1 cm = 40
m or less.
4.9 Detailed design for cross drainage and masonry structures are
usually
drawn to scale of 1 cm = 1 m. For details of any complicated portion of the
structure enlarged scales up to 8 cm = 1 m or up to half full size may be
employed. However, the size of drawing should not exceed the standard
size. Cross sections of streams should be to a scale of not less than 1 cm
= 10 m.
Drawings of road intersections should be prepared showing all details of
pavement, shoulders, islands etc. to scale.
4.10Land plans for quarries: Where quarries for construction materials
are to be acquired for new projects, separate land plans should be
prepared. The size of these maps and scales may be similar to those
suggested under land acquisition.
4.11 Estimates
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
The project estimates should consist of general abstract of cost and
detailed estimates for each major head. If the project work is proposed to
be executed in stages, the estimate should be prepared for each stage
separately.
5 Project Report
The first phase of project report soon after completing the preliminary
surveys, feasibility and EIA studies is to prepare a 'Feasibility Report'.
The Detailed Project Report (DPR) should be prepared after completing
all the detailed studies including final location survey, preparation of
longitudinal and cross sections, soil and material surveys, drainage
studies, etc. The design details of the pavements and all CD structures
including major bridges should be carried out and the relevant drawings
prepared as specified in the terms of reference for the project preparation.
6 HIGHWAY PROJECTS
General
In a new highway project, the engineer has to plan, design and construct
either a net-work of new roads or a road link. There are also projects
requiring re-design and re-alignment of existing roads of upgrading the
geometric design standards. Once a highway is constructed, development
takes place along the adjoining land and subsequent changes in
alignment or improvements in geometric standards become very difficult.
A badly al igned highway is not only a source of potential traffic hazard,
but also causes a considerable increase in transportation cost and strain
on the drivers and the passengers. Therefore, proper investigation and
planning are most important in a road project, keeping in view the present
day needs as well as the future developments of the region.
6.1 New Highway Project
The new highway project work may be divided into the following stages:
(i)Selection of route, finalization of highway alignment and geometric
design details
(ii)Collection of materials and testing of sub grade soil and other
construction materials, mix design of pavement materials and design
details of pavement layers
(iii)Construction stages including quality control
6.2 Route selection
The selection of route is made keeping in view the requirements of
alignment and geological, topographical and other features of the locality
as explained However special care should be taken as regards the
geometric design standards of the road for possible upgrading of speed
standards in future, without being necessary to re. align the road. After the
alignment if finalized, the plans and working drawings are prepared
6.3 Materials and design
The soil samples collected from the selected route during the soil surveys
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
are tested in the laboratory in order to design the required pavement
thickness and the design of embankment and cut slopes. The basic
construction materials such as selected soil, aggregates etc. are collected
from the nearest borrow pits and quarries and stacked along the road
alignment after subjecting these materials to the specified laboratory tests.
In order to design the mixes for the pavement component layers and to
specify quality control test values during road construction, mix design
tests are carried out in the laboratory.
6.5.4 Construction
The construction of the road may be divided into two stages, (i) earth work
(ii) pavement construction. The earth work consists of excavation and
construction of the embankments. During the excavation for highway cuts,
the earth slopes, their protection and construction of drainage network are
taken care of. Highway embankments may be best constructed by rolled
-fill method by compacting the soil in layers under controlled moisture and
density using suitable rollers. In the case of high embankments, the
stability of the embankment foundation and slopes and the possible
settlement of the embankment with time are to be investigated. The
pavement construction is subsequently taken up starting with the
preparation of sub grade and the construction of sub-base, base and
surface courses of the pavement.
OBJECTIVE TYPE QUESTION:
1. A district road with a bituminous pavement has a horizontal curve of
1000 m for a design speed of 75 km ph. The super-elevation is
A. 1 in 40
B. 1 in 50
C. 1 in 60
D. 1 in 70
E. none of these.
2. The minimum value of camber provided for thin bituminous surface hill
roads, is
A. 2.2%
B. 2.5%
C. 3.0%
D. 3.5%
3. Design of horizontal and vertical alignments, super-elevation, sight
distance and grades, is worst affected by
A. width of the vehicle
B. length of the vehicle
C. height of the vehicle
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
D. speed of the vehicle
4. Thickness of a pavement may be reduced considerably by
A. compaction of soil
B. stabilization of soil
C. drainage of soil
D. combination of all the above.
5. The total length of a valley formed by two gradients - 3% and + 2%
curve between the two tangent points to provide a rate of change of
centrifugal acceleration 0.6 m/sec2, for a design speed 100 km ph, is
A. 16.0 m
B. 42.3 m
C. 84.6 m
D. none of these.
6. For the movement of vehicles at an intersection of two roads, without
any interference, the type of grade separator generally preferred to, is
A. delta
B. trumpet
C. diamond interchange
D. clover leaf.
7. If the ruling gradient on any highway is 3%, the gradient provided on
the curve of 300 metre radius, is
A. 2.00%
B. 2.25%
C. 2.50%
D. 2.75%
E. 3.00%
8. As per recommendations of I.R.C., traffic volume study is carried out
for rural roads for 7 days continuously during
A. harvesting
B. lean season
C. harvesting and lean season
D. none of these.
9. The minimum ratio of the radii of two circular curves of a compound
curve, is kept
A. 1.25
B. 1.5
C. 1.75
D. 2.0
10. Pick up the incorrect statement from the following. The super-elevation
on roads is
A. directly proportional to width of pavement
B. directly proportional to velocity of vehicles
C. inversely proportional to acceleration due to gravity
39
INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
D. inversely proportional to the radius of curvature.
KEY
1)a 2) b 3) d 4) d 5) c 6) d 7) d 8) c 9) b 10) b
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
B-Highway materials and testing
1.SUB GRADE SOIL
Soil is an accumulation or deposit of earth material, derived naturally from
the disintegration of rocks or decay of vegetation, that can be excavated
readily with power equipment in the field or disintegrated by gentle
mechanical means in the laboratory. The supporting soil beneath
pavement and its special under courses is called sub grade. Undisturbed
soil beneath the pavement is called natural sub grade. Compacted sub
grade is the soil compacted by controlled movement of heavy compactors.
FIG-1 SUB GRADE SOIL
1.2 SOIL TYPES
• The wide range of soil types available as highway construction
materials have made it obligatory on the part of the highway
engineer to identify and classify different soils.
• Broadly, the soil types can be categorized as Laterite soil, Moorum
/ red soil, Desert sands, Alluvial soil, Clay including Black cotton soil.
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
FIG-2 SOIL TYPES
Gravel: These are coarse materials with particle size under 2.36 mm with
little or no fines contributing to cohesion of materials.
Moorum: These are products of decomposition and weathering of the
pavement rock. Visually these are similar to gravel except presence of
higher content of fines.
Silts: These are finer than sand, brighter in color as compared to clay, and
exhibit little cohesion. When a lump of silty soil mixed with water,
alternately squeezed and tapped a shiny surface makes its appearance,
thus dilatancy is a specific property of such soil.
Clays: These are finer than silts. Clayey soils exhibit stickiness, high
strength when dry, and show no dilatancy. Black cotton soil and other
expansive clays exhibit swelling and shrinkage properties. Paste of clay
with water when rubbed
1.3 TESTS ON SOIL
Sub grade soil is an integral part of the road pavement structure as it
provides the support to the pavement from beneath. The sub grade soil
and its properties are important in the design of pavement structure. The
main function of the sub grade is to give adequate support to the
pavement and for this the sub grade should possess sufficient stability
under adverse climatic and loading conditions. Therefore, it is very
essential to evaluate the
sub grade by conducting tests.
The tests used to evaluate the strength properties of soils may be
broadly divided into three groups:
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
Shear tests
Bearing tests
Penetration tests
1.3.1 CALIFORNIA BEARING RATIO TEST
California Bearing Ratio (CBR) test was developed by the California
Division of Highway as a method of classifying and evaluating soil-sub
grade and base course materials for flexible pavements. CBR test, an
empirical test, has been used to determine the material properties for
pavement design. Empirical tests measure the strength of the material
and are not a true representation of the resilient modulus. It is a
penetration test wherein a standard piston, having an area of 3 in2 (or 50
mm diameter), is used to penetrate the soil at a standard rate of 1.25
mm/minute. The pressure up to a penetration of 12.5 mm and its ratio to
the bearing value of a standard crushed rock is termed as the CBR. In
most cases, CBR decreases as the penetration increases. The ratio at 2.5
mm penetration is used as the CBR. In some case, the ratio at 5 mm may
be greater than that at 2.5 mm. If this occurs, the ratio at 5 mm should be
used. The CBR is a measure of resistance of a material to penetration of
standard plunger under controlled density and moisture conditions. The
test procedure should be strictly adhered if high degree of reproducibility
is desired. The CBR test may be conducted in re-moulded or undisturbed
specimen in the laboratory. The test is simple and has been extensively
investigated for field correlations of flexible pavement thickness
requirement.
FIG-3 CALIFORNIA BEARING RATIO TEST
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
1.3.2 PLATE BEARING TEST
Plate bearing test is used to evaluate the support capability of subgrades, bases and in some cases, complete pavement. Data from the
tests are applicable for the design of both flexible and rigid
pavements. In plate bearing test, a compressive stress is applied to
the soil or pavement layer through rigid plates relatively large size
and the deflections are measured for various stress values. The
deflection level is generally limited to a low value, in the order of 1.25
to 5 mm and so the deformation caused may be partly elastic and
partly plastic due to compaction of the stressed mass with negligible
plastic deformation. The plate-bearing test has been devised to
evaluate the supporting power of sub grades or any other pavement
layer by using plates of larger diameter.
The plate-bearing test was originally meant to find the modulus of
sub grade reaction in the Westergaard's analysis for wheel load
stresses in cement concrete pavements.
FIG-4
2. PAVEMENT MATERIALS
2.1 Aggregates
Aggregate is a collective term for the mineral materials such as sand,
gravel, and crushed stone that are used with a binding medium (such
as water, bitumen, Portland cement, lime, etc.) to form compound
materials (such as bituminous concrete and Portland cement
concrete). By volume, aggregate generally accounts for 92 to 96
percent of Bituminous concrete and about 70 to 80 percent of
Portland cement concrete. Aggregate is also used for base and sub44
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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(Prepared By: Mr. Saurabh, Assistant Professor, CE)
base courses for both flexible and rigid pavements. Aggregates can
either be natural or manufactured.
2.2 DESIRABLE PROPERTIES
Strength
The aggregates used in top layers are subjected to (i) Stress action
due to traffic wheel load, (ii) Wear and tear, (iii) crushing. For a highquality pavement, the aggregates should possess high resistance to
crushing, and to withstand the stresses due to traffic wheel load.
Hardness
The aggregates used in the surface course are subjected to constant
rubbing or abrasion due to moving traffic. The aggregates should be
hard enough to resist the abrasive action caused by the movements
of traffic. The abrasive action is severe when steel tyers vehicles
moves over the aggregates exposed at the top surface.
Toughness
Resistance of the aggregates to impact is termed as toughness.
Aggregates used in the pavement should be able to resist the effect
caused by the jumping of the steel tyred wheels from one particle to
another at different levels causes severe impact on the aggregates
Shape of aggregates
Aggregates which happen to fall in a particular size range may have
rounded, cubical,
angular, flaky or elongated particles. It is evident that the flaky and
elongated particles
will have less strength and durability when compared with cubical,
angular or
rounded particles of the same aggregate. Hence too flaky and too
much elongated
aggregates should be avoided as far as possible.
Adhesion with bitumen
The aggregates used in bituminous pavements should have less
affinity with water
when compared with bituminous materials, otherwise the
bituminous coating on the
aggregate will be stripped o in presence of water.
Durability
The property of aggregates to withstand adverse action of weather
is called soundness. The aggregates are subjected to the physical
and chemical action of rain and bottom water, impurities there-in and
that of atmosphere, hence it is desirable that the road aggregates
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
used in the construction should be sound enough to withstand the
weathering action
2.3 AGGREGATE TESTS
In order to decide the suitability of the aggregate for use in
pavement construction, following tests are carried out:
Crushing test
Abrasion test
Impact test
Soundness test
Shape test
Specific gravity and water absorption test
Bitumen adhesion test
2.3.1 AGGREGATE TESTS
Crushing test
One of the models in which pavement material can fail is by crushing
under compressive stress. A test is standardized by IS:2386 part-IV
and used to determine the crushing strength of aggregates. The
aggregate crushing value provides a relative measure of resistance
to crushing under gradually applied crushing load.
Fig-5 CRUSHING TEST
2.3.2 ABRASION TEST
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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Abrasion test is carried out to test the hardness property of
aggregates and to decide whether they are suitable for different
pavement construction works. Los Angeles abrasion test is a
preferred one for carrying out the hardness property and has been
standardized in India (IS:2386 part-IV). The principle of Los Angeles
abrasion test is to find the percentage wear due to relative rubbing
action between the aggregate and steel balls used as abrasive
charge.
FIG-6
2.3.3Impact test
The aggregate impact test is carried out to evaluate the resistance
to impact of aggregates.
Aggregates to be used for wearing course, the impact value
shouldn't exceed 30 percent. For bituminous macadam the
maximum permissible value is 35 percent. For Water bound
macadam base courses the maximum permissible value defined by
IRC is 40 percent
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
FIG-7
2.3.4 Soundness test
Soundness test is intended to study the resistance of aggregates to
weathering action, by conducting accelerated weathering test
cycles. The Porous aggregates subjected to freezing and thawing
are likely to disintegrate prematurely. To ascertain the durability of
such aggregates, they are subjected to an accelerated soundness
test as spaced in IS:2386 part-V.
2.3.5 Shape tests
The particle shape of the aggregate mass is determined by the
percentage of flaky and elongated particles in it.
Aggregates which are flaky or elongated are detrimental to higher
workability and stability of mixes.
The flakiness index is defined as the percentage by weight of
aggregate particles whose least dimension is less than 0.6 times
their mean size. Test procedure had been standardized in India
(IS:2386 part-I)
fig-8
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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2.3.6 The flakiness index is defined as the percentage by weight of
aggregate particles whose least dimension is less than 0.6 times
their mean size. Test procedure had been standardized in India
(IS:2386 part-I) The elongation index of an aggregate is defined as
the percentage by weight of particles whose greatest dimension
(length) is 1.8 times their mean dimension. This test is applicable to
aggregates larger than 6.3 mm.
This test is also specified in (IS:2386 Part-I).
Specific Gravity and water absorption
The specific gravity and water absorption of aggregates are
important properties that are required for the design of concrete and
bituminous mixes.
Fig-9 Tests for aggregates with IS codes
3 PAVEMENT MATERIALS
3.1 Bitumen
Bituminous materials or asphalts are extensively used for roadway
construction, primarily because of their excellent binding
characteristics and water proofing properties and relatively low cost.
Bituminous materials consists of bitumen which is a black or dark
coloured solid or viscous cementations substances consists chiefly
high molecular weight hydrocarbons derived from distillation of
petroleum or natural asphalt, has adhesive properties, and is soluble
in carbon disulphide. Tars are residues from the destructive
distillation of organic substances such as coal, wood, or petroleum
and are temperature sensitive than bitumen. Bitumen will be
dissolved in petroleum oils where unlike tar.
3.2 Production of Bitumen
bitumen is the residue or by-product when the crude petroleum is
refined. A wide variety of refinery processes, such as the straight
distillation process, solvent extraction process etc. may be used to
produce bitumen of different consistency and other desirable
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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properties. Depending on the sources and characteristics of the
crude oils and on the properties of bitumen required, more than one
processing method may be employed.
3.3 DIFFERENT FORMS OF BITUMEN
3.3.1 Cutback bitumen
Normal practice is to heat bitumen to reduce its viscosity. In some
situations, preference is given to use liquid binders such as cutback
bitumen. In cutback bitumen suitable solvent is used to lower the
viscosity of the bitumen. From the environmental point of view also
cutback bitumen is preferred. The solvent from the bituminous
material will evaporate and the bitumen will bind the aggregate.
Cutback bitumen is used for cold weather bituminous road
construction and maintenance. The distillates used for preparation
of cutback bitumen are naphtha, kerosene, diesel oil, and furnace oil.
There are different types of cutback bitumen like rapid curing (RC),
medium curing (MC), and slow curing (SC). RC is recommended for
surface dressing and patchwork.
3.3.2 Bitumen Emulsion
Bitumen emulsion is a liquid product in which bitumen is suspended
in a finely divided condition in an aqueous medium and stabilised by
suitable material. Normally cationic type emulsions are used in India.
The bitumen content in the emulsion is around 60% and the
remaining is water. When the emulsion is applied on the road it
breaks down resulting in release of water and the mix starts to set.
The time of setting depends upon the grade of bitumen. The
viscosity of bituminous emulsions can be measured as per IS: 88871995. Three types of bituminous emulsions are available, which are
Rapid setting (RS), Medium setting (MS), and Slow setting (SC).
FIG-10
3.3.3 Bituminous primers
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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In bituminous primer the distillate is absorbed by the road surface
on which it is spread. The absorption therefore depends on the
porosity of the surface. Bitumen primers are useful on the stabilised
surfaces and water bound macadam base courses. Bituminous
primers are generally prepared on road sites by mixing penetration
bitumen with petroleum distillate.
FIG-11
3.3.4 Modified Bitumen
Certain additives or blend of additives called as bitumen modifiers
can improve properties of Bitumen and bituminous mixes. Bitumen
treated with these modifiers is known as modified bitumen. Polymer
modified bitumen (PMB)/ crumb rubber modified bitumen (CRMB)
should be used only in wearing course depending upon the
requirements of extreme climatic variations.
3.4 REQUIREMENTS OF BITUMEN
The desirable properties of bitumen depend on the mix type and
construction. In general, Bitumen should posses following desirable
properties.
The bitumen should not be highly temperature susceptible: during
the hottest weather the mix should
not become too soft or unstable, and during cold weather the mix
should not become too brittle causing cracks.
The viscosity of the bitumen at the time of mixing and compaction
should be adequate. This can be achieved by use of cutbacks or
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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emulsions of suitable grades or by heating the bitumen and
aggregates prior to mixing.
There should be adequate affinity and adhesion between the
bitumen and aggregates used in the mix.
3.5 TESTS ON BITUMEN
There are a number of tests to assess the properties of bituminous
materials. The
following tests are usually conducted to evaluate different properties
of bituminous materials.
1. Penetration test
2. Ductility test
3. Softening point test
4. Specific gravity test
5. Viscosity test
6. Flash and Fire point test
7. Float test
8. Water content test
9. Loss on heating test
3.5.1 PENETRATION TEST
It measures the hardness or softness of bitumen by measuring the
depth in tenths of a millimetre to which a standard loaded needle will
penetrate vertically in 5 seconds. BIS had standardised the
equipment and test procedure. The penetrometer consists of a
needle assembly with a total weight of 100g and a device for
releasing and locking in any position. The bitumen is softened to a
pouring consistency, stirred thoroughly and poured into containers
at a depth at least 15 mm in excess of the expected penetration. The
test should be conducted at a specified temperature of 25o C. It may
be noted that penetration value is largely influenced by any
52
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
inaccuracy with regards to pouring temperature, size of the needle,
weight placed on the needle and the test temperature.
A grade of 40/50 bitumen means the penetration value is in the
range 40 to 50 at standard test conditions.
In hot climates, a lower penetration grade is preferred.
FIG-12
3.5.2 DUCTILITY TEST
Ductility is the property of bitumen that permits it to undergo great
deformation or elongation. Ductility is defined as the distance in cm, to
which a standard sample or briquette of the material will be elongated
without breaking.
The ductility value gets affected by factors such as pouring temperature,
test temperature, rate of pulling etc. A minimum ductility value of 75 cm
has been specified by the BIS.
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
FIG-13
3.5.3 SOFTENING POINT TEST
Softening point denotes the temperature at which the bitumen
attains a particular degree of softening under the specifications of
test. The test is conducted by using Ring and Ball apparatus. A brass
ring containing test sample of bitumen is suspended in liquid like
water or glycerine at a given temperature.
FIG-14
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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A steel ball is placed upon the bitumen sample and the liquid
medium is heated at a rate of 5o C per minute. Temperature is noted
when the softened bitumen touches the metal plate which is at a
specified distance below
3.5.4 SPECIFIC GRAVITY TEST
In paving jobs, to classify a binder, density property is of great
use. In most cases bitumen is weighed, but
when used with aggregates, the bitumen is converted to volume
using density values. The density of bitumen is greatly incensed by
its chemical composition. Increase in aromatic type mineral
impurities cause an increase in specific gravity.
The specific gravity of bitumen is defined as the ratio of mass of
given volume of bitumen of known content to the mass of equal
volume of water at 27o C. The specific gravity can be measured using
either pycnometer or preparing a cube specimen of bitumen in semi
solid or solid state. The specific gravity of bitumen varies from 0.97
to 1.02.
3.5.6 VISCOSITY TEST
Viscosity denotes the fluid property of bituminous material and it is a
measure of resistance to flow. At the application temperature, this
characteristic greatly influences the strength of resulting paving mixes.
Low or high viscosity during compaction or mixing has been observed to
result in lower stability values. At high viscosity, it resists the comp active
effort and thereby resulting mix is heterogeneous, hence low stability
values.
And at low viscosity instead of providing a uniform film over aggregates,
it will lubricate the aggregate particles.
Orifice type viscometers are used to indirectly find the viscosity of liquid
binders like cutbacks and emulsions.
The viscosity expressed in seconds is the time taken by the 50 ml
bitumen material to pass through the orifice of a cup, under standard test
conditions and specified temperature. Viscosity of a cutback can be
measured with either 4.0 mm orifice at 25o C or 10 mm orifice at 25 or
40o C.
3.5.7 FLASH AND FIRE POINT TEST
At high temperatures depending upon the grades of bitumen
materials leave out volatiles. And these volatiles catch fire which is
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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very hazardous and therefore it is essential to qualify this
temperature for each bitumen grade. BIS defined the flash point as
the temperature at which the vapour of bitumen momentarily catches
fire. in the form of ash under specified test conditions. The fire point
is defined as the lowest temperature under specified test conditions
at which the bituminous material gets ignited and burns.
FIG-15
3.5.8 FLOAT TEST
Normally the consistency of bituminous material can be measured either
by penetration test or viscosity test.
But for certain range of consistencies, these tests are not applicable and
Float test is used. The apparatus consists of an aluminium float and a
brass collar filled with bitumen to be tested. The specimen in the mould is
cooled to a temperature of 5oC and screwed in to float. The total test
assembly is floated in the water bath at 50oC and the time required for
water to pass its way through the specimen plug is noted in seconds and
is expressed as the float value.
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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(Prepared By: Mr. Saurabh, Assistant Professor, CE)
FIG-16
3.5.9 WATER CONTENT TEST
It is desirable that the bitumen contains minimum water content to
prevent foaming of the bitumen when it is heated above the boiling
point of water. The water in a bitumen is determined by mixing
known weight of specimen in a pure petroleum distillate free from
water, heating and distilling of the water. The weight of the water
condensed and collected is expressed as percentage by weight of
the original sample. The allowable maximum water content should
not be more than 0.2% by weight.
3.5.10 LOSS ON HEATING TEST
When the bitumen is heated it loses the volatility and gets hardened.
About 50gm of the sample is weighed and heated to a temperature of
1630C for 5hours in a specified oven designed for this test. The sample
specimen is weighed again after the heating period and loss in weight is
expressed as percentage by weight of the original sample. Bitumen used
in pavement mixes should not indicate more than 1% loss in weight, but
for bitumen having penetration values 150-200 up to 2% loss in weight is
allowed.
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
TABLE-I TEST OF BITUMEN WITH IS CODES
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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(Prepared By: Mr. Saurabh, Assistant Professor, CE)
UNIT-2
2.A. Introduction to geometric design
Overview
The geometric design of highways deals with the dimensions and layout of
visible features of the highway. The emphasis of the geometric design is to
address the requirement of the driver and the vehicle such as safety, comfort,
efficiency, etc. The features normally considered are the cross-section
elements, sight distance consideration, horizontal curvature, gradients, and
intersection. The design of these features is to a great extend influenced by
driver behaviour and psychology, vehicle characteristics, traffic
characteristics such as speed and volume. Proper geometric design will help
in the reduction of accidents and their severity. Therefore, the objective of
geometric design is to provide optimum efficiency in traffic operation and
maximum safety at reasonable cost. The planning cannot be done stage
wise in this case like that of a pavement, but has to be done well in advance.
The main components that will be discussed are:
1.
2.
3.
4.
5.
6.
7.
8.
Factors affecting the geometric design,
Highway alignment, road classification,
Pavement surface characteristics,
Cross-section elements including cross slope, various widths of
roads and features in the road margins.
Sight distance elements including cross slope, various widths and
features in the road margins.
Horizontal alignment which includes features like super elevation,
transition curve, extra widening and set back distance.
Vertical alignment and its components like gradient, sight distance
and design of length of curves.
Intersection features like layout, capacity, etc.
2.1 Factors affecting geometric design
A number of factors affect the geometric design and they are discussed in
detail in the following sections
2.1.1 Design speed
Design speed is the single most important factor that affects the geometric
design. It directly affects the sight distance, horizontal curve, and the length
of vertical curves. Since the speed of vehicles vary with driver, terrain etc, a
design speed is adopted for all the geometric design.
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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(Prepared By: Mr. Saurabh, Assistant Professor, CE)
Design speed is defined as the highest continuous speed at which individual
vehicles can travel with safety on the highway when weather conditions are
conducive. Design speed is different from the legal speed limit which is the
speed limit imposed to curb a common tendency of drivers to travel beyond
an accepted safe speed. Design speed is also different from the desired
speed which is the maximum speed at which a driver would travel when
unconstrained by either traffic or local geometry.
Since there are wide variations in the speed adopted by different drivers, and
by different types of vehicles, design speed should be selected such that it
satisfies nearly all drivers. At the same time, a higher design speed has
cascading effect in other geometric designs and thereby cost escalation.
Therefore, an 85th percentile design speed is normally adopted. This speed
is defined as that speed which is greater than the speed of 85% of drivers.
In some countries this is as high as 95 to 98 percentile speed.
2.1.2 Topography
The next important factor that affects the geometric design is the
topography. It is easier to construct roads with required standards for a
plain terrain. However, for a given design speed, the construction cost
increases multiform with the gradient and the terrain. Therefore, geometric
design standards are different for different terrain to keep the cost of
construction and time of construction under control. This is characterized
by sharper curves and steeper gradients.
Other factors
In addition to design speed and topography, there are various other factors
that affect the geometric design and they are briefly discussed below:
•
•
•
Vehicle: The dimensions, weight of the axle and operating
characteristics of a vehicle influence the design aspects such as
width of the pavement, radii of the curve, clearances, parking
geometrics etc. A design vehicle which has standard weight,
dimensions and operating characteristics are used to establish
highway design controls to accommodate vehicles of a designated
type.
Human: The important human factors that influence geometric
design are the physical, mental and psychological characteristics of
the driver and pedestrians like the reaction time.
Traffic: It will be uneconomical to design the road for peak traffic
flow. Therefore, a reasonable value of traffic volume is selected as
the design hourly volume which is determined from the various traffic
data collected. The geometric design is thus based on this design
volume, capacity etc.
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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(Prepared By: Mr. Saurabh, Assistant Professor, CE)
•
•
•
Environmental: Factors like air pollution, noise pollution etc. should
be given due consideration in the geometric design of roads.
Economy: The design adopted should be economical as far as
possible. It should match with the funds allotted for capital cost and
maintenance cost.
Others: Geometric design should be such that the aesthetics of the
region is not affected.
We will discuss on alignment, classification and factors affecting GD.
2.2 Road classification
The roads can be classified in many ways. The classification based on
speed and accessibility is the most generic one. Note that as the
accessibility of road increases, the speed reduces. (See figure 1).
Accordingly, the roads can be classified as follows in the order of increased
accessibility and reduced speeds.
•
•
•
•
•
Freeways: Freeways are access-controlled divided highways. Most
freeways are four lanes, two lanes each direction, but many freeways
widen to incorporate more lanes as they enter urban areas. Access is
controlled through the use of interchanges, and the type of
interchange depends upon the kind of intersecting road way (rural
roads, another freeway etc.)
Expressways: They are superior type of highways and are designed
for high speeds ( 120 km/hr is common), high traffic volume and
safety. They are generally provided with grade separations at
intersections. Parking, loading and unloading of goods and
pedestrian traffic is not allowed on expressways.
Highways: They represent the superior type of roads in the country.
Highways are of two types - rural highways and urban highways.
Rural highways are those passing through rural areas (villages) and
urban highways are those passing through large cities and towns, ie.
urban areas.
Arterials: It is a general term denoting a street primarily meant for
through traffic usually on a continuous route. They are generally
divided highways with fully or partially controlled access. Parking,
loading and unloading activities are usually restricted and regulated.
Pedestrians are allowed to cross only at intersections/designated
pedestrian crossings.
Local streets : A local street is the one which is primarily intended for
access to residence, business or abutting property. It does not
normally carry large volume of traffic and also it allows unrestricted
parking and pedestrian movements.
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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•
Collector streets: These are streets intended for collecting and
distributing traffic to and from local streets and also for providing
access to arterial streets. Normally full access is provided on these
streets. There are few parking restrictions except during peak hours.
Figure 1: Speed vs accessibility
2.2.1 Nagpur classification
In Nagpur road classification, all roads were classified into five categories as
National highways, State highways, Major district roads, Other district roads
and village roads.
National highways
•
•
•
•
•
•
They are main highways running through the length and breadth of
India connecting major ports, foreign highways, capitals of large states
and large industrial and tourist centers including roads required for
strategic movements.
It was recommended by Jayakar committee that the National highways
should be the frame on which the entire road communication should
be based.
All the national highways are assigned the respective numbers.
For e.g. the highway connecting Delhi-Ambala-Amritsar is denoted as
NH-1 (Delhi-Amritsar), where as a bifurcation of this highway beyond
Fullundar to Srinagar and Uri is denoted as NH-1_A.
They are constructed and maintained by CPWD.
The total length of National highway in the country is 58,112 Kms, and
constitute about 2% of total road networks of India and carry 40% of
total traffic.
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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State highways
•
•
•
They are the arterial roads of a state, connecting up with the national
highways of adjacent states, district headquarters and important cities
within the state
They also serve as main arteries to and from district roads.
Total length of all SH in the country is 1,37,119 Kms.
Major district roads
•
•
Important roads with in a district serving areas of production and
markets, connecting those with each other or with the major
highways.
India has a total of 4,70,000 kms of MDR.
Other district roads
•
Roads serving rural areas of production and providing them with
outlet to market centers or other important roads like MDR or SH.
Village roads
•
•
They are roads connecting villages or group of villages with each
other or to the nearest road of a higher category like ODR or MDR.
India has 26,50,000 kms of ODR+VR out of the total 33,15,231 kms
of all type of roads.
2.2.2 Modern-Lucknow classification
The roads in the country were classified into 3 classes:
Primary roads
•
•
Expressways
National highways
Secondary roads
•
•
State highways
Major district roads
Tertiary roads
•
•
Other district roads
Village roads
2.3 Roads classification criteria
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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(Prepared By: Mr. Saurabh, Assistant Professor, CE)
Apart from the classification given by the different plans, roads were also
classified based on some other criteria. They are given in detail below.
2.3.1 Based on usage
This classification is based on whether the roads can be used during different
seasons of the year.
•
All-weather roads: Those roads which are negotiable during all
weathers, except at major river crossings where interruption of traffic
is permissible up to a certain extent are called all weather roads.
•
Fair-weather roads: Roads which are negotiable only during fair
weather are called fair weather roads.
2.3.2 Based on carriage way
This classification is based on the type of the carriage way or the road
pavement.
•
Paved roads with hards surface : If they are provided with a hard
pavement course such roads are called paved roads.(eg: stones,
Water bound macadam (WBM), Bituminous macadam (BM), concrete
roads)
•
Unpaved roads: Roads which are not provided with a hard course of
atleast a WBM layer they is called unpaved roads. Thus earth and
gravel roads come under this category.
2.3.3 Based on pavement surface
Based on the type of pavement surfacing provided, they are classified as
surfaced and unsurfaced roads.
•
Surfaced roads (BM, concrete): Roads which are provided with a
bituminous or cement concreting surface are called surfaced roads.
•
Unsurfaced roads (soil/gravel): Roads which are not provided with a
bituminous or cement concreting surface are called unsurfaced roads.
Other criteria
Roads may also be classified based on the traffic volume in that road, load
transported through that road, or location and function of that road.
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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(Prepared By: Mr. Saurabh, Assistant Professor, CE)
•
Traffic volume : Based on the traffic volume, they are classified as
heavy, medium and light traffic roads. These terms are relative and so
the limits under each class may be expressed as vehicles per day.
•
Load transported : Based on the load carried by these roads, they can
be classified as class I, class II, etc. or class A, class B etc. and the
limits may be expressed as tonnes per day.
•
Location and function : The classification based on location and
function should be a more acceptable classification since they may be
defined clearly. Classification of roads by Nagpur Road plan is based
on the location and function which we had seen earlier
2.4 Highway alignment
Once the necessity of the highway is assessed, the next process is deciding
the alignment. The highway alignment can be either horizontal or vertical and
they are described in detail in the following sections.
2.4.1 Alignment
The position or the layout of the central line of the highway on the ground
is called the alignment. Horizontal alignment includes straight and curved
paths. Vertical alignment includes level and gradients. Alignment decision
is important because a bad alignment will enhance the construction,
maintenance and vehicle operating costs. Once an alignment is fixed and
constructed, it is not easy to change it due to increase in cost of adjoining
land and construction of costly structures by the roadside.
Requirements
The requirements of an ideal alignment are
•
•
•
The alignment between two terminal stations should be short and
as far as possible be straight, but due to some practical
considerations deviations may be needed.
The alignment should be easy to construct and maintain. It should
be easy for the operation of vehicles. So, to the maximum extend
easy gradients and curves should be provided.
It should be safe both from the construction and operating point of
view especially at slopes, embankments, and cutting. It should have
safe geometric features.
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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(Prepared By: Mr. Saurabh, Assistant Professor, CE)
•
The alignment should be economical and it can be considered so
only when the initial cost, maintenance cost, and operating cost are
minimum.
2.4.2 Factors controlling alignment
We have seen the requirements of an alignment. But it is not always possible
to satisfy all these requirements. Hence we have to make a judicial choice
considering all the factors.
The various factors that control the alignment are as follows:
•
Obligatory points: These are the control points governing the highway
alignment. These points are classified into two categories. Points
through which it should pass and points through which it should not
pass. Some of the examples are:
o bridge site: The bridge can be located only where the river has
straight and permanent path and also where the abutment and
pier can be strongly founded. The road approach to the bridge
should not be curved and skew crossing should be avoided as
possible. Thus to locate a bridge the highway alignment may be
changed.
o mountain: While the alignment passes through a mountain, the
various alternatives are to either construct a tunnel or to go
round the hills. The suitability of the alternative depends on
factors like topography, site conditions and construction and
operation cost.
o intermediate town: The alignment may be slightly deviated to
connect an intermediate town or village nearby.
These were some of the obligatory points through which the alignment
should pass. Coming to the second category, that is the points through which
the alignment should not pass are:
•
•
•
religious places: These have been protected by the law from being
acquired for any purpose. Therefore, these points should be avoided
while aligning.
very costly structures: Acquiring such structures means heavy
compensation which would result in an increase in initial cost. So the
alignment may be deviated not to pass through that point.
lakes/ponds etc: The presence of a lake or pond on the alignment path
would also necessitate deviation of the alignment.
2.4.3 Traffic: The alignment should suit the traffic requirements. Based on
the origin-destination data of the area, the desire lines should be drawn. The
new alignment should be drawn keeping in view the desire lines, traffic flow
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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pattern etc. Geometric design: Geometric design factors such as gradient,
radius of curve, sight distance etc. also govern the alignment of the highway.
To keep the radius of curve minimum, it may be required to change the
alignment. The alignments should be finalized such that the obstructions to
visibility do not restrict the minimum requirements of sight distance. The
design standards vary with the class of road and the terrain and accordingly
the highway should be aligned. Economy:The alignment finalised should be
economical. All the three costs i.e. construction, maintenance, and operating
cost should be minimum. The construction cost can be decreased much if it
is possible to maintain a balance between cutting and filling. Also try to avoid
very high embankments and very deep cuttings as the construction cost will
be very higher in these cases.
Other considerations : various other factors that govern the alignment are
drainage considerations, political factors and monotony.
•
•
•
•
Drainage:
Political: If a foreign territory comes across a straight alignment, we will
have to deviate the alignment around the foreign land.
Monotony: For a flat terrain it is possible to provide a straight
alignment, but it will be monotonous for driving. Hence a slight bend
may be provided after a few kilometres of straight road to keep the
driver alert by breaking the monotony.
Hydrological (rainfall/water table):i
2.4.4 Special consideration for hilly areas
Alignment through hilly areas is slightly different from aligning through a flat
terrain. For the purpose of efficient and safe operation of vehicles through a
hilly terrain special care should be taken while aligning the highway. Some
of the special considerations for highway alignment through a hilly terrain is
discussed below.
•
•
•
Stability of the slopes: for hilly areas, the road should be aligned
through the side of the hill that is stable. The common problem with
hilly areas is that of landslides. Excessive cutting and filling for road
constructions give way to steepening of slopes which in turn will affect
the stability.
Hill side drainage: Adequate drainage facility should be provided
across the road. Attempts should be made to align the roads in such a
way where the number of cross drainage structures required are
minimum. This will reduce the construction cost.
Special geometric standards: The geometric standards followed in hilly
areas are different from those in flat terrain. The alignment chosen
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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(Prepared By: Mr. Saurabh, Assistant Professor, CE)
•
•
•
should enable the ruling gradient to be attained in minimum of the
length, minimizing steep gradient, hairpin bends and needless rise and
fall.
Ineffective rise and fall: Efforts should be made to keep the ineffective
rise and excessive fall minimum
Summary
This lecture covers a brief history of highway engineering, highlighting
the developments of road construction. Significant among them are
Roman, French, and British roads. British road construction practice
developed by Macadam is the most scientific and the present day
roads follows this pattern. The highway development and classification
of Indian roads are also discussed. The major classes of roads include
National Highway, State highway, District roads, and Village roads.
Finally, issues in highway alignment are discussed.
Cross sectional elements
Overview
The features of the cross-section of the pavement influences the life of the
pavement as well as the riding comfort and safety. Of these, pavement
surface characteristics affect both of these. Camber,kerbs, and geometry of
various cross-sectional elements are important aspects to be considered in
this regard. They are explained briefly in this chapter.
Pavement surface characteristics
For safe and comfortable driving four aspects of the pavement surface are
important; the friction between the wheels and the pavement surface,
smoothness of the road surface, the light reflection characteristics of the top
of pavement surface, and drainage to water.
Friction
Friction between the wheel and the pavement surface is a crucial factor in
the design of horizontal curves and thus the safe operating speed. Further,
it also affect the acceleration and deceleration ability of vehicles. Lack of
adequate friction can cause skidding or slipping of vehicles.
•
•
Skidding happens when the path traveled along the road surface is
more than the circumferential movement of the wheels due to friction
Slip occurs when the wheel revolves more than the corresponding
longitudinal movement along the road.
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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(Prepared By: Mr. Saurabh, Assistant Professor, CE)
Various factors that affect friction are:
•
•
•
•
Type of the pavement (like bituminous, concrete, or gravel),
Condition of the pavement (dry or wet, hot or cold, etc),
Condition of the tyre (new or old), and
Speed and load of the vehicle.
The frictional force that develops between the wheel and the pavement is
the load acting multiplied by a factor called the coefficient of friction and
denoted as . The choice of the value of is a very complicated issue since
it depends on many variables. IRC suggests the coefficient of longitudinal
friction as 0.35-0.4 depending on the speed and coefficient of lateral friction
as 0.15. The former is useful in sight distance calculation and the latter in
horizontal curve design.
Unevenness
It is always desirable to have an even surface, but it is seldom possible to
have such a one. Even if a road is constructed with high quality pavers, it is
possible to develop unevenness due to pavement failures. Unevenness
affect the vehicle operating cost, speed, riding comfort, safety, fuel
consumption and wear and tear of tyres.
Unevenness index is a measure of unevenness which is the cumulative
measure of vertical undulations of the pavement surface recorded per unit
horizontal length of the road. An unevenness index value less than 1500
mm/km is considered as good, a value less than 2500 mm.km is
satisfactory up to speed of 100 kmph and values greater than 3200 mm/km
is considered as uncomfortable even for 55 kmph.
Light reflection
•
•
•
White roads have good visibility at night, but caused glare during day
time.
Black roads has no glare during day, but has poor visibility at night
Concrete roads has better visibility and less glare
It is necessary that the road surface should be visible at night and reflection
of light is the factor that answers it.
Drainage
The pavement surface should be absolutely impermeable to prevent
seepage of water into the pavement layers. Further, both the geometry and
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texture of pavement surface should help in draining out the water from the
surface in less time.
Camber
Camber or cant is the cross slope provided to raise middle of the road
surface in the transverse direction to drain off rain water from road surface.
The objectives of providing camber are:
•
•
•
Surface protection especially for gravel and bituminous roads
Sub-grade protection by proper drainage
Quick drying of pavement which in turn increases safety
Too steep slope is undesirable for it will erode the surface. Camber is
measured in 1 in n or n% (Eg. 1 in 50 or 2%) and the value depends on the
type of pavement surface. The values suggested by IRC for various
categories of pavement is given in Table 1. The common types of camber
are parabolic, straight, or combination of them (Figure-2)
Figure 2: Different types of camber
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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(Prepared By: Mr. Saurabh, Assistant Professor, CE)
Width of carriage way
Width of the carriage way or the width of the pavement depends on the width
of the traffic lane and number of lanes. Width of a traffic lane depends on the
width of the vehicle and the clearance. Side clearance improves operating
speed and safety. The maximum permissible width of a vehicle is 2.44 and
the desirable side clearance for single lane traffic is 0.68 m. This require
minimum of lane width of 3.75 m for a single lane road (Figure 3a). However,
the side clearance required is about 0.53 m, on either side and 1.06 m in the
center. Therefore, a two lane road require minimum of 3.5 meter for each
lane (Figure 3b). The desirable carriage way width recommended by IRC is
given in Table-2
Table 2: IRC Specification for carriage way width
Figure 3a 3b: Lane width for single- and two-lane roads
Kerbs
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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(Prepared By: Mr. Saurabh, Assistant Professor, CE)
Kerbs indicate the boundary between the carriage way and the shoulder or
islands or footpaths. Different types of kerbs are (Figure 4):
•
•
•
•
Low or mountable kerbs : This type of kerbs are provided such that
they encourage the traffic to remain in the through traffic lanes and
also allow the driver to enter the shoulder area with little difficulty.
The height of this kerb is about 10 cm above the pavement edge with
a slope which allows the vehicle to climb easily. This is usually
provided at medians and channelization schemes and also helps in
longitudinal drainage.
Semi-barrier type kerbs : When the pedestrian traffic is high, these
kerbs are provided. Their height is 15 cm above the pavement edge.
This type of kerb prevents encroachment of parking vehicles, but at
acute emergency it is possible to drive over this kerb with some
difficulty.
Barrier type kerbs : They are designed to discourage vehicles from
leaving the pavement. They are provided when there is considerable
amount of pedestrian traffic. They are placed at a height of 20 cm
above the pavement edge with a steep batter.
Submerged kerbs : They are used in rural roads. The kerbs are
provided at pavement edges between the pavement edge and
shoulders. They provide lateral confinement and stability to the
pavement.
Figure 4: Different types of kerbs
Road margins
The portion of the road beyond the carriageway and on the roadway can be
generally called road margin. Various elements that form the road margins
are given below.
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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Shoulders
Shoulders are provided along the road edge and is intended for
accommodation of stopped vehicles, serve as an emergency lane for
vehicles and provide lateral support for base and surface courses. The
shoulder should be strong enough to bear the weight of a fully loaded truck
even in wet conditions. The shoulder width should be adequate for giving
working space around a stopped vehicle. It is desirable to have a width of
4.6 m for the shoulders. A minimum width of 2.5 m is recommended for 2lane rural highways in India.
Parking lanes
Parking lanes are provided in urban lanes for side parking. Parallel parking
is preferred because it is safe for the vehicles moving on the road. The
parking lane should have a minimum of 3.0 m width in the case of parallel
parking.
Bus-bays
Bus bays are provided by recessing the kerbs for bus stops. They are
provided so that they do not obstruct the movement of vehicles in the
carriage way. They should be at least 75 meters away from the intersection
so that the traffic near the intersections is not affected by the bus-bay.
Service roads
Service roads or frontage roads give access to access controlled highways
like freeways and expressways. They run parallel to the highway and will be
usually isolated by a separator and access to the highway will be provided
only at selected points. These roads are provided to avoid congestion in the
expressways and also the speed of the traffic in those lanes is not reduced.
Cycle track
Cycle tracks are provided in urban areas when the volume of cycle traffic is
high Minimum width of 2 meter is required, which may be increased by 1
meter for every additional track.
Footpath
Footpaths are exclusive right of way to pedestrians, especially in urban
areas. They are provided for the safety of the pedestrians when both the
pedestrian traffic and vehicular traffic is high. Minimum width is 1.5 meter
and may be increased based on the traffic. The footpath should be either
as smooth as the pavement or more smoother than that to induce the
pedestrian to use the footpath.
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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(Prepared By: Mr. Saurabh, Assistant Professor, CE)
Guard rails
They are provided at the edge of the shoulder usually when the road is on
an embankment. They serve to prevent the vehicles from running off the
embankment, especially when the height of the fill exceeds 3 m. Various
designs of guard rails are there. Guard stones painted in alternate black and
white are usually used. They also give better visibility of curves at night under
headlights of vehicles.
Width of formation
Width of formation or roadway width is the sum of the widths of pavements
or carriage way including separators and shoulders. This does not include
the extra land in formation/cutting. The values suggested by IRC are given
in Table-3
Table 3: Width of formation for various classed of roads
Right of way
Right of way (ROW) or land width is the width of land acquired for the road,
along its alignment. It should be adequate to accommodate all the crosssectional elements of the highway and may reasonably provide for future
development. To prevent ribbon development along highways, control lines
and building lines may be provided. Control line is a line which represents
the nearest limits of future uncontrolled building activity in relation to a road.
Building line represents a line on either side of the road, between which and
the road no building activity is permitted at all. The right of way width is
governed by:
•
Width of formation: It depends on the category of the highway and
width of roadway and road margins.
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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(Prepared By: Mr. Saurabh, Assistant Professor, CE)
•
•
•
•
•
Height of embankment or depth of cutting: It is governed by the
topography and the vertical alignment.
Side slopes of embankment or cutting: It depends on the height of the
slope, soil type etc.
Drainage system and their size which depends on rainfall, topography
etc.
Sight distance considerations : On curves etc. there is restriction to the
visibility on the inner side of the curve due to the presence of some
obstructions like building structures etc.
Reserve land for future widening: Some land has to be acquired in
advance anticipating future developments like widening of the road.
Table 4: Normal right of way for open areas
Figure 5: A typical Right of way (ROW)
The importance of reserved land is emphasized by the following. Extra width
of land is available for the construction of roadside facilities. Land acquisition
is not possible later, because the land may be occupied for various other
75
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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(Prepared By: Mr. Saurabh, Assistant Professor, CE)
purposes (buildings, business etc.) The normal ROW requirements for built
up and open areas as specified by IRC is given in Table 4 A typical cross
section of a ROW is given in Figure-5
Summary
The characteristics of cross-sectional elements are important in highway
geometric design because they influence the safety and comfort. Camber
provides for drainage, frictional resistance and reflectivity for safety etc. The
road elements such as kerb, shoulders, carriageway width etc. should be
adequate enough for smooth, safe and efficient movement of traffic. IRC has
recommended the minimum values for all these cross-sectional elements.
Problems
IRC recommends the value for coefficient of lateral friction as
0.05
0.5
0.15
0.005
The height of semi-barrier type kerbs above the pavement edge is
10cm
15cm
20cm
25cm
2.B. Sight distance
2.1 Overview
The safe and efficient operation of vehicles on the road depends very much
on the visibility of the road ahead of the driver. Thus the geometric design of
the road should be done such that any obstruction on the road length could
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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(Prepared By: Mr. Saurabh, Assistant Professor, CE)
be visible to the driver from some distance ahead . This distance is said to
be the sight distance.
Types of sight distance
Sight distance available from a point is the actual distance along the road
surface, over which a driver from a specified height above the carriage way
has visibility of stationary or moving objects. Three sight distance situations
are considered for design:
•
•
•
•
•
Stopping sight distance (SSD) or the absolute minimum sight
distance
Intermediate sight distance (ISD) is defined as twice SSD
Overtaking sight distance (OSD) for safe overtaking operation
Head light sight distance is the distance visible to a driver during
night driving under the illumination of head lights
Safe sight distance to enter into an intersiection.
The most important consideration in all these is that at all times the driver
traveling at the design speed of the highway must have sufficient
carriageway distance within his line of vision to allow him to stop his vehicle
before colliding with a slowly moving or stationary object appearing suddenly
in his own traffic lane.
The computation of sight distance depends on:
•
Reaction time of the driver
Reaction time of a driver is the time taken from the instant the object
is visible to the driver to the instant when the brakes are applied. The
total reaction time may be split up into four components based on
PIEV theory. In practice, all these times are usually combined into a
total perception-reaction time suitable for design purposes as well as
for easy measurement. Many of the studies shows that drivers
require about 1.5 to 2 secs under normal conditions. However, taking
into consideration the variability of driver characteristics, a higher
value is normally used in design. For example, IRC suggests a
reaction time of 2.5 secs.
•
Speed of the vehicle
The speed of the vehicle very much affects the sight distance. Higher
the speed, more time will be required to stop the vehicle. Hence it is
evident that, as the speed increases, sight distance also increases.
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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(Prepared By: Mr. Saurabh, Assistant Professor, CE)
•
Efficiency of brakes
The efficiency of the brakes depends upon the age of the vehicle,
vehicle characteristics etc. If the brake efficiency is 100%, the vehicle
will stop the moment the brakes are applied. But practically, it is not
possible to achieve 100% brake efficiency. Therefore the sight
distance required will be more when the efficiency of brakes are less.
Also for safe geometric design, we assume that the vehicles have
only 50% brake efficiency.
•
Frictional resistance between the tyre and the road
The frictional resistance between the tyre and road plays an
important role to bring the vehicle to stop. When the frictional
resistance is more, the vehicles stop immediately. Thus sight
required will be less. No separate provision for brake efficiency is
provided while computing the sight distance. This is taken into
account along with the factor of longitudinal friction. IRC has
specified the value of longitudinal friction in between 0.35 to 0.4.
•
Gradient of the road.
Gradient of the road also affects the sight distance. While climbing up
a gradient, the vehicle can stop immediately. Therefore sight distance
required is less. While descending a gradient, gravity also comes into
action and more time will be required to stop the vehicle. Sight
distance required will be more in this case
2.2 Stopping sight distance
Stopping sight distance (SSD) is the minimum sight distance available on a
highway at any spot having sufficient length to enable the driver to stop a
vehicle traveling at design speed, safely without collision with any other
obstruction.
There is a term called safe stopping distance and is one of the important
measures in traffic engineering. It is the distance a vehicle travels from the
point at which a situation is first perceived to the time the deceleration is
complete. Drivers must have adequate time if they are to suddenly respond
to a situation. Thus, in highway design, sight distance at least equal to the
safe stopping distance should be provided. The stopping sight distance is
the sum of lag distance and the braking distance. Lag distance is the
distance the vehicle traveled during the reaction time and is given by ,
where is the velocity in
. Braking distance is the distance travelled
by the vehicle during braking operation. For a level road this is obtained by
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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(Prepared By: Mr. Saurabh, Assistant Professor, CE)
equating the work done in stopping the vehicle and the kinetic energy of the
vehicle. If is the maximum frictional force developed and the braking
distance is , then work done against friction in stopping the vehicle
is
where
is the total weight of the vehicle. The kinetic
energyat the design speed is
Therefore, the SSD = lag distance + braking distance and given by:
where v is the design speed in
acceleration due to gravity and
of friction
,
is the reaction time in
,
is the
is the coefficient of friction. The coefficient
is given below for various design speed.
When there is an ascending gradient of say
%, the component of gravity
adds to braking action and hence braking distance is decreased. The
component of gravity acting parallel to the surface which adds to the the
braking force is equal to
and work done:
. Equating kinetic energy
79
INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
Similarly the braking distance can be derived for a descending gradient.
Therefore the general equation is given by Equation 2
2.3 Overtaking sight distance
Figure 1: Time-space diagram: Illustration of overtaking sight distance
The overtaking sight distance is the minimum distance open to the vision of
the driver of a vehicle intending to overtake the slow vehicle ahead safely
against the traffic in the opposite direction. The overtaking sight distance or
passing sight distance is measured along the center line of the road over
which a driver with his eye level 1.2 m above the road surface can see the
top of an object 1.2 m above the road surface.
The factors that affect the OSD are:
•
•
•
Velocities of the overtaking vehicle, overtaken vehicle and of the
vehicle coming in the opposite direction.
Spacing between vehicles, which in-turn depends on the speed
Skill and reaction time of the driver
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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(Prepared By: Mr. Saurabh, Assistant Professor, CE)
•
•
Rate of acceleration of overtaking vehicle
Gradient of the road
The dynamics of the overtaking operation is given in the figure which is a
time-space diagram. The x-axis denotes the time and y-axis shows the
distance traveled by the vehicles. The trajectory of the slow moving vehicle
(B) is shown as a straight line which indicates that it is traveling at a constant
speed. A fast moving vehicle (A) is traveling behind the vehicle B. The
trajectory of the vehicle is shown initially with a steeper slope. The dotted line
indicates the path of the vehicle A if B was absent. The vehicle A slows down
to follow the vehicle B as shown in the figure with same slope from
to
Then it overtakes the vehicle B and occupies the left lane at time
. The
time duration
.
is the actual duration of the overtaking operation.
The snapshots of the road at time
, and
are shown on the left side of
the figure. From the Figure 1, the overtaking sight distance consists of three
parts.
•
the distance traveled by overtaking vehicle A during the reaction
time
•
the distance traveled by the vehicle during the actual overtaking
operation
•
is the distance traveled by on-coming vehicle C during the
overtaking operation ( ).
Therefore:
(1)
It is assumed that the vehicle A is forced to reduce its speed to , the
speed of the slow moving vehicle B and travels behind it during the reaction
time
of the driver. So
is given by:
(2)
Then the vehicle A starts to accelerate, shifts the lane, overtake and shift
back to the original lane. The vehicle A maintains the spacing before and
after overtaking. The spacing in
is given by:
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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(3)
Let
be the duration of actual overtaking. The distance traveled by B
during the overtaking operation is
. Also, during this time, vehicle A
accelerated from initial velocity
and overtaking is completed while
reaching final velocity . Hence the distance traveled is given by:
(4)
The distance traveled by the vehicle C moving at design
speed
during overtaking operation is given by:
(5)
The the overtaking sight distance is (Figure 1)
(6)
where
is the velocity of the slow moving vehicle in
, the reaction
time of the driver in
, is the spacing between the two vehicle in
given
by equation 3 and is the overtaking vehicles acceleration in
. In
case the speed of the overtaken vehicle is not given, it can be assumed that
it moves 16 kmph slower the the design speed.
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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The acceleration values of the fast vehicle depends on its speed and given
in Table 2.
Table 2: Maximum overtaking acceleration at different speeds
Note that:
•
•
On divided highways,
need not be considered
On divided highways with four or more lanes, IRC suggests that it is
not necessary to provide the OSD, but only SSD is sufficient
2.4 Overtaking zones
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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Figure 2: Overtaking zones
Overtaking zones are provided when OSD cannot be provided throughout
the length of the highway. These are zones dedicated for overtaking
operation, marked with wide roads. The desirable length of overtaking zones
is 5 time OSD and the minimum is three times OSD (Figure-2)
2.5 Sight distance at intersections
At intersections where two or more roads meet, visibility should be provided
for the drivers approaching the intersection from either sides. They should
be able to perceive a hazard and stop the vehicle if required. Stopping sight
distance for each road can be computed from the design speed. The sight
distance should be provided such that the drivers on either side should be
able to see each other. This is illustrated in the figure-3
84
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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Figure 3: Sight distance at intersections
Design of sight distance at intersections may be used on three possible
conditions:
•
•
•
Enabling approaching vehicle to change the speed
Enabling approaching vehicle to stop
Enabling stopped vehicle to cross a main road
Summary
One of the key factors for the safe and efficient operation of vehicles
on the road is sight distance. Sight distances ensure overtaking and
stopping operations at the right time. Different types of sight distances
and the equations to find each of these had been discussed here.
2.6 Problems
1. Calculate SSD for =50kmph for (a) two-way traffic in a two lane
road (b) two-way traffic in single lane road. (Hint: f=0.37, t=2.5) [Ans:
(a)61.4 m (b) 122.8 m.
Given:
=50km/hr = 13.9m/s
distance=lag distance
=0.37 = 2.5 sec stopping
braking distance
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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Stopping Distance = 61.4 m
Stopping sight distance when there are two lanes = stopping
distance= 61.4m.
Stopping sight distance for a two way traffic for a single lane =
2[stopping distance]=122.8m
2. Find minimum sight distance to avoid head-on collision of two cars
approaching at 90 kmph and 60 kmph. Given t=2.5sec, f=0.7 and
brake efficiency of 50 percent in either case. (Hint: brake efficiency
reduces the coefficient of friction by 50 percent). [Ans:
SD=153.6+82.2=235.8m]
Given:
=90 Km/hr.
= 60 Km/hr.
= 2.5sec. Braking
efficiency=50%. =.7.
Stopping distance for one of the cars
Coefficient of friction due to braking efficiency of 50% = 0.5*0.7=0.35.
Stopping sight distance of first car=
= 153.6m
Stopping sight distance of second car=
= 82.2m
Stopping sight distance to avoid head on collision of the two
approaching cars
+
=235.8m.
3. Find SSD for a descending gradient of 2% for V=80kmph. [Ans:
132m].
Given: Gradient(n) = -2
= 80 Km/hr.
86
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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SSD on road with gradient = 132m.
4. Find head light sight distance and intermediate sight distance for
V=65 kmph. (Hint: f=0.36, t=2.5 s, HSD=SSD, ISD=2*SSD) [Ans:
91.4 and 182.8 m]
Given:
=65km/hr
=0.36 = 2.5 sec
Headlight Sight distance = 91.4m.
Intermediate Sight distance= 2[SSD]= 182.8m.
5. Overtaking and overtaken vehicles are at 70 and 40 kmph
respectively. find (i) OSD (ii) min. and desirable length of overtaking
zone (iii) show the sketch of overtaking zone with location of sign
post (hint: a=0.99 m/sec2) [Ans: (i) 278 m (ii) 834 m/1390]
6. Calculate OSD for V=96 kmph. Assume all other data. (Hint: Vb=9616kmph. a=0.72, t=2.5s) [Ans: OSD one way 342m, OSD two way
646m]
2-C-Horizontal alignment I
Overview
Horizontal alignment is one of the most important features influencing the
efficiency and safety of a highway. A poor design will result in lower speeds
and resultant reduction in highway performance in terms of safety and
comfort. In addition, it may increase the cost of vehicle operations and lower
the highway capacity. Horizontal alignment design involves the
understanding on the design aspects such as design speed and the effect of
horizontal curve on the vehicles. The horizontal curve design elements
include design of super elevation, extra widening at horizontal curves, design
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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of transition curve, and set back distance. These will be discussed in this
chapter and the following two chapters.
2.1 Design Speed
The design speed, as noted earlier, is the single most important factor in
the design of horizontal alignment. The design speed also depends on the
type of the road. For e.g, the design speed expected from a National
highway will be much higher than a village road, and hence the curve
geometry will vary significantly.
The design speed also depends on the type of terrain. A plain terrain can
afford to have any geometry, but for the same standard in a hilly terrain
requires substantial cutting and filling implying exorbitant costs as well as
safety concern due to unstable slopes. Therefore, the design speed is
normally reduced for terrains with steep slopes.
For instance, Indian Road Congress (IRC) has classified the terrains into
four categories, namely plain, rolling, mountainous, and steep based on the
cross slope as given in table 1. Based on the type of road and type of
terrain the design speed varies. The IRC has suggested desirable or ruling
speed as well as minimum suggested design speed and is tabulated in
table 2
Table 1: Terrain classification
The recommended design speed is given in Table 2.
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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2.2 Horizontal curve
The presence of horizontal curve imparts centrifugal force which is a reactive
force acting outward on a vehicle negotiating it. Centrifugal force depends
on speed and radius of the horizontal curve and is counteracted to a certain
extent by transverse friction between the tyre and pavement surface. On a
curved road, this force tends to cause the vehicle to overrun or to slide
outward from the centre of road curvature. For proper design of the curve,
an understanding of the forces acting on a vehicle taking a horizontal curve
is necessary. Various forces acting on the vehicle are illustrated in the
figure 1.
Figure 1: Effect of horizontal curve
They are the centrifugal force (P) acting outward, weight of the vehicle (W)
acting downward, and the reaction of the ground on the wheels (
and
). The centrifugal force and the weight are assumed to be from
the centre of gravity which is at h units above the ground. Let the wheel
base be assumed as b units. The centrifugal force
in
is given by
(1)
where
is the weight of the vehicle in
,
in
, is the acceleration due to gravity in
of the curve in .
is the speed of the vehicle
and
is the radius
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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The centrifugal ratio or the impact factor
is given by:
(1)
The centrifugal force has two effects: A tendency to overturn the vehicle
about the outer wheels and a tendency for transverse skidding. Taking
moments of the forces with respect to the outer wheel when the vehicle is
just about to override,
At the equilibrium over turning is possible when
and for safety the following condition must satisfy:
(2)
The second tendency of the vehicle is for transverse skidding. i.e. When
the the centrifugal force is greater than the maximum possible
transverse skid resistance due to friction between the pavement surface
and tyre. The transverse skid resistance (F) is given by:
where
and
is the fractional force at tyre
and
,
and
is
the reaction at tyre and , is the lateral coefficient of friction and
is
the weight of the vehicle. This is counteracted by the centrifugal force (P),
and equating:
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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At equilibrium, when skidding takes place (from equation1)
and for safety the following condition must satisfy:
(3)
Equation 2 and 3 give the stable condition for design. If equation 2 is
violated, the vehicle will overturn at the horizontal curve and if equation 3 is
violated, the vehicle will skid at the horizontal curve
2.3 Analysis of super-elevation
Super-elevation or cant or banking is the transverse slope provided at
horizontal curve to counteract the centrifugal force, by raising the outer edge
of the pavement with respect to the inner edge, throughout the length of the
horizontal curve. When the outer edge is raised, a component of the curve
weight will be complimented in counteracting the effect of centrifugal force.
In order to find out how much this raising should be, the following analysis
may be done. The forces acting on a vehicle while taking a horizontal curve
with superelevation is shown in figure 2
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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Figure 2: Analysis of super-elevation
Forces acting on a vehicle on horizontal curve of radius
of
at a speed
are:
•
•
•
•
the centrifugal force acting horizontally out-wards through the center
of gravity,
the weight of the vehicle acting down-wards through the center of
gravity, and
the friction force between the wheels and the pavement, along the
surface inward.
At equilibrium, by resolving the forces parallel to the surface of the
pavement we get,
•
•
•
where
is the weight of the vehicle, is the centrifugal force,
the coefficient of friction, is the transverse slope due to
superelevation. Dividing by
, we get:
is
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(1)
•
•
We have already derived an expression for P/W.By substituting this
in equation 1, we get:
(2)
•
•
This is an exact expression for superelevation. But
normally,
and
,
,
and for small
, then equation 2 becomes:
(3)
•
•
where,
friction
is the rate of super elevation,
,
the speed of the vehicle in
the coefficient of lateral
,
the radius of the
•
curve in
and
.
Three specific cases that can arise from equation 3 are as follows:
1
•
If there is no friction due to some practical reasons, then
•
and
•
equation 3 becomes
. This results in the situation where the
pressure on the outer and inner wheels are same; requiring very high
super-elevation .
2
If there is no super-elevation provided due to some practical reasons,
•
then
and equation 3 becomes
high coefficient of friction.
3
•
. This results in a very
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•
If
and
given by
then for safe traveling speed from equation 3 is
where
is the restricted speed.
2.4 Horizontal alignment II
Overview
This section discusses the design of super elevation and how it is
attained. A brief discussion on pavement widening at curves is also
given.
2.4.1 Guidelines on super elevation
While designing the various elements of the road like super elevation, we
design it for a particular vehicle called design vehicle which has some
standard weight and dimensions. But in the actual case, the road has to cater
for mixed traffic. Different vehicles with different dimensions and varying
speeds ply on the road. For example, in the case of a heavily loaded truck
with high centre of gravity and low speed, super elevation should be less,
otherwise chances of toppling are more. Taking into practical considerations
of all such situations, IRC has given some guidelines about the maximum
and minimum super elevation etc. These are all discussed in detail in the
following sections.
2.4.1.1 Design of super-elevation
For fast moving vehicles, providing higher super elevation without
considering coefficient of friction is safe, i.e. centrifugal force is fully
counteracted by the weight of the vehicle or super elevation. For slow moving
vehicles, providing lower super elevation considering coefficient of friction is
safe, i.e. Centrifugal force is counteracted by super elevation and coefficient
of friction . IRC suggests following design procedure:
Step 1
Find
for 75 percent of design speed, neglecting
, i.e
.
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Step 2
If
, then
, else if
go to step 3.
Step 3
Find
for the design speed and max , i.e
If
, then the maximum
else go to step 4.
.
is safe for the design speed,
Step 4
Find the allowable speed
for the maximum
and
,
If
then the design is adequate, otherwise use
speed adopt control measures or look for speed control measures.
2.4.1.2 Maximum and minimum super-elevation
Depends on (a) slow moving vehicle and (b) heavy loaded trucks with high
CG. IRC specifies a maximum super-elevation of 7 percent for plain and
rolling terrain, while that of hilly terrain is 10 percent and urban road is 4
percent. The minimum super elevation is 2-4 percent for drainage purpose,
especially for large radius of the horizontal curve.
Attainment of super-elevation
1. Elimination of the crown of the cambered section by:
1. rotating the outer edge about the crown : The outer half of the
cross slope is rotated about the crown at a desired rate such that
this surface falls on the same plane as the inner half.
2. shifting the position of the crown: This method is also known as
diagonal crown method. Here the position of the crown is
progressively shifted outwards, thus increasing the width of the
inner half of cross section progressively.
2. Rotation of the pavement cross section to attain full super elevation
by:There are two methods of attaining superelevation by rotating the
pavement
1. rotation about the center line : The pavement is rotated such that
the inner edge is depressed and the outer edge is raised both
by half the total amount of superelevation, i.e., by
respect to the centre.
with
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2. rotation about the inner edge: Here the pavement is rotated
raising the outer edge as well as the centre such that the outer
edge is raised by the full amount of superelevation with respect
to the inner edge.
2.4.2 Radius of Horizontal Curve
The radius of the horizontal curve is an important design aspect of the
geometric design. The maximum comfortable speed on a horizontal curve
depends on the radius of the curve. Although it is possible to design the
curve with maximum superelevation and coefficient of friction, it is not
desirable because re-alignment would be required if the design speed is
increased in future. Therefore, a ruling minimum radius
can be
derived by assuming maximum superelevation and coefficient of friction.
(1)
Ideally, the radius of the curve should be higher than
. However,
very large curves are also not desirable. Setting out large curves in the field
becomes difficult. In addition, it also enhances driving strain.
2.4.3 Extra widening
Extra widening refers to the additional width of carriageway that is required
on a curved section of a road over and above that required on a straight
alignment. This widening is done due to two reasons: the first and most
important is the additional width required for a vehicle taking a horizontal
curve and the second is due to the tendency of the drivers to ply away from
the edge of the carriageway as they drive on a curve. The first is referred as
the mechanical widening and the second is called the psychological
widening. These are discussed in detail below.
2.4.4 Mechanical widening
The reasons for the mechanical widening are: When a vehicle negotiates a
horizontal curve, the rear wheels follow a path of shorter radius than the front
wheels as shown in figure 4. This phenomenon is called off-tracking, and has
the effect of increasing the effective width of a road space required by the
vehicle. Therefore, to provide the same clearance between vehicles traveling
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in opposite direction on curved roads as is provided on straight sections,
there must be extra width of carriageway available. This is an important
factor when high proportion of vehicles are using the road. Trailor trucks also
need extra carriageway, depending on the type of joint. In addition speeds
higher than the design speed causes transverse skidding which requires
additional width for safety purpose. The expression for extra width can be
derived from the simple geometry of a vehicle at a horizontal curve as shown
in figure 4. Let
is the radius of the outer track line of the rear wheel,
is
the radius of the outer track line of the front wheel is the distance between
the front and rear wheel, is the number of lanes, then the mechanical
widening
(refer figure 3) is derived below:
Therefore the widening needed for a single lane road is:
(1)
If the road has lanes, the extra widening should be provided on each lane.
Therefore, the extra widening of a road with lanes is given by,
(2)
Please note that for large radius,
curve,then
, which is the mean radius of the
is given by:
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(3)
Psychological widening
Widening of pavements has to be done for some psychological reasons also.
There is a tendency for the drivers to drive close to the edges of the
pavement on curves. Some extra space is to be provided for more clearance
for the crossing and overtaking operations on curves. IRC proposed an
empirical relation for the psychological widening at horizontal curves
:
(4)
Therefore, the total widening needed at a horizontal curve
is:
Figure 3: Extra-widening at a horizontal curve
Summary
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In our country, the design of super-elevation follows IRC guidelines wherein
the initial design is done by considering 75% of design speed and the safety
of design is assessed. Pavement is to be given extra width at curves to
account for mechanical and psychological aspects.
Problems
1. A national highway passing through a rolling terrain has two
horizontal curves of radius 450 m and 150 m. Design the required
super-elevation for the curves as per IRC guidelines.
Solution
Assumptions
The ruling design speed for NH passing through a rolling terrain is 80
kmph. The coefficient of lateral friction
super elevation =0.07.
=0.15. The maximum permissible
Case: Radius = 450m
Step 1
Find
for 75 percent of design speed, neglecting
, i.e
.
Step 2
. Hence the design is sufficient.
Answer: Design superelevation: 0.06.
Case: Radius = 150m
Step 1
Find
for 75 percent of design speed, neglecting
.
provided =
, i.e
Max. to be
Step 3
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Find
for the design speed and max ,
i.e
.
Step 4
Find the allowable speed
for the maximum
and f=0.15
2.Given R=100m, V=50 kmph, f=0.15. Find:
1.
if full lateral friction is assumed to develop [Ans: 0.047]
2. find needed if no super elevation is provided [Ans: 0.197]
3. Find equilibrium super-elevation if pressure on inner and outer outer
wheel should be equal (Hint: f=0) [Ans: 0.197]
3.Two lane road, V=80 kmph, R=480 m, Width of the pavement at the
horizontal curve=7.5 m. (i) Design super elevation for mixed traffic. (ii) By
how much the outer edge of the pavement is to be raised with respect to the
centerline, if the pavement is rotated with respect to centerline. [Ans:(i) 0.059
(ii) 0.22m] 4.Design rate of super elevation for a horizontal highway curve of
radius 500 m and speed 100 kmph. [Ans: e=0.07, f=0.087 and with in limits]
Given V=80 kmph, R=200m Design for super elevation. (Hint: f=0.15) [Ans:
Allowable speed is 74.75 kmph and e=0.07]
5.Calculate the ruling minimum and absolute minimum radius of horizontal
curve of a NH in plain terrain. (Hint:
=100kmph,
=80kmph.,
e=0.07, f=0.15) [Ans: 360 and 230 m] 6.Find the extra widening for W=7m,
R=250m, longest wheel base, l=7m, V=70kmph. (Hint: n=2) [Ans:0.662m]
7.Find the width of a pavement on a horizontal curve for a new NH on rolling
terrain. Assume all data. (Hint: V=80kmph for rolling terrain, normal W=7.0m,
n=2, l=6.0m, e=0.07, f=0.15). [Ans:
HC=7.71m
=230m, We=0.71, W at
2.5 Horizontal alignment III
Overview
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In this section we will deal with the design of transition curves and setback
distances. Transition curve ensures a smooth change from straight road to
circular curves. Setback distance looks in for safety at circular curves taking
into consideration the sight distance aspects. A short note on curve
resistance is also included
2.5.1 Horizontal Transition Curves
Transition curve is provided to change the horizontal alignment from straight
to circular curve gradually and has a radius which decreases from infinity at
the straight end (tangent point) to the desired radius of the circular curve at
the other end (curve point) There are five objectives for providing transition
curve and are given below:
1. to introduce gradually the centrifugal force between the tangent point
and the beginning of the circular curve, avoiding sudden jerk on the
vehicle.This increases the comfort of passengers.
2. to enable the driver turn the steering gradually for his own comfort and
security,
3. to provide gradual introduction of super elevation, and
4. to provide gradual introduction of extra widening.
5. to enhance the aesthetic appearance of the road.
Type of transition curve
Different types of transition curves are spiral or clothoid, cubic parabola,
and Lemniscate. IRC recommends spiral as the transition curve because:
1. it fulfills the requirement of an ideal transition curve, that is;
1. rate of change or centrifugal acceleration is consistent
(smooth) and
2. radius of the transition curve is
at the straight edge and
changes to at the curve point (
field implementation is very easy.
) and calculation and
Length of transition curve
The length of the transition curve should be determined as the maximum of
the following three criteria: rate of change of centrifugal acceleration, rate of
change of superelevation, and an empirical formula given by IRC.
1. Rate of change of centrifugal acceleration
At the tangent point, radius is infinity and hence centrifugal acceleration is
zero. At the end of the transition, the radius R has minimum value R. The
rate of change of centrifugal acceleration should be adopted such that the
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design should not cause discomfort to the drivers. If
of centrifugal acceleration, it can be written as:
Therefore, the length of the transition curve
in
is the rate of change
is
(1)
where is the rate of change of centrifugal acceleration given by an
empirical formula suggested by by IRC as below:
(2)
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2. Rate of introduction of super-elevation
Raise ( ) of the outer edge with respect to inner edge is given
by
. The rate of change of this raise from to
is
achieved gradually with a gradient of in
over the length of the transition
curve (typical range of
is 60-150). Therefore, the length of the transition
curve
is:
(3)
3. By empirical formula
IRC suggest the length of the transition curve is minimum for a plain and
rolling terrain:
(4)
and for steep and hilly terrain is:
(5)
and the shift
as:
(6)
The length of the transition
equations 1, 3 and 4or5, i.e
curve
is
the
maximum
of
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2.5.2 Setback Distance
Setback distance
or the clearance distance is the distance required from
the centerline of a horizontal curve to an obstruction on the inner side of the
curve to provide adequate sight distance at a horizontal curve. The setback
distance depends on:
1. sight distance (OSD, ISD and OSD),
2. radius of the curve, and
3. length of the curve.
Case (a)
For single lane roads:
(1)
Therefore,
(2)
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Figure 4: Set-back for single lane roads (
)
For multi lane roads, if is the distance between centerline of the road and
the centerline of the inner lane, then
(3)
(4)
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Figure 5: Set-back for multi-lane roads (
)
Case (b)
For single lane:
Figure 6: Set back for single lane roads (
)
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The set back is the sum of
and
given by:
(1)
where
. For multi-lane road
, and
is given by
2.5.3 Curve Resistance
When the vehicle negotiates a horizontal curve, the direction of rotation of
the front and the r ear wheels are different. The front wheels are turned to
move the vehicle along the curve, whereas the rear wheels seldom turn.
This is illustrated in figure 7.
Figure 7: Curve resistance
The rear wheels exert a tractive force in the PQ direction . The tractive
force available on the front wheels is
in the PS direction as shown
in the figure 1. This is less than the actual tractive force, applied.
Hence, the loss of tractive force for a vehicle to negotiate a horizontal
curve is:
Problems
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1. Calculate the length of transition curve and shift for V=65kmph,
R=220m, rate of introduction of super elevation is 1 in 150, W+We=7.5
m. (Hint: c=0.57) [Ans:
=47.1m,
=39m (e=0.07, pav. rotated
w.r.t centerline),
=51.9m, s=0.51m, =52m]
2. NH passing through rolling terrain of heavy rainfall area, R=500m.
Design length of Transition curve. (Hint: Heavy rainfall. Pavement
surface rotated w.r.t to inner edge. V=80kmph, W=7.0m, N=1 in 150)
[Ans:
c=0.52,
=42.3,
=63.7m
(e=0.057,
W+We=7.45),
=34.6m, =64m]
3. Horizontal curve of R=400m, L=200 m. Compute setback distance
required to provide (a) SSD of 90m, (b) OSD of 300 m. Distance
between center line of road and inner land (d) is 1.9m. [Ans:
(a)
m]
, m=4.4 m (b)OSD L, for multi lane, with d=1.9, m=26.8
2-D-Vertical alignment
Overview
The vertical alignment of a road consists of gradients(straight lines in a
vertical plane) and vertical curves. The vertical alignment is usually drawn
as a profile, which is a graph with elevation as vertical axis and the horizontal
distance along the centre line of the road as the the horizontal axis. Just as
a circular curve is used to connect horizontal straight stretches of road,
vertical curves connect two gradients. When these two curves meet, they
form either convex or concave. The former is called a summit curve, while
the latter is called a valley curve. This section covers a discussion on
gradient and summit curves.
2.1 Gradient
Gradient is the rate of rise or fall along the length of the road with respect to
the horizontal. While aligning a highway, the gradient is decided for designing
the vertical curve. Before finalizing the gradients, the construction cost,
vehicular operation cost and the practical problems in the site also has to be
considered. Usually steep gradients are avoided as far as possible because
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of the difficulty to climb and increase in the construction cost. More about
gradients are discussed below.
Effect of gradient
The effect of long steep gradient on the vehicular speed is considerable.
This is particularly important in roads where the proportion of heavy
vehicles is significant. Due to restrictive sight distance at uphill gradients
the speed of traffic is often controlled by these heavy vehicles. As a result,
not only the operating costs of the vehicles are increased, but also
capacity of the roads will have to be reduced. Further, due to high
differential speed between heavy and light vehicles, and between uphill
and downhill gradients, accidents abound in gradients.
Representation of gradient
The positive gradient or the ascending gradient is denoted as
and the
negative gradient as
. The deviation angle
is: when two grades
meet, the angle which measures the change of direction and is given by
the
algebraic
difference
between
the
two
grades
. Example: 1 in 30 =
3.33%
is a steep gradient, while 1 in 50 = 2%
is a flatter
gradient. The gradient representation is illustrated in the figure 1.
Figure 1: Representation of gradient
Types of gradient
Many studies have shown that gradient upto seven percent can have
considerable effect on the speeds of the passenger cars. On the contrary,
the speeds of the heavy vehicles are considerably reduced when long
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gradients as flat as two percent is adopted. Although, flatter gradients are
desirable, it is evident that the cost of construction will also be very high.
Therefore, IRC has specified the desirable gradients for each terrain.
However, it may not be economically viable to adopt such gradients in
certain locations, steeper gradients are permitted for short duration.
Different types of grades are discussed below and the recommended type
of gradients for each type of terrain and type of gradient is given in table 1.
Table 1: IRC Specifications for gradients for different roads
Terrain
Ruling
Limitings
Exceptional
Plain/Rolling
3.3
5.0
6.7
Hilly
5.0
6.0
7.0
Steep
6.0
7.0
8.0
Ruling gradient, limiting gradient, exceptional gradient and minimum
gradient are some types of gradients which are discussed below.
Ruling gradient
The ruling gradient or the design gradient is the maximum gradient with
which the designer attempts to design the vertical profile of the road. This
depends on the terrain, length of the grade, speed, pulling power of the
vehicle and the presence of the horizontal curve. In flatter terrain, it may
be possible to provide flat gradients, but in hilly terrain it is not economical
and sometimes not possible also. The ruling gradient is adopted by the
designer by considering a particular speed as the design speed and for a
design vehicle with standard dimensions. But our country has a
heterogeneous traffic and hence it is not possible to lay down precise
standards for the country as a whole. Hence IRC has recommended some
values for ruling gradient for different types of terrain.
Limiting gradient
This gradient is adopted when the ruling gradient results in enormous
increase in cost of construction. On rolling terrain and hilly terrain it may
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be frequently necessary to adopt limiting gradient. But the length of the
limiting gradient stretches should be limited and must be sandwiched by
either straight roads or easier grades.
Exceptional gradient
Exceptional gradient are very steeper gradients given at unavoidable
situations. They should be limited for short stretches not exceeding about
100 metres at a stretch. In mountainous and steep terrain, successive
exceptional gradients must be separated by a minimum 100 metre length
gentler gradient. At hairpin bends, the gradient is restricted to 2.5%.
Critical length of the grade
The maximum length of the ascending gradient which a loaded truck can
operate without undue reduction in speed is called critical length of the
grade. A speed of 25 kmph is a reasonable value. This value depends on
the size, power, load, grad-ability of the truck, initial speed, final desirable
minimum speed etc
Minimum gradient
This is important only at locations where surface drainage is important.
Camber will take care of the lateral drainage. But the longitudinal drainage
along the side drains require some slope for smooth flow of water. Therefore
minimum gradient is provided for drainage purpose and it depends on the
rain fall, type of soil and other site conditions. A minimum of 1 in 500 may be
sufficient for concrete drain and 1 in 200 for open soil drains are found to
give satisfactory performance.
2.2 Creeper lane
When the uphill climb is extremely long, it may be desirable to introduce an
additional lane so as to allow slow ascending vehicles to be removed from
the main stream so that the fast moving vehicles are not affected. Such a
newly introduced lane is called creeper lane. There are no hard and fast rules
as when to introduce a creeper lane. But generally, it can be said that it is
desirable to provide a creeper lane when the speed of the vehicle gets
reduced to half the design speed. When there is no restrictive sight distance
to reduce the speed of the approaching vehicle, the additional lane may be
initiated at some distance uphill from the beginning of the slope. But when
the restrictions are responsible for the lowering of speeds, obviously the lane
should be initiated at a point closer to the bottom of the hill. Also the creeper
lane should end at a point well beyond the hill crest, so that the slow moving
vehicles can return back to the normal lane without any danger. In addition,
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the creeper lane should not end suddenly, but only in a tapered manner for
efficient as well as safer transition of vehicles to the normal lane.
Grade compensation
While a vehicle is negotiating a horizontal curve, if there is a gradient also,
then there will be increased resistance to traction due to both curve and the
gradient. In such cases, the total resistance should not exceed the resistance
due to gradient specified. For the design, in some cases this maximum value
is limited to the ruling gradient and in some cases as limiting gradient. So if
a curve need to be introduced in a portion which has got the maximum
permissible gradient, then some compensation should be provided so as to
decrease the gradient for overcoming the tractive loss due to curve. Thus
grade compensation can be defined as the reduction in gradient at the
horizontal curve because of the additional tractive force required due to curve
resistance (
), which is intended to offset the extra tractive force
involved at the curve. IRC gave the following specification for the grade
compensation.
1. Grade compensation is not required for grades flatter than 4%
because the loss of tractive force is negligible.
2. Grade compensation is
curve in meters.
%, where
is the radius of the horizontal
3. The maximum grade compensation is limited to
%
2.3 Summit curve
Summit curves are vertical curves with gradient upwards. They are formed
when two gradients meet as illustrated in figure 1 in any of the following
four ways:
1. when a positive gradient meets another positive gradient [figure 2a].
2. when positive gradient meets a flat gradient [figure 2b]. .
3. when an ascending gradient meets a descending gradient [figure 2c].
.
4. when a descending gradient meets another descending gradient
[figure 2d]. .
Type of Summit Curve
Many curve forms can be used with satisfactory results, the common
practice has been to use parabolic curves in summit curves. This is
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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(Prepared By: Mr. Saurabh, Assistant Professor, CE)
primarily because of the ease with it can be laid out as well as allowing a
comfortable transition from one gradient to another. Although a circular
curve offers equal sight distance at every point on the curve, for very small
deviation angles a circular curve and parabolic curves are almost
congruent. Furthermore, the use of parabolic curves were found to give
excellent riding comfort.
Figure 2: Types of summit curves
Design Consideration
In determining the type and length of the vertical curve, the design
considerations are comfort and security of the driver, and the appearance of
the profile alignment. Among these, sight distance requirements for the
safety is most important on summit curves. The stopping sight distance or
absolute minimum sight distance should be provided on these curves and
where overtaking is not prohibited, overtaking sight distance or intermediate
sight distance should be provided as far as possible. When a fast moving
vehicle travels along a summit curve, there is less discomfort to the
passengers. This is because the centrifugal force will be acting upwards
while the vehicle negotiates a summit curve which is against the gravity and
hence a part of the tyre pressure is relieved. Also if the curve is provided with
adequate sight distance, the length would be sufficient to ease the shock due
to change in gradient. Circular summit curves are identical since the radius
remains same throughout and hence the sight distance. From this point of
view, transition curves are not desirable since it has varying radius and so
the sight distance will also vary. The deviation angle provided on summit
curves for highways are very large, and so the a simple parabola is almost
congruent to a circular arc, between the same tangent points. Parabolic
curves is easy for computation and also it had been found out that it provides
good riding comfort to the drivers. It is also easy for field implementation.
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Due to all these reasons, a simple parabolic curve is preferred as summit
curve.
Length of the summit curve
The important design aspect of the summit curve is the determination of
the length of the curve which is parabolic. As noted earlier, the length of
the curve is guided by the sight distance consideration. That is, a driver
should be able to stop his vehicle safely if there is an obstruction on the
other side of the road. Equation of the parabola is given by
,
where
, where N is the deviation angle and is the length of the In
deriving the length of the curve, two situations can arise depending on the
uphill and downhill gradients when the length of the curve is greater than
the sight distance and the length of the curve is greater than the sight
distance.
Let
is the length of the summit curve,
is the SSD/ISD/OSD,
is the
deviation angle,
driver's eye height (1.2 m), and
the height of the
obstruction, then the length of the summit curve can be derived for the
following two cases. The length of the summit curve can be derived from
the simple geometry as shown below:
Case a. Length of summit curve greater than sight distance(
Figure 3: Length of summit curve (
)
)
The situation when the sight distance is less than the length of the curve
is shown in figure 3.
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Case b. Length of summit curve less than sight distance
The second case is illustrated in figure 4
Figure 4: Length of summit curve (
)
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From the basic geometry, one can write
(1)
Therefore for a given
,
and
above equation with respect to
Solving the quadratic equation for
to get minimum
, differentiate the
and equate it to zero. Therefore,
,
(2)
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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Now we can substitute
back to get the value of minimum value of
a given
. Therefore,
,
Solving for
,
and
for
,
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(3)
(4)
When stopping sight distance is considered the height of driver's eye
above the road surface (
) is taken as 1.2 metres, and height of object
above the pavement surface (
) is taken as 0.15 metres. If overtaking
sight distance is considered, then the value of driver's eye height (
the height of the obstruction (
) and
) are taken equal as 1.2 metres.
Summary
Different types of gradients and IRC recommendations for their maximum
and minimum limit were discussed. At points of combination of horizontal
curve and gradient, grade compensation has to be provided. Due to changes
in grade in the vertical alignment of the highway, vertical curves become
essential. Summit curve, which is a type of vertical curve was discussed in
detail in the chapter. One of the application of summit curves that can be
seen usually in the urban areas are where fly-overs come.
Problems
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1. A vertical summit curve is formed by
3.0% and
5.0%.
Design the length of the summit curve for V=80 kmph. (Hint:
SSD=128m). [Ans: 298m]
2.
=1 in 1-,
1 in 120. Design summit curve for V=80kmph,
OSD=470m. [Ans: L=417m]
3.
and
, SSD=180m, OSD=640m. Due to site
constraints, is limited to 500m. Calculate the length of summit
curve to meet SSD, ISD and OSD. Discuss results. [Ans: L for
SSD=240m, okay, L for OSD=1387m,
ISD=439m ok.]
500m not ok, L for
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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UNIT-3
Road Safety Auditing
Introduction
•
•
•
•
In most regions of the world
over 1.2 million people die every year due to road crashes.
about 50 million suffer non-fatal injuries.
In India, in 2010, No. of accidents around 5 lakhs and casualties
134,513 die & 5 lakh injured.
• It means that 1 road accident every minute & 1 road accident death
every four minutes.
• 53.1% of road accident victims were in the age group of 25 to 65
years.
NHAI lunched massive Road Safety Audit Programs to carry out the
audit at different stages.
On 11 May 2011, the Decade of Action for Road Safety 2011-2020 was
launched in more than 100 countries including India, with one goal: to
prevent five million road traffic deaths globally by 2020.
1. What is Road Safety Audit?
DEFINATION
“A means of checking the design, implementation and operation of road
projects against a set of safety principles as a means of accident
prevention and treatment”.
Road Safety Audit may be defined as the formal examination of the
planning, design and construction of road projects, And of the
characteristics and operation of an existing road
• By independent and qualified examiners,
• To identify any potentially unsafe feature or operational
arrangement that may adversely affect the safety of any road
user.
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It is also the systematic checking of the safety aspects of new/existing
highway and traffic management schemes, including modifications to
existing layouts.
Safety Audit can be applied on (a) new roads (b) existing roads.
On new projects safety audit will lead to avoiding building road crashprone situations and on existing roads audit will lead to improved roads
from the safety point of view.
2 Objectives
Minimize the risk of road accidents.
Minimize the need for remedial work after construction.
Reduce the whole-life costs of the project
Improve the awareness of the safe design in the planning, design,
construction and maintenance of roads
3 Scope of study
Future accident can be minimized.
The loss of human lives can be reduced.
The expenditure can be saved in remedial work.
4 Criteria of auditors
4.1 Skills and Experience are required.
Usually people competent and experienced in the work associated with
traffic accident investigations and countermeasures have most of the
basic skills required for the road safety audit.
4.2 Independence of Auditors.
• The credibility and effectiveness of RSA is greatly influenced by the
degree of independence of the auditors from the planning, design or
construction teams involved in the development of the project.
4.3 Accreditation of auditors.
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• The individual people undertaking an RSA must have an accreditation
for this work and be identified in the Audit Report which this accreditation
be based on an assessment of the person’s knowledge of road safety
principles, practices, training courses and general knowledge and
experience in road and highway engineering.
4.4 Arrangements for doing the audit.
• The arrangement for doing the project during the stages is involved three
parties: The designer of the project (Contractor), The client (Road
authority, represented by the Project manager) and the auditor
(Consultant engaged by the client).
5. Application of road safety audit
Road safety audit may be carried out at any or all following stages
Stage 1: Feasibility& Planning stage
It’s the earliest recognized stage and may not be applicable where this
stage will identify safety, problems associated with the overall concept for
a project, road network safety implications, route options, intersection and
interchanges types and locations.
A safety audit can influence
the scope of a project
route choice
selection of design standards
impact on existing road network
provisions of interchanges or intersections
access control
number of lanes
route terminals, stage development, etc.
Stage 2: - Draft design
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This audit stage is undertaken on completion of a draft plan or a
preliminary design. Typical considerations include
Horizontal and vertical alignment
Sightlines
Intersection layouts
Lane and shoulder width
Super elevation
Overtaking lanes
Provisions for parked and stationary vehicles
Provisions for bicyclists and pedestrians
Effects of departures from standards and guidelines
Safety during construction, etc.
It is at this stage that many of the traffic engineering features of a project
are established. Most of these, such as cross section elements,
intersection/interchange layout, lane and carriageway layout, traffic
control options and alignment standards.
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FIG-1 Stages of RSA
Stage 3: - Detailed design
This stage is on completion of detailed design, normally before
preparation of contract documents, considerations include:
Line markings
Signing
Delineation
Lighting
Intersection details
Clearance to roadside objects
Provision to road user groups with special requirements
Temporary traffic management and control during construction
Drainage
Roadside objects
Landscaping
Batters
Guard fencing, etc.
In carrying out detailed design, designers are continually making balances
and judgments to the project. This stage will test the design decisions
made against road safety objectives and also identify potential hazards
resulting from adverse combinations of choosing a series of design
criteria.
Stage 4: - Pre- opening
Audit at this stage involves all site inspections of a project. The actual
placement of items such as guard railing, traffic signing, street lighting,
landscapes etc… should be given to checking that the respective needs
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of all road user groups meet desirable safety standards which that will be
the last chance to make sure that the project opens to traffic in the best
condition to provide safe and efficient operations.
Prior to opening of the road to traffic
The audit would involve driving, riding and walking through the project
to check the adequacy for the needs of all road users.
• Involve night-time inspection
• Inspection of both wet and dry conditions
It would consider similar issues raised in stage 2 and 3, but with the
view of assessing their adequacy as actually constructed.
Taking specific note of variations that might have occurred from the
lans in the process of construction.
Stage 5: - In- service
Systematic examination of sections of the existing road network to
assess the adequacy of the road, intersection, roadside, etc. from an
explicit safety viewpoint
This can have two applications: Monitoring a new scheme after it is opened to traffic.
i.e. in the weeks and months following the stage 4 audit
Safety audit of an existing road network with a view of identifying safetyrelated deficiencies.
6 Checklists
A set of checklists
Use of checklists which show type of issues and problems that can
potentially arise at the relevant stage of the project.
Checklists are a memory prompt.
When using checklists, it is less likely to overlook problems.
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They cannot be a substitute for expertise.
One of the main benefits of checklists is that designers can use that to
audit themselves before their work gets to the auditor.
CHECKLIST
Stage 6: - Audit of existing road
S.NO Description
Yes/no Photo for example
1
Carry
out
an
inspection
-don’t
forget to take the
results of accident
analysis
and
relevant checklists
with you
2
Does the actual
function of the road
correspond to its
intended function?
3
Is the prevailing
speed level
as desired?
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
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4
Do road users park
in ways that
could
constitute
hazards?
5
Do plantations
obscure
visibility or mask
the view of
signs?
6
Are the surface
and carriageway
markings in good
condition (signs
of rutting, poor
drainage)?
7
Are there any signs
that road users?
drive over islands
or kerbs or that
the routes taken by
motorists
through junctions
and bends are
less than ideal?
Are there signs of
other conflict?
situations and
minor accidents
(skid marks,
broken
glass/plastic,
etc.)?
8
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9
10
Are the specified
distances to rigid
obstacles
maintained
(plantations
and road
equipment, etc.) for
all
groups of road
user?
Is speed limit at all
points where it is
necessary?
11
Are the shoulders
satisfying them?
intended function?
12
Are the sign posts
provided are
sufficient?
13
Does the width of
berm adequate?
14
Will it be possible
to carry out
maintenance work
safely and without
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15
16
using carriage way
or cycle path?
Is there a suitable
gradient or is the
carriage way laid at
a suitable height
above the
shoulder?
Are there any unlit
areas that could
conceal hazards?
17
Guardrails hedges and railings:
a) Are all vulnerable areas
protected?
b) Are bridge pillars steel posts
etc., protected by guard rails
necessary?
c) Are there places where hedges
are
necessary to prevent pedestrians
from
crossing?
d) Are the chosen hedges or guard
rails
light enough?
18
Plantations:
a) Will plantations obscure
visibility?
b) Will fully grow trees or any other
rigid obstacles be observed?
c) Can maintenance be carried out
safely?
Reference
IRC: SP-88-2010
RSA report published by Dhiraj N Kumar & Arun S Bagi
RSA report published by NIMS university, Rajasthan.
Other research papers published online.
SlideShare.
Traffic data by sayajigunj head quarter, Baroda.
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http://pmgsy.nic.in/Road%20Safety%20Audit%20Guide.doc
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UNIT-4
Highway construction
INTRODUCTION
Development of a country depends on the connectivity of various places
with adequate road network.
Roads constitute the most important made of communication in areas
where railways have not developed much
India has one of the largest road’s networks in the world (over 3 million
km at present).
PAVEMENT
Pavement is load bearing and load distributary component of a road.
• PURPOSE OF PAVEMENT1. Load support.
2. Smoothness.
3. Drainage.
4. All weather operation.
5. Direction and guidance.
• TYPES OF PAVEMENT STRUCTURE –
1. Flexible Pavement. (Hot mix asphalt (HMA) pavements)
Flexible pavements are those which are surfaced with bituminous or
asphalt materials. It’s flexible since the total pavement structure bends or
deflects due to the traffic loads. Generally, this type of pavement requires
some sort of maintenance or restoration every 10 to 15 years.
2. Rigid Pavement. (Portland cement concrete (PCC) pavements)
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A rigid pavement structure is composed of a hydraulic cement concrete surface
course and concealed base and sub base courses. The surface course is the rigid
layer and provides the majority of strength.
While, in case of rigid pavements most of the load carries by slab itself and slight
load goes to the underlying strata.
Construction of Subgrade
Materials- Selected Soil , Moorum , Gravel , Aggregate maximum 50 mm.
Construction Method –
•The subgrade is constructed by spreading the loose soil and compacting
the same at optimum moisture content of the soil in layer.
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•The maximum compacted thickness of each layer is generally limited to
200 mm as per MORTH.
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FIG-WMM PLANT
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BITUMEN ROAD CONSTRUCTION PROCEDURE
1.Preparation of the existing base course layer
The existing surface is prepared by removing the pot holes or rust if any.
The irregularities are filled in with premix chippings at least a week before
laying surface course.
2. Application of Tack Coat
It is desirable to lay AC layer over a bituminous base or binder course. A
tack coat of bitumen is applied at 6.0 to 7.5 kg per 10 sq.marea, this
quantity may be increased to 7.5 to 10 kg for non-bituminous base.
3. Preparation and placing of Premix
The premix is prepared in a hot mix plant of a required capacity with the
desired quality control. The bitumen may be heated upto150 –177 degC
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and the aggregate temperature should not differ by over 14 degC from the
binder temperature. The hot mixed material is collected from the mixture
by the transporters, carried to the location is spread by a mechanical
paver at a temperature of 121 to 163 degC. the camber and the thickness
of the layer are accurately verified.
4. Rolling
A mix after it is placed on the base course is thoroughly compacted by
rolling at a speed not more than 5km per hour.
The initial or break down rolling is done by 8 to 12 tonnesroller and the
intermediate rolling is done with a fixed wheel pneumatic roller of 15 to 30
tonneshaving a tyrepressure of 7kg per sq.cm. the wheels of the roller are
kept damp with water. The final rolling or finishing is done by 8 to 10
tonnetandem roller.
5. Quality control of bituminous concrete construction
The routine checks are carried out at site to ensure the quality of the
resulting pavement mixture and the pavement surface.
Equipment:
Compacting material (vibratory roller)
Dozer and scraper
Power shover, shovels
Concrete mixer
Watering devices
Mild steel sections and blocks
Barricading
Signage board
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It works at a maximum milling depth of 50 mm, reprofiling the pavement
by means of modern levelling technology to produce a level surface. The
slightly roughened surface texture produced by fine milling offers.
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E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
Construction of Concrete Pavements
Objectives
The objective of this lecture is to discuss step by step process of concrete
pavement construction
Concrete pavement construction process
The construction of concrete pavement involves sequential construction
of subgrade, sub-base/ base and the concrete slab. These are discussed
in the following.
Subgrade preparation
Subgrade preparation involves cleaning, earthwork (excavation or filling
of soil, replacement of weak soil, soil stabilization etc.) and compaction.
Where the concrete layer is laid directly over the subgrade, the subgrade
is moist at the time concrete is placed. If the subgrade is dry, water could
be sprinkled over the surface before laying any concrete course, however,
care should taken so that soft patches or water pools are not formed at
the surface (IRC:15-2002, Chakroborty and Das 2003). As an alternative
arrangement, concreting could be done over a water proof polyethylene
sheet, and in that case moistening the subgrade surface becomes
redundant. This polyethylene sheet acts as a capillary cut-off layer
(IRC:15 2002). Figure-31 presents a photograph of subgrade construction
in progress.
Construction of Base/ Sub-base
A base/ sub-base to the concrete pavement provides uniform and
reasonably firm support, prevents mud-pumping , and acts as capillary
cut-off. Sub-base for concrete pavement could be constituted with brick
flat soling, WBM, granular aggregates, crushed concrete, slag, stabilized
soil etc. As per IRC:15 (2002), sub-base could be of three types with (i)
Granular material (for example, brick soling with one layer of sand under
it, WBM, well graded granular materials etc.) (ii) Stabilized soil (iii) Semirigid material, (for example, lime burnt clay puzzolana concrete, lime flyash concrete, lean cement concrete roller compacted concrete etc.).
Following contains a brief discussion on dry lean cement (DLC) concrete
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
as sub-base, which is popularly being adopted for the current concrete
pavement construction in India.
Dry lean cement concrete as sub-base
The thickness of DLC, generally recommended is 100mm or 150mm
(IRC:SP-49 1998). The maximum aggregate to cement ratio is 15:1. The
average compressive strength of DLC cubes at 7 days, as recommended
by Indian guidelines (IRC:SP-49 1998) should not be less than 10 MPa,
tested on 5 samples and individual compressive strength should not be
less than 7.5 MPa, at 7 days (MORT&H 2001, IRC:SP-49 1998).
(A) is the outer edge, and (B) is the inner edge of the pavement
Figure-1 Compaction sequence for DLC ( courtesy: Mr.
Ashutosh Gautam, Project Director, NHAI, Kanpur )
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
Figure-2 Laying of DLC ( photo courtesy: Mr. Ashutosh Gautam,
Project Director, NHAI, Kanpur )
Before construction of DLC sub-base, the prepared subgrade is sprinkled
with water to moisten the surface. The material is to be laid uniformly by
a paver without any segregation . The paving machine should have high
amplitude paving bars. The curing of DLC can be done by spraying liquid
curing compound, or by covering the surface by gunny bags. As per Indian
guidelines, the construction of cement concrete pavement can only start
after 7 days of DLC construction (MORT&H 2001, IRC:SP-49 1998).
Figure-2 presents a schematic diagram of the sequence of rolling for DLC
construction, and Figure-33 presents a photograph of DLC construction.
Construction of concrete slab
General
The concrete surfacing could be made up of plain concrete or reinforced concrete. Reinforced
concrete has been discussed later in a different lecture. The proportions between cement,
aggregate and water is determined by standard concrete mix design technique.
Premature setting and segregation is to be avoided while transporting the concrete mix through
the access haul road and continuous stirring may be helpful in such a case. The spreading of
concrete should be done uniformly such that no segregation of materials takes place. A separation
membrane, made up of impermeable plastic/ polyethylene sheet (of thickness of the order of 150
micron) is sometimes laid over the sub-base, without creases, on to which concrete slab is laid
(IRC:15 2002). Figure-34 presents a photograph of laying polyethylene sheet over DLC.
Figure-34 Laying of polyethylene sheet over DLC ( photo courtesy: Mr. Ashutosh Gautam, Project
Director, NHAI, Kanpur )
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
Compaction and surface finishing
Concrete is spread evenly and is rodded with suitable equipment such that formation of honeycombing or voids can be avoided. At the same time, over-compacting needs to be avoided, which
can cause segregation and loss of entrained air ( Swanlund and Vanikar 2002 ). The working
of fixed form and slip form pavers are different - and has been discussed briefly in the following:
Fixed form paving system
In fixed-form paver system, generally, separate powered machines for spreading, compacting and
finishing are used. The spreader spreads concrete evenly through reversible auger to the
desired surcharge level (O'Flaherty 2002). The rotary strike-off paddles trim minor irregularities in
the surface of the surcharge concrete and adjusts with the carriage-way cross-slope . The
compaction beam applies vibration to the concrete with pre-designed amplitude and frequency
(O'Flaherty 2002). This vibration also helps to put the dowel and tie bars at their desired positions
(for a single layer construction).
The wet formed joint groove is made by introducing vertical cut immediately after compaction is
over and inserting a preformed cellular permanent strip . As an alternative, saw joint groove can
be made after the concrete is sufficiently hardened and can maintain the sharp edge itself
(O'Flaherty 2002).
The finishing of the surface is made, generally, with a pair of finishing beams . The leading beam
vibrates and smoothens the surface, and the rear beam acts as float . The beams are oriented
obliquely so that it causes less damage to the joints (O'Flaherty 2002).
Slip form paving system
Slip-form paving machine is a self-propelled system that can automatically spread, trim, compact
and finish the surface in a synchronized manner through its feedback sensors. Placing of dowel/
tie bars at their pre-designed locations are done by the slip-form pavers. The introduction of joint
grooves, surfacing texturing and spraying of curing compound etc. are done by the
equipment those follow the paver (O'Flaherty 2002).
Slip-form paver requires guide-wires, parallel to edge of construction and maintained at fixed
height, installed on the both side. The alignment of the slip-form paver is controlled automatically
with respect to the guide-wires. Correct and precise alignment of the guide-wires is therefore
extremely important. The hopper/ spreader maintains a constant surcharge of the concrete above
the conforming plate level. The conforming plate, vibrators, strike off paddles and the finishing
screed gives the final shape of the concrete pavement (O'Flaherty 2002). Figure-35 explains
schematically the operation of a typical slip-form paver, and Figure-36 a photograph of concrete
pavement construction by a slip form paver.
Texturing
Finished concrete has a smooth surface; texturing of concrete surface is done to impart
required skid resistance to the concrete surface. The texturing is done by means of wire brushing
or grooving along the transverse direction. Initial texturing may be done at the time of construction
of the paver itself (refer Figure 37). Final texturing is done no sooner the sheen of the concrete
surface goes off ( Swanlund and Vanikar 2002 ).
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
Figure-37 Texturing of finished surface by texturing machine ( photo courtesy: Mr. Ashutosh
Gautam, Project Director, NHAI, Kanpur )
Concrete curing
Curing is a process in which requisite moisture content and temperature is maintained so that
concrete achieves its design strength through hydration of cement. For initial curing, curing
compound with high water retentivity may be spread over the finished surface to prevent rapid
drying of water. For final curing, continuous ponding or moistened hessain/ gunny bags should be
kept for about a fortnight (refer Figure 38). As an alternative arrangement to ponding, impervious
liquid maybe spread over the surface so as to restrict evaporation of water from the laid concrete.
Forms are removed from the freshly prepared concrete layer after about curing of fourteen
hours (IRC:15 2002, Chakroborty and Das 2003).
Figure-38 Curing of finished concrete pavement ( photo courtesy: Mr. Ashutosh Gautam, Project
Director, Kanpur, NHAI )
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
Figure-35 Schematic diagram explaining operation of a typical slip-form paver
Figure-36 Construction of concrete pavement slab with slip-form paver ( photo courtesy: Mr. Ashutosh
Gautam, Project Director, NHAI, Kanpur )
Opening to traffic
After curing period is over, and before opening the road to traffic, the temporary seal material is to be removed,
and the joints are to filled with recommended joint sealing compound. The pouring of sealing material is monitored
carefully such that it is not spilled over the pavement surface. Construction of joints and joint sealing have been
discussed separately (IRC:15 2002,Chakorborty and Das 2003)
Recapitulation
•
•
•
•
The construction of concrete pavement involves construction of subgrade, sub-base/ base
and the concrete slab.
Subgrade preparation involves cleaning, earthwork (excavation or filling of soil,
replacement of weak soil, soil stabilization etc.) and compaction.
The various steps involved in cemented/concrete layer construction, depending on
requirements, are spreading, trimming, compacting, jointing, finishing, curing, texturing etc.
The construction cemented/ concrete is generally done by automated equipment, called
paver.
Pavers are of two types, fixed form and slip form. Slip-form paving machine is a selfpropelled system that can perform paving in a synchronized manner through its feedback
sensors.
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
Construction of joints
Objectives
This lecture discusses about construction of pavement joints and related
issues.
Introduction
The various types of joints and their functions have been introduced in the lecture entitled 'basic
concepts of pavement analysis and design. Schematic diagrams of some of the typical joint
configurations have been presented in Figure-39.
From construction point of view, concrete pavement joints could be formed or sawed. Formed
joints could be keyed or butt-type and can be of tied or untied variety. Expansion joints are in
general formed and tied, contraction joints are generally sawed type (could be tied or untied).
(a) Expansion joint with dowel bar
(b) Contraction joint as dummy joint
(c) Contraction joint with dowel bar
(d) Longitudinal joint as plain butt joint
(e) Longitudinal joint with tie bar
(f) Tongue and groove longitudinal joint
Figure-39 Schematic diagram of some typical joint configurations.
Sawing is done as concrete achieves adequate strength, usually after 4 to 12 hours after
placement (Swanlund and Vanikar 2002) of concrete. The timing of sawing is important. Premature
sawing will cause spalling and raveling of concrete, and if sawing is late, shrinkage cracks will
appear (refer Figure-40). Sawing is generally done in two stages - the initial saw cut is further
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
widened in the second stage of sawing. The transverse and longitudinal joints in sub-base and
those of in the concrete pavement are generally placed in staggered way.
Figure- 40 Joint sawing time window.
Joint sealant
Each joint has some gap. This joint gap is filled up by joint fillers . Then, joint sealers are poured over the joint
fillers, so as to prevent water to percolate through the joints and also to make a smooth surface for travel. As per
the present day practice, a single material is used to both fill and seal, and a term joint sealant has subsequently
evolved (ACPA 2005).
Three basic categories of joint sealants are (i) hot poured liquid sealants (example, bituminous, polymer, rubber
materials ) (ii) cold poured liquid sealants (example, polysulfides, polyurethanes, silicone ) and (iii) preformed
elastomeric sealants (example, extruded neoprene rubber ). Elastomeric sealants exert resistive force towards
the movement of the joints.
Prior to filling, the joint is cleaned by compressed air jets (MORT&H 2001). Beaker rod of circular cross-section,
typically made up of foam like material, is inserted to the joints before putting sealants. Joint sealants should be
poured into the groove/ gap when the gapis in maximum expanded form. Suitable primer is sometimes applied to
ensure good bonding between the cut surface and the sealant (IRC:15-2002). The height of filled joint sealant
should be less than the thickness of the concrete slab. Schematic diagram of contraction joint with field poured
and preformed type of sealants have been presented in Figure-41.
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
Figure-41 Schematic diagram of contraction joint with field poured and preformed type of
sealants.
Joint finishing
After putting the joint sealant, finishing the surface is essential so as to prevent rough ride.
Squeegee, flat pate or overbanding are the various methods of finishing the surface. The technique
adopted for surface finish depends on the type of sealant used. Traffic should be allowed only after
the sealing material is adequately set. Figure-42 presents photograph of various stages of concrete
pavement joint construction.
(a) Initial joint cutting
(b) Widening of initial joint cut
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
(c) Insertion of baker rod
(d) Filling joint with sealant
Figure- 42 Various stages of joint construction ( photo courtesy: Mr. Jamil Ahmed, Consulting
Engineering Service, New Delhi ).
Recapitulation
•
•
•
•
Concrete pavement joints could be formed or sawed.
For sawing proper selection of time window is important, failing of which concrete will
either spall or crack.
Some of the basic varieties of joint sealants are hot poured liquid, cold poured liquid and
preformed elastomeric sealants. Elastomeric sealants exert resistive force towards the
movement of the joints.
Ideally, joint sealants should be poured into the joint gap when it is in maximum expanded
form
Maintenance of concrete pavements
Objectives
This objective of this lecture is to discuss the maintenance issues specific to concrete pavement.
Introduction
Any in-service pavement shows signs of distresses, and subsequently requires maintenance to
retain its serviceability. Various distresses that may occur to the concrete pavement can be, in
general, classified as follows (TFHRC 2006):
1. Cracking
▪
▪
▪
Corner breaks
Longitudinal cracking
Transverse cracking
2. Joint deficiencies
▪ Joint seal damage
▪ Spalling of joints
3. Surface defects
▪ Map cracking and scaling
▪ Polished aggregate
▪ Popouts
▪ Loss of skid resistance
4. Miscellaneous distresses
▪ Blowups
▪ Lane-to-shoulder drop-off and separation
▪ Patch
▪ Punch out
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
▪
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
Water bleeding and pumping
Pictorial description and discussion on various types of pavement distresses can be obtained
from reference TFHRC 2006. The following section discusses various maintenance actions
undertaken on concrete pavement towards rehabilitation and preservation of concrete
pavements.
Rehabilitation and preservation of concrete pavements
Repair of early distresses
Some of the early distresses in concrete pavement and their maintenance actions are
discussed in the following:
Plastic shrinkage cracking: Plastic shrinkage cracks appear in the form of parallel surface cracks
on the surface due to rapid evaporation of water from the surface. The depth of such cracks can
be estimated through coring technique . This can be repaired by sealing the surface cracks by
injecting low viscosity epoxy, high molecular weight methacrylate (IPRF 2003) etc.
Edge slump: When the slip-form paver moves forward, the edge of concrete slab being unsupported, sometimes slumps at isolated locations. This edge slump seriously affects the
performance of the constructed pavement. The repair can be done by separately placing fresh
concrete (and not mortar) to the affected portions. Such repair should be conducted before
application of any curing compound (IPRF 2003).
Joint spalling: Joint spalling may occur due to (i) early joint sawing, (ii) use of wrong blade type,
or (iii) poor operation of the sawing equipment. Reforming manually the affected portions with fresh
concrete is recommended for isolated joint spalling problems.
Full depth cracking: Full depth cracking of newly constructed pavement can occur due to one or
combination of the following reasons (IPRF 2003):
Provide a link to the 'Slip form paving system' discussed in lecture 'construction of concrete
pavement'
• Late transverse joint sawing or insufficient depth of sawing.
• Misaligned dowel bars.
• Excessive curling and/or warping.
• Rapid surface cooling.
• Early age loading by construction equipment.
• Excessive drying shrinkage.
• Excessive base frictional restraint.
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
Complete replacement of the affected slab is generally recommended for such a situation. The
removal of the affected slab should be done panel by panel using some saw cutting tool (IPRF
2003), and not by any impact-type tool.
Repair of other common distresses
Joint seal failure: If the pavement is not badly deteriorated, but the joint seals are showing signs of
failure (i.e. missing or debonded sealant) - joint resealing is an appropriate action (ACPA 1993).
Hot or cold poured liquid sealants can be used for resealing purpose. The old sealant needs to
be removed, and the side walls of the joints need to be cleaned and made free from dust and
moisture before applying fresh sealants.
Loss of support: The locations of loss of support can be detected by falling weight deflectometer,
or other non-destructive techniques, like infrared thermography, ground penetrating radar etc
(Gordon et al. 1998, Moropoulou et al. 2001). One of the popular ways of treating loss of support
is by slab stabilization, where slab is not lifted, but the voids are filled by under-sealing, sub-sealing
or pressure grouting (ACPA 1994). Examples of these grouting materials are flyash grouts,
asphalt, polyurethane etc.
Partial depth cracking: Partial depth repairing is done when the distress is confined to upper surface
of the slab, spalling or fatigue cracking is less severe, and the joints are still functional etc.
Conventional portland cement, polymer based concrete or other cementations materials are used
for repair purpose. The type of the material chosen is based on (i) curing time, (ii) ambient
temperature, (iii) depth of cracks, (iv) expected performance etc (ACPA 1998). The repair area can
be decided by sounding technique with the help of a simple hammer.
Concrete is removed by sawing and light hammering from the chosen rectangular area, cleaned
and bonding and patching materials are applied (ACPA 1998). For cracks of low severity, crackstitching can be performed, which involves applying steel reinforced cement, which helps to hold
the cracks tightly (ACPA 1997).
Full depth cracking: Full depth repair is recommended for cracks extended to the full depth of the
pavements. Full depth repair takes care of blowups, corner breaks, transverse cracking,
longitudinal cracking, severe joint spalling etc (ACPA 1995). Conventional portland cement
concrete, with suitable additives, if required, is generally used for full depth repair. Same
procedure, as that of partial depth repair, is adopted for the full depth. Epoxy coated dowel bar/ tie
bars are suitably replaced in their designed positions. Compacting, finishing, curing, sawing, joint
sealing, texturing etc are done as required (ACPA 1995).
Surface irregularities and loss of skid resistance: The improvement of skid resistance and
removal of surface irregularities can be done by grinding and grooving . Equipment fitted with
closely spaced diamond blades/ discs are used for this purpose (ACPA 2000, Villemagne et al.
1996 ). Sometimes, riding quality related defects are treated with suitable bituminous surfacing
(Villemagne et al. 1996) or thin concrete overlay .
Weak load transfer at joints : Weak load transfer at the joints happen due to failure of dowel
bars. New set of dowel bars (or wedging system ) can be placed by machining by impact or by
sawing (Villemagne et al. 1996). However, replacement of dowel bars is a difficult, costly and timetaking process. Blocking of the whole joint with pressure grouting could be another alternative.
Closing remarks
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INTERNATIONAL INSTITUTE OF TECHNOLOGY & MANAGEMENT, MURTHAL SONEPAT
E-NOTES, Subject: Transportation Engineering Subject Code: CE 208 C Course: B. TECH
Branch: Civil Engineering, Sem-4th, unit:ALL
(Prepared By: Mr. Saurabh, Assistant Professor, CE)
The proper timing at which maintenance needs to be initiated, is an important consideration.
Sometimes certain limiting values are suggested on the functional or structural serviceability (say,
in terms of present serviceability rating, international roughness index etc.) conditions of the
pavement. If the serviceability rating falls below (or exceeds) certain specified limits, maintenance
of pavement is initiated.
Recapitulation
•
•
•
•
Various distresses of concrete pavement can be grossly categorized as, cracking, joint
deficiencies, surface defects and other types.
Maintenance strategies adopted for treatment of early stage distress of concrete pavement
are generally different than the treatment of distresses which show up gradually with the
movement of traffic.
Most of the structural repair techniques of concrete pavement generally involve application
of fresh concrete or other types binding agents. Slab replacement is generally suggested
for major distresses. Joint filling, re-grooving, re-texturing can be considered as some of
the functional maintenance strategies.
Selection of proper timing for maintenance activity is an important consideration.
Sometimes, certain limiting values of structural or functional serviceability conditions are
suggested; if the serviceability rating falls below/ exceeds certain specified limits,
maintenance of pavement is initiated
160