Importance-and-Components-of-Transportation
HIGHWAY AND RAILROAD ENGINEERING
Transportation Engineering Specialties
TRANSPORTATION
• The specialties in transportation engineering
• the act or process of moving people or things
are planning, design, construction, traffic
from one place to another
management and operations, and maintenance.
•
a way of travelling from one place to another
•
a system for moving passengers or goods from
one place to another
•
Transportation is essential for a nation’s
development and growth.
•
•
Transportation has played a significant role by
facilitating trade, commerce, conquest, and
social interaction, while consuming a
considerable portion of time and resources.
The primary need for transportation has been
economic, involving personal travel in search of
food or work, travel for the exchange of goods
and commodities, exploration, personal
fulfillment, and the improvement of a society or
a nation.
•
Transportation should be safe and
environmentally friendly
•
- It is the application of technology and scientific
principles to the planning, functional design
operation and management of facilities for any
mode of transportation in order to provide for
the safe, efficient, rapid, comfortable,
convenient, economical and environmentally
compatible movement of people as well as
goods.
IMPORTANCE OF TRANSPORTATION
Transportation and Economic Growth
• The speed, cost, and capacity of available
transportation have a significant impact on the
economic vitality of an area and the ability to
make maximum use of its natural resources.
Social Costs and Benefits of Transportation
 The history of transportation illustrates that the
way people move is affected by technology,
cost, and demand.
CYCLE PROCESS
•
Planning
•
Design
•
Construction
•
Traffic Management and Operation
•
Maintenance
Planning involves the selection of projects for design
and construction
Design involves the specification of all features of the
transportation project
Construction involves all aspects of the building process
Traffic management and operations involves studies to
improve capacity and safety
Maintenance involves all work necessary to ensure that
the highway system is kept in proper working order
TRANSPORTATION SYSTEM
 A transportation system may be defined as a
planned network of elements or physical
components that play different roles in the
transportation of goods and persons from one
place to another.
• Transportation systems are complex, dynamic
and internally interconnected, as well as
interconnected with other complex dynamic
systems (e.g., the environment, the economy).
•
The transportation system in a developed
nation is an aggregation of vehicles, guideways, terminal facilities, and control systems
that move freight and passengers.
HIGHWAY AND RAILROAD ENGINEERING
COMPONENTS
OF TRANSPORTATION SYSTEM
Disadvantage
MODES -They represent the conveyances, mostly
•
taking the form of vehicles that are used to support the
mobility of passengers or freight. Some modes are
designed to carry only passengers or freight, while
others can carry both.
It is relatively more expensive mode of
transport.
•
It is not suitable for transporting heavy and
bulk goods.
•
It is affected by adverse weather conditions.
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It is not suitable for short distance travel.
•
In case of accidents, its results in heavy losses
of goods, property and life.
Air Transport- includes all transport through the air by
aircraft. In an urban or regional context, this air
transport includes local air traffic such as small airplanes
or helicopters. From a broader perspective air transport
within urban or regional areas include passenger and
freight air routes that cross urban or regional areas. In
the context of urban security air transport is explicitly
high impact.
MODES OF TRANSPORT
- As experienced during 9/11 and other
terrorist threats the consequences of failing security are
devastating. Air traffic is therefore extremely well
monitored, both in terms of passengers or freight as in
terms of routing and operations management.
Land Transport - Land transportation simply
means any form of transportation that takes place on
land. This can be through road, rail, it can be facilitated
by animals such donkeys and camels or use a
combination of the wheel with electric or fuel powered
engines to move people and freight quickly and
efficiently. Land transport is the most common means
of transport in most places in the world.
Example: Hot Air Balloons, Airplanes, Helicopters
•
Air Transport
•
Advantages:
•
It is the fastest mode of transportation.
•
•
It is very useful in transporting goods and
passenger to the area, which are not accessible
by any other means.
•
•
It is the most convenient mode of
transportation during natural calamities.
•
It provides vital support to the national security
and defense.
Rail - the movement of passengers and goods
using wheeled vehicles, made to run on railway
tracks.
Road - route or way on land between two
places, which allow travel, including a horse,
cart, or motor vehicle.
Human-powered - the transport of people
and/or goods of walking, running and
swimming.
Animal-powered - the use of working animals
for the movement of people and goods.
Railway Transport -is the movement of
passengers and goods using wheeled vehicles, made to
run on railway tracks.
Advantages:
• It is a convenient mode of transport for
travelling long distances.
• It is relatively faster than road transport.
• It is suitable for carrying heavy goods in large
quantities over long distances.
• Its operation is less affected by adverse
weathers conditions like rain, floods, fog, etc.
Disadvantages:
•
•
•
•
HIGHWAY AND RAILROAD ENGINEERING
It is relatively expensive for carrying goods and
• The cost of maintaining and constructing routes
passengers over short distances.
is very low most of them are naturally made.
It is not available in remote parts of the
• It promotes international trade.
country.
It provides service according to fixed time
Disadvantages:
schedule and is not flexible for loading or
unloading of goods at any place.
• The depth and navigability of rivers and canals
It involves heavy losses of life as well as goods
vary and thus, affect operations of different
in case of accident.
transport vessels.
Road Transport - means transportation of goods
and personnel from one place to the other on roads.
Road is a route between two destinations, which has
been either paved or worked on to enable
transportation by way of motorized and non-motorized
carriages.
Advantages:
• It is a relatively cheaper mode of transport as
compared to other modes.
• Perishable goods can be transported at a faster
speed by road carriers over a short distance.
• It is a flexible mode of transport as loading and
unloading is possible at any destination. It
provide door-to-door service.
Disadvantages:
• Due to limited carrying capacity road transport
is not economical for long distance
transportation of goods.
• Transportation of heavy goods or goods in bulk
by road involves high cost.
Water transport
-is movement by means of a watercraft such as
a barge, boat, ship or sailboat over a body of water, suc
h as a sea, ocean, lake, canal or river. The need for
buoyancy is common to watercraft, making the hull a
dominant aspect of its construction, maintenance and
appearance. It is the least expensive and slowest mode
of freight transport. It is generally used to transport
heavy products over long distances when speed is not
an issue. Example: sailboats, ships, submarines, hoover
crafts, water planes, surf board, and ferries.
Advantages:
•
It is a relatively economical mode of
transportation for bulky and heavy goods.
•
It is safe mode of transport with respect to
occurrence of accidents.
•
It is slow moving mode of transport and
therefore not suitable for transport of
perishable goods.
•
It is adversely affected by weather conditions.
•
Sea transport requires large investment on
ships and their maintenance.
Other modes
Pipeline transport sends goods through a pipe,
most commonly liquid and gases are sent, but
pneumatic tubes can also send solid capsules using
compressed air. For liquids/gases, any chemically stable
liquid or gas can be sent through a pipeline. Shortdistance systems exist for sewage, slurry, water and
beer, while long-distance networks are used for
petroleum and natural gas.
Cable transport is a broad mode where vehicles are
pulled by cables instead of an internal power source. It
is most commonly used at steep gradient. Typical
solutionsinclude aerial tramway, elevators, escalator a
nd ski lifts; some of these are also categorized as
conveyor transport.
Space transport is transport out of Earth's
atmosphere into outer space by means of a spacecraft.
While large amounts of research have gone into
technology, it is rarely used except to put satellites into
orbit, and conduct scientific experiments.
2.INFRASTRUCTURES
The physical support of transport modes,
where routes “links” (e.g. rail tracks, canals or highways)
and terminals “nodes” (e.g. ports or airports) are the
most significant components.-
HIGHWAY AND RAILROAD ENGINEERING
3.NETWORKS
-A system of linked locations that are used to
represent the functional and spatial organization of
transportation. This system indicates which locations
are connected and how they are serviced. Within a
network some locations are more accessible (more
connections) than others (less connections).
Hierarchical Networks
 Highways
o Expressway
o Arterial Streets
o Collector Streets
o Local Streets
Expressway - is a divided highway facility having
two or more lanes in each direction for the exclusive
use of traffic, with full control of access and egress.
In the highway hierarchy, Expressway is the only facility
that provides complete uninterrupted flow.
An Expressway is composed of three subcomponents:
Basic freeway segment, weaving areas, and ramp
junctions.
Arterial Streets - A major surface street with
relatively long trips between major points, and with
through-trips entering, leaving, and passing through the
urban area.
Sub-Arterial Streets - A signalized street that
primarily serves through-traffic and that secondarily
provides access to abutting properties, with signal
spacing of 3.0 km or less.
Collector Streets - A surface street providing land
access and traffic circulation within residential,
commercial, and industrial areas. The function of
collector street is to collect traffic from local streets and
feed it to the arterial and sub-arterial streets or viceversa.
Local Streets - These streets provide access to the
abutting properties. Unrestricted parking and
pedestrian movement is allowed on these streets.
Pedestrian-Vehicle-Flow-Motion-Studies
HIGHWAY AND RAILROAD ENGINEERING
dynamic spatial requirements for avoiding
Pedestrian Characteristics
collisions with other pedestrians.
The pedestrian is a major user of roadway system; when
the system fails, he or she is a major victim. Certain
• A walking pedestrian requires a certain amount
segments of the pedestrian population – notably the
of forward space. This forward space is a
very young and the very old – are either unaware of
critical dimension, since it determines the speed
rules of safe pedestrian behavior or unresponsive to
of the trip and the number of pedestrians that
efforts to enforce pedestrian traffic regulations.
are able to pass a point in a given time period.
Traffic engineers are challenged to design safe and
The forward space is categorized into a pacing
convenient pedestrian facilities that will function well
zone and a sensory zone.
even for those persons who will fully or ignorantly
disobey rules of safe walking behavior. Such facilities
serve small children as well as elderly and physically
handicapped persons.
Designers of pedestrian facilities require knowledge of
the space requirements as walking speeds of individual
walkers as well as an understanding of traffic flow
characteristics of groups of pedestrians.
•
Research shown that one pedestrian following
another prefers to leave an average distancespacing between himself and the lead
pedestrian of about 8-ft (2.4 m). This
corresponds to an average time-spacing of
about 2 seconds between pedestrians walking
in time.
Information required by the designer are:
 Space Requirements (needs) for Pedestrians
 Walking and Running Speeds
 Walking and Running Speeds
Under free-flow conditions pedestrian walking
speeds tends to be approximately normally
distributed. Under such conditions, Pedestrian
walking speeds: 2.5 to 6.0 ft./sec (0.8 to 1.8
m/sec)Mean walking speeds: 4.0 to 4.5 ft./sec (1.2
to 1.4 m/sec)
 Traffic Flow Characteristics of Pedestrians
 Space Requirements (needs) for Pedestrians
A study indicated that for the 95th percentile:
•
Shoulder Breadth 22.8” = 579 mm
•
Body Depth 13.0”
•
We should give the pedestrian slightly more
spaces to avoid bodily contact with others & for
things, that may pedestrian carry with them .
So, an elliptical shape with a 24-in. (610mm)
major axis and an 18-in. (457mm) minoe axis
has been used for determining the pedestrian
standing area.
= 333 mm
•
It should be emphasized that 18 x 24-in ellipse is
useful primarily for the determination of space
needs or capacities for elevators or other
conveyances or locations where the pedestrians
are standing rather than walking.
•
For design of sidewalks or other pedestrian
corridors, one needs to be concerned with
A pedestrian walking rate of 4.0 ft./sec (1.2 m/sec)
is generally assumed for the timing of pedestrian
traffic signals. In areas where are large numbers of
elderly pedestrians, AASHTO recommends the use
of a 2.8 ft./sec (0.9 m/sec) walking rate.
 Walking and Running Speeds
The presence of significant numbers of handicapped
persons would also dictate the use of a lower rate
of movement.
Also, walking speeds decrease with increase in
pedestrian density. Empirical studies indicate that
for an average of 25 ft2 (2.3 m2) or more per
pedestrian, walking speeds are only slightly affected
by pedestrian conflicts. But when the available
space per pedestrian drops below 25 ft2 (2.3 m2),
the average walking speed decreases sharply.
HIGHWAY AND RAILROAD ENGINEERING
- It is the average number of pedestrians
per unit of area within a walkway or
Running Speed= 7.80 ft./sec (2.38 m/sec)
queuing area, expressed as pedestrians
per square meter (p/m2).
Fastest Running Speed = 33 ft./sec (10 m/sec)
 Running Speeds

Pedestrian Space
 Traffic Flow Characteristics of Pedestrian

Pedestrian
It is a person traveling on foot, whether walking or
running. In some communities, those traveling using
tiny wheels such a s r ol l e r sk a t e s , sk a t e b oa r d s
, a n d scoot e r s , a s w e l l as wheelchair users are
also included as pedestrians. In modern times, the
Pedestrian Speed-Density Relationships
The fundamental relationship
between
speed, density, and volume for pedestrian flow is
analogous to vehicular Flow. As volume and
density increase, pedestrian speed declines. As density
increases and pedestrian space decreases, the degree of
m obil i t y a ff or d e d t o t h e i n d i v i d u a l
pedestrian declines, as does the average speed of the
pedestrian stream.usually refers to someone walking on
a road or pavement, but this was not the case
historically.

Pedestrian Speed
-
It is the average pedestrian walking
speed, generally expressed in units of
meters per second (m/sec).
Pedestrian Flow Rate
-
It is the number of pedestrians passing
a point per unit of time, expressed as
pedestrian per 15 minute or pedestrian
per minute. Point refers to a line of
sight across the width of a walkway
perpendicular to the pedestrian path.
 Pedestrian Flow per Unit of Width
- It is the average flow of pedestrians per unit of
effective walkway width, expressed as pedestrians per
minute per meter (p/min/m).

It is the average area provided for each
pedestrian in a walkway or queuing
area, expressed in terms of square
meter per pedestrian. This is the
inverse of density, and is often a more
practical unit for analyzing pedestrian
facilities.
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Pedestrian Density

Platoon
It refers to a number of pedestrians
walking together in a group, usually
involuntarily, as a result of signal
control and other factors.
-
Pedestrian Speed-Density Relationships
-The fundamental relationship between
speed, density, and volume for pedestrian flow is
analogous to vehicular flow.
As volume and density
increase, pedestrian speed declines. As density
increases and pedestrian space decreases, the degree
of m obil i t y a ff or d e d
to
the indiv
i d u a l pedestrian declines, as does the average speed
of the pedestrian stream.
The relationship among density, speed, and
flow for pedestrians is similar to that for vehicular
traffic streams, and is expressed in
q
ped
=k
ped
*u
ped
where:
qped= unit flow rate (p/min/m),
uped= pedestrian speed (m/min),
kped= pedestrian density (p/m2 ).
Factors Affecting Pedestrian Demand
o The nature of the local community - Walking is
more likely to occur in a community that has a
high proportion of young people
o Car ownership -The availability of the private
car reduces the amount of walking, even for
short journey
o Local land use activities- Walking is primarily
used for short distance trips. Consequently the
distance between local origins and destinations
(e.g. homes and school, homes and shops) is an
HIGHWAY AND RAILROAD ENGINEERING
important factor influencing the level of
Design Principle of Pedestrian
demand, particularly for the young and elderly.
Facilities
o Quality of provision- If good quality pedestrian
 Sidewalk
facilities are provided, then demand will tend
 Crosswalk
to increase.
 Traffic Islands
 Pedestrian Overpass & Underpass
Data Collection
 Street Corner
Before deciding on the appropriate extent and
standard of pedestrian facilities, it is important to
assess the potential demand.
 Sidewalks
The possible methods of obtaining such estimates are:
Sidewalks are pedestrian lanes that provide people with
o Manual Count
space to travel within the public right-of-way that is
o Video Survey
separated from roadway vehicles. They also provide
o Attitude Survey
places for children to walk, run, skate, ride bikes, and
play. Sidewalks are associated with significant
Manual Count
reductions in pedestrian collisions with motor vehicles.
Count the flow of pedestrian through a junction, across
Width: The minimum clear width of a pedestrian access
a road, or along a road section/footway manually using
route shall be 1.22 meters exclusive of the width of
manual clicker and tally marking sheet. Manual counts
curb. It varies according to pedestrian flow rate and
need to satisfy the following conditions.
different Level of Service.
 The day(s) of the week and month(s) of the year
Cross Slope: The cross slope of the pedestrian access
when observations are made must be
route shall be maximum of 1:48.
representative of the demand. School holidays,
Surfaces: Surface should be firm, stable, slip resistance
early closing, and special events should be
and prohibit openings & avoid service elements (i.e.
avoided since they can result in non-typical
manholes, etc.)
conditions.
 The survey locations need to be carefully
selected in order to ensure that
 Crosswalks
the total existing demand is observed.
Marked crosswalks indicate optimal or preferred
locations for pedestrians to cross and help designate
Video Survey
right-of-way for motorists to yield to pedestrians.
Cameras are setup at the selected sites and video
Crosswalks are often installed at signalized
recording taken of the pedestrians during the selected
intersections and other selected locations. It should be
observation periods. A suitable vantage point for the
located at all open legs of signalized intersection. It
camera is important. Such survey produces a
should be perpendicular to roadway.
permanent record of pedestrian movement and their
interaction with vehicles. In it the record of behavior
The parallel line should be 0.2-0.6 m in width
pattern is also obtained which helps in analyzing the
and min. length 1.8 m (standard 3m). Marking may be
crossing difficulties.
of different type to increase visibility like as solid,
standard, continental, dashed, zebra, ladder. It is
Attitude Survey
shown in the figure.
Detailed questionnaire requires enabling complete
information about pedestrian’s origins and destination
points, also can gather information on what new
 Traffic Islands
facilities, or improvements to existing facilities, need to
Traffic islands to reduce the length of the crossing
be provided to divert trips to walking, or increase the
should be considered for the safety of all road users. It
current pedestrian activities.
is used to permit safe crossing when insufficient gap in
two directions traffic & helps elderly, children and
disabled.
It works best when refuge area median is greater than
cross walk width or 3.6 m, have a surface area of at
least 4.6 m2, are free of obstructions, have adequate
HIGHWAY AND RAILROAD ENGINEERING
drainage, and provide a flat, street level surface to
Vehicle Characteristics
provide accessibility to people with disabilities.
Criteria for the geometric design of highways
-The Refuge area width should be at least 1.2 m
wide and depend upon traffic speed. It should be 1.5m
wide on streets with speeds between 40- 48 kph, 1.8 m
wide(48-56 kph), and 2.4 m (56-72 kph).
 Pedestrian Overpass & Underpass
-Pedestrian facilities at-grade and as directly as
possible are always preferred. However, where grade
separation is indicated, paths that are attractive,
convenient and direct can become well-used and highly
valued parts of a city’s pedestrian infrastructure.
These are expensive method but eliminate all or most
conflicts. These may be warranted for critical locations
such as schools factory gates, sports arenas, and major
downtown intersections (specially in conjunction with
transit stations).
Minimum width is required 1.22 m, although 1.83 is
preferred.
 Street Corner
Available Time-Space: The total time-space available
for circulation and queuing in the inter-section corner
during an analysis period is
the product of the net corner area and the length of
the analysis period. For street corners, the analysis
period is one signal cycle and therefore is equal to the
cycle length. The following equation is u sed to com pu
te t im e- space available at an intersection corner.
Intersection Corner Geometry is shown.
TS = C(Wa * Wb – 0.215R2)
where:
TS= available time-space(m2-sec)
Wa= effective width of sidewalk a(m)
Wb= effective width of sidewalk b(m)
R= radius of corner curb (m)
C= cycle length (s)
Pedestrian signals are designed basically
considering minimum time gap required for crossing
the pedestrians. This minimum time gap can be
calculated by using following gap equation.
WherE:
Gs = min. time gap (sec)
W = width of crossing section (m)
tc = consecutive time between two pedestrian
(sec) ts = startup time (sec)
N = number of rows
uped = pedestrian speed (m/sec)
are partly based on the
static, kinematic, and dynamic characteristics
of vehicles.
• Static characteristics include the weight and
size of the vehicle.
• Kinematic characteristics involve the motion
of the vehicle
without considering the forces that cause the
motion.
• Dynamic characteristics involve the forces
that cause the motion of the vehicle.
Since nearly all highways carry both passengerautomobile and truck traffic, it is essential that design
criteria take into account the characteristics of
different types of vehicles.
A thorough knowledge of these characteristics will aid
the highway and/or traffic engineer in designing
highways and traffic-control systems that allow the
safe and smooth operation of a moving vehicle,
particularly during the basic maneuvers of passing,
stopping, and turning.
The characteristics of the design vehicle are
then used to determine criteria for geometric design,
intersection design, and sight-distance requirements.
• Static Characteristics
The size of the design vehicle for a highway is an
important factor in the determination of design
standards for several physical components of the
highway. The static characteristics of vehicles expected
to use the highway are factors that influence the
selection of design criteria for the highway.
These include lane width, shoulder width, length and
width of parking bays, and lengths of vertical curves.
The axle weights of the vehicles expected on the
highway are important when pavement depths and
maximum grades are being determined.
-It is therefore necessary that all vehicles be
classified so that representative static characteristics
for all vehicles within a particular class can be provided
for design purposes.
AASHTO has selected four general classes of vehicles:
• Passenger Cars (sport/utility vehicles,
minivans, vans, pick-up trucks)
HIGHWAY AND RAILROAD ENGINEERING
Buses (city transit, school buses,
rom = xî
articulated buses)
where
• Trucks (single-unit trucks, truck tractorrom = position vector for min T
semitrailer combinations, truck tractors
î = a unit vector parallel to lime om
with semitrailer in combination with full
x = distance along the straight line
trailers, etc.)
• Recreational Vehicles (motor homes,
The velocity and acceleration for m may be simply
cars with camper trailers, cars with
expressed as:
boat trailers, motor homes pulling cars)
um = r’om = x’î
In carrying out the design of any of the
am = r’’om = x’’î
intersections, the minimum turning radius for
where:
um = velocity of the vehicle at point m
the selected design vehicle traveling at a speed
am = acceleration of the vehicle at point m
of 16 kph should be provided.
x’ = dx/dt
Minimum turning radii at low speeds (16 kph or
x” = d2x/dt2
less) are dependent mainly on the size of the
vehicle.
Minimum
safe
radius for
a
given design speed from the
Two cases are of interest:
rate
of super elevation and side1) Acceleration is assumed constant.
friction factor.
2) Acceleration is a function of velocity.
•
•
•
•
R = V2 / 127( 0.01e+ f)
• Kinematic Characteristics
Kinematic characteristics involve the motion of the
vehicle without considering the forces that cause the
motion. The primary element among kinematic
characteristics is the acceleration capability of the
vehicle.
Acceleration capability is important in several traffic
operations, such as passing maneuvers and gap
acceptance. Also, the dimensioning of highway features
such as freeway ramps and passing lanes is often
governed by acceleration rates.
Therefore , a study of the kinematic characteristics
of the vehicle primarily involves a study of how
acceleration rates influence the elements of motion,
such as velocity and distance.
A study of the kinematic characteristics of the
vehicle primarily involves a study of how acceleration
rates influence the elements of motion, such as velocity
and distance.
We therefore review in this section the
mathematical relationships among acceleration,
velocity, distance, and time.
Let us consider a vehicle moving along a straight
line from point 0 to point m, a distance x in a reference
plane T. The position vector of the vehicle after time t
may be expressed as:
Acceleration Assumed Constant
When the acceleration of the vehicle is
assumed to be constant, Th e con st a n t s C 1 a n d C 2 a
r e determined either by the initial conditions on
velocity and position or by using known positions of the
vehicle at two different times.
x‘ = at + C1
x = ½ at2 + C1t + C2
Acceleration as a Function of Velocity
The assumption of constant acceleration has
some limitations, because the accelerating capability of
a vehicle at any time t is related to the speed of the
vehicle at that time (ut). The lower the speed, the
higher the acceleration rate that can be obtained.
Figures 3.4a and 3.4b show maximum acceleration
rates for passenger cars and tractor-semitrailers at
different speeds on level roads.
•
Dynamic Characteristics
Several forces act on a vehicle while it is in
motion that tends it to retard by at least five (5) types
of resistance:
 Inertial Resistance
 Grade Resistance
 Rolling Resistance
 Curve Resistance
 Air Resistance
HIGHWAY AND RAILROAD ENGINEERING
For trucks, the rolling resistance can be obtained from,
 Inertial Resistance
Inertia is the tendency of a body to resist
acceleration: the tendency to remain at rest or to
remain in motion in a straight line unless acted upon by
some force. The force, Fi required to overcome a
vehicle’s inertia is,
F= m * a = �
Where:
m = vehicle mass (kg-sec2/m)
a = acceleration (m/sec2)
w= vehicle weight (kg)
g = accelerative force due to gravity (9.8 m/sec2)
 Grade Resistance
When a vehicle moves up a grade, a component
of the weight of the vehicle acts downward, along the
plane of the highway. This creates a force acting in a
direction opposite that of the motion. This force is the
grade resistance. A vehicle traveling up a grade will
therefore tend to lose speed unless an accelerating
force is applied.
Fg= m * g * sin Ɵ
Where:
m = vehicle mass (kg-sec2/m)
g = accelerative force due to gravity (9.8 m/sec2)
Ɵ = angle of incline (degrees)
 Rolling Resistance
-A vehicle does not operate on a smooth,
frictionless surface. There is resistance to motion as the
tires roll over irregularities in the surface. This
resistance, termed rolling resistance, Fr , includes that
caused by the flexing of the tires and the internal
friction of the moving parts of the vehicle.
Rolling resistance is higher on low-quality pavement
surfaces, and it increases with increase in vehicle
speed.
The rolling resistance force for passenger cars on a
smooth pavement can be determined from the relation
Fr = (Ca + 0.278Cbu) * W
Where:
Fr = rolling resistance force (kg)
Ca = constant (typically 0.02445 for trucks)
Cb = constant (typically 0.00147 s/m for trucks)
u = vehicle speed (kph)
W = gross vehicle weight (kg)
 Curve Resistance
-When a passenger car is maneuvered to take a
curve, external forces act on the front wheels of the
vehicle. These forces have components that have a
retarding effect on the forward motion of the vehicle.
The sum effect of these components constitutes the
curve resistance. This resistance depends on the radius
of the curve, the gross weight of the vehicle, and the
velocity at which the vehicle is moving.
Fc = ½ (��
Where:
v = the vehicle velocity (m/sec)
W = the vehicle weight (kg)
g = the acceleration of gravity (9.8 m/sec2)
R = the radius of curvature (m)
 Air Resistance
-Air resistance includes the force required to
move air from a vehicle’s pathway as well as the
frictional effects of air along its top, sides, and
undercarriage. It is a function of the frontal crosssectional area of the vehicle and the square of the
vehicle speed.
Fa = ½ * CD * A * (ρ * v2)
Where:
CD = aerodynamic drag coefficient (typically 0.4 for
passenger cars and 0.5 to 0.8 for trucks)
A = frontal cross-sectional area (m2)
ρ = air density (kg-sec2/m)
v= vehicle velocity (m/sec)
Fr = (Crs + 0.077Ccru2) * W
Where:
Fr = rolling resistance force (kg)
Crs = constant (typically 0.012 for passenger cars)
Crv = constant (typically 7x10-6 sec2/m2 for passenger
cars)
u = vehicle speed (kph)
W = gross vehicle weight (kg)
Power Requirements
-Power is the rate at which work is done. It is
usually expressed in horsepower (a U.S. unit of
measure), where 1 horsepower is 746 Watts. The power
Prequired to overcome the various resistances (inertia,
grade, rolling curve, air) and to propel a vehicle.
HIGHWAY AND RAILROAD ENGINEERING
P= R*v, watts
where:
R= sum of the various resistances (N)
v= vehicle velocity (m/sec)
Braking Distance
-The action of the forces on the moving vehicle
and the effect of perception-reaction time are used to
determine important parameters related to the
dynamic characteristics of the vehicles.
These include the braking distance of a vehicle and the
minimum radius of a circular curve required for a
vehicle traveling around a curve with speed u where u
> 16 km/h.
Db= v 2 /?
where:
d = braking distance (m)
v = design speed (m/sec)
a = deceleration rate (m/sec2)
Stopping Sight Distance
The minimum distance required to stop a vehicle
traveling near the design speed before it reaches a
stationary object in vehicle’s path. This stationary
object may be another vehicle or some other object
within the roadway.
The minimum stopping sight distance is based on the
sum of two distances:
1. The distance traveled from the time the
object is sighted to the instant the
brakes are applied.
2. The distance required for stopping the
vehicle after the brakes are applied.
SSD = 퐮t
u2
��(� ±�)
where: t = perception-reaction (sec), usually 0.75
seconds
u
=
v el ocity
at
which the
v ehicl e
was
t r av el in g when the
brakes were applied (m/s).