RIICWD508E
PREPARE DETAILED DESIGN
OF
RURAL ROADS
STUDENT GUIDE
SOME COMMON INFRASTRUCTURE TERMINOLOGIES
Adverse Crossfall: A slope on a curved pavement which generates forces detracting from the ability of a vehicle
to maintain a circular path.
Alignment: The geometric form of the centreline (or other reference line) of a carriageway in both the horizontal
and vertical directions.
Arterial Road: A road with a prime function to provide for major regional and inter-regional traffic movements.
Auxiliary Lane: A portion of the carriageway adjoining the through traffic lanes, used for purposes
supplementary to the through traffic movement.
Barrier: An obstruction placed to prevent vehicle access to a particular area.
Barrier Kerb: A kerb with a profile and height sufficient to prevent or discourage vehicles moving off the
carriageway.
Carriageway: That portion of a road or bridge devoted particularly to the use of vehicles, inclusive of the
shoulders and auxiliary lanes.
Centreline: The basic line which defines the axis or alignment of the centre of a road or other works.
Clearance: The space between a moving and a stationary object.
Crossfall: The slope, measured at right angles to the alignment, of the surface any part of a carriageway.
Crown: The highest point on the cross section of a carriageway with two-way crossfall.
Cycle Lane: A paved area adjacent to and flush with the traffic lane pavement for the movement of cyclists.
Design Speed: A minimal speed fixed to determine the geometric features of a road.
Design Vehicle: A hypothetical road vehicle whose mass, dimensions and operating characteristics are used to
determine geometric requirements.
Drainage: Natural or artificial means for the interception and removal of surface of subsurface water.
Footpath: A public way reserved for the movement of pedestrians and manually propelled vehicles.
Formation: The surface of the finished earthworks, excluding cut or fill batters.
Grade: A length of carriageway sloping longitudinally. The rate of longitudinal rise (or fall) of a carriageway
with respect to the horizontal, expressed as a percentage. To design the longitudinal profile of a road. To
secure a predetermined level or inclination to a road or other surface. To shape or smooth an earth, gravel,
or other surface by means of a grader of similar implement. To mix aggregates according to a particle size
distribution.
Grade Separation: The separation of road, rail, or other traffic so that crossing movements, which would
otherwise conflict, are at different elevations.
Horizontal Curve: A curve in the plan or horizontal alignment of a carriageway.
Interchange: A grade separation of two or more roads with one or more interconnecting carriageways.
Intermediate Sight Distance: A distance, adopted for reasons of economy, which models an overtaking vehicle
completing, or aborting, an overtaking manoeuvre before reaching an opposing vehicle.
Intersection: A place at which two or more roads at grade or with grade separation.
Intersection Angle: An angle between two successive straights on the centreline of a carriageway. The angles
between the centrelines of two intersecting carriageways.
Intersection (at-grade): An intersection where carriageways cross at a common level.
Intersection Leg: Any one of the carriageways radiating from and forming part of an intersection.
K Value: The constant rate of change of grade of a parabolic vertical curve expressed as a percentage.
Kerb: A raised border of rigid material formed at the edge of a carriageway.
Kerb Clearances: A distance by which the kerb should be set back to maintain the maximum capacity of the
traffic lane.
Lane (Traffic): A portion of the paved carriageway marked out by kerbs, painted line, or barriers, which carries
a single line of vehicles in one constant direction.
Lane Separator: A separator provided between lanes carrying traffic in the same direction to discourage or
prevent lane changing, or to separate a portion of a speed change lane from through lanes.
Lateral Friction: The force which, when generated between the tyre and the road surface assists a vehicle to
maintain a circular path.
Level of Service (LOS): A qualitative measure describing operational conditions within a traffic stream and their
perception by motorists and passengers.
Line of Sight: The direct line of uninterrupted view between a driver and an object specified height above the
carriageway in the lane of travel.
Longitudinal Friction Factor: The friction between vehicle tyres and the road pavement measured in the
longitudinal direction.
Longitudinal Section: A vertical section, usually with an exaggerated vertical scale, showing the existing and
design levels along a road design line, or another specified line.
Median: A strip of road, not normally intended for use by traffic, which separates carriageways for traffic in
opposite directions.
Median Island: A short length of median serving a localised purpose in an otherwise undivided road.
Median Opening: A gap in a median provided for crossing and turning traffic.
Normal Cross Section: The cross section of the carriageway where it is not affected by superelevation or
widening.
One-way Road: A road or street on which all vehicular traffic travels in the same direction.
Overtaking: The manoeuvre I which a vehicle moves from a position behind to a position in front of another
vehicle travelling in the same direction.
Overtaking Distance: The distance required for one vehicle to overtake another vehicle.
Pavement: That portion of a road designed for the support of, and to form the running surface for, vehicular
traffic.
Property Line: The boundary between a road reserve and the adjacent land.
Rate of Rotation: The rate of rotation required to achieve a suitable distance to uniformly rotate the crossfall
from normal to full superelevation. The usual value adopted is 0.025 rad/sec; 0.035 rad / sec is the
maximum value.
Reaction Distance: The distance travelled during the reaction time.
Reaction Time: The time between the driver’s reception of stimulus and taking appropriate action.
Re-alignment: An alteration to the control line of a road which may affect only its vertical alignment but, more
usually, alters its horizontal alignment.
Reverse Curve: A section of road alignment consisting of two arcs curing in opposite directions and having a
common tangent point or being joined by short transition curve.
Road(way): A route trafficable by motor vehicles; in law, the public right-of-way between boundaries of
adjoining property.
Roundabout: An intersection where all traffic travels in one direction around a central island.
Rural road: Normally a sealed unkerbed road with free draining pavement and table drains instead of gutters. In
urban areas, rural type roads may be provided where there is no adjacent urban development. The term
rural road does not imply “low standard” road or “short life” road. If such requirements exist, they are
explicitly specified by the Client.
Sag Curve: A concave vertical curve in the longitudinal profile of a road.
Shoulder: The portion of formed carriageway that is adjacent to the traffic lane and flush with the surface of the
pavement.
Sideways Friction Co-efficient: The ratio of the resistance to sideways motion of the tyre of a vehicle (on a
specified pavement) and the normal force on that wheel due to the vehicle mass.
Sight Distance:
- Approach Sight Distance: The distance required for a driver to perceive marking or hazards on the road
surface and to stop.
- Car Stopping Distance: The distance required for a car driver to perceive an object on the road and to
stop before striking it.
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Entering Sight Distance (ESD): The sight distance required for minor road drivers to enter a major road
via a left or right turn, such that traffic on the road is unimpeded.
- Manoeuvre Sight Distance: The distance required for an alert car driver to perceive an object on the road
and to take evasive action.
- Overtaking Sight Distance: The sight distance required for a driver to initiate and safely complete an
overtaking manoeuvre.
- Railway Crossing Sight Triangle: The clear area required for a truck driver to perceive a train
approaching an uncontrolled railway crossing and to stop the truck.
- Safe Intersection Sight Distance: The distance required for a driver in a major road to observe a vehicle
entering from a side road, and to stop before colliding with it.
- Sight Distance Through Underpass: The distance required for a truck driver to see beneath a bridge
located across the main road, to perceive any hazard on the road ahead, and to stop.
- Truck Stopping Sight Distance: The distance required for a truck driver to perceive an object on the
road and to stop before striking it.
Skid Resistance: The frictional relationship between a pavement surface and vehicle tyres during braking or
cornering manoeuvres. Normally measured of wet surfaces, it varies with the speed and the value of ‘slip’
adopted.
Slope: The inclination of a surface with respect to the horizontal, expressed as rise or fall in a certain longitudinal
distance. An inclined surface.
Speed: 85th Percentile: The speed at which 85 percent of car drivers will travel slower and 1 percent will travel
faster.
Operating Speed of Trucks: The 85th percentile speed of trucks measured at a time when traffic volumes are
low.
Section Operating Speed: The value at which vehicle speeds on a series of curves tend to stabilise and is related
to the range of radii on the curves.
Stopping Sight Distance: The sight distance required by an average driver, travelling at a given speed, to react
and stop.
Sub-arterial Road: Road connecting arterial roads to areas of development and carrying traffic directly from on
part of a region to another.
Superelevation: A slope on a curved pavement selected to enhance forces assisting a vehicle to maintain a
circular path.
Superelevation Development: The area in which the transverse slopes on a carriageway are gradually changed
from normal crossfall to superelevation.
Table Drain: The side drain of a road adjacent to the shoulder, having its invert lower than the pavement base
and being part of the formation.
Terrain: Topography of the land.
Traffic: A generic term covering all vehicles, people, and animals using a road.
Traffic Island: A defined area, usually at an intersection, from which vehicular traffic is excluded. It is used to
control vehicular movements and as a pedestrian refuge.
Traffic Lane: A portion of the paved carriageway marked out by kerbs, painted line, or barriers, which carries a
single line of vehicles in one constant direction.
Traffic Sign: A sign to regulate traffic and warn or guide drivers.
Transition Curve: A curve of varying radius used to model the path of a vehicle as the driver moves the steering
wheel from straight to a horizontal curve of constant radius.
Typical Cross Section: A cross section of a carriageway showing typical dimensional details, furniture locations
and features of the pavement construction.
Verge: That portion of the formation not covered by the carriageway or footpath.
Vertical Alignment: The longitudinal profile along the centreline of a road.
Vertical Curve: A curve (generally parabolic) in the longitude profile of a carriageway to provide for a change
of grade at a specified vertical acceleration.
1. RURAL ROADS
Background:
The determination of some Controlling Criteria and other Elements of Design are based on the Urban or Rural
nature of a roadway. Categorization of a project as either Urban or Rural therefore needs to be established before
appropriate design standards can be selected. The Urban or Rural nature of a roadway cannot be established
simply by looking at traffic volumes or speeds or by selecting from a table. When an Engineering Instruction
requires the determination of the Urban or Rural nature of a roadway, the following Guidance should be applied.
Guidance:
This guidance provides a tool by which the Urban or Rural nature of a roadway can be defined. For each project,
a roadway evaluation is necessary, and an Urban/Rural categorization made that can be supported by the project
team. A roadway may not always fit neatly into one of these categories, and use of engineering judgment will be
required.
Rural Roadways
Roadways that are not considered Urban in nature will be considered Rural. Rural roadways will generally be
characterized by moderate to high posted speeds, infrequent entrances and low residential or commercial
development. Open drainage is generally prevalent. A Rural Road is a road located outside of the boundaries of
an urban area. Rural roads carry lower traffic volumes and are not subject to as many constraints as urban roads
Urban Roadways and Streets
Roadways that are Urban in nature will generally be characterized by low to moderate posted speeds, frequent
entrances, and moderate to heavy residential or commercial development. Curbed sections with closed drainage
will generally be prevalent, although open drainage sections may be interspersed. Intersections, sidewalks, and
on-street parking are often characteristic of Urban roadways.
Low-Speed Urban Streets
Urban roadways with relatively low posted speeds and variable rates of speed resulting from more frequent
conflicts are categorized as Low-Speed Urban Streets. These streets will generally be characterized by frequent
entrances and heavy residential or commercial development. They generally include curb and sidewalk sections,
often with building fronts adjacent to or near the back of sidewalk. Frequent intersections, cross walks, and onstreet parking are usually present.
1.1 Classification of Rural Roads Based on Functionality
Residential Streets
The primary function of residential streets is to provide access to abutting property. This classification consists
of the largest portion of the street and road network and provides the linkage to connect to higher types of
facilities. Motorists’ speeds may be low, or higher, depending on the standards to which the specific facility is
designed.
Most trips on residential streets are short, and traffic volumes are low. Truck traffic is usually limited to vehicles
that provide residential services such as trash pickup, moving vans, heating oil delivery, etc.
Collector Streets
Collector or feeder streets connect the residential street system with arterial routes. This classification of street
serves dual functions of both land access and through traffic movement. The mileage of collectors in any one
jurisdiction may be very small. Generally, collectors have moderate amounts of low-to-intermediate-speed traffic,
including some bus traffic, and heavy trucks.
Arterial Streets
Arterial streets provide the highest operating speeds and the highest levels of traffic service. They serve the major
corridors of traffic and are usually multiple lanes in urban areas. They are typically high-volume facilities that
connect major activity centres.
As with the design of residential and collector facilities, many localities have adopted standards for the design
and construction of arterials. All applicable local and state codes, standards, and specifications should be
complied with when designing and constructing these facilities. The information contained in this Design Guide
should augment local guidelines in assuring the proper planning and design of arterials.
Although arterials frequently carry very large traffic volumes and heavy truck traffic, pavement designs
recommended herein are applicable only to facilities having a low percentage of truck traffic. Design of Asphalt
Concrete pavements for trucking highways requires considerable expertise and detailed analysis.
Low-Volume Secondary and Rural Roads
Low-volume rural roads consist of local roads and collectors whose primary function is to provide access to
abutting property and from there to arterial routes. Motorists’ speeds may be low, or higher depending on the
standards to which the specific facility is designed.
Truck traffic is usually low, consisting of some bus traffic and heavy trucks. Most traffic consists of vehicles
providing local service such as heating oil and gasoline, local farm traffic, and farm vehicles.
High-Volume Secondary and Rural Roads
High-volume rural roads consist of arterial roads and the highway system. They provide the highest operation
speeds and highest level of traffic service. These roads serve as the major corridors of traffic and frequently have
multiple lanes.
These roads frequently carry large traffic volumes and heavy truck traffic. The information contained within this
guide should augment local guidelines in assuring proper planning and design of high-volume roads. The values
found here are only applicable to low truck volumes. Design of Asphalt Concrete pavements for trucking
highways requires considerable expertise and detailed analysis.
1.2 Classification of Roads Based on Operating Speeds
Drivers have an expectation that rural roads that carry relatively high volumes of traffic will provide geometry
that allows them to travel at higher speeds. This is especially the case where the road is constructed in flat or
undulating country. Where there is an obvious reason for a lower standard of geometry (e.g. rugged or steep
terrain), drivers expect that they will have to travel at lower speeds and therefore are more prepared to adjust
to lower standard geometry than where there is no apparent reason for it. Drivers do not adjust their speeds
to the function or classification of the road but to the perceived physical limitations and the prevailing traffic
conditions. It is worth noting however, that drivers are less likely to appropriately respond to sections of lower
standard geometry on more important roads. This is especially the case where the section of road is not long
enough to have drivers feel that their desired speed is no longer appropriate.
Regardless of functional classification, rural roads can be classed in terms of their general operating
characteristics as:
• high speed rural roads
• intermediate speed rural roads
• low speed rural roads.
High Speed Rural Roads
These are roads that are designed for operating speeds in excess of 90 km/h. This may include freeways, which
are intended to provide a high quality of service for large traffic volumes. Operating speeds on high speed roads
are not constrained by the largely consistent geometry of the road but by a number of other factors, which include:
• the degree of risk drivers are prepared to accept
• speed limits and the level of enforcement of those limits
• vehicle performance.
The standard of horizontal and vertical geometry for these roads typically supports a high desired speed and
permits (and indeed encourages) uniform operating speeds. On these types of roads, the desired speed will
equal the operating speed. Consequently, they should have a single design speed.
Sometimes, a design speed higher than the operating speed is used on rural highways in order to promote a
higher quality of service.
Figure 1.1: Examples of high speed roads
Intermediate Speed Rural Roads
Minimum operating speeds on these roads are generally constrained by the geometry to about 70–90 km/h.
Drivers will however, accelerate whenever the opportunity arises, such as on any straight or large radius curve.
Speeds will increase up to the desired speed where possible, which may be up to 110 km/h. Horizontal curve radii
on these roads are generally in excess of 160 m, and the vertical alignment usually has little effect on operating
speeds.
Figure 1.2: Examples of intermediate speed roads
Low Speed Rural Roads
These are roads having many curves with radii less than 150 m. Operating speeds on the curves generally vary
from 50–70 km/h. Rural roads usually only have these characteristics when difficult terrain and costs preclude
the adoption of higher standard geometry. The alignments provided in these circumstances could be expected to
produce a high degree of driver alertness, so those lower standards are both expected and acceptable. These roads
often have a reduced speed limit (typically 60 to 80 km/h), which helps to lower the desired speed. As with
intermediate speed rural roads, drivers will slow down for horizontal curves where necessary, then accelerate
whenever the opportunity arises on large radius horizontal curves or long straights. Long steep grades may
influence operating speeds but the size of crest vertical curves will not.
The most pragmatic approach to the design of individual elements in such constrained situations is to provide the
best curvature practicable, and to check that it is within the minimum standards for the operating speed.
Figure 1.3: Examples of low speed roads
2. GENERAL ROAD DESIGN PRINCIPLES & OBJECTIVES
Definition Of Road Design
Design is the process of originating and developing a plan for an aesthetic and/or functional object, requiring
research, thought, modelling, iterative adjustment, and redesign.
Road design is a complex task in which judgement and experience play significant roles. Design is the process
of selecting and combining appropriate elements that will develop a fit-for-purpose solution. It is an iterative
process that requires a designer to exercise their judgement and experience whilst also practically applying
accepted technical guidelines and continually evaluating the design to assist in the selection of the appropriate
values for the design elements.
In road design, the result of the design process is presented in drawings and 3D modelling and in specifications
to allow the road to be constructed. The philosophy and principles set out in these documents underpin the creation
of a successful design. Every road project is a unique undertaking and can never be precisely repeated. There are
no ‘off the shelf’ solutions that will fully address all situations encountered, and the rigid and unthinking
application of charts, tables and figures is unlikely to lead to a successful design outcome.
Good design requires creative input based on experience and a sound understanding of the principles to develop
an optimum solution that is within the context of the project and balances often competing and contradictory
factors.
Designers choose the features of the road, primary design elements and design dimensions based on technical
guides, calculations, and their own experience and judgement. While these may be considered in sequence,
consideration of these in isolation from each other is not design. It is essential that designers understand the effects
(particularly on safety) of combining limiting values of different design elements under different circumstances.
In situations where road designs are not constrained by topography, natural or man-made features, environmental
considerations, or budgetary requirements, the most suitable detailing of a design should not be difficult.
However, many situations arise in which constraints apply and, in such cases, the experience and judgement of
the designer, together with relevant research and literature, play a significant role in developing the most
appropriate outcomes.
All road design is a compromise between the ideal and what is a reasonable solution. It needs to consider the
objectives of the project, the objectives of road design and the context of the site. Due to the nature of the design
process, the final design solution cannot generally be considered as ‘correct’ or ‘incorrect’ but rather as more or
less efficient (in terms of moving traffic), safe (in terms of fatal and serious injury crash reduction), or costly (in
terms of construction costs, life-cycle costs, and environmental impacts).
Roads should be designed to:
• provide safe, short, and fast thoroughfare and access to all road users, being motor vehicles, cyclists, and
pedestrians.
• clearly convey the primary function to road users and encourage appropriate driver behaviour.
• deliver traffic volumes at speeds compatible with function.
• provide convenient location for services.
• provide an opportunity for landscaping.
• allow for parking, where appropriate.
• have due regard to topography, geology, climate, environment, and heritage of the site.
• provide low cost of ownership.
• comply with these Standards and relevant AUSTROADS, and other State Road Authorities’ Guidelines
and/or Standards.
ROAD DESIGN PRINCIPLES:
A design should be developed with consideration of the Definition of Road Design in accordance with the
following principles of road design:
- Personnel: A design must be undertaken by a qualified road designer under the supervision of a
professional engineer, both with appropriate road design experience in line with the scope of the project.
Qualifications must be acceptable to Australian and New Zealand agencies. Designs are normally
undertaken by engineering teams with input provided by various other professional disciplines.
- Project objectives: A design should meet the objectives of the project while mindful of the objectives for
the road link and network. The design team must understand the scope and intention of the project and its
relationship to the development of the road network to be able to meet the project objectives.
- Fit-for-purpose: A design must be fit-for-purpose, whilst trying to achieve the highest possible standard
of design, operational efficiency, and safety within the context of the site, the project scope and budget.
The design team must understand the purpose and function of the road as well as project scope to
appropriately apply relevant guidelines and engineering judgement to develop a design solution that is fitfor-purpose. A design should cater for all road-engineering disciplines (geometric design, safety, traffic,
drainage, pavements, asset management, etc).
- Site specifics: A design must be context-sensitive and consider and incorporate input of all appropriate
disciplines and stakeholders to ensure the objectives of road design and a balance of often competing and
contradictory factors are achieved. The design team must consider the context of the site as each site is
unique. What has worked at one site may not be appropriate for another site. The design team must
consider the advice and input of other disciplines and stakeholders.
- Value engineering: A design should demonstrate cost-effectiveness through value engineering processes,
cost benefit analysis and consideration of whole-of-life costs. Decisions are subject to appropriate
review/governance to demonstrate this. Funding for road infrastructure is often limited, therefore the
design team must be able to demonstrate value for money by utilising cost-effective treatments, options,
and solutions.
- Design element combinations: A design cannot be considered fit-for-purpose and/or conforming if it
simply adopts design minima, particularly in combination, for most or all elements of the design. Most
criteria (range/desirable/absolute) have been researched and/or developed in isolation (there may be some
implicit relationships) and therefore when used in combination with other elements, while conforming to
the published guidelines, may result in a solution that compromises safety and/or operational efficiency.
- External factors: The design team must consider all environmental, cultural heritage and social issues
and requirements and mitigate any adverse impacts in the most appropriate way possible to satisfy project
objectives.
- Road users: A design should consider and cater for all road users. It is important that no road user group
safety is adversely affected by a proposed design solution.
- Emerging driver-assist technologies: The increased potential of vehicles to supplement driver
capabilities should be considered. This includes consideration of infrastructure for cooperative intelligent
transport systems (C-ITS), either at the time of construction, or for such technologies to be provided in
the future.
- Future planning: A design should meet current needs whilst also providing for future needs. The design
team should ensure that the project accommodates potential future enhancement of the infrastructure (e.g.,
allowing for future connections within an interchange) or at least does not restrict future enhancement.
- Innovation: A design should be developed in accordance with accepted design guidance. Innovative
designs may be developed using the foundations provided in accepted design guidance; however, all other
road design principles should be maintained. Where accepted design guidance does not provide required
warrants and/or dimensional criteria, the design team is responsible for the development of such guidance
through a robust engineering and peer review process (to seek acceptance/approval). Any developed
guidance must be evidence-based or developed through appropriate, accepted theories and be able to
withstand scrutiny by qualified professional civil engineer(s) with appropriate road design experience.
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Performance: A design should maintain or improve the performance of an existing road. The
improvement of one or more elements should not adversely affect the performance of another. Most road
projects now relate to maintenance and enhancement of an existing asset. It is necessary to understand
what parts of the design guide relevant and what parts are not appropriate for the project. A final design
solution should not result in the unintentional migration of operational issues to another part of the
network.
Justification: Design decisions must be documented including context, basis, and rationale. Design
solutions and decisions made should be justified and defendable. This principle is crucial for innovative
design treatments or solutions (when outside accepted guidance), trials of new treatments and design
exceptions. Most road agencies/jurisdictions will have systems/processes in place to specify the
documentation of design processes/decisions.
Balance: A design should be able to demonstrate it meets/balances all the above principles within the
limits of the project scope, constraints and is complementary to the network. Design is about achieving
an appropriate balance for the project across all aspects, and it is important to understand that the balance
achieved for one project will likely be different for another.
OBJECTIVES OF ROAD DESIGN
Roads will continue to be an important part of our transport system for the foreseeable future, providing for the
safe and efficient movement of people and goods. Road projects are developed to meet increasing travel demand,
address crash problems, rehabilitate existing infrastructure, or for a combination of these reasons. A balanced
approach towards road planning and design can improve operational efficiency, road safety and public amenity,
and minimise the effects of noise, vibration, pollution, and visual intrusion on the areas through which a road
pass.
Road designs should incorporate the Safe System approach which ensures that the needs of all road users are
considered in all aspects of the design process. The objectives of new and existing road projects should be
carefully considered to achieve the safest possible road while balancing the level of traffic service provided,
whole-of-life costs, flexibility for future upgrading or rehabilitation, and environmental impact.
These objectives should address areas including:
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strategic fit with relevant government policies, strategies, and plans
the nature and magnitude of transport demand
road safety to reduce death and serious injury to all road users
community views and expectations
travel times and costs
freight costs
public transport provision
provision for cyclists and pedestrians.
3. FUNDAMENTAL CONSIDERATIONS FOR DESIGN
Roads need to provide for the safe, convenient, effective and efficient movement of persons and goods. The
design of roads should be based on the capabilities and behaviour of all road users, including pedestrians, cyclists,
motorcyclists, and on the performance and physical characteristics of vehicles (including public transport). At
the same time, consideration must also be given to the whole range of economic, social, environmental and other
factors that may be involved.
DESIGN PARAMETERS
- Location
The basic premise of whether a road is located in an urban or rural area will to a certain extent impact on the
attributes for which it is designed. Rural roads generally carry lower traffic volumes and are not subject to as
many constraints as urban roads. Public expectation also differs in relation to operating speeds, abutting access,
geometry and cross-section.
- Road Classification
Most road agencies have developed a functional hierarchy for their road networks. This hierarchy enables each
authority to systematically plan and develop their network to meet the needs for local access, cross town/city
travel, intrastate and interstate travel. Further information about this topic can be found in the Guide to Road
Design Part 2: Design Considerations (Austroads 2015c).
- Traffic Volume and Composition
The development of the cross-section and geometry of a road are generally based on the expected traffic volumes
and composition of that traffic for example, the number or percentage of trucks, their size and characteristics.
arious methods have been established internationally to measure existing volumes and determine the likely future
use of a facility.
Austroads has developed the Network Design for Road Safety (Stereotypes for Cross-sections and Intersections)
User Guide (Austroads 2020c) to provide guidance on implementing different cross-section designs for 13 road
stereotypes based on various attributes such as road function, geometry, speed limits and traffic volumes. Further,
the Guide to Traffic Management Part 3: Transport Study and Analysis Methods (Austroads 2020a) provides
specific information regarding the analysis required to determine the capacity requirements for a length of
roadway.
Designers need to consider future traffic demands for a road section to determine the required cross-sectional
configuration. Consideration should be given to the staged construction or widening of roads over this design
period.
Design requirements for roads are typically assessed by reference to forecasts of Annual Average Daily Traffic
(AADT). Design hour volumes may be derived by consideration of the flow pattern across hours of the year. A
30th highest hourly volume is often adopted as a design volume for rural roads. On the other hand, the derivation
of urban design hour volumes, particularly for major arterial roads, will necessitate the use of complex traffic
modelling techniques and consideration of the purpose of the road within the urban road network. In areas of high
peak or seasonal demands, such as recreational or harvest routes, special consideration may be required. In the
absence of such information. In addition to capacity considerations, traffic volume and composition is a key input
to the structural design of pavements, culverts and bridges, and functional design of intersections.
- Vulnerable Road Users
In addition to being designed for safe and efficient movement of cars and trucks, roads should be designed to
provide for the safe and convenient passage of pedestrians, cyclists and motorcyclists. These users are at elevated
risk of incurring a fatal or serious injury in a collision with motor vehicles. Some information on footpaths is
provided in Section 4.12.3 of this guide whilst mid-block bicycle lanes and paths are covered in Section 4.9. In
addition, designers are referred to the Guide to Road Design Part 6A: Pedestrian and Cyclist Paths (Austroads
2009a).
Where intersections are being designed to accommodate pedestrians and cyclists, reference should be made to
the following parts of the Guide to Road Design as well as relevant jurisdictional supplements and Australian
Standards:
• Part 4: Intersections and Crossings: General (Austroads 2009b)
• Part 4A: Unsignalised and Signalised Intersections (Austroads 2010a)
• Part 4B: Roundabouts (Austroads 2015d)
• Part 4C: Interchanges (Austroads 2015e).
Motorcyclists are more vulnerable than most other road users due to their unique operating characteristics. For
this reason it is most important that motorcyclist’s safety needs are considered during design, construction,
maintenance and management of roads. Consequently road designers should appreciate that some design issues
or situations that may arise could place motorcyclists at greater risk than drivers of other types of vehicles.
- Design Speed and Operating Speed
The design speed is a speed fixed for the design and correlation to the geometric features of a carriageway that
influence vehicle operation. It is selected during the design process and is related to either the intended operating
speed or the posted speed limit of a road or section of road. Operating speed can be measured for an existing road.
If the operating speed varies along the road, the design speed must vary accordingly. Identification of the
operating speed is fundamental to the development of any roadway facility.
- Alignment Controls
Prior to setting out a proposed alignment, it is necessary to identify any controls on its position. Mandatory
controls are those which should not be changed for legal, environmental or economic reasons. Discretionary
controls are those that are desirable to observe, but which may be altered when the alignment is being reviewed
and optimised to account for conflicting objectives. The designer should request clear directions from the client
on each project to determine which controls are to be regarded as mandatory and which are discretionary.
Common principal controls influencing alignments include:
• speed group
• operating speed
• terrain
• cadastral boundaries
• planning scheme boundaries
• matching to existing roads or access points
• significant stream crossings
• historical buildings
• cultural heritage sites
• environmentally sensitive sites
• geology
• providing appropriate sight distances
• providing overtaking opportunities
• costs
• aesthetics
• major utility services.
On low and intermediate speed roads, operating speeds are constrained by the radii of curves, and care should be
taken to ensure that radii used are compatible with the 85th percentile operating speed of traffic. Designers should
also refer to Section 3.1 of the Guide to Road Design Part 2: Design Considerations (Austroads 2015c) for a
checklist of design considerations.
- Design Vehicle
The physical and operating characteristics of vehicles using the road influence specific elements in the geometric
design, e.g. tracking of large vehicles on small radius horizontal curves. The classification and function of the
road may determine the type of vehicle operating on a length of road. The design and check vehicle needs to be
appropriate for classification and function of the road. For example, some roads carry relatively high volumes of
B-doubles or Type 1 and 2 road trains and where this is the case, these vehicles may be more suitable as the
design or check vehicle.
Information regarding the choice and application of design vehicles can be found in the Guide to Road Design
Part 4: Intersections and Crossings: General (Austroads 2009b). The design vehicle is a hypothetical vehicle
whose dimensions and operating characteristics are typically used to establish traffic lane widths, intersection
layout and road geometry. Historically, four general classes of vehicles have been selected for design purposes,
namely:
• design prime mover and semi-trailer (19.0 m)
• design single unit truck/bus (12.5 m)
• service vehicle (8.8 m)
• design car (5.0 m).
Other larger vehicles such as B-doubles or Type 1 and 2 road trains can be regularly found in some rural (and
increasingly urban) areas of Australia. Each road agency has specific practices regarding the use of larger vehicles
and should be consulted when evaluating the choice of the design vehicle for any road project. Designers should
also consider the implications of seasonal cartage routes where larger vehicles may be required in large numbers
for relatively short time periods. Designers should consult the Austroads Design Vehicles and Turning Path
Templates (Austroads 2013a) or the NZ Transport Agency New Zealand On-road Tracking Curves for Heavy
Motor Vehicles (Land Transport New Zealand 2007) for specific details regarding vehicle turn paths of standard
design vehicles.
Recent initiatives to improve freight productivity in Australia have seen the development of vehicles using
‘performance based standards’ (PBS). Rather than being prescriptive in the dimensions, masses and turning paths,
like for the design vehicles listed above, PBS vehicles must only meet minimum design criteria that are specified
by the National Transport Commission (NTC). These criteria have been developed to meet the needs of the
existing road network, e.g. lane widths or the space generally available for turns within intersections. Designers
should note that whilst specific turning templates are not typically available for PBS vehicles (although they can
be developed for specific vehicles), one of the performance standards for these vehicles is that they should have
a swept path whilst turning, which is roughly equivalent to a B-double or Type 1 or 2 road train. Designers should
consult the NTC PBS vehicle guidelines for further information www.ntc.gov.au.
- Use of Roads as Emergency Aircraft Runway Strips
Roads in remote areas may be designed and constructed to operate as emergency runway strips where access to
medical facilities by road may not be a viable option due to flooding of roads or distance/time constraints. This
combined facility may be provided in those remote areas where there are no runway strips for the Royal Flying
Doctor Service (RFDS) or State Emergency Services (SES) emergency evacuations, and construction of a
permanent runway strip is not warranted due to limited usage of the facility. However, if a suitable permanent
runway strip is available nearby then the RFDS are required by law to use it and an emergency runway strip
should not be provided.
- Environmental Considerations
The various impacts of roads are of growing concern to individuals and communities. It is important to fully
consider the impact of these issues in any road design. Reduction of adverse environmental impact should be one
of the main objectives of any road project both during construction and operation.
Careful design of roads can incorporate the means to ameliorate the environmental intrusion of road infrastructure
and associated traffic. In particular, consideration should be given to visual amenity through the use of
landscaping and creativity with structures and noise barriers. Traffic related intrusions perceived by people
include:
• visual
• noise
• vibration
• pedestrian delay and severance
• air pollution
• erosion
• risk of accidents and intimidation of vulnerable road users
• deterioration of water quality and the increase in water quantity from urbanisation
• adverse effect on environmentally sensitive areas, such as from clearing of vegetation.
Further information about these issues can be found in the Guide to Road Design Part 6B: Roadside Environment
(Austroads 2015b).
- Access Management
Access management is the process of controlling the movement of traffic between a road and adjacent land. The
purpose of access management is to protect the safety and efficiency of the traffic function of the road, while
acknowledging the needs and amenable use of adjacent land, through the provision of safe and appropriate access.
Some road agencies may have well-developed access management policies and designers should consult the
relevant authority when considering this issue.
Designers should consult the Guide to Traffic Management Part 5: Link Management (Austroads 2020b) and
any relevant road agency guidelines for further guidance.
- Drainage
Consideration of issues associated with drainage of the road and surrounding land can significantly affect the
geometry and cross-section of the road. Provision of drainage structures at watercourses affects the grading of
the road and the choice of drainage system can affect the cross-section or formation width, maintenance
requirements and cost of the project, especially if underground piped drainage networks are considered. Surface
flows along the pavement are especially important in the context of minimising the chances of vehicles
aquaplaning by choosing appropriate combinations of crossfall and grade.
Information relating to the design of drainage for roads can be found in the Guide to Road Design, namely:
• Part 5: Drainage: General and Hydrology Considerations (Austroads 2013b)
• Part 5A: Drainage: Road Surface, Network, Basins and Subsurface (Austroads 2013c)
• Part 5B: Drainage: Open Channels, Culverts and Floodways (Austroads 2013d).
- Utility Services
The location of utility services should be considered early in the design process as they can have a significant
impact on design decisions, construction and maintenance costs. Road improvement or upgrade projects will
generally involve service relocations that may provide physical or economic constraints to the design. The
provision of utility services adjacent to or across greenfield road developments should consider the future role of
the transport corridor to minimise or avoid future service relocations associated with construction or upgrading
of the facility. Consolidated services to assist in the identification and location of underground public utilities are
now available for most urban areas. These services are an efficient initial interface between the designer and
service agencies to enable the early consideration of services to occur.
- Topography/Geology
Site-specific features have a large impact on the cost of road projects, which may influence the extent of the road
project that is constructed or how much funding remains available to fund other road improvements across the
network. To ensure that limited funds are effectively spent on appropriate designs, due regard must be given to
designing with the terrain rather than against it. For example:
• balanced earthworks limit the cost of importing additional fill materials or disposing of it off-site
• ensuring that the grade line stays above non-rippable rock which negates the need for blasting
• keeping the grade line above the water table to limit moisture ingress to the pavement and possibly avoid
- the need for drainage blankets.
The Guide to Road Design Part 7: Geotechnical Investigation and Design (Austroads 2008a) provides further
information about geotechnical issues that should be considered by the road designer.
4. THE ROAD DESIGN PROCESS & DOCUMENTATION
The road design process encompasses a range in project size and complexity from small projects (minor
improvements, intersection upgrade) to major projects (network expansion, 'greenfields' work on major arterials
and freeways).
Depending on the size and complexity of the project, several design phases may be required. These phases form
a continuum and generally begin by examining options to establish a preferred solution and developing it to a
level that will give confidence to the client and finally detail the design. The names given to these phases vary
between road agencies and it is, therefore, necessary to refer to local jurisdictions for local terminology and
specific requirements.
Planning and design are each iterative processes, requiring assumptions to be made using the available data. As
the project proceeds and more data become available, the validity of the assumptions needs to be checked and
necessary modifications made. Essential to the planning process are road designs that are accurate enough to
demonstrate the feasibility of various options and to confidently define right-of-way requirements. Design is a
product and the systems that are put in place should conform to the model for Quality management systems –
requirements, set out in AS/NZS ISO 9001:2016.
It should be noted that while compliance with standards and this guideline should ensure an acceptable design, it
does not necessarily ensure ‘good design’. Good design is achieved when the outcome not only conforms with
but exceeds expectations. Designers should be encouraged to explore several solutions so that the outcome is the
best available balance within the project constraints.
The design should be tailored to meet the needs of current and future generations through the integration of many
factors which might generally be described as including user safety, workplace safety, environmental protection,
social advancement, and economic prosperity. This may require challenging the limits originally set for the
project.
The design process can be summarised in the following elements:
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
planning and developing the processes required to realise the design
determining the requirements for the design
reviewing the requirements for the design
determining the arrangements for communicating with the client
controlling the design in stages and determining the appropriate reviews and authorities
determining the controls that will apply to the interfaces between design stages
determining what inputs are required
determining what outputs of the design process are required and in what form
reviewing the design at suitable stages in its development
verifying that the design outputs have met the input requirements
validating the project outcome to ensure that it can meet the intended use
controlling any design changes
undertaking a quality system audit
controlling the presentation of outputs
developing procedures to manage design exceptions.
DESIGN REPORT
Throughout the phases of design, a ‘live’ document in the form of a Design Report provides a summary of existing
conditions, design objectives, assumptions, constraints, design methodology, safety in design, safe system
principles and details of any elements using EDD or DE. The designer commences preparation of the report at
the start of the project and the report is reviewed and evolves through each phase of the design. The report content
should reflect project risk level at the stage of design that is complete.
Users should check the requirements for the project and/or jurisdictional requirements to determine the extent of
reporting required.
Design Report Content
The following provides an extensive list of content to be considered in a design report. Depending on the size
and complexity of a project, individual reports may be required for each technical discipline during each phase
of a project. Practitioners should liaise with jurisdictions regarding the extent of reporting required.
Document management
• amendment records
• distribution list
• document ownership and use
• document status e.g., revision number, author, reviewer, and approval for use
• the author’s company contact details
• file and project numbers.
Project background and purpose
• project name
• location
• design report phase e.g., concept, preliminary, final or per cent complete
• project number or contract number
• document status e.g., draft, final
• project description and context
• definition of the problem(s) and existing conditions
• guides and standards used to inform the design
• existing constraints e.g., physical, heritage, environmental, services
• details of hold points where relevant
• stakeholders
i Design Process Flowchart
PHASES OF ROAD DESIGN
The design of major road infrastructure is essentially delivered in three phases as shown in Figure ii. Some phases
may not be required, depending on road agency requirements. Often, the first two phases are not undertaken for
minor works. Whilst the representation of the overall design process is shown to be ‘linear’, it should be noted
that design is iterative and that changes, particularly as more detailed information becomes available, may cause
earlier phases to be revisited.
ii-Phases in the design process
Phase 1 – Establish the Preferred Solution
The establishment of a preferred solution comprises the following steps:
• Review the design brief and clarify the aims of the project.
• Define the study area.
• Identify options within that area.
• Undertake initial studies.
• Develop the concept design for each option.
• Analyse the options (including a Safe System assessment and road safety audit).
• Recommend a preferred option.
While the roles of the authorities will depend on the road agency, these steps are generally held to be within the
realm of the project manager, and the level of design involvement in each step will depend on the authorities, the
nature of the project and relationships. Again, it should be noted that the process is iterative and issues arising in
later steps may cause a re-evaluation of earlier ones including the definition of the study area.
Review the design brief and clarify the aims of the project
Before undertaking any work, it is essential to clarify the aims of the project with the client and project manager.
This will ensure that there is a common understanding of the desired outcome, the timeframe and the financial
constraint before any work begins. This step should also establish whether there is information available from
previous planning and/or earlier designs, plus any known constraints (financial, physical, environmental,
legislative, and social). Failure to establish these aims initially may lead to subsequent frustration, delay, illfeeling, rework, and additional and thus unnecessary cost.
All inputs should be reviewed for adequacy and the designer should identify whether any additional inputs are
required. Generally, preliminary investigations will be required. Confirm that the typical cross-section is
applicable.
Define the study area
This step is critical because it sets the boundaries outside of which options will not generally be considered. The
boundaries are not just planar but should be three dimensional and include setting any height and depth
restrictions.
For the designer, many of these inputs will be determined by others and will be considered by the designer as
inputs to the design process and dealt with. If not, there may be some other imposed constraint, such as a coastline,
that will limit the range of options and hence help define the study area. The project brief should identify the
study area and its constraints. Major issues typically pre-determined for the designer are whether the solution
must be restricted to the existing road corridor and the nature of the typical cross-section (i.e., whether the crosssection has been established as part of broader network corridor planning).
Identifying options within that area
Ideally, the aim is to identify all plausible solutions. However, in some circumstances there are an 'infinite' number
of solutions; this is generally taken to require a sufficiently broad enough range of options to allow for sensitivity
to be assessed.
Typically, a project team will be utilised to identify the broad options and the designer will then provide sufficient
detail to establish the advantages and disadvantages of each.
Undertake initial studies
To identify the broad strategic options, several preliminary investigations may need to be undertaken. The degree
to which these investigations are undertaken will depend on an assessment of risk and the level of current
information and understanding available. Options can be ruled out if a ‘fatal flaw’ factor can be identified.
Investigations by, or on behalf of, the project team might be carried out in the following areas of impact:
• community interests (both local and impacted) and those of other stakeholders (e.g., other government
agencies, industry groups)
• environment e.g., habitat (flora/fauna), heritage etc.
• hydrology e.g., flooding, outfalls (Austroads 2013b)
• geotechnical (Appendix B)
• traffic analysis, including major and minor road connections (Austroads 2020b)
• land acquisition and property access impacts
• pedestrian and cyclist provisions (Austroads 2016a and 2017b)
• utility impacts (Austroads 2020a)
• any other constraints/issues and opportunities specific to the project.
Develop the concept design for each option
Develop the concept design for each solution option to the extent necessary to allow the comparison of options.
While this will again typically be done by a project team, most of the development is generally done by the
designer.
Analyse the options
This should be done in accordance with road agency requirements but will typically involve the use of a decisionmaking aid, for example, a value management workshop. The output from this will be an options comparison
report typically detailing the road agency requirements and reporting against them for each option. A Safe System
assessment and a road safety audit should be undertaken on each design option to ensure well informed decisions
are being made, which consider the road safety risk associated with the design and alignment with the Safe System
approach.
Recommend a preferred option
Depending on the jurisdictional requirements, the recommendation of a preferred option may require additional
steps including outlining some of the valid options from which the preferred solution was selected. Ultimately
the recommended solution must be accepted/approved by the client before subsequent work is undertaken.
Phase 2 – Further Develop the Solution
Having decided on a preferred option, the next phase in the design development process requires the further
development of that preferred solution to give sufficient confidence that it can be built and meet all requirements.
In some jurisdictions it may also form the basis for the formal environment assessment. The design should now
be developed in sufficient detail to allow:
• individual elements to be recognised and analysed
• the relationship and interaction of those elements to be clear
• options for change to elements within the design to be identified.
It should comprise the following steps:
• Review the design brief.
• Review the preferred option (if Phase 1 output has been provided).
• Undertake supplementary studies.
• Develop the design.
Review the design brief
The designer should review the design brief. Note that there may be a significant time lapse between Phase 1 and
Phase 2, and it is therefore essential that the design intent is clearly transferred between phases and welldocumented outputs including the design report will assist with this. It is good practice for the designer to reaffirm
the previous recommendations/decisions with the client and project manager (who may be new to the project)
before proceeding with further development as described in this phase.
Review all inputs for adequacy and identify whether any additional inputs are required. Generally, more detailed
investigations will be required.
Confirm that the typical cross-section is still applicable and is appropriate. As the overall decision process is
‘linear’, it should be noted that changes, particularly to the scope, may cause the previous phase to be revisited.
It may be difficult to change once this phase is completed.
Review the preferred option design
The designer should also comprehend the requirements, issues, and other information from Phase 1. This is
especially important where a new team is engaged to deliver this next phase of the design. It is essential that
further development/rework of the design is not undertaken without first understanding the context of the design
from an earlier phase. Then the preferred option should be reviewed against the project and design requirements.
Undertake supplementary studies
The preliminary investigations undertaken for Phase 1 of the design process will most likely not be adequate for
the further development of the preferred option. The degree to which these supplementary investigations are
undertaken will again depend on an assessment of risk and the level of current information and understanding
available. The results should provide enough information to allow a sufficiently high level of confidence that the
project can be built and that it will meet the design requirements.
Develop the design
This step in the further development of the design completes this phase and should provide sufficiently detailed
design documentation (including plans and design report) to allow for:
• compliance with applicable statutory and regulatory requirements to be confirmed
• any environmental assessments to be undertaken
•
sufficient guidance to be provided to allow for the next phase, that of detailed design, to be undertaken
with minimum risk.
Again, it should be noted that the process is iterative and issues arising in the development of the design for the
preferred option may cause a refinement of the previously approved design including adjustments to line and
level. A primary output is a set of coordinated alignments that satisfy geometric design standards. The aim is to
not only produce a conforming design but one that results in the best design solution for the site-specific situation.
Phase 3 – Detailed Design: The Design for Construction
Having developed the preferred solution, the last phase in the design development requires the production of
sufficient detail to allow the work to be constructed and meet all requirements. A detailed design should be
suitable for inviting tenders and should allow for all aspects of the construction to be completed. It may comprise
the following steps:
• Review the design brief.
• Review the developed option.
• Undertake supplementary studies.
• Develop the design.
• Review the design during construction.
• Prepare the construction record.
Review the design brief
Review all inputs for adequacy and identify whether any additional inputs are required. More detailed
investigations may be required for individual elements. Whilst confirming that the typical cross-section is still
applicable and is appropriate, this should not change from that used in Phase 2, because it is usually difficult to
change at this stage due to impacts on broader network decision making.
Review the developed option
The designer should also comprehend the requirements, issues, and other information from Phase 2. This is
especially important where a new team is engaged to deliver this next phase of the design.
Then the preferred option should be reviewed against the design requirements, especially the requirements arising
from any consultation or formal assessment of the Phase 2 output and in this regard, the environmental assessment
may be critical.
Undertake supplementary studies
The more detailed investigations undertaken for Phase 2 of the design process may still not be adequate for the
further development of the preferred option, especially the results of any consultations and assessments
undertaken on the Phase 2 output. The degree to which these supplementary investigations are undertaken will
again depend on an assessment of risk, particularly construction cost, and the level of current information and
understanding available. They should provide enough information to allow a sufficiently high level of confidence
that the design can be built and that it will meet the design requirements.
Develop the design
As noted above, the purpose of this phase of the design is to provide sufficient detail to allow for tendering and
construction purposes and will, amongst other outputs, include:
• finalised design documentation, whether electronic or hard copy
• a schedule of all quantities
• appropriate inputs to the construction specifications
• confirmation of compliance with applicable statutory and regulatory requirements.
Review the design during construction
Remedial design or further design development during the construction phase may be necessary for several
reasons including:
• tender reference design not being a fully developed detail design
• alternatives put forward during the tender process and accepted
• non-conformance during construction
• accepted changes whether initiated by the construction contractor or otherwise
• previously unidentified inputs, for example, utilities
• an error in the design.
5. ROAD DESIGN APPLICATION
Road Characteristics and Use
The standards adopted for road projects have traditionally been influenced by the functional classification of the
road. For example, roads of higher classification had a major role in the transportation task and therefore required
a higher standard of design. Roads fall into a hierarchy of functional classes ranging from major arterial roads to
local access roads.
The recognition of more sustainable forms of transport in urban areas has led to consideration of a road user
hierarchy in addition to the traditional road hierarchy. The road user hierarchy indicates the relative priorities to
be accorded to road user categories in the operations of the road network. In accordance with this, pedestrian
activity is often identified for priority consideration on some sections. This needs to be integrated and balanced
with priorities arising from the prevailing functional road classifications.
Rural roads of higher functional class generally cater for a higher (though normally still modest) proportion of
longer-length journeys, and it may be appropriate to select higher design standards for such roads so that the
quality of service is more appropriate to the longer trip duration. Crash risk and Safe System principles should be
considered before any decisions are made. Austroads has defined a system of functional classification for rural
roads.
In rural areas, the Class 1 and 2 roads are generally freeways or major highways that have a high standard for
two-way two-lane roads. They are usually roads of national or state importance in terms of communication and
the economy. Class 3 roads would generally be main roads of a satisfactory but lesser standard than the Class 1
and 2 roads.
Austroads has also adopted a rural route numbering hierarchy to assist road user guidance. This hierarchy
identifies arterial routes as M, A, B or C routes and, like the classification in Table 1, is also related to the route
characteristics. This is discussed in more detail in the Austroads (2016b and 2019c).
The functional classification of urban roads (refer to Table 4.2) is usually less clear than that of rural roads, as
urban roads generally are flanked by dense development that requires frequent access at the boundary of the road.
Historical requirements for kerbside parking and other uses (e.g., public transport routes or bicycle routes) further
complicate functional definitions.
Most urban arterial roads continue to function as major through traffic routes, but the management of these roads
often requires space to be dedicated to public transport or bicycle use in preference, or in addition to private car
travel. There is also a trend on inner suburban roads for speed limits to be set at more appropriate Safe System
speed limits to address pedestrian safety issues while sections of inner-city streets (formerly through arterial
routes) are sometimes converted to pedestrian areas or shared zones. This is discussed in more detail in the Guide
to Traffic Management. Consequently, the function of sections of road may change over time in accordance with
community values.
Road class
Arterial roads
Class 1
Table 1 - Austroads functional classification of rural roads
Route classification
Route characteristics
M
Class 2
A
Class 3
B or C
Local roads
Class 4
Class 5
Those roads, which form the principal
avenues
for
communications
between major regions, including
direct connections between capital
cities.
Those roads, not being Class 1, whose main
function is to form the principal
avenue of communication for
movements between:
• a capital city and adjoining states and their
capital cities; or
• a capital city and key towns; or
• key towns.
Those roads, not being Class 1 or 2, whose
main function is to form an avenue
of communication for movements:
• between important centres and the Class 1
and Class 2 roads and/or key towns;
or
• between important centres; or
• of an arterial nature within a town in a rural
area.
Those roads, not being Class 1, 2 or 3, whose main function
is to provide access to abutting property (including
property within a town in a rural area).
Those roads, which provide almost exclusively for one
activity or function, which cannot be assigned to
Classes 1 to 4.
6. PAVEMENT DESIGN SYSTEMS
General
The aim of pavement design is to select the most economical pavement thickness and composition which will
provide a satisfactory level of service for the anticipated traffic.
To achieve this goal, the designer must have sufficient knowledge of the materials, the traffic, the local
environment – and their interactions – to be able to predict the performance of any pavement composition. In
addition, the designer must have knowledge of what level of performance, and what pavement condition, will be
considered satisfactory in the circumstances for which the pavement structure is being designed.
Because of the many variables and interactions which influence the result, it is appropriate to adopt a systematic
approach to pavement design. Depending on the amount of data which has to be provided or, conversely, on the
number of assumptions which have to be made, a pavement design procedure may be very complex at one extreme
or very simple at the other.
Sound pavement performance depends on a number of factors and relies on a ‘cradle to grave’ approach, managed
by experienced professional staff. The primary factors are:
• design – including materials assessment and pavement composition
• construction – to meet design requirements, including quality, tolerances and drainage
• maintenance – to maintain pavement integrity.
Common Pavement Types
In designing a new pavement one of the first tasks is to select one or more pavement types for detailed design.
The choice of pavement type varies markedly with the function of the road, traffic loading, availability of
materials, and the environment.
Lightly-trafficked roads usually comprise unbound granular pavements with thin bituminous surfacings. Where
an asphalt surfacing is provided it is common for the thickness of asphalt to be 25–50 mm.
More heavily trafficked roads may require the asphalt to extend to more than the surface layer, with the asphalt
commonly supported by a granular subbase.
Some heavily-trafficked roads (e.g. freeways) have high level performance requirements and need to be designed
to minimise traffic delays due to road maintenance during their service lives. Such pavements commonly have a
design traffic loading exceeding 107 ESA and are sometimes referred to as ‘heavy-duty’ pavements.
The following pavement types, often used in conjunction with high material standards, may be considered heavyduty pavements:
• deep strength asphalt, with thick asphalt on cement stabilised granular subbase
• flexible composite, comprising a thick asphalt on lean-mix concrete subbase
• full depth asphalt
• unbound granular with sprayed seal surfacing
• jointed plain (unreinforced) concrete pavements
• jointed reinforced concrete pavements
• continuously reinforced concrete pavements.
Such heavy-duty pavements are commonly supported by higher strength, stable materials consisting of granular
subbases and/or selected subgrade materials.
Role of Traffic in Pavement Design
A road pavement must be wide enough and of suitable geometry to permit all vehicles to safely operate at an
acceptable speed. In addition, it must be strong enough to cater for both the heaviest of these vehicles and the
cumulative effects of the passage of all vehicles. While the first of these requirements is in the province of
geometric design, the second is the responsibility of the pavement designer.
Vehicular traffic consists of a mixture of vehicles ranging in the extreme from bicycles to triple road trains. The
Austroads Vehicle Classification System, shown in Table 7.1, details the range of vehicles commonly using
Australian roads, whilst the dominant vehicles in each of the 12 Vehicle Classification System classes in Table
7.1 are shown in Figure 7.1.
The damage caused to a pavement by the passage of a heavy vehicle depends not only on its gross weight
but also on how this weight is distributed to the pavement. In particular, it depends on:
• the number of axles on the vehicle
• the manner in which these axles are grouped together – into axle groups
• the loading applied to the pavement through each of these axle groups – the axle group load.
Fig: Classification of Vehicles by Austroads
The design tyre-pavement contact stresses for pavement analysis are taken as 750 and 800 kPa. However, data
collected in Tasmania by Chowdhury and Rallings (1994) indicates that tyre inflation pressures vary widely –
from 500 to 1200 kPa.
The cumulative loading on a pavement over a period of time is, in essence, an account of every axle group
traversing the pavement during this time period, together with its type and its load. This cumulative loading is
specified by:
• the cumulative number of axle groups traversing the pavement during the period
• the proportions of each axle group type in this total
• for each axle group type, the frequency distribution of the axle group loads.
For pavement design purposes, the following (heavy vehicle) axle group types are identified:
• single axle with single tyres (SAST)
• single axle with dual tyres (SADT)
• tandem axle with single tyres (TAST)
• tandem axle with dual tyres (TADT)
• triaxle with dual tyres (TRDT)
• quad-axle with dual tyres (QADT).
Overview of Procedure for Determining Design Traffic
The pavement design task is to select a suitable pavement configuration for the trafficked portion of a
carriageway. This trafficked way may vary from a single lane catering for (with appropriate shoulders) traffic
travelling in both directions, ranging up to six or more lanes for single-direction traffic. For multi-lane
carriageways, the same pavement configuration is usually adopted for all lanes. The main reasons for this are:
• avoidance of steps in the finished surface of the subgrade – with the associated risk of water becoming trapped
at the base of the step
• avoidance of vertical planes of weakness formed within the pavement at the vertical interfaces between distinct
material types
• construction expediency.
Selection of the pavement configuration is on the basis that the pavement will provide adequate service for the
cumulative traffic expected over a designer-specified time-span – the design period. Adequate service implies
that the pavement will not require major rehabilitation during the design period.
The sequence of steps leading to the specification of the design traffic for a project is as follows:
1. Select a design period.
2. Identify the most heavily-trafficked lane in the carriageway – designated the design lane.
3. Estimate the average daily number of heavy vehicles in the design lane during the first year of the
4.
5.
6.
7.
8.
9.
project’s life.
Estimate heavy traffic growth throughout the design period.
Estimate the average number of axle groups per heavy vehicle.
Combine the above three estimates to calculate the cumulative heavy vehicle axle groups over the
design
Period.
Estimate the proportion of axle group types and the distribution of axle group loads.
Express the cumulative traffic loading in a form suitable for the pavement design procedure to be used.
Selection of Design Period
Identification of Design Lane
Initial Daily Heavy Vehicles in the Design Lane
To calculate the cumulative HVAG in the design lane (Equation 30), an estimate is required of the average
over the first year (of the project’s operation) of the daily number of heavy vehicles in the design lane. This
averaging over an entire year is conducted to ensure that the estimate is unaffected by day-to-day (or, often of
more significance, season-to-season) fluctuations in daily traffic loadings.
Any of the following methods – listed in descending order of accuracy – may be used to estimate the initial daily
number of heavy vehicles. The designer is encouraged to adopt a method commensurate with the importance of
the project, availability of relevant data, and resources available for data collection.
1. WIM survey data either collected specifically for the project or recently collected for other purposes. WIM
data also provides the number of axle groups per heavy vehicle required to estimate the cumulative number of
HVAG and the distribution of axle group types and loads required to calculate the design traffic for flexible and
rigid pavements.
2. Use of data obtained from vehicle classification counters. Such data will furnish the number of vehicles of
various types (Table 7.1) as well as data on the number of axle groups per heavy vehicle required to estimate the
cumulative number of HVAG. In addition, classification counters will provide information on the proportions of
axle group types required to calculate the design traffic for both flexible and rigid pavements (Section 7.5).
Classification counters, however, do not provide information on the distribution of axle loads within each axle
group type. Consequently, the use of classification counter data requires a traffic load distribution to be selected.
3. Use of data obtained from single tube axle counters, or manual traffic count surveys, together with an estimate
of the proportion of heavy vehicles. However, as tube counters do not provide load or axle type data, the use of
this data is very dependent on the engineering judgement of the designer.
For the latter method, the equation to derive the initial daily heavy vehicles (𝑁𝑖) traversing the design lane is
(Equation 30).
𝑁𝑖 = 𝐴ADT× 𝐷F× %𝐻V/100 × 𝐿DF
……………..
(Eq 30)
where
𝑁𝑖
= initial daily heavy vehicles in the design lane
𝐴𝐴DT = Annual Average Daily Traffic 2 in vehicles per day in the first year
𝐷F
= direction factor is the proportion of the two-way AADT travelling in the direction of the design lane
%𝐻V = average percentage of heavy vehicles
𝐿DF = lane distribution factor, proportion of heavy vehicles in the design lane
Cumulative Number of Heavy Vehicles when Below Capacity
Part of the task of estimating the cumulative traffic (in the design lane) over the design period is to estimate the
likely changes in daily traffic loading during this period. Once these changes have been estimated, their effects
are then incorporated in the estimate of cumulative loading.
Changes can occur both in the (daily) volume of traffic using the road and also in the sizes of loads carried by
heavy vehicles. Because these two types of change have distinct traits and also distinct effects on the resultant
cumulative traffic loading, it is appropriate to consider them separately. The growth in traffic volumes is
considered in this section.
If the project is a re-alignment, a re-construction or an overlay, then it is appropriate to base the estimation of
growth in traffic volumes on historical data for the existing road. If the project is a greenfield project, then the
estimation should be based on the growth experienced by similar roads in the vicinity, coupled with consideration
of the additional traffic to be generated by the ensuing land development in the corridor serviced by the new road.
Based on historical evidence, it is reasonable to expect that the daily volume of traffic (both light and heavy
vehicles) will increase either for the entire design period or up to the stage where the traffic capacity of the road
is reached. This evidence also indicates that the growth is geometric in nature, i.e. it can be modelled by
conventional compound growth formulae.
The compound growth of traffic volumes is usually (and conveniently) specified as a percentage increase in
annual traffic volumes – a typical statement being ‘the annual growth rate is R%’.
Adopting this specification of growth and with compound growth occurring throughout the design period, the
cumulative growth factor (CGF), when constant, over the design period is readily calculated as follows (Equation
31).
Cumulative Heavy Vehicle Axle Groups
Determination of Basic Thickness
The thickness of material required over the in situ subgrade is determined using the empirical design chart given
in Figure 8.4. Note that Figure 8.4 is applicable to pavements with design traffic loading of 10^5 to 10^8 ESA.
section 12.8 describes procedures for design of lightly-trafficked flexible pavements.
Note the mechanistic-empirical design procedures, as described in Section 8.2.7, yield a similar total granular
thickness as Figure 8.4 using a top granular vertical modulus of 350 MPa.
Pavement Composition
The total thickness of material over the in situ subgrade may be made up of the following materials:
• unbound granular base and subbase courses
• selected subgrade materials
• lime-stabilised subgrade and/or lime-stabilised selected subgrade materials, provided the material has sufficient
lime to ensure design properties are achieved long-term (refer to Part 4D Stabilised Materials, Austroads 2006a).
These thickness design procedures may be conservative for materials designed using Method A which includes
a minimum unconfined compressive strength of 1 MPa. If the amount of lime is insufficient to achieve long-term
strength, no allowance should be made for the increase in subgrade CBR due to stabilisation.
The composition of the pavement structure is made up by providing sufficient cover over the in situ subgrade and
each successive material course. The thickness of cover required over a material is determined from its design
CBR. If the design CBR value of a material is less than 30%, then the cover required to inhibit deformation is
determined as for an in situ subgrade material, from Figure 8.4.
For Lesser Design Traffic Values, another Design Chart is used by the Empirical Method. It is as follows in fig
12.2:
7. ECONOMIC COMPARISON OF DESIGNS
General
In comparing various alternative pavement types and configurations, cost is a prime consideration. This Part
provides the means for designing a range of feasible pavements for a given set of design parameters. To determine
the most economical pavement, a cost comparison must be made.
Alternative projects should be evaluated primarily according to the criterion of minimum total (whole-of-life)
cost, giving consideration also to the safety and service of road users and others that may be affected by the
construction. In many cases, designers do not have information to reliably consider future maintenance and
strengthening costs of various alternatives. However, some details are available (e.g. Bennett & Moffatt 1995,
Porter & Tinni 1993).
Road user costs are usually excluded from the analysis partly because of lack of reliable information but mainly
because they are essentially similar for alternatives, provided minimum levels of serviceability are maintained.
However, the exclusion of road user costs needs to be carefully considered, particularly for projects carrying high
traffic volumes, as traffic disruption costs caused by maintenance activities can incur significant road user costs.
In addition to the above, other criteria which may need to be considered are:
• the potential for differential settlement over the road alignment
• the scale of the project
• the requirement to construct under traffic
• noise and spray effects
• maintenance requirements.
Despite the apparent simplicity of the models, designers are advised to consider carefully the results of any
economic comparison of design alternatives and not to rely on it as the sole determinant of the most appropriate
option.
Method for Economic Comparison
There are several methods for economic comparison of alternative designs. The ‘present worth’ method is given
here as it effectively allows for both uniform series and sporadic events (e.g. routine and periodic maintenance)
which will occur during the service life of the pavement. With the present worth method, all costs are converted
into capital sums of money which, invested now for an analysis period, would provide the sums necessary for
construction of a project and subsequent maintenance during that period.
In estimating present worth the principal elements are:
• construction costs
• maintenance and rehabilitation costs, including routine periodic maintenance and structural rehabilitation
• salvage value of the pavement at the end of the analysis period
• real discount rate
• analysis period.
Two factors not directly accounted for in the model but which have an influence on the comparative costs are the
growth in traffic over the analysis period and the availability of funds, which influences the duration of the
analysis period. It is important that designers run the model using a range of traffic growths and investment
periods to gauge its sensitivity to these factors.
It is important to recognise that the process of deflating future costs assumes that funds will be available over the
analysis period at a level consistent with the adopted discount rate. As this may not occur, the sensitivity of the
model to a range of discount rates should also be investigated.
The economic model also may not account for substantial differences in the social, political or environmental
impacts of future maintenance and rehabilitation activities associated with designs. For instance, one alternative
may require reconstruction involving a total road closure at the end of the analysis period whereas another may
be able to be rehabilitated under traffic but on a more frequent basis. Clearly both would involve some level of
social disruption for the community that may not be properly reflected in the economic comparison.
8. GEOMETRIC CONSISTENCY
General
Many characteristics of a road link are already established (e.g., topography, traffic volume and composition),
but the geometric form is largely under the control of the designer. The provision of consistent geometric design
along roads, particularly roads in rural environments, is an important aspect of road safety. There should certainly
be ‘no surprises’ for drivers, such as an isolated sharp curve in a section of road where all other curves have large
radii.
Different road classifications are used to indicate the type of service provided. In addition, there are significant
variations in topography from area to area and these need to be accommodated in the designs. There should be
consistency of design for each road classification, in each terrain type, regardless of location (Transport
Association of Canada 1999).
This approach leads to the concept of the ‘self-explaining road’ (Fuller & Santos 2002), that is, a road whose
features tell the driver what type of road it is and therefore what can be expected in terms of the elements of the
design. This provides a confidence in expectations for the driver, who then operates the vehicle in accordance
with those expectations, which in turn are in tune with the nature of the road. Design consistency can be addressed
in three areas:
•
•
•
cross-section
operating speed
driver workload.
It is also important that consistency be achieved in the type of intersections selected and their layout along a route
so that driver expectations are met. For example, all other things being equal, the lack of a right-turn lane at one
intersection when right turn lanes have generally been provided along a route may not be anticipated by some
drivers, resulting in rear-end crashes.
Cross-section and Network-wide Design
Roads of the same classification, in similar terrain, should have similar cross-sections. It is particularly important
that the cross-section be consistent along any one route, so that drivers are not faced with unexpected changes.
Where terrain on a route change and it is considered necessary to reduce cross-section dimensions for financial
or environmental reasons, the safety implications should be assessed.
There will be cases where changes in cross-section dimensions along a route are unavoidable (e.g., where a fourlane divided road becomes a two-lane, two-way road). In these cases, the designer should manage the situation
by providing a well-designed transition between the two cross-sections with appropriate tapers and signing.
Austroads have developed a network-wide design approach (refer to Austroads (2020h)) which provides further
guidance on developing consistent network-wide safety plans to support safer, self-explaining roads for all road
users. This methodology uses existing risk assessment tools (including both AusRAP and ANRAM) to precalculate a predicted number of FSIs and Star Rating for a cross-section design. It can be used to prepare corridor
vision standards that assist in developing design responses at a network level. Decisions made at that level will
need to be embedded in project scope requirements to inform subsequent detailed design.
Design Speed
The design of a road must be appropriate for the operating speeds of the vehicles using the road, and the desired
or expected speed should be determined in the early stages of the project. The design speed selected for the road
environment should consider the principles of the Safe System approach. It should match the road environment
to ensure the safety of all road users.
The selected design speed will affect virtually every aspect of the design – horizontal and vertical curvature, sight
distances, lane width, superelevation, roadside clearances, and barriers. Every effort should be made to design
the road to facilitate, and implicitly encourage, a consistent operating speed. Multiple-vehicle crash rates and
rates of fatal and serious injuries (FSI) are closely related to the differences in speed between vehicles. These
differences can be caused by drivers travelling substantially slower or faster than the average speed of the traffic,
or by individual drivers adjusting their speed to negotiate intersections, property entrances and changes in
geometry. The greater and more frequent the speed differences, the greater the probability of a higher crash rate
and fatal or serious injuries.
Designers can therefore enhance the safety of a road by producing a design that encourages a consistent speed of
operation. There are some situations, however, where a change in topography requires substantial reduction in
the design speed. In these circumstances, it is preferable for the horizontal curve radii to be gradually reduced
through a series of curves with appropriate warning signs in place.
Road networks that do not provide an appropriate road hierarchy may lead to inconsistent speeds of operation.
An appropriate mix of higher and lower-order roads in the network, access control and appropriate integration of
development can help to resolve these issues.
Driver Workload
Driver workload also has a marked effect on performance at both ends of the spectrum. If driver workload is too
low, the driver’s attention (i.e., level of alertness) will be too low, with probable loss of vigilance, and the driver
may even fall asleep at the wheel. At the other end of the spectrum, if the driver’s brain activity level is too high
(e.g., stress, information overload, emotional situations), they may compensate by ignoring some relevant
information, leading to unsafe operation of the vehicle.
In these circumstances, driver response to unexpected situations may be too slow or inappropriate. It is important
that the designer ensure that abrupt increases in driver workload are avoided, as these provide the potential for
higher collision rates. These increases can be caused by:
•
•
•
•
•
the nature of the feature (e.g., an intersection or lane drop is more critical than a change in shoulder width)
limited sight distance to the feature
dissimilarity of the feature to the previous feature (causing surprise to the driver)
large percentages of drivers unfamiliar with the road (e.g., a road with a high volume of tourist traffic as
opposed to a local road)
a high demand on the driver’s attention after a period of lesser demand (e.g., a sharp curve at the end of a
long straight).
Performance-based Design
Ultimately, the key function of a road is to cater for the performance characteristics of its users (motorised or
otherwise). It is recognised that in some circumstances, site, or project-specific constraints – including financial
– may prohibit the use of one or more design parameters that would typically be preferred.
Performance-based design anticipates the performance effects of design decisions on aspects that include:
• traffic operational efficiency
• existing and expected future crash frequency and severity
• construction cost
• future maintenance cost
• functional classification
• use by each transportation mode
• accessibility for persons with disabilities
• available right-of-way
Existing and potential future development
• operational flexibility during future incidents and maintenance activities
• stakeholder input
• community impacts and quality of life
• historical structures
• impacts on the natural environment.
•
Performance-based analysis provides a key basis for the exercise of design flexibility. Flexible design emphasises
the role of the planner and designer in determining appropriate design dimensions based on project-specific
conditions and existing and future roadway performance more than on meeting specific nominal design criteria.
In the past, designers sought to assure good traffic operational and safety performance for the design of specific
projects primarily by meeting the dimensional design criteria in the road design guides. This approach was
appropriate in the past because the relationship between design dimensions and future performance was poorly
understood. Recent research has improved our knowledge of the relationship between geometric design features
and traffic operations for all modes of transportation and has developed new knowledge about the relationship of
geometric design features to crash frequency and severity (AASHTO 2018).
In these circumstances, deviations from typical best practice may be acceptable if there is sufficient evidence to
demonstrate that performance for all road users will achieve an acceptable standard – particularly with regards to
safety.
Traffic Speed:
Traditionally, design speed has been a basic parameter in determining road standards and is a function of the load
classification. However, Guide to the Geometric Design of Major Urban Roads and Guide to the geometric
Design of Rural Roads have introduced an operating speed concept. Operating speed in these guidelines is defined
as 85th percentile speed of cars when traffic volumes are low.
For rural roads, the methodology for the geometric design has moved to the use of “Section Operating Speed”.
For major urban roads, geometric design for cars is based on the operating speed that is 10km/h higher than the
legal speed limit. For local roads, since low standard and low design speed roads tend to return operating speeds
higher than the arbitratory speed limits, operating speed is used to assess the need for traffic calming measures in
suburban areas.
Unless otherwise sign posted, the following general legal speed limits are in force in the TAS:
• 100km/h on parkways and rural roads.
• 80km/h on all arterial roads and some sub-arterial roads.
• 60km/h on some sub-arterial roads and major collector roads.
• 50km/h on minor collector roads and access streets.
Traditionally, access streets are designed for 40km/h (horizontal alignment) and 60km/h (vertical alignment)
design speed.
Sight Distance:
A minimum stopping sight distance should be provided at all points along the road. Stopping sight distance is a
function of vehicle speed, reaction time, eye height and object height. The recommended values of the object
heights are given in Table 3.1.
Table: Object heights
Object height (m)
Situation
0.00
0.20
Intersections
General situations
0.60
Car taillights
1.05
Entering sight distance
A car driver eye height of 1.05m is used for the geometric design of both urban and rural roads. For commercial
vehicles, a driver eye height of 1.8m is used for general geometric design. A driver eye height of 2.5m is used for
checking sight distances on sag curves.
For the geometric design of major urban roads, a reaction time of 2.0 seconds is to be used. For the geometric
design of rural roads, a reaction time of 2.5 seconds is to be used. In situations where the adoption of a reaction
time of 2.5 seconds would result in impractical solutions, a reaction time of 2.0 seconds may be considered.
Crossectional Properties Of Road
The type of cross-section to be used in the development of any road project depends on:
• urban or rural location
• the functions of the road, for example, through route or local access
• new road or treatment of an existing road
• traffic volume and mixture
• number and type of trucks
• provision for public transport
• walking and cycling needs
• creating accessible environments for all
• place funcion and associated space requirements (for example outdoor dining)
• environmental constraints, for example, topography, existing public utility services, existing road reserve
widths, significant vegetation, geology
• local road-making materials available.
Decisions around widths adopted for the various cross-section elements should not be made in isolation as each
element (lane width, shoulder width, etc.) has a relationship with the other which influences the overall outcome.
The challenge is often to optimally allocate road space within an available cross-section to provide the most
appropriate road safety, amenity and operational outcomes. For further information on the contribution of crosssection elements, refer to Austroads (2020c).
A key consideration in determining the appropriate cross-section of a road is to understand the type and mix of
people and traffic expected to use the road. With a growing public awareness of sustainability and the impact that
congestion and pollution have on the environment and well-being of people, road designers need to be conscious
of the effort that various road agencies are expending to provide road space for all types of transport, including:
• pedestrians
• personal mobility devices
• bicycles
• motorcycles
• road based public transport (buses and trams)
• cars
• trucks (including high productivity freight vehicles)
• animals (stock routes/crossings).
Road Crossfall
Crossfall is the slope of the surface of a carriageway measured normal to the design line or road centreline. The
purpose of crossfall is to drain the carriageway on straights and curves and to provide superelevation on horizontal
curves. The pavement crossfall on straights for various pavement types is given in Table 4.2.
Crossfalls flatter than 2% do not drain adequately, and even 2% should only be prescribed for concrete pavements
where levels and surface finish are tightly controlled. Unless compaction and surface shape are well controlled
during construction, pavements with less than 2.5% crossfall will hold small ponds on the surface, which may
cause potholes to develop and hasten pavement failure. Rutting of the pavement is also more likely to hold water,
increasing the risk of pavement deterioration and vehicle aquaplaning when the pavement crossfall is less than
3%.
Traffic Lane Widths
Current Australian and New Zealand practice is to provide standard traffic lane widths of 3.5 m. Traffic lanes are
measured to the face of the kerb or to the lane line for multi-lane roads, or roads with shoulders. Road agencies
may also choose to provide an additional clearance to the face of the kerb to account for shy line effects, or for
kerb profiles that have a wider channel (e.g. 450 mm) in areas of high rainfall. Refer to Figure 4.8 for the definition
of the components of kerb and channel.
Rural Road Widths
The desirable lane width on rural roads is 3.5 m. This width allows large vehicles to pass or overtake without
either vehicle having to move sideways towards the outer edge of the lane. The lane width and the road surface
condition have a substantial influence on the safety and comfort of users of the roadway. In rural applications the
additional costs that will be incurred in providing wider lanes will be partially offset by the reduction in longterm shoulder maintenance costs. Narrow lanes result in a greater number of wheel concentrations in the vicinity
of the pavement edge and will also force vehicles to travel laterally closer to one another than would normally
happen at the design speed. Drivers tend to reduce their travel speed, or shift closer to the lane/road centre (or
both) when there is a perception that a fixed hazardous object is too close to the nearside or offside of the vehicle.
When there is a perceived fixed hazard, there is a movement by the vehicle towards the opposite lane line.
Single carriageways
On many roads in Australia, traffic volumes are less than 150 vehicles per day. Some of these are arterial roads
passing through sparsely settled flat country where the terrain leads to a high operating speed. Where traffic
volumes are less than 150 vehicles per day and, particularly, where terrain is open, single lane carriageways may
be used. The traffic lane width adopted on such roads should be at least 3.7 m (refer Table 4.5). A width of less
than 3.7 m can result in excessive shoulder wear. A width greater than 4.5 m but less than 6.0 m may lead to two
vehicles trying to pass with each remaining on the seal. This potentially increases head-on accidents. The width
of 3.5 m ensures that one or both vehicles must have the outer wheels on the shoulders while passing. On two
lane sealed roads, the total width of seal should desirably be not less than 7.2 m to allow adequate width for
passing.
Divided carriageways
Divided roads are provided where traffic volumes are high and it is necessary to provide motorists with a
satisfactory level of service or where a section of road has an unacceptable number of crashes, particularly headon crashes.
Austroads (2010c) showed that casualty crash rates were 1.6 times higher on undivided rural roads than on divided
rural roads. Although there are many other differences between the two road types besides the presence of a
median the finding shows that lack of a separation between opposing traffic is a significant risk contributing
factor. The finding also showed that severity of crashes on undivided roads was generally higher. This was most
likely due to the occurrence of high speed head-on crashes on undivided roads which are very rare on divided
roads.
Table 4.6 shows traffic lane and shoulder widths on rural roads with divided carriageways, including rural
freeways. Each of the two carriageways should have at least two traffic lanes so that overtaking is possible. With
each carriageway, the left shoulder should be at least 2 m wide, but preferably wider to accommodate a brokendown vehicle.
SHOULDERS
Road shoulders are provided to carry out two functions; structural and traffic. The structural function of the
shoulder is to provide lateral support to the road pavement layers.
The traffic functions of the shoulder are:
• an initial recovery area for any errant vehicle
• a refuge for stopped vehicles on a firm surface at a safe distance from traffic lanes
• a trafficable area for emergency use
• space for cyclists
• clearance to lateral obstructions
• provision of additional width for tracking of large vehicles
Width
Shoulder width is measured from the outer edge of the traffic lane to the edge of usable carriageway and excludes
any berm, verge, rounding or extra width provided to accommodate guideposts and guard fencing. Wide shoulders
have the following advantages:
• Space is available for a stationary vehicle to stand clear of the traffic lanes; a vehicle standing partly on a
shoulder and partly on a traffic lane may be a hazard.
• Space is available on which vehicles may deviate to avoid colliding with other vehicles and on which a driver
may regain control of an errant vehicle.
• The resulting wider formations increase driver comfort and the quality of service of the road.
• They contribute to improved sight distance across the inside of horizontal curves.
On a divided road with two lanes in each direction, it is desirable to provide shoulders at least 2.5 m wide on the
left side of each carriageway and 1.0 m wide on the median side of each carriageway. If the divided road has
three or more lanes in each direction, it is preferable to have wide shoulders on both sides of both carriageways,
especially where there is a median barrier adjacent to the shoulder. This limits the number of lanes a vehicle may
have to cross in the event of breakdowns to stop clear of the traffic lanes, allows for the provision of emergency
telephone points and for the operation of emergency services, tow trucks or maintenance vehicles.
Shoulder Sealing
Shoulders may be wholly or partially sealed. Sealing of shoulders is frequently done to reduce maintenance costs
and to improve moisture conditions under pavements, especially under the outer wheel path. However, a most
important benefit of sealed shoulders is that they reduce crash rates, particularly with respect to run-off-road
crashes, with most of the benefit being achieved by a shoulder seal width of 0.5 to 1.5 m.
The desirable width of sealed shoulder depends on many factors including:
• traffic composition
• AADT
• access
• operating speed
• rainfall
• shoulder pavement.
A full width seal should be considered under the following conditions:
• adjacent to a lined table drain, kerb or dyke
• where a safety barrier is to be provided
• on the shoulders of a superelevated curve
• on floodways
• where rigid pavement is proposed
• where environmental conditions require it
• where needed to reduce maintenance
• in high rainfall areas.
Shoulder Crossfalls
Shoulders generally should be steeper than the adjacent traffic lanes to assist surface drainage (marginal increase
of 1%). However, where the shoulder consists of full depth pavement and is sealed, its slope may be the same as
the adjacent pavement in order to facilitate construction.
On superelevated sections of roads, the shoulder on the high side and low side must have the same crossfall as
the traffic lanes. A crossfall of 5% or more extended across the verge may lead to more frequent maintenance and
should be monitored.
On straights the shoulder crossfall is shown in Table 4.8.
Verge
In Australia, the verge is considered to be the section of the road formation that joins the shoulder with the batter.
In New Zealand, the verge is defined as that area of the road reserve located between the shoulder hinge point
and the legal road boundary. For the purposes of this guide, the extent of the verge is limited to that shown on
Figure 4.2, i.e. between the shoulder and the batter.
The main functions of the verge are to provide:
• a traversable transition between the shoulder and the batter slope to assist controllability of errant vehicles
• a firm surface for stopped vehicles at a safe distance from traffic lanes
• support for the boxing edge, shoulder material and kerb and channel
• space for installation of road agency infrastructure such as guide posts and road safety barriers
• space to accommodate infrastructure belonging to other services such as gas, electricity, water and public
transport
• reduced scouring due to road storm water run-off.
It should be noted that verges are not usually provided in urban areas where kerb and channel is constructed
except:
• along freeways
• where guard fence is provided
• along a short fill between adjacent cuts where continuity of kerb and channel is required.
Verge Widths
Examples of verge widths for various functions of verges are shown in Table 4.9. Verge widths on arterial roads
should also be selected according to the lateral change of grade A, and modified if required to accommodate road
safety barriers.
Medians
A median is commonly provided to improve the safety and operation of major urban and rural roads with multiple
lanes in each direction. Medians may be raised or depressed as shown in Figure 4.21. The main functions of
medians are to:
• separate and reduce conflict between opposing traffic flows, effectively reducing the possibility of head-on
collisions
• prevent indiscriminate crossing and turning movements
• shelter right-turning and crossing vehicles at intersections
• shelter road furniture and traffic control devices, such as signs, traffic signals and street lighting
• provide a pedestrian refuge which enables pedestrians to cross the road one carriageway at a time
• reduce the impact of headlight glare and air turbulence from opposing streams of traffic
• provide scope for improvement of visual amenity by landscaping
• accommodate level differences between carriageways
• provide a safety barrier
• provide an emergency stopping area on multi-lane roads
• provide a recovery area for errant vehicles.
Footpaths
Footpaths are a part of the urban border set aside for the use of pedestrians (and cyclists in some Australian
states). Footpaths are either located adjacent to the roadway or separated from it by the nature strip. The decision
as to whether a footpath is included in the cross section on both sides of the road, only one side or not at all will
depend on local guidance requirements and connectivity to the wider pedestrian network.
The width of a footpath for pedestrians is dependent on its location, purpose and the anticipated demand on the
facility The width of the footpath may need to be greater than the recommended minimums in the following
situations:
• at a pedestrian crossing point to allow people to pass those waiting
• at a bus stop
• where service poles or structures restrict the width
• where higher pedestrian volumes are anticipated (e.g. near shops)
• where outdoor dining is present.
These requirements should be considered early in the design process to avoid compromised designs where pinch
points become necessary or require costly retrofit. Innovations and better use of existing road space can contribute
to maintaining and enhancing the place function of street design.
Bus Stops in Rural
Bus stops in rural and outer urban areas are often located in the road shoulder between the carriageway and table
drain, with few or no passenger facilities. Shoulder bus stops have different requirements and constraints to those
found in urban areas.
The careful selection and assessment of locations for shoulder bus stops can assist in meeting the needs of various
stakeholders effectively. When the opportunity arises to site a new stop or review the site of an existing bus stop,
the following should be considered:
• Bus stops and stopping areas should not be located near or on curves along a road. These locations may not
provide sufficient sight distance for bus drivers to identify and stop at the bus stop, or adequate view of
approaching vehicles when pulling out of the shoulder. Further, it may not provide sufficient sight distance to
allow motorists to stop behind the stationary bus.
• Locating the stop adjacent to a table drain should be avoided if possible as it becomes an obstacle for passengers
boarding the bus, especially for disabled passengers.
• The bus stop should be located near an existing footpath to provide access to the bus stop and to minimise the
cost of providing access.
• Bus stops should not be located where there is insufficient area for installation of paved, all weather surface for
passengers to wait safely. The bus stop should be located where adequate roadside width is available. Where there
is no other option, consideration should be given to not installing the bus stop.
• Bus stopping areas should be ideally located on sealed shoulders as this minimises the cost of maintenance.
Bus stop waiting areas need to be visible to passing drivers and separated from other road users, and where there
is high risk, the waiting area should be protected from errant vehicles. In Australia the provision of a hardstand
area is considered to be a basic requirement for all new or upgraded bus stops in accordance with the Disability
Discrimination Act 1992. It provides passengers with a stable and even surface to wait for and board a bus,
especially for disabled passengers. It assists bus drivers to maintain a clean bus interior and minimises the
potential slip hazards in the bus for other passengers. The provision of a paved, all weather area, sufficient to
allow all passengers adequate room to stand without overcrowding, should be provided.
Bus shelters should be considered at locations where there is a high level of passenger patronage. The shelter
should be located such that the bus driver is able to see waiting passengers. The speed environment and physical
features should be considered in the location of the shelter in relation to the traffic lanes.
Desirably, the shelter should be located beyond the clear zone so as not to become a hazard to road users. The
minimum shoulder width required for a bus stopping area is 3 m, which allows the bus to stop without delaying
traffic. Where insufficient shoulder width is available, designers should extend the width of the shoulder locally,
to allow the bus to fully pull into the bus stopping area. This may also involve drainage works for any table drain
present. Alternatively, another location for the bus stop should be considered.
The length of a bus stopping area should be sufficient to allow the bus to start moving before re-entering traffic
lanes. Compared to a standing start, providing a short length for acceleration reduces bus driver and motorist
frustration, with less disruption to the flow of traffic. The minimum length recommended is 15 m consistent with
a taper on a bus bay. Where possible, a longer sealed distance may be provided (e.g. up to 30–50 m in intermediate
speed environments) to cater for bus acceleration, especially in higher speed zones.
Ideally, bus stops should not be located on unsealed shoulders, as the frequent repeated heavy vehicle loading
and braking cause greater wear, requiring frequent maintenance intervention to repair rutting and potholes. Where
bus stops are proposed on roads with unsealed shoulders, consideration should be given to locally sealing the bus
stopping area with a similar surface treatment as the rest of the road. In some situations, the existing shoulder
material may not support the increased loadings and will require reconstruction/strengthening. Similar treatments
should also be applied to the acceleration and deceleration tapers of the bus stopping area.
School bus stops
School bus stops are slightly different to normal rural bus stops in that they are only available for use by school
children. These stops are only active at two times in the day (pick-up in the morning and drop-off in the afternoon)
and can move location to suit the needs of passengers (a stop may not be required once a child has completed
school). The needs of school children using these bus stops are similar to those of normal rural bus stops with
regard to the location and facilities that they provide, however designers should be cognisant of the age and
behaviours of children. Designers should consult relevant road agency guidelines (where available) for further
information on this topic.
Depending mainly on the number of school children using a bus stop, consideration should be given to providing
the following facilities. (For safety, all facilities for children should be on the side of the bus stop furthest from
the road).
• Waiting Areas – Where needed, waiting areas should be provided at school bus stops for school children to
assemble and disperse. These areas should be level, well drained and free from tripping hazards and may be
gravelled and sealed. It is desirable to provide shade.
• Parking Facilities – Provision of safe parking facilities should be considered at school bus stops where parents
with vehicles assemble to drop-off/collect children. Adequate area should be available to permit parents to park
their vehicle, drop-off the children and collect them safely with minimum disruption to the children and traffic.
• Travel Paths for Pedestrians – Safe travel paths should be available for children to walk to and from the school
bus stop (e.g. from a separate parking area). The need for children to walk along the edge of a vehicle carriageway
should be avoided where possible, especially on roads where the traffic speed, volume and proportion of heavy
vehicles are high. Preferably, paths at the maximum distance from the traffic lanes should be provided for children
to use. In some cases, facilities for bicycles on off-road paths and storage for bicycles should be considered.
9. SIGHT DISTANCE
Sight distance is defined as the distance, measured along the carriageway, over which visibility occurs between
a driver and an object, single vehicle sight distance (refer to Figure below) or between two drivers at specific
heights above the carriageway in their lane of travel.
For safe and efficient traffic operation on the road, sufficient sight distance must be provided to enable drivers to
perceive and react to any hazardous situation. A driver’s sight distance should be as long as practicable, but it is
often restricted by crest vertical curves and obstructions on horizontal curves and the designer should consider
all of these elements when developing the horizontal and vertical geometry of the road.
The concept of sight distance provides a parameter that can be calculated and related to the geometry of the road.
This concept is based on a number of somewhat stylised assumptions of particular hazards and corresponding
driver behaviour. The hazard is assumed to be an object, of sufficient size to cause a driver to take evasive action,
intruding into the driver’s field of view.
Sight Distance Parameters
In order to use sight distance as a calculable parameter for the geometric design of roads, assumptions must be
made about the following elements:
• object height
• driver eye height
• driver perception – reaction time.
The values chosen for different scenarios are outlined later in this section, but they have been developed using
local and international research and engineering judgement.
This Guide does not consider sight distances at intersections, specifically Safe Intersection Sight Distance (SISD),
Minimum Gap Sight Distance (MGSD) and Approach Sight Distance (ASD). Values for these sight distance
parameters can be found in the Guide to Road Design Part 4A: Unsignalised and Signalised Intersections
(Austroads 2010a). Designers need to consider the implications that intersection sight distances can have for the
development of the geometry of a road project.
Car Stopping Sight Distance
The concept of car stopping sight distance is illustrated in Figure 5.2. It is generally measured between the driver’s
eye (1.1 m) and a 0.2 m high, stationary object on the road. The object height of 0.2 m represents a hazard that
cannot be driven over and hence requires the vehicle to stop to avoid a collision. However, there are special cases
when a lower object height is used (e.g. to the pavement level at floodways).
In cases of sighting over roadside barriers in constrained cases, it may not always be practical to provide car
stopping sight distance to a 0.2 m high object – refer Table 5.1 for heights in these instances. Note 1 of Table 5.7
indicates that minimum shoulder widths and minimum manoeuvre times apply where object heights of greater
than 0.2 m are used for stopping sight distance over barriers. These minimum values are given in Table 5.7 and
must be provided to enable drivers to avoid hazards that are lower than the chosen design object height.
Sight Distance Requirements on Horizontal Curves with Roadside Barriers/Wall/Bridge Structures
Application of the normal stopping sight distance requirements over/around roadside barriers and structures on
horizontal curves can produce excessive lateral offsets in particular circumstances. This can have the following
adverse operational effects:
• cars and trucks parking in the widened area, reducing sight distance
• errant vehicles potentially impacting the barrier at a greater angle, increasing the severity of these types of
accidents
• cost of providing the widened area becomes prohibitively expensive.
Experience shows that the criteria in this section provide acceptable sight distance for these circumstances. This
supersedes the previous common practice of dismissing sight distance criteria altogether based on the grounds of
being uneconomic.
Flowcharts and a table to assist with determining sight distance requirements over/around roadside barriers and
structures on horizontal curves are included in Appendix.
10.COORDINATION OF HORIZONTAL AND VERTICAL ALIGNMENT
Principles
In engineering terms, road alignments have to service traffic in terms of providing a route that meets the
constraints imposed by vehicle dynamics, occupant comfort, and topography. This means that most road
alignments are in fact complex three-dimensional splines that do not have a simple mathematical definition.
This problem has historically been addressed by reducing the three-dimensional alignment to two,
wodimensional alignments. In each case, the alignments are made up of geometric elements that are convenient
to calculate and construct yet still ensure that vehicle dynamic constraints are met. Even with the advent of
computers, this approach has still proven to be the most convenient for both design and construction. To use
complex three-dimensional models would introduce unnecessary complexity into the process but it is necessary
to ensure that the two alignments are properly coordinated and complement each other.
The interrelationship of horizontal and vertical alignment is best addressed in the concept and preliminary design
phases of the project. At this stage, appropriate trade-offs and balances between design speed and the character
of the road – traffic volume, topography and existing development – can be made. Because they must be
complementary, horizontal and vertical geometry can ruin the best parts and accentuate the weak points of each
element. Excellence in the combination of their designs increases efficiency and safety, encourages uniform
speed, and improves appearance – almost always without additional cost.
Where possible, horizontal and vertical geometry should be coordinated for appearance and safety. In principle,
co-ordination means that horizontal and vertical curves should either be completely superimposed or completely
separated. The related horizontal and vertical elements should be of similar lengths, with the vertical curve
contained within the horizontal curve. This arrangement should produce the most pleasing, flowing threedimensional result, which is more likely to be in harmony with the natural landform. Where the horizontal and
vertical geometry is unable to be coordinated, the designer should review the alignments and modify the design
to minimise any impacts.
In urban situations it is frequently the case that such aesthetic considerations will be very difficult or expensive
to apply. Many major urban roads are developed by widening established streets, or by intermittent alignment
improvements. In consequence, the existing street locations and levels, and abutting development, will exert a
strong influence on the alignment of major urban roads.
Safety Considerations
The following relationships between horizontal and vertical alignment should be applied to the design wherever
possible for safety, aesthetic and drainage reasons:
• A crest can obscure the horizontal alignment and the severity of a horizontal curve. Minimum radius horizontal
curves should not, therefore, be used with crest vertical curves. Lateral shifts in the alignment on crests can lead
to confusion and accidents. Lateral shifts of approximately one lane width are particularly hazardous as shown
on Figure 6.1.
Crest vertical curves should be contained within horizontal curves to enhance the appearance of the crest by
reducing the three-dimensional rate of change of direction. This also improves safety by indicating the direction
of curvature before the road is obscured by the crest.
• The design speed of the road in both planes must be the same. This improves driver awareness of the speed
environment.
• A small movement in one dimension should not be combined with a large movement in the other.
• Sharp horizontal curves should not be introduced at or near the top of a crest vertical curve. The change in
alignment may be very difficult to see at night.
• If the crest curve restricts the driver’s view of the start of the horizontal curve, a driver may be confused and
turn incorrectly. This is particularly dangerous when sharp horizontal curves are located near the crests of vertical
curves (Figure 6.2).
• Sharp reverse horizontal curves are undesirable in association with a crest vertical curve. The crest can obscure
the reverse alignment.
• A crest vertical curve or a sharp horizontal curve should not occur at or near an intersection or rail crossing.
For good design, the horizontal curve shall indicate the change in direction before introduction of the vertical
curve in both directions of travel. That is, the horizontal curve must be longer than the vertical curve as shown
on Figure 6.3.
• Carriageway narrowing, changes from divided to undivided road, traffic islands and median noses should not
be located at horizontal or vertical curves unless adequate visibility is available to ensure approaching drivers are
aware of what is occurring. Also designs should ensure that stopping sight distance to the road surface is provided
at lane diverges and lane merges.
• Hidden dips, minimum re-sheets over existing pavements or minimisation of earthworks on new construction,
which create dips in the road, may reduce overall safety. Designers should avoid creating dips in vertical
alignments where possible. Typical examples are shown on Figure 6.5 and Figure 6.6, with Figure 6.7 providing
guidance to improve grading. Where correction of an existing alignment is uneconomic, other cues should be
provided for drivers, such as guide posts.
• The situation illustrated in Figure 6.5 is most undesirable as there is a potential hazard that a driver may attempt
to overtake, unaware that a vehicle is approaching in the opposite direction. Although shallow dips (Figure 6.6)
are less hazardous, approaching drivers cannot know whether a dip hides an on-coming vehicle. Dips should be
avoided on long uniform grades (Figure 6.7), particularly on straight alignments.
• Compound curves; uni-directional curves of considerably different radii should be avoided (Section 7.5).
The vertical curve overlaps one end of the horizontal curve
If a vertical crest curve overlaps either the beginning or the end of the horizontal curve, drivers have little time to
react to the horizontal curve once it comes into view. This is a particularly unsafe practice if there is a decrease
in the operating speed at the start of the horizontal curve.
The defect may be corrected in both cases by completely separating the curves. If this is uneconomic, the curves
must be adjusted so that they are coincident at both ends, if the horizontal curve is of short radius. If the horizontal
curve is of longer radius, they need be coincident at only one end.
The vertical curve overlaps both ends of the horizontal curve
If a vertical crest curve overlaps both ends of a sharp horizontal curve, a hazard may be created because a vehicle
has to undergo a sudden change of direction during passage of the vertical curve while sight distance is reduced.
This creates the same problems as discussed above.
The corrective action is to make the curves coincident at one end so as to bring the crest on to the horizontal
curve.
Insufficient separation between the curves
If there is insufficient separation between the ends of the horizontal and vertical curves, a false reverse curve may
appear on the outside edge-line at the beginning of the horizontal curve, or on the inside edge-line at the end of
the horizontal curve. Corrective action consists of increasing the separation between the curves.
Dissimilar length horizontal and vertical geometric elements
A short movement in one plane should not be placed within a large movement in the other. A particular instance
where this can lead to safety problems is when a small depression in the vertical alignment results in a ‘hidden
dip’. An example of a hidden dip is shown in Figure 6.5.
Corrective action consists of making both ends of horizontal and vertical curves coincident, thus producing
similar length curves. An alternative treatment is to completely separate the curves.
Long flat grades
Long straights with flat grades make it difficult for drivers to judge the distance and speed of approaching vehicles
leading to overtaking accidents. An approaching vehicle more than 2500 m away on a straight seems to be
standing still but the same situation on a large curve provides the driver with a changing perspective allowing
some judgement of speed and distance. This situation is exacerbated at night with visibility restricted to that
provided by headlights.
Roller coaster grading
Long straight sections are prone to ‘roller coaster’ grading (Figure 6.9) with the added potential for hidden dips.
Designers should take care that the features are not incorporated into the design by using appropriate curvature
in both planes and checking lines of sight for hidden dips.
Steep or prolonged downhill gradient
Steep downhill gradients, or even a gradual downhill gradient over a prolonged length, can lead to involuntarily
high operating speeds. The downstream geometric design must take account of this increased speed and drivers’
perceptions. Out-of-context, low radius or compound curves, that may be difficult to read or misleading for
drivers in these contexts should be avoided.
11.ELEMENTS OF HORIZONTAL GEOMETRY
General
Horizontal alignment of a road is a basis for definition of strings of characteristic points determined from typical
cross section (centerline line, edges of carriageway, edges of road formation, longitudinal drains etc.) in a
horizontal X-Y plane. The geometry of the road strings is made up of a series of connected curves, straights, and
spirals.
Physics of vehicular movement and the vehicle speed dictate selection of appropriate elements of horizontal
alignment. These elements should also be aesthetically pleasing and result in cost effective solutions. Refer to
Guide to the Geometric Design of Major Urban Roads and Guide to the Geometric Design of Rural Roads for
further discussion on the movement on a circular path.
Horizontal alignment
Traditionally, the horizontal alignment of a road normally comprises of a series of straights and circular arcs,
which may be connected by transition (spiral) curves. Recently, curvilinear horizontal alignment is frequently
used in flat terrain in lieu of long straights, especially in the design of major dual carriageway roads. Curvilinear
alignments are more aesthetically pleasing and blend better with environment, resulting in less ecological impact
and lower construction cost.
Straights longer than 20Vd expressed as meters should be avoided.
The following are common types of complex horizontal curves:
• Compound curves. Compound curves comprise of two or more adjoining curves of different radii in
the same direction.
• Broken back curves. Broken back curves are horizontal curves in the same direction joined by a
straight.
• Reverse curves. Reverse curves are adjoining horizontal curves in opposite direction, either back-toback or connected by a straight or spiral.
• Transition curves. Transition curves are normally used to join straights and circular curves. They
provide for a comfortable transition between two elements with a different curvature and provide room
for transition of crossfall to the full superelevation. The most frequently used form of transition curves
is clothoid or Euler spiral. Transition curves should be omitted for sections of roads with operating
speed not exceeding 60km/h.
The minimum curve length is required to provide satisfactory appearance and avoid kinks in the horizontal
alignment.
On curves with radii less than 200m, lane widening is required to accommodate standard design vehicle (i.e.,
19m long semi-trailer). Where the required lane widening on a curve is greater than 4.6m, cars have a tendency
to travel two abreast. Thus, the full pavement should be constructed across the 4.6m width, with the constant line
width (normally 3.5m) line-marked around the curve. Small radius curves shall be checked against the sight
distance requirements, since the sight distance may be limited by proximity of lateral obstructions such as cut
batters, vegetation, bridge piers and signs.
Superelevation
Superelevation is introduced to help vehicles to negotiate circular path by reducing friction demand.
Superelevation also provides driver guidance into the curve. The superelevation to be adopted is chosen primarily
on the basis of safety, but other factors are comfort and appearance. The superelevation applied to a road should
take into account:
• operating (design) speed of the curve, which is taken as the speed at which the 85th percentile driver is expected
to negotiate it.
• tendency of very slow moving vehicles to track towards the centre
• stability of high laden trucks where adverse crossfall is considered, and the need to increase superelevation on
downgrades
• difference between inner and outer formation levels, especially in flat country or urban areas
• length available to introduce the necessary superelevation.
However, it is noted that although the dynamics of vehicle movement show that the selection of superelevation
is important for traffic safety, research findings suggest that it does not make much of a difference in the selection
of driver speed, which is primarily based on horizontal curvature.
The proportion of centripetal acceleration as a result of the combination of superelevation and sideways friction
needs to be controlled to provide a consistent driving experience.
There are a number of methods to determine the superelevation (and hence resultant side friction) for curves with
a radius larger than the minimum radius for a given design speed. It must also be reiterated that the use of such
curves should be checked to ensure that the length does not cause the operating speed to increase beyond the
curve design speed when the design speed is less than 110 km/h.
Length of Superelevation Development
The length required to develop superelevation should be adequate to ensure a good appearance and give
satisfactory riding qualities. The higher the speed or wider the carriageway, the longer the superelevation
development will need to be to meet the requirements of appearance and comfort.
Relative Grade
The relative grade is the percentage difference between the grade at the edge of the carriageway and the grade of
the axis of rotation. This difference should be kept below the values shown in Table 7.10 to achieve a reasonably
smooth appearance.
12.ELEMENTS OF VERTICAL GEOMETRY
General principles
Vertical alignments are designed with respect to sight distances, which in turn are a function of speed. As an
absolute minimum, a safe stopping sight distance must be provided at every point on the vertical alignment.
Typical controls for the vertical geometry, in no specific order, are:
• topology.
• geology.
• existing intersections.
• property accesses and driveways.
• required clearances for structures.
• required clearances for services; and
• pedestrian and cycling requirements.
In addition to checking for the required minimum lateral clearance, overpasses and large trees should be checked
for truck sight stopping distance. For this purpose, driver eye height shall be set to 2.5m and the target height to
0.6m (taillights of the vehicle in front).
Grades
The minimum grade is a function of road drainage. On rural roads, in cuttings and at the superelevation transitions,
grades should be adequate for at least table drains or gutters, i.e., minimum 0.5% to 1.0%. In fill and outside the
superelevation transitions, unkerbed roads could have 0% grade providing that table drains have positive gradient.
On all kerbed roads in the TAS, the desirable minimum grade shall be 1.0%. Flatter grades (between 0.5% and
1.0%) may be permitted subject to the designer providing satisfactory evidence that drainage provision and the
proposed construction practices are such that no ponding shall occur. Grades flatter that 0.5% may be permitted
only in exceptional circumstances (i.e., widening of existing pavement). The designer shall outline procedures
that will ensure that the finished gutter profile and pavement surface are free draining, and that the width of flow
is within the requirements.
Unkerbed roads may be provided as the first stage of kerbed roads. To minimize abortive work and maximize
utilization of the most expensive single road component (the pavement), it is a good practice to adopt grades as
required for the kerbed roads.
The maximum grade is a function of site conditions, vehicle dynamics, road construction cost and maintenance
cost. Depending on the design speed and terrain, maximum grades vary from 3% to 10% and more. The minimum
length of grade is governed by appearance. The maximum length of grade, especially steep grade, is governed by
the operating speed of a typical loaded truck (uphill) and the risk of brake failure (downhill). Table 8.2 shows the
effect of grade on vehicle performance and lists road types that would be suitable for these grades. Vehicles can
tolerate relatively short lengths of steeper grades better than longer lengths of less steep grades.
Vertical curves
Vertical curves are used to provide transition between different grades and increase sight distance across the two
grades. The most common form of the vertical curve is a parabola, which is an approximation of a circular curve.
Convex vertical curves are referred to as crest or summit curves. Concave vertical curves are commonly known
as sag curves. Three criteria are used to determine the length of a vertical curve:
• sight distance, usually sight stopping distance.
• appearance; and
• comfort, i.e., vertical acceleration.
In case of crest curves, the third (comfort) criterion is met if the sight distance and appearance criteria are met.
However, on low-speed suburban roads, meeting the appearance criterion may not be possible. In such cases, the
length of the vertical curve adopted from the sight distance criterion should be also checked for comfort.
In case of sag curves, appearance and comfort are normally the governing criteria. Sight distance is checked for
overhead obstructions (if present) and/or for headlight sight distance (for operating speeds above 80km/h).
Contrary to the horizontal curves, reverse vertical curves with common tangent points are acceptable.
The designer should check the resulting grade from superimposing superelevation and longitudinal grade for
drainage considerations. Some combination of long transitions and steep grades result in sheet flows along the
road and slow evacuation of the surface water across the road. Refer to Chapter 1 Stormwater for detail
requirements.
Design form
Horizontal and vertical alignments should be in tune with each other. Good three-dimensional co-ordination of
the horizontal and vertical alignment of a road improves traffic safety and aesthetics.
Careful consideration is needed when deciding on the initial position of the alignment. Incorrect selection of the
alignment results in high cost of the road.
The operating speed in both horizontal and vertical projections should be the same or, as a minimum, of the same
order. However, the combination of minimum elements of plan and profile should be avoided, as it is likely to
produce an unsatisfactory solution.
Where adopted, minimum sight distances shall be checked three dimensionally. The designer should remember
that the combined road alignment must be safe for all users in all conditions.
13.DESIGN CONSIDERATIONS
Functional Classification of Road Network
The Department of State Growth uses a road hierarchy road classification system for its entire road network. The
categories in the road hierarchy are:
•
•
•
•
•
Category 1: Trunk Roads – The primary freight and passenger roads connecting Tasmania
Category 2: Regional Freight Roads – Tasmania’s major regional roads for carrying freight
Category 3: Regional Access Roads – The main access roads to Tasmania’s regions, carrying less
heavy freight
Category 4: Feeder Roads – Allowing safe travel between towns, major tourist destinations and
industrial areas
Category 5: Other Roads – The remainder of the State Roads
Performance Based Standards Vehicle Types and Network
The national Performance Based Standards (PBS) are designed to allow innovation in the development of road
freight vehicles that will operate within specified safety, geometric and pavement loading parameters.
PBS classifications adopted in Tasmania are listed in Table T3.7.1 – PBS Classifications. Table 3.6.1. – PBS
Classifications
PBS Level Vehicle Configuration
Example Vehicle
1
Length ≤ 20m (General Access)
19m semi-trailer
2A
Length ≤ 26m
26m B-double
3A
26m < Length ≤ 3.65m
36.2m A-double
Access Maps of Tasmania’s PBS Networks, and the limitations on those networks, are available on the
Department of State Growth website at:
www.transport.tas.gov.au/vehicles_and_vehicle_inspections/heavy_vehicles/Heavy_vehicle_access
The typical design vehicle for each road category is nominated in Section T3.8, however the typical design vehicle
should be checked against the Access Maps.
Design considerations include all the things that are important from an engineering and community perspective
that impact the outcome of the design. They must include providing the safest possible design within the
economic, social, and environmental considerations for the development of a road project. Design characteristics
and values adopted must provide a satisfactory service to road users and be economically viable within the
financial, topographical, and environmental constraints that may exist.
At the highest level, the inputs will relate to project objectives that may be influenced by planning schemes,
budgets, and government policies concerning transportation, sustainable development, and the environment. At
a project level the inputs may relate to detailed engineering requirements such as geotechnical information,
availability of materials or the occupational health and safety of road workers.
14.WORKPLACE HEALTH AND SAFETY/SAFE DESIGN
Overview
Decisions made during the design process influence the way in which a project will be built, maintained, operated,
and ultimately decommissioned. The risks posed to workers vary with the different approaches taken and there
is an onus on designers to minimise those risks wherever possible. This obligation to worker safety is different to
meeting road user safety objectives, although one solution may meet both aims.
Fundamentally, designers should ask themselves the question, ‘How can I prepare my design to improve the
health and safety of all people involved in the construction, maintenance, operation, and decommissioning of this
project?’
It should be noted that whilst this question is posed to designers, it is unlikely that they will be making these
decisions in isolation. The ultimate authority will depend on the road agency, but it would be expected that a team
with broad skills including those involved in approval of the project scope, the project manager and
representatives from the target work groups will assist with making these decisions.
The decisions made in this regard should then be documented. Typically, this would occur within the design
report, but some design projects may be sufficiently large and/or complex that a separate report is appropriate. It
should be noted that some road agencies require a separate report.
The following outlines a generic process which can be followed to help designers identify potential safety issues
and thereby implement mitigation measures. These considerations may form part of the documentation for the
design.
These considerations are required at all phases of design, typically at similar times to road safety audits. Initially,
the safety risks identified for each option in the first phase would form one input into the decision-making process
to establish the preferred option. Then those documented risks would be passed to the next phase. They would be
refined and indeed may change as more detail is developed for the preferred option. In the third phase, final
decisions are taken about whether the design can be changed to influence occupational health and safety.
Ultimately, some matters will be left for the constructor to handle, based on their construction methodology,
choice of construction plant, choice of materials etc.
It is important to review the interaction between designed components to ensure that they collectively deliver safe
operations.
Scope
The procedure is relevant for application to all road and traffic design projects and to all phases of design as
described above.
The project stages to be addressed during the safe design development include:
• construction
• maintenance
• operation
• decommissioning.
For each stage, safety risks to all likely project users are to be considered, including:
• preconstruction activities (survey, geotechnical investigations, other site investigations)
• construction groups
• maintenance workers (operations, general and specified users, other workers likely to work within the road
reserve utilities, tram/bus shelter cleaners)
• demolition workers.
Regular site visits and consultation with target groups should be maintained during the prescribed phases to assist
with continuous improvement in the design checklists.
Documentation
The documentation, probably a part of the design report for the project, is a record of the identification of
occupational health and safety (OH&S) risks pertaining to the project and the steps taken to eliminate or mitigate
those risks through the project’s life cycle.
As such it is a document that is created with the first design phase of the project and the issues raised would be
passed on to later stages for review, incorporation, and further improvement.
One possible use of the final phase output might be to clarify risks which could not be designed out and which
need to be considered for the construction, maintenance, operations, and decommissioning phases of the project.
Hence, the report should fully document the following:
•
•
•
•
the safety impacts that may have either arisen or been modified because of the design
how those safety impacts have been addressed and mitigated in the design
at detail design stage, identify issues that could not be designed out in the detail design which have
been/should be incorporated in the specification for construction
at detail design stage and potentially at the end of construction, identify issues that could not be designed
out in the detail design and that have arisen during the construction which have been/should be
incorporated in the specification for maintenance, operation, and decommissioning activities of the project.
Procedure
Responsibility for actions and authorities for approval will be road agency and consultant dependent. Typical
responsibilities are:
•
•
•
•
•
•
•
•
•
•
prepare generic lists of issues to assist with consistency
identify target groups for the particular project, including any need for experts
formulate the team
workshop the generic issues and identify any additional project-specific safety issues
consider options and evaluate them
prepare a separate report where required by the client, the road agency or legislation
include safety issues in the design report where a standalone report is not required
approve report (if required), otherwise sign off on report and submit for client acceptance
incorporate the outcomes in the design
confirm the design changes have been made.
15.DESIGN REVIEW, VERIFICATION AND VALIDATION
Overview
The terms ‘review’, ‘verification’ and ‘validation’ are discussed in some detail in subsequent clauses. However,
it is worth bearing in mind a simple differentiation for them.
It is noted that:
• verification may be described as ‘designing the product right’
• validation may be described as ‘you designed the right product’.
To continue this simplification, review may then be put in terms of ‘checking to see that verification will be
successful but that in addition you have designed the best product’.
Design Review
Design reviews are key elements of the quality system implemented at planned hold points on the design program.
ISO 9001 Cl 7.3.4 sets out two functions for the design review process:
• to evaluate the ability of the results of design development to meet requirements
• to identify any problems and propose necessary actions.
The first point to note is that it is an evaluation; a critical examination. Secondly, it is an assessment of ability,
which combined with other statements, requires an element of prediction. Thirdly, it does not refer to the quality
of the design process but rather refers to the results of the process. In road design, the results are more than just
the physical road infrastructure but also include the often un-stated but necessary ability to be able to build it.
It goes on to require that participants in such reviews shall include representatives of functions concerned with
the design stage being reviewed and this again supports the review being undertaken during the design
development process.
The second bullet point above, ‘to identify any problems and propose necessary actions’ implies that the review
is targeted toward identifying problems during the design development and not after, so that they can be corrected
in a timely fashion.
Note that the fundamental requirements detailed above are concerned with the design's ability to meet, not exceed,
requirements. In road design, the review process also has a wider function, reflected in some definitions of the
term. This wider role is concerned with assessing whether the design will be the best possible within the
constraints, and to achieve this, it is necessary to have a skilled and independent designer as part of the review
team to challenge the choices made during the design development process.
Review should include consideration of all aspects of the design to assist with the evaluation and with completing
quality assurance requirements including:
•
•
•
•
•
•
•
•
availability of design documentation including drawings (project electronic model), design report and
specifications
the quality of the design itself
structural and other engineering aspects
constructability
safety in design
design integration
design interfaces
any unusual features of the design
•
•
road safety audits performed and recorded at all stages
engineering design certification (where required by the road agency).
It should be noted that review within the team sometimes called ‘checking’, or ‘self-checking’ is part of the design
development process. Review should be carried out throughout the design development on one or more aspects
of a design available at that stage of completion.
Timing and depth of design review
The number and timing of design reviews may vary depending on the type and complexity of the project, taking
the client’s requirements into consideration.
The authority for determining the frequency and the depth of each review required for a project will vary with
the project but should be based on an assessment of:
•
•
•
•
•
the type of project
project complexity
project risk
knowledge and skills of the designer(s) involved
technology being utilised
and considering the client’s requirements. Review activities must be adequately resourced and sufficient time
should be allocated. Design reviews should be undertaken at the end of each phase of the design and at key points
within each phase including:
•
•
•
•
development of traffic engineering layouts and the establishment of horizontal and vertical alignment
prior to approval to the drainage strategy
prior to fixing boundaries
during the overview of the final design prior to signing of the drawings.
The review must be undertaken sufficiently early in each design phase to enable any recommended changes to
be incorporated at minimum cost. Where the client has provided a conceptual or functional design that has not
been subject to a road safety audit, one shall be undertaken as part of the data correlation and review process to
ensure the road safety aspects of the design have been addressed.
Design review process
The important aspects of this process that must be addressed include:
• Planned hold points for design reviews shall be included on the program.
• Road safety audit components of the design review shall be carried out as required.
• Issues raised in previous design review reports have been addressed by the design team and the outcomes
recorded.
• All design checks shall be recorded to establish traceability and to demonstrate the depth of checking that has
occurred. All design checking documentation shall be signed off and dated.
• A clear and concise design review report should be prepared, covering (a) road safety findings and
recommendations if not reported separately, and (b) assessment of the total design for function, safety,
constructability, maintainability, durability, project-specific requirements, statutory and regulatory requirements,
aesthetics, and economy.
• Design discrepancies are adequately reviewed and resolved taking into consideration the effect of design
changes on already completed work and adjacent sections of design.
Figure below illustrates the design review process.
Design Development Verification
Design development verification is a key element of the quality system implemented at planned hold points on
the design program.
ISO 9001 Cl 7.3.4 sets out one function for the design verification process to ensure that the design development
outputs have met the input requirements. Verification may be described as a review with the aim of certification.
Therefore, it has the characteristics generally required of review together with the act of certification. In summary,
verification may be simply described as ‘designing the product right’. There are some differences between
verification and review, in that verification:
•
•
•
•
does not require that participants shall include representatives of the design team
is not usually held during the design development but rather at the end of it
is not targeted toward identifying problems during the design development so that they might have been
corrected in a timely fashion
does not have the function of identifying whether the design could be better, simply whether it conforms.
Verification must include consideration of all aspects of the design to assist with the evaluation and with the
certification including:
•
•
•
•
•
•
•
•
•
•
availability of design documentation including drawings (project electronic model), design report and
specifications
the quality of the design itself
structural and other engineering aspects
constructability
safety in design
design integration
design interfaces
any unusual features of the design
road safety audits performed and recorded at all stages
engineering design certification (where required by the road agency).
The fundamental purpose of the design verification is to assess the compliance of the project components with
the client requirements. These include design standards, principles, constructability, maintenance and cost and
the broader issues of road network strategies, aesthetics, environment and community concerns and their
integration. The objectives of the design verification are to ensure that the design:
•
•
•
•
•
meets client requirements
complies with statutory and regulatory requirements
is practical, cost-efficient and provides a sound approach to road safety
criteria, assumptions, and consideration are correct
documentation is accurate and functional.
Design verifying requirements
The verification practices employed should be appropriate to the cost of the work, the complexity of the design,
and the client’s requirements. Verification of the design shall not be limited to checking of the original arithmetic
calculations. Design verification shall ensure that:
•
•
the correct inputs have been used
there have been no omissions
•
•
the design outputs can be traced to the design inputs including any variations agreed by the client
any variations have been subject to the same checking processes as the original design.
Verification may include:
• performing alternative calculations
• checking a sample of the design calculations
• comparing the new design with a similar proven design
• undertaking tests and demonstrations of new appurtenances
• reviewing the design stage documents before release
Design Development Validation
Design validation is a key element of the quality system implemented at a planned hold point(s) at the completion
of a design program. ISO 9001 Cl 7.3.4 sets out one function for the design validation process to ensure that the
resulting product can meet the requirement for the specified application or intended use. For road infrastructure
this requires that validation is the process whereby it is determined whether the project meets the needs of the
intended user of the infrastructure. Note that this may include those not directly using but affected by the
infrastructure.
In summary, validation may be simply described as ‘you designed the right product. Therefore, the fundamental
purpose of the design validation is to assess the effectiveness of the project design (and implementation) and
might include:
• road safety
• road network efficiency
• life expectations
• aesthetics
• environment and community concerns
• constructability
• maintainability
• cost.
The methods used will vary and depend on both the product and the aspect of it being considered. In road design
it is difficult to test the product completely until it has been built. Thus, validation is often deferred until
completion. However, it is possible to partially complete validation using modelling on a complete design and by
appropriate consultation.
Methods available for validation would include:
• consultation during development and after the project has been completed
• modelling based on the design
• inspections of completed product including the road safety audit required after completion of the project
• surveys conducted on the finished product including network efficiency and accident history
• complaints register.
Design validation requirements
The validation practices employed should be appropriate to the cost of the work, the complexity of the design,
and the client’s requirements. It is important that issues identified in the validation process be captured,
those related to the design process for the project. Because of the nature of road infrastructure, it is not
usually efficient or effective to make changes after a project has been constructed. However, if issues
related to design are identified, then corrective action can and should be incorporated into the quality
system for subsequent projects.
16.DESIGN AUDIT PROCESS
ISO 9001 requires at Clause 8.2.2 that the design organisation:
…shall conduct internal audits at planned intervals to determine whether the quality management system
a) conforms to requirements, and
b) is effectively implemented and maintained.
It should be noted that internal audits are also called first party audits and that external audits are generally those
termed second- and third-party audits (Notes 1 and 2 to Cl 3.1 AS/NZS 19011:2019).
Road agencies (or other clients) may conduct or require that second party audits be carried out either as a part of
prequalification/registration or as part of a design contract for a specific project. Road agencies (or other clients)
may require that third party audits be carried out either as a part of prequalification/registration or as part of a
design contract for a specific project.
Road agency design audits have been typically classed as ‘system' or ‘product’ audits. Whilst a system audit may
use a specific project to access the designer's quality management system, it is aimed at the elements of the system
that are in use, whereas a product audit is targeting conformance to specified requirements the Guide to Road
Design or other road agency reference document. It would be expected that a product audit would also trace nonconformances back to system deficiencies.
Purpose
The purpose of the design process audit is to ensure that the control process has been completed in accordance
with the program and quality plan, and that all client requirements and issues have been addressed and closed
out.
The objective is to establish that:
• the requirements of the designer's quality management system have been met
• the requirements of ISO 9001 have been met
• all requirements raised either by the client or project team that will affect the quality assurance of the
project have been addressed and closed out
• all programmed checks and reviews of the design and plan production have been adequately completed
discrepancies that have been identified are adequately addressed and closed out.
Design process audit procedure
Typically, an internal auditor would undertake the audit in consultation with the project team.
A critical part of the audit process is determining the scope of the audit. In design, the scope may be set in
conjunction with the design phase (Section 4.2) being considered and the stage reached within that design phase.
Some important aspects of this procedure are:
•
•
•
•
•
the traceability and completeness of all checking and review documentation including supervisor’s checks
the adequate review and resolution of design discrepancies, taking into consideration the effect of the
changes/amendments on the total project
the traceability of the design documentation such as variation orders, approval and agreement to design
modifications and extension of time
the traceability of design requirements in the design outputs
closing out of all corrective action requests (CARs) raised against the project.
Where any part of the control process or requirements are incomplete or difficult to establish, a non-conformance
needs to be issued. The design process review will not be completed until all non-conformances have been
addressed and the short-term corrective action has been closed out.
The design process review shall be conducted as a quality compliance audit. To achieve an adequate rating for
any item objective evidence must be provided.
Design Product Audit
The purpose of the design product audit is to ensure that the design has been completed in accordance with the
requirements of the design reference documents (including Parts 1 to 7 of the Guide to Road Design where this
is the primary reference) and that all client requirements and issues have been addressed and closed out.
The objective is to establish that:
•
•
•
•
the requirements of the client's design reference documents have been met and exceeded
all requirements raised either by the client or project team that will affect the quality assurance of the
project have been addressed and closed out
discrepancies that have been identified are adequately addressed and closed out
related system deficiencies have been identified.
Design product audit procedure
Typically, an audit team, including specialists in the design disciplines being audited would undertake the audit
in consultation with the project team.
A critical part of the audit process is determining the scope of the audit. In design, the scope may be set in
conjunction with the design phase (Section 4.2) being considered and the stage reached within that design phase.
Some important aspects of this procedure are:
•
•
•
•
•
•
•
checking conformity of the design to requirements
assessing whether the design is the ‘best’ design that can be produced
review and resolution of design discrepancies, taking into consideration the effect of the
changes/amendments on the total project
the traceability of the design documentation such as variation orders, approval and agreement to design
modification and extension of time
the traceability of design requirements in the design outputs
identifying non-conformances and the related system deficiencies
closing out of all non-conformances and corrective action requests (CARs) raised against the project.
Where any part of the design has been found to be incorrect, a non-conformance shall be issued, the related
system deficiency identified, and a corrective action request issued on the system. The design product audit cannot
be completed until all non-conformances have been addressed and the corrective actions have been closed.
T3.7
Specific Standards and Guidelines: Geometric Design
Cross Section Width (m) (7)(8)
Design
Road
Category
AADT
(cvpd)
1
≥ 12,000
Carriageway
Vehicle
Seal
Lane
Shoulder (9) Median
2+2
Divided
PBS-L3A
20.1
3.5
2.0
2.1 (13) (FSB)
< 12,000 (1) 2+1
Divided
PBS-L3A
16.6
3.5
2.0 (10)
2.1 (14) (FSB)
Function
7.0
Dependent
Single
PBS10.0
Undivid
L
ed (2)
2
A
4.0
2.0 (LHS)
1.0 (RHS)
1.5
5
Required where two
opposing ramps
None (15)
All
2
3
4&5
Typical
≥ 3,000
Ramps
< 3,000 (1) Single
Undivided (3)
PBS-
≥ 5,000
Single
Undivided (4)
PBS-
< 5,000 (1) Single
Undivided (5)
PBS-
All
PBS-
Single
Undivided (6)
3.
9.0
3.
1.0 (11)
5
None (15)
9.0
3.
1.0 (11)
5
None (15)
8.2
3.
1.0 (11)
1
None (15)
7.2
3.
0.5 (11)(12)
1
None
3.1
None (12)
None
None
None
L
2
A
L
2
A
L
2
A
L
2
A
4&5
All
Constrained
Alignments
Single
GA
Undivided (6)
6.2
4&5
Unsealed
Single
Undivided
6.2
N/A
Pavement
All
GA
1.Projected traffic volumes to be considered (i.e., if volumes are expected to exceed cvpd limit within 20 years,
a higher level of service should be considered).
2.Overtaking lanes may be required at regular selected locations. Divided multi-lane carriageways may be
required where volumes are nearing or exceeding 12,000 cvpd.
3.Overtaking lanes may be required at isolated selected locations.
4.Overtaking lanes may be required at regular selected locations. Divided multi-lane carriageways may be
required where volumes are nearing or exceeding 12,000 cvpd.
5.Overtaking lanes, slow vehicle turns outs or stopping bays may be required at isolated selected locations.
6.Slow vehicle turn outs and/or stopping bays may be required at isolated selected locations.
7.Typical verge width of 0.5m to be applied.
8.Minimum width between safety barriers on two-way single carriageway roads to be 8.0m.
9.Where kerb and channel are provided, the shoulder width may be reduced by the width between the lip line and
line of kerb.
10.2.5m where barrier required on single lane section.
Appendix A – Schedule of References
Austroads Guidelines
Guide to Road Design
Part 2
Design Considerations
Part 3
Geometric Design
Part 4
Intersections and Crossings - General
Part 4A
Unsignalized and Signalized Intersections
Part 4B
Roundabouts
Part 4C
Interchanges
Part 5
Drainage design
Part 6
Roadside Design, Safety and Barriers
Part 6A
Pedestrian and Cyclists Paths
Part 6B
Roadside Environment
Guide to Road Safety
Part 3
Speed Limits and Speed Management
Part 4
Local Government and Community Road Safety
Part 5
Road Safety for Rural and Remote Areas
Part 6
Road Safety Audit
Part 7
Road Network Crash Assessment and Management
Part 8
Treatment of Crash Locations
Part 9
Roadside Hazard Management
AS/NZS 1158 (set)
Lighting for roads and public spaces set
AS/NZS 1158.4
Lighting for roads and public spaces – Lighting of Pedestrian Crossings
AS 1348
Road and traffic engineering – glossary of terms
AS 1428.1
Design for access and mobility - general requirements for access – new building work
AS 1428.2
Design for access and mobility: enhanced and additional requirements - buildings and facilities
AS 1742.2
Manual of uniform traffic control devices - traffic control devices for general use
AS 1742.3
Manual of uniform traffic control devices - traffic control for works on roads
AS 1742.7
Manual of uniform traffic control devices - railway crossings
AS 1742.9
Manual of uniform traffic control devices - bicycle facilities
AS 1742.10
Manual of uniform traffic control devices - pedestrian control and protection
AS 1742.11
Manual of uniform traffic control devices - parking controls
AS 1742.12
Manual of uniform traffic control devices - bus, transit, tram, and truck lane
AS 1742.13
Manual of uniform traffic control devices - local area traffic management
AS 1742/15
Manual of uniform traffic control devices - direction signs, information signs and route
numbering
Lighting poles and bracket arms: preferred dimensions
AS 1798
AS 2876
Concrete Krebs and channels (gutters)- manually or machine placed
AS/NZS 2890 (set) Parking facilities set
AS/NZS 3000
Electrical installations (known as the Australian/New Zealand wiring rules)
AS/NZS 3008.1.1
Electrical installations -selection of cables – cables for alternating voltages up to and
including 0.6/1 kV – typical Australian installation conditions
AS/NZS 3008.1.2
Electrical installations - selection of cables – cables for alternating voltages up to and
including 0.6/1 kV – typical New Zealand installation conditions
AS/NZS 3725
Design for installation of buried concrete pipes
AS/NZS 3845
Road Safety barrier systems
AS 3996
Access covers and grates
AS/NZS 4058
Precast concrete pipes (pressure and non-pressure)
AS 4282
Control of the obtrusive effects of outdoor lighting
AS/NZS ISO 31000 Risk Management – Principles & Guidelines
Codes
International Standards
ISO 11819-1
Acoustics - measurement of the influence of road surfaces on traffic noise - statistical passby method
Cross Sections and Clearances
The following information previously formed the typical cross section classifications. It has been retained in this
interim version for reference only. The intent is to adopt the typical cross section details in the body of this
Specification.
NOTE:
The Department will provide direction on the cross section to be used. For roads within urban and township areas
further details are provided in Austroads Guide to Road Design Part 3 Geometric Design.
Road Design Cross Section Selection
AADT
Road
Catego
ry
1
Type
>5,000
2500-5000
1000-2500
<1,000
Trunk
A1
A1
A1
B1
2
Freight
A1
B1
C1
C1
3
Access
C1
D1
D1
D2
4
Feeder
D1
D1
D2
E1
5
Other
D2
E1
E1
5
Unsealed
<300
F1
F2
Cross Section Widths
Road
Bridge
Section
Reference
Traffic
Lane Width
Road
Shoulders
Long
Short
Bridge Shoulder Bridge Shoulder
Maximum Length
For Short Bridge
A1
3.50m
2.0m
1.0m
2.0m
75m
B1
3.50m
1.5m
1.0m
1.5m
30m
C1
3.50m
1.0m
1.0m
1.0m
N/A
D1
3.00m
1.0m
1.0m
1.0m
N/A
D2
3.00m
0.5m
0.5m
0.5m
N/A
E1
2.75m
0.5m
0.5m
0.5m
N/A
Interchange
Ramps
4.0m
1.0mLeft
0.5m Right
1.0m Left
0.5m Right
1.0m Left
0.5m Right
N/A
Road Design Cross Sections (Unsealed)
Cross Section Widths
Road
Bridge
Section
Reference
Trafficable
Width
Road
Shoulders
Long
Short
Bridge Shoulder Bridge Shoulder
F1 Single Lane
6.50m
1.0m
0m
0m
9m
F2 Single Lane
5.50m
0.6m
0m
0m
N/A
Desired speed-no alignment effect
Source: Part 3, Table 3.2
Desired Speed –Rural, influenced by geometry
Source: Part 3, Table 3.3
Max Length For
Short Bridge
Estimating Car Acceleration on Straights
Source: Part 3, Figure 3.6
Estimating Car Deceleration on Curves
Source: Part 3, Figure 3.7
Rural Cross Section
Road widths
Selecting the width of lanes, shoulders for arterial roads:
•Types of vehicles
•Design speed
•High occupancy lane
•Bicycle lane
•Parking
Source: Part 3, Table 4.3, 4.4 4.5, 4.6 for lane and/or shoulder widths (Following Tables)
Some typical widths
Typical pavement crossfall on straights
Shoulder Crossfalls
Typical Batter Slopes
Median Widths
Part 3: Table 4.15
Height Parameters
Vertical Clearances
Part 3: Table 8.1
Effect of Grade on Vehicle Speed
Rainfall
Source: based on Commonwealth of Australia (Geoscience Australia) 2016.
Fraction impervious vs development category
Flow hazard regimes for people
Source: © Commonwealth of Australia (Geoscience Australia) 2016.
Channels –Manning’s n
Source: Austroads Guide to Road Design Part 5B: Open Channels, Culverts, and Floodway’s
Suggested Clear Zone Distances
Batter Slopes
Barrier Offset at Kerb
Cyclist design envelope
Geometric Design for Bicycle Paths
Table: Intersection Types refer to AGTM Part 6 Table 2.1
Table: Design and checking vehicles and typical turning radii
Approach Sight Distances and Vertical Curves
Safe Intersection Sight Distances and Vertical Curves
Deceleration Lengths for Turning Lanes
Acceleration Lanes
Central Island Radius
Circulating Carriageway Widths
Video References of Road Construction / Design / Concepts
1. Process of Road Construction.
https://www.youtube.com/watch?v=aDe03CSlTSU
2. Design components of roads.
https://www.youtube.com/watch?v=9XIjqdk69O4
https://www.youtube.com/watch?v=SNKuX5OTICg
3. Basic Geometric Road Design
https://www.youtube.com/watch?v=BirxNhlYxuo
4. Austroads Guide to Road Design Part 3: Session 1 of 2
https://www.youtube.com/watch?v=z25CLDGWtiE
5. Rainfall Data from Australian Government
http://www.bom.gov.au/water/designRainfalls/revised-ifd/
6. For traffic Data:
https://geocounts.com/traffic/au/stategrowth#