Austroads Publications Online


Guide to Road Design Part 3: Geometric Design (2016 Edition)

Log in or Register to Download free PDF

Publication no: AGRD03-16 Pages: 374
Published: 28 September 2016


Guide to Road Design Part 3: Geometric Design provides road designers and other practitioners with information about the geometric design of road alignments.

Design parameters include: road classification; design speeds; design vehicles; alignment controls; cross-section components, including travel lanes, shoulders and verges; and provisions for public transport and cyclists.

Speed parameters include: operating speed, desired speed and design speed; and their relationship with each other.

Horizontal and vertical alignments include development and application of: circular curves; superelevation; grades; vertical curves; procedures for the grading of a road alignment; and determination of sight distances across vertical curves.


Webinar: Austroads Guide to Road Design Part 3: Geometric Design

In October 2016 Austroads delivered a two-part webinar providing an overview of the updated Guide to Road Design Part 3: Geometric Design. The first session covers design objectives, speeds and cross sections. The second session covers horizontal and vertical alignment, and superelevation. The recordings are below. PDFs of the presentation can also be downloaded:

Session one presentation slides | 1.3 MB PDF
Session two presentation slides | 1.8 MB PDF

The webinars are presented by Peter Aumann, Principal Research Engineer, ARRB Group. Peter specialises in road design with a cross over in traffic management and road safety. He has played a pivotal role in the 2016 update of the Guide.


This third edition of the Guide contains minor editorial and technical changes throughout. Key new information and updates are:

  • Section 1.4: Additional information and expansion on the design objectives.
  • Section 2.2: Additional information on vulnerable road users, particularly motorcyclists (Section 2.2.4) and new information on emergency aircraft runway strips (Section 2.2.8).
  • Section 3.5: Guidance for determining desired speed for rural roads and on steep grades (Section 3.5.1 – 3.5.4).
  • Section 4.2: Additional guidance on crown line (Section 4.2.3) and rural road lane and shoulder widths (Section 4.2.6).
  • Section 4.3: Additional guidance on shoulder widths and sealing (Section 4.3.3 – 4.3.4).
  • Section 4.4: Additional guidance on verge slopes (Section 4.4.2) and rounding (Section 4.4.3).
  • Section 4.8: Additional information on providing bicycle lanes (Section 4.8.4 – 4.8.12).
  • Section 7.7: New guidance on a procedure for designing superelevation (Section 7.7.1) and development of superelevation on shoulders (Section 7.7.12).
  • Section 8.2: New information outlining a procedure for checking critical vertical clearance points (Section 8.2.2).
  • Section 9.9: Additional guidance on selecting a starting and terminating point of an auxiliary lane Section 9.9.1.
  • New Appendices:
    • Appendix B: Emergency aircraft runway strips
    • Appendix E: Narrow median treatments with wire rope safety barrier
    • Appendix F: Guidance for wide centreline treatments
    • Appendix G: Flowcharts and table for determining stopping sight distance requirements for curves with barriers.


Table of Contents

1. Introduction
  • 1.1 Purpose
  • 1.2 Scope of this Part
  • 1.3 Design Criteria in Part 3
  • 1.4 Objectives of Geometric Design
  • 1.5 Road Safety
  • 1.5.1 Providing for a Safe System
  • 1.6 Design Process
2. Fundamental Considerations
  • 2.1 General
  • 2.2 Design Parameters
  • 2.2.1 Location
  • 2.2.2 Road Classification
  • 2.2.3 Traffic Volume and Composition
  • 2.2.4 Vulnerable Road Users
  • 2.2.5 Design Speed and Operating Speed
  • 2.2.6 Alignment Controls
  • 2.2.7 Design Vehicle
  • 2.2.8 Use of Roads as Emergency Aircraft Runway Strips
  • 2.2.9 Environmental Considerations
  • 2.2.10 Access Management
  • 2.2.11 Drainage
  • 2.2.12 Utility Services
  • 2.2.13 Topography/Geology
3. Speed Parameters
  • 3.1 General
  • 3.2 Terminology
  • 3.2.1 Posted Speed Limit
  • 3.2.2 Operating Speed (85th Percentile Speed)
  • 3.2.3 Desired Speed
  • 3.2.4 Design Speed
  • 3.2.5 Vehicle Speeds on Roads
  • 3.3 Operating Speeds on Urban Roads
  • 3.3.1 Freeways (Access Controlled Roads)
  • 3.3.2 High Standard Urban Arterial and Sub-arterial Roads
  • 3.3.3 Urban Roads with Varying Standard Horizontal Curvature
  • 3.3.4 Local Urban Roads
  • 3.4 Operating Speeds on Rural Roads
  • 3.4.1 High Speed Rural Roads
  • 3.4.2 Intermediate Speed Rural Roads
  • 3.4.3 Low Speed Rural Roads
  • 3.5 Determining Desired Speed
  • 3.5.1 Existing Rural Roads
  • 3.5.2 New Rural Roads
  • 3.5.3 Desired Speed on Steep Grades
  • 3.5.4 Additional Considerations when Using the Operating Speed Model
  • 3.6 Determining Operating Speeds Using the Operating Speed Model
  • 3.6.1 General
  • 3.6.2 Operating Speed Estimation Model
  • 3.6.3 Car Acceleration on Straights Graph
  • 3.6.4 Car Deceleration on Curves Graph
  • 3.6.5 Section Operating Speeds
  • 3.6.6 Use of Operating Speed in the Design of Rural Roads
  • 3.7 Operating Speed of Trucks
  • 3.8 Operating Speeds for Temporary Works (Including Side Tracks)
4. Cross-section
  • 4.1 General
  • 4.1.1 Functional Classification of Road Network
  • 4.1.2 Consideration of Staged Development
  • 4.2 Traffic Lanes
  • 4.2.1 General
  • 4.2.2 Road Crossfall
  • 4.2.3 Crown Lines
  • 4.2.4 Traffic Lane Widths
  • 4.2.5 Urban Road Widths
  • 4.2.6 Rural Road Widths
  • 4.3 Shoulders
  • 4.3.1 Function
  • 4.3.2 Width
  • 4.3.3 Shoulder Sealing
  • 4.3.4 Sealed Shoulder Widening on the Outside of Curves
  • 4.3.5 Shoulder Crossfalls
  • 4.4 Verge
  • 4.4.1 Verge Widths
  • 4.4.2 Verge Slopes
  • 4.4.3 Verge Rounding
  • 4.5 Batters
  • For earth cut batters, earth fill batters and rock fill batters:
  • For rock cut batters:
  • 4.5.1 Benches
  • 4.5.2 Batter Rounding
  • 4.5.3 Earth Bunds or Mounds
  • 4.6 Roadside Drainage
  • 4.6.1 Table Drains
  • 4.6.2 Catch Drains
  • 4.6.3 Median Drains
  • 4.6.4 Kerb and Channel
  • 4.7 Medians
  • 4.7.1 Median Width
  • 4.7.2 Median Slopes
  • 4.7.3 Median Transitions
  • 4.7.4 Median Openings
  • 4.7.5 Median Surfacing
  • 4.8 Bicycle Lanes
  • 4.8.1 General
  • 4.8.2 Road Geometry
  • 4.8.3 Gradients
  • 4.8.4 Cross-section and Clearances
  • 4.8.5 Separated Bicycle Lanes
  • 4.8.6 Contra-flow Bicycle Lanes
  • 4.8.7 Exclusive Bicycle Lanes
  • 4.8.8 ‘Peak Period’ Exclusive Bicycle Lanes
  • 4.8.9 Sealed Shoulders
  • 4.8.10 Bicycle/Car Parking Lanes
  • 4.8.11 Wide Kerbside Lanes
  • 4.8.12 Supplementary Treatments
  • 4.9 High Occupancy Vehicle (HOV) Lanes
  • 4.9.1 General
  • 4.9.2 Bus Lanes
  • 4.9.3 Tram/Light Rail Vehicle (LRV) Lanes
  • 4.10 On-street Parking
  • 4.10.1 General
  • 4.10.2 Parallel Parking
  • 4.10.3 Angle Parking
  • 4.10.4 Centre-of-road Parking
  • 4.10.5 Parking for Motorcycles
  • 4.10.6 Parking for People with Disabilities
  • 4.11 Service Roads, Outer Separators and Footpaths
  • 4.11.1 Service Roads
  • 4.11.2 Outer Separator
  • 4.11.3 Urban Border
  • 4.12 Bus Stops
  • 4.12.1 General
  • 4.12.2 Urban
  • 4.12.3 Rural
5. Sight Distance
  • 5.1 General
  • 5.2 Sight Distance Parameters
  • Object height
  • 5.2.1 Driver Eye Height
  • 5.2.2 Driver Reaction Time
  • 5.2.3 Longitudinal Deceleration
  • 5.3 Stopping Sight Distance (SSD)
  • 5.3.1 Car Stopping Sight Distance
  • 5.3.2 Truck Stopping Sight Distance
  • 5.4 Sight Distance on Horizontal Curves
  • 5.4.1 Benching for Visibility on Horizontal Curves
  • 5.5 Sight Distance Requirements on Horizontal Curves with Roadside Barriers/Wall/Bridge Structures
  • 5.5.1 Requirements where Sighting over Roadside Barriers is Possible
  • 5.5.2 Requirements where there is no Line of Sight over Roadside
  • 5.6 Overtaking Sight Distance
  • 5.6.1 General
  • 5.6.2 Overtaking Model
  • 5.6.3 Determination of Overtaking Provision
  • 5.6.4 Determination of Percentage of Road Providing Overtaking
  • 5.7 Manoeuvre Sight Distance
  • 5.8 Intermediate Sight Distance
  • 5.9 Headlight Sight Distance
  • 5.10 Horizontal Curve Perception Sight Distance
  • 5.11 Other Restrictions to Visibility
6. Coordination of Horizontal and Vertical Alignment
  • 6.1 Principles
  • 6.2 Safety Considerations
  • The vertical curve overlaps one end of the horizontal curve
  • The vertical curve overlaps both ends of the horizontal curve
  • Insufficient separation between the curves
  • Dissimilar length horizontal and vertical geometric elements
  • Long flat grades
  • Roller coaster grading
  • 6.3 Aesthetic Considerations
  • 6.3.1 Coincident Horizontal and Vertical Curves
  • 6.3.2 Horizontal Curves
  • 6.3.3 Vertical Curves
  • 6.4 Drainage Considerations
7. Horizontal Alignment
  • 7.1 General
  • 7.2 Horizontal Alignment Design Procedure
  • Step 1
  • Step 2
  • Step 3
  • Step 4
  • Step 5
  • Step 6
  • 7.3 Tangents
  • 7.4 Circular Curves
  • 7.4.1 Horizontal Curve Equation
  • 7.5 Types of Horizontal Curves
  • 7.5.1 Compound Curves
  • 7.5.2 Broken Back Curves
  • 7.5.3 Reverse Curves
  • 7.5.4 Transition Curves
  • 7.6 Side Friction and Minimum Curve Size
  • 7.6.1 Minimum Radius Values
  • 7.6.2 Minimum Horizontal Curve Lengths and Deflection Angles Not Requiring Curves
  • 7.7 Superelevation
  • 7.7.1 Superelevation Design Procedure
  • 7.7.2 Linear Method
  • 7.7.3 Maximum Values of Superelevation
  • 7.7.4 Minimum Values of Superelevation
  • 7.7.5 Application of Superelevation
  • 7.7.6 Length of Superelevation Development
  • 7.7.7 Rate of Rotation
  • 7.7.8 Relative Grade
  • 7.7.9 Design Superelevation Development Lengths
  • 7.7.10 Positioning of Superelevation Runoff without Transitions
  • 7.7.11 Positioning of Superelevation Runoff with Transitions
  • 7.7.12 Superelevation Development on Shoulders
  • 7.7.13 Development of Superelevation to Avoid Drainage Problems
  • 7.8 Curves with Adverse Crossfall
  • 7.9 Pavement Widening on Horizontal Curves
  • 7.10 Curvilinear Alignment Design in Flat Terrain
  • 7.10.1 Theoretical Considerations
  • 7.10.2 Advantages of Curvilinear Alignment
8. Vertical Alignment
  • 8.1 General
  • 8.2 Vertical Controls
  • 8.2.1 General
  • 8.2.2 Critical Vertical Clearance Points
  • 8.2.3 Flood Levels or Water Table
  • 8.2.4 Vertical Clearances
  • 8.2.5 Underground Services
  • 8.2.6 Other Vertical Clearance Considerations
  • 8.2.7 Vehicle Clearances
  • 8.3 Grading Procedure
  • Step 1
  • Step 2
  • Step 3
  • Step 4
  • Step 5
  • Step 6
  • Step 7
  • 8.4 Grading Point
  • 8.4.1 Two-lane – Two-way Roads
  • 8.4.2 Divided Roads
  • 8.4.3 Profiles along Kerb and Channel
  • 8.5 Grades
  • 8.5.1 General
  • 8.5.2 Vehicle Operation on Grades
  • 8.5.3 Maximum Grades
  • 8.5.4 Length of Steep Grades
  • 8.5.5 Steep Grade Considerations
  • 8.5.6 Minimum Grades
  • 8.6 Vertical Curves
  • 8.6.1 General
  • 8.6.2 Forms and Types of Vertical Curves
  • 8.6.3 Crest Vertical Curves
  • 8.6.4 Sag Vertical Curves
  • 8.6.5 Sight Distance Criteria (Sag)
  • 8.6.6 Reverse/Compound/Broken Back Vertical Curves
  • 8.6.7 Minimum Length of Vertical Curves
  • 8.6.8 Maximum Grade Change without a Vertical Curve
  • 8.7 Earthworks
  • 8.7.1 Earthworks Balance
  • 8.7.2 Earthworks Quantities
9. Auxiliary Lanes
  • 9.1 General
  • 9.2 Types of Auxiliary Lanes
  • 9.3 Speed Change Lanes
  • 9.3.1 Acceleration Lanes
  • 9.3.2 Deceleration Lanes
  • 9.4 Overtaking Lanes
  • 9.4.1 General
  • 9.5 Climbing Lanes
  • 9.5.1 General
  • 9.5.2 Warrants
  • 9.5.3 Length
  • 9.6 Slow Vehicle Turnouts
  • 9.6.1 Partial Climbing Lanes
  • 9.6.2 Slow Vehicle Turnouts
  • 9.7 Descending Lanes
  • 9.8 Carriageway Requirements
  • 9.9 Geometric Requirements
  • 9.9.1 Starting and Termination Points
  • 9.9.2 Tapers
  • 9.9.3 Cross-section
10. Bridge Considerations
  • 10.1 General
  • 10.2 Cross-section
  • 10.3 Horizontal Geometry
  • 10.3.1 Superelevation
  • 10.4 Vertical Geometry
References
Appendix A Extended Design Domain (EDD) For Geometric Road Design
  • A.1 General
  • A.2 EDD Cross-section Widths for Two-lane, Two-way Rural Roads
  • A.2.1 Urban Road Widths
  • A.2.2 Rural Two-lane Two-way Road Widths
  • A.3 EDD for Stopping Sight Distance
  • A.3.1 Application of EDD for Stopping Sight Distance
  • Compliance with EDD for stopping sight distance
  • General considerations
  • Formulae
  • A.3.2 Base and Check Cases
  • Base cases
  • Check cases
  • Optional check cases
  • A.3.3 Vertical Height Parameters
  • A.3.4 Driver Reaction Time
  • A.3.5 Longitudinal Deceleration
  • A.3.6 EDD Stopping Sight Distance for Cars
  • Application of the base cases
  • Application of the check cases
  • A.3.7 Shoulder/Traversable Widths and Manoeuvre Times
  • Shoulder/Traversable area
  • A.3.8 EDD Crest Vertical Curve Size
  • A.3.9 Sight Distance Requirements on Horizontal Curves where there is no Line of Sight over Barriers/Structures
  • A.4 EDD for Horizontal Curves with Adverse Superelevation
Appendix B Emergency Aircraft Runway Strips
  • B.1 General Standards and Applications
  • B.2 Site Location Criteria
  • B.3 Design Requirements
Appendix C Speed Parameter Terminology
  • C.1 Design Speed Value
  • C.2 Desired Speed
  • C.3 Limiting Curve Speed
  • C.4 Operating Speed of Trucks
  • C.5 Section Operating Speed
  • C.6 Speed Environment
Appendix D Example Calculation of the Operating Speed Model
  • D.1 Using the Operating Speed Model
  • D.1.1 Details of Example
  • D.1.2 Determination of Desired Speed
  • D.1.3 Length of Road to be Analysed
  • D.1.4 Identification of Sections
  • D.1.5 Estimating Actual Operating Speeds on a Section of Road
  • Step 1 – Estimate speed at end of Section 1 (point B).
  • Step 3 – Estimate departure speed on first curve in Section 3 (point D).
  • Step 4 – Estimate departure speed on second curve in Section 3 (point E).
  • Step 5 – Estimate departure speed on third curve in Section 3 (point F).
  • Step 6 – Estimate departure speed on single curve in Section 4 (point G).
  • Step 7 – Estimate departure speeds on curves in Section 5 (points H and I).
  • Step 8 – Estimate speed at the end of the 270 m straight that is Section 6 (point J).
  • Step 9 – Estimate departure speed on single curve in Section 7 (point K).
  • Step 10 – Estimate speed at the end of the 710 m straight that is Section 8 (point L).
  • D.2 Additional Considerations when Using the Operating Speed Model
  • D.2.1 Increase in Desired Speed
  • D.2.2 Decrease in Desired Speed
  • D.2.3 Increase in Speed on a Chain of ‘Short’ Elements
  • D.2.4 Effects of Grades
  • D.2.5 Effect of Cross-section
  • D.2.6 Effect of Pavement Condition
Appendix E Narrow Median Treatments with Wire Rope Safety Barrier (WRSB)
  • E.1 Background
  • E.2 Wire Rope Safety Barrier – Issues to Consider
Appendix F Guidance for Wide Centre Line Treatments (WCLT)
  • F.1 Purpose
  • F.2 Background
  • F.3 Application
  • F.4 Dimensions and Design of WCLT
  • F.4.1 Minimum length of WCLT
  • Cross-section of WCLT
  • Retrofitting WCLT to seals wider than specified for NDD or EDD
  • F.5 WCLT at Intersections
  • F.6 WCLT Over Narrow Structures
  • F.6.1 Single narrow structure
  • F.6.2 Successive narrow structures
  • F.7 WCLT at Overtaking Lanes/Climbing Lanes
  • F.8 WCLT Signage and ATLM Requirements
  • F.8.1 Signs
  • Audio Tactile Line Markings (ATLM)
  • F.9 Design Exceptions (Departures)
  • Temporary treatments
  • F.10 Widening to Incorporate a WCLT
Appendix G Flow Charts and Table for Determining Stopping Sight Distance Requirements for Curves with Barriers
  • G.1 Car Stopping Sight Distance Requirements on Horizontal Curves with Roadside Barriers
  • G.2 Truck Stopping Sight Distance Requirements on Horizontal Curves with Roadside Barriers
  • G.3 Minimum Radii for Lateral Clearance Required on Curves with Barrier
Appendix H Theory of Movement in a Circular Path
  • H.1 Movement in a Circular Path
  • H.2 Side Friction Force on Vehicle
  • H.2.1 Sliding
  • H.2.2 Overturning
  • H.2.3 Other Factors affecting Truck Stability
Appendix I Reverse Curves
Appendix J Transition Curves (Spirals)
  • J.1 General
  • J.1.1 Effect on Braking
  • J.1.2 Effect on Overtaking
  • J.1.3 Effect on Design
  • J.2 Use of Transitions
  • J.3 Types of Transitions
  • J.4 Characteristics of the Euler Spiral (Clothoid)
  • Basic relationships for clothoid transition curves
Appendix K Vertical Curve Curvature Formulae
  • K.1 General
  • K.2 Vertical Curve Formulae
Commentary 1
Commentary 2
Commentary 3
Commentary 4
Commentary 5
Commentary 6
Commentary 7
Commentary 8
Commentary 9
Commentary 10
Commentary 11
Commentary 12
Commentary 13
Commentary 14
Commentary 15
Commentary 16
Commentary 17
Commentary 18
  • C18.1 Superelevation Development Lengths
Commentary 19
Commentary 20
Commentary 21
Commentary 22

This website is operated by CanPrint Communications on behalf of Austroads. If you have any questions, please use the feedback form or call us on 1300 889 873, between 8:00 am and 5:00 pm AEST. If you are outside Australia please call us on +61 2 6293 8381.

Terms of Use