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Road Design

Cover of Guide to Road Design Part 3: Geometric Design
Guide to Road Design Part 3: Geometric Design
  • Publication no: AGRD03-26
  • ISBN: 978-1-923617-38-4
  • Published: 26 June 2026
  • Edition: 4.0

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.

Summary report

A summary of the changes in the current edition is outlined in the report Updates to Austroads Guide to Road Design: Parts 1, 3, 4, 4A, 6, 6A, 6B and 7 (AP-R766-26).

Edition 4.0 published June 2026

This edition includes:

  • Clarifying statements and additional examples for designers on adopting a Safe System (Section 1.5), design parameters (Section 2.2), operating speeds (Section 3.3) and desired speed (Table 3.2).
  • Additional information on the functional classification of road network (Section 4.1.1) urban road widths (Tables 4.3 and 4.4) and medians (Section 4.7)
  • minor editorial and technical changes throughout.

Superseded editions:

Edition 3.4 published February 2021

Edition 3.3 published June 2020

Edition 3.2 published in July 2017

Edition 3.1 published December 2016

Edition 3.0 published September 2016

Edition 2.0 published October 2010

Edition 1.0 published October 2009

  • 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 Definitions
      • 3.2.1 Design Speed
      • 3.2.2 Desired Speed
      • 3.2.3 Limiting Device Speed
      • 3.2.4 Limiting Curve Speed
      • 3.2.5 Operating Speed
      • 3.2.6 Target Speed
      • 3.2.7 Posted Speed
      • 3.2.8 Speed Environment
    • 3.3 Relationship Between Speed Measures
    • 3.4 Further Comment on Speed Measures
      • 3.4.1 Design Speed
      • 3.4.2 Operating Speed
      • 3.4.3 Desired Speed
      • 3.4.4 Operating Speed Model
      • 3.4.5 Limiting Curve Speed
      • 3.4.6 Determining the speed limit
      • 3.4.7 Speed Classification of Roads
    • 3.5 Operating Speeds on Urban Roads
      • 3.5.1 Freeways (Access Controlled Roads)
      • 3.5.2 High Standard Urban Arterial and Sub-arterial Roads
      • 3.5.3 Urban Roads with Varying Standard Horizontal Curvature
      • 3.5.4 Local Urban Roads
    • 3.6 Operating Speeds on Rural Roads
      • 3.6.1 High Speed Rural Roads
      • 3.6.2 Intermediate Speed Rural Roads
      • 3.6.3 Low Speed Rural Roads
    • 3.7 Determining Desired Speed
      • 3.7.1 Existing Rural Roads
      • 3.7.2 New Rural Roads
      • 3.7.3 Desired Speed on Steep Grades
      • 3.7.4 Additional Considerations when Using the Operating Speed Model
    • 3.8 Determining Operating Speeds Using the Operating Speed Model
      • 3.8.1 General
      • 3.8.2 Operating Speed Estimation Model
      • 3.8.3 Car Acceleration on Straights Graph
      • 3.8.4 Car Deceleration on Curves Graph
      • 3.8.5 Section Operating Speeds
      • 3.8.6 Use of Operating Speed in the Design of Rural Roads
    • 3.9 Operating Speed of Trucks
    • 3.10 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
      • 4.5.1 Batter slope
      • 4.5.2 Catchlines
      • 4.5.3 Benches
      • 4.5.4 Batter Rounding
      • 4.5.5 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 Narrow Median Treatment with Flexible Safety Barrier
      • 4.7.3 Wide Centre Line Treatment
      • 4.7.4 Other Median Treatments
      • 4.7.5 Choice of Median Treatment for Two-lane, Two-way Roads
      • 4.7.6 Median Slopes
      • 4.7.7 Median Transitions
      • 4.7.8 Median Openings
      • 4.7.9 Median Surfacing
    • 4.8 Footpaths
    • 4.9 Bicycle Lanes
      • 4.9.1 General
      • 4.9.2 Road Geometry
      • 4.9.3 Gradients
      • 4.9.4 Cross-section and Clearances
      • 4.9.5 Separated Bicycle Lanes
      • 4.9.6 Contra-flow Bicycle Lanes
      • 4.9.7 Exclusive Bicycle Lanes
      • 4.9.8 ‘Peak Period’ Exclusive Bicycle Lanes
      • 4.9.9 Sealed Shoulders
      • 4.9.10 Bicycle/Car Parking Lanes
      • 4.9.11 Wide Kerbside Lanes
      • 4.9.12 Supplementary Treatments
    • 4.10 High Occupancy Vehicle (HOV) Lanes
      • 4.10.1 General
      • 4.10.2 Bus Lanes
      • 4.10.3 Tram/Light Rail Vehicle (LRV) Lanes
    • 4.11 On-street Parking
      • 4.11.1 General
      • 4.11.2 Parallel Parking
      • 4.11.3 Angle Parking
      • 4.11.4 Centre-of-road Parking
      • 4.11.5 Parking for Motorcycles
      • 4.11.6 Parking for People with Disabilities
    • 4.12 Service Roads, Outer Separators and Footpaths
      • 4.12.1 Service Roads
      • 4.12.2 Outer Separator
      • 4.12.3 Urban Border
    • 4.13 Bus Stops
      • 4.13.1 Passenger waiting area
      • 4.13.2 Urban
      • 4.13.3 Rural
    • 4.14 Shared Spaces and Shared Zones
  • 5. Sight Distance
    • 5.1 General
    • 5.2 Sight Distance Parameters
      • 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
      • 5.4.2 Effect of Crossfall on Sight Distance
    • 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
      • 5.5.3 Sight Distance for Median Barriers Retrofitted in Rural Two-Way Carraigeways
    • 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
    • 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
    • 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
      • 7.6.3 Minimum Curve Radius for Motorways
    • 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
    • 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
      • 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
      • A.3.2 Base and 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
      • A.3.7 Shoulder/Traversable Widths and Manoeuvre Times
      • 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 Mid-block Treatments for Safe System Speeds
    • B.1 Pedestrian Refuges
    • B.2 Medians
    • B.3 Advance Curve Warning Signs
    • B.4 Chevron Alignment Markers
    • B.5 Advisory Speed Signs
  • Appendix C Emergency Aircraft Runway Strips
    • C.1 General Standards and Applications
    • C.2 Site Location Criteria
    • C.3 Design Requirements
  • Appendix D Additional Speed Parameters
    • D.1 Section Operating Speed
    • D.2 Speed Environment
    • D.3 Posted Speed Limit
  • Appendix E Example Calculation of the Operating Speed Model
    • E.1 Using the Operating Speed Model
      • E.1.1 Details of Example
      • E.1.2 Determination of Desired Speed
      • E.1.3 Length of Road to be Analysed
      • E.1.4 Identification of Sections
      • E.1.5 Estimating Actual Operating Speeds on a Section of Road
    • E.2 Additional Considerations when Using the Operating Speed Model
      • E.2.1 Increase in Desired Speed
      • E.2.2 Decrease in Desired Speed
      • E.2.3 Increase in Speed on a Chain of ‘Short’ Elements
      • E.2.4 Effects of Grades
      • E.2.5 Effect of Cross-section
      • E.2.6 Effect of Pavement Condition
  • Appendix F Flow Charts and Table for Determining Stopping Sight Distance Requirements for Curves with Barriers
    • F.1 Car Stopping Sight Distance Requirements on Horizontal Curves with Roadside Barriers
    • F.2 Truck Stopping Sight Distance Requirements on Horizontal Curves with Roadside Barriers
    • F.3 Minimum Radii for Lateral Clearance Required on Curves with Barrier
  • Appendix G Theory of Movement in a Circular Path
    • G.1 Movement in a Circular Path
    • G.2 Side Friction Force on Vehicle
      • G.2.1 Sliding
      • G.2.2 Overturning
      • G.2.3 Other Factors affecting Truck Stability
  • Appendix H Reverse Curves
  • Appendix I Transition Curves (Spirals)
    • I.1 General
      • I.1.1 Effect on Braking
      • I.1.2 Effect on Overtaking
      • I.1.3 Effect on Design
    • I.2 Use of Transitions
    • I.3 Types of Transitions
    • I.4 Characteristics of the Euler Spiral (Clothoid)
  • Appendix J Vertical Curve Curvature Formulae
    • J.1 General
    • J.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
  • Commentary 19
  • Commentary 20
  • Commentary 21
  • Commentary 22
  • Commentary 23
    • C23.1 Lane Merge Geometry
    • C23.2 Merges on Left-hand Curves
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