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Road Design

Cover of Guide to Road Design Part 6: Roadside Design, Safety and Barriers
Guide to Road Design Part 6: Roadside Design, Safety and Barriers
  • Publication no: AGRD06-24
  • ISBN: 978-1-922700-46-9
  • Published: 18 August 2024
  • Edition: 4.1

Guide to Road Design Part 6: Roadside Design, Safety and Barriers provides guidance on roadside design and in particular guidance on evaluating the risk of a roadside and the selection and use of road safety barrier systems.

Roadsides have to accommodate many features that support the road and the safe and efficient operation of traffic, and have to be designed with regard to environmental requirements. Part 6 should therefore be read in conjunction with other Parts of the Guide to Road Design.

Part 6 provides information to enable designers to understand the principles that lead to the design of safer roads, identify hazards, undertake a risk assessment process of roadside hazards, establish the need for treatment of hazards and determine the most appropriate treatment. Methods of evaluating the effectiveness of treatment options are summarised. A comprehensive design process, guidance and design considerations are provided for the selection of a suitable barrier and for the lateral and longitudinal placement of barrier systems.

Edition 4.0 includes new sections describing the fundamentals of safety barrier systems (Section 5) and design advice for other road safety devices (Section 7). A new Appendix G describes the length of need calculations and provides examples. Other sections have been updated and rewritten to reflect the new guidance.

Edition 4.1 corrects Table 6.13  Run out areas for terminals and crash cushions  (plastic water filled terminal run out area at 70km/hr).

Watch a webinar about the recent changes to Part 6.

Edition 4.1 corrects Table 6.13  Run out areas for terminals and crash cushions  (plastic water filled terminal run out area at 70km/hr).

Edition 4.0 includes new sections describing the fundamentals of safety barrier systems (Section 5) and design advice for other road safety devices (Section 7). A new Appendix G describes the length of need calculations and provides examples. Other sections have been updated and rewritten to reflect the new guidance.

Edition 3.2 published in January 2022 provides a minor update to Section 5.1 and Commentary C1.3 and updates references throughout.

Edition 3.1 published in November 2020 corrects the risk score formula for rollover events in Tables B.11, B.12, B.14, B.15, B.16 and B.18.

Edition 3.0 published in August 2020 contains changes throughout Sections 1, 2 and 3. The major change has been to the risk assessment process including the Network Risk considerations in Section 2. Other changes include:

  • the use of graphical techniques to evaluate roadside risk, including the Network Roadside Risk Intervention threshold (NRRIT)
  • the use of jurisdictional policies and corridor safety visions to define appropriate roadside treatments
  • the recognition that an agency may use and alternative network-wide risk assessment methodology to identify where to treat the risk
  • Sections 4 to 6 have had minor changes and it is expected that significant changes will be made to these sections in the next edition
  • a new section on Work Zone Safety Barrier Systems is included in Section 7 but will be reviewed in the next edition
  • new appendices on the risk assessment process have been added.

Edition 2.1 published August 2018 [format update only]

Edition 2.0 published October 2010 [appendix references were updated]

Edition 1.0 published November 2009

  • 1. Introduction to Roadside Design
    • 1.1 Context Sensitive Designs
    • 1.2 Purpose
    • 1.3 Reading this Part in the Context of Part 1
      • 1.3.1 Combining Design Parameters and Consistent Design
      • 1.3.2 Progressive Safety Updates to the Guide to Road Design
    • 1.4 Scope of this Part
      • 1.4.1 AGRD Part 6A: Paths for Walking and Cycling
      • 1.4.2 AGRD Part 6B: Roadside Environment
    • 1.5 Principles Considered in Roadside Design to Achieve the Safest System
      • 1.5.1 Safe System Principle
      • 1.5.2 Road Network Efficiency Principle
      • 1.5.3 Community Wellbeing Principle
      • 1.5.4 Environmental Sustainability Principle
      • 1.5.5 Utility Services Principle
      • 1.5.6 Investment Benefit Principle
      • 1.5.7 Safety in Design Principle
    • 1.6 Roadside Safety Design
      • 1.6.1 General
      • 1.6.2 Road Environments that Promote Safer Travel
      • 1.6.3 Design for Risk Reduction
      • 1.6.4 Appropriate Barriers and Other Treatments
    • 1.7 Terminology
    • 1.8 Overview of the Roadside Risk Assessment Process
      • 1.8.1 Network Risk Assessment
      • 1.8.2 Assessment of the Road Segment against National Practices, Jurisdictional Policies and the Corridor Safety Vision
      • 1.8.3 Road Program or Project Risk Assessment
    • 1.9 Calculating a Risk Score
      • 1.9.1 Overview of the Simplified Process for Calculating the Risk Score for a Roadside Cross Section
      • 1.9.2 Description of Significant Hazards
      • 1.9.3 Description of Less Significant Hazards
      • 1.9.4 Measuring the Lateral Distance to a Hazard
      • 1.9.5 Operating and Design Speed
      • 1.9.6 Terrain Type
      • 1.9.7 Background and Isolated Hazards
      • 1.9.8 Risk Score Charts for Undivided Rural Roads
      • 1.9.9 Grade and Curve Radii Factors for Rural Roads Risk Score Values
      • 1.9.10 Risk Score Charts for Divided Urban Roads
      • 1.9.11 Risk Score Charts for Roadside Safety Barriers
      • 1.9.12 When should the process in Appendix B be used?
      • 1.9.13 Hazards for Motorcyclists and Other Vulnerable Road Users
      • 1.9.14 Hazards for Heavy Vehicle Occupants
  • 2. Network Risk Assessment
    • 2.1 General
    • 2.2 Corridor Safety Visions
      • 2.2.1 Adverse Crash History
    • 2.3 Treatment of Roads Based on Policies and Practices
      • 2.3.1 Treatment of Roads Based on National Practices
      • 2.3.2 Treatment of Roads Based on Jurisdictional Policies
    • 2.4 The Network Roadside Risk Intervention Threshold (NRRIT)
      • 2.4.1 Application to Greenfield and Brownfield Sites
      • 2.4.2 Establishing the NRRIT
      • 2.4.3 Setting an NRRIT Based on Two-lane Undivided Rural Roads
      • 2.4.4 Setting an NRRIT Based on Urban Roads
    • 2.5 Example of Setting an NRRIT
  • 3. Program and Project Risk Assessment
    • 3.1 Overview of the Risk Evaluation Process
    • 3.2 Concepts Used in Evaluating the Risk at Particular Sites
    • 3.3 Step 1: Assess Against National Practices, Jurisdictional Policies and Corridor Visions
    • 3.4 Step 2: Compare the Risk Score with the NRRIT
      • 3.4.1 Adverse Crash History
      • 3.4.2 Examples of the Use of the Procedure
    • 3.5 Step 3: Identify, Evaluate and Rank Risk Mitigation Options
      • 3.5.1 Identify the Options
      • 3.5.2 Evaluate the Risk Associated with a Roadside Treatment Using a Qualitative Assessment
      • 3.5.3 Evaluate the Risk Associated with a Roadside Treatment Using a Quantitative Assessment
      • 3.5.4 Rank Treatment Options
    • 3.6 Step 4: Design the Recommended Roadside Treatments
  • 4. Treatment Options
    • 4.1 General
    • 4.2 Summary of Treatment Options
    • 4.3 Effectiveness of Treatment Options
    • 4.4 Treatments for Different Hazards
      • 4.4.1 Treatments for Trees
      • 4.4.2 Treatments for Steep Downgrades
      • 4.4.3 Treatments for Medians
      • 4.4.4 Treatments for Embankment Slopes
      • 4.4.5 Treatments for Drains
      • 4.4.6 Treatments for Culverts
      • 4.4.7 Treatments for Rock Face Cuttings
      • 4.4.8 Treatments for Spalls and Rock Pitching
      • 4.4.9 Treatments for Poles
      • 4.4.10 Treatments for Traffic Signal Poles
      • 4.4.11 Treatments for Sign Gantries, Sign Cantilever Supports and Bridge Piers
      • 4.4.12 Treatments for Sign Supports
      • 4.4.13 Treatments for Separating other Road or Transit Carriageways
      • 4.4.14 Treatments for Separating Cycleways and Pedestrian Paths from Roads
      • 4.4.15 Treatments for Pavement drop off
      • 4.4.16 Treatments for Other Hazards
  • 5. Fundamentals of Safety Barrier Systems
    • 5.1 General
    • 5.2 The Evaluation of Barriers and Safety Devices
      • 5.2.1 Australian and New Zealand Standard AS/NZS 3845
      • 5.2.2 MASH - Manual for Assessing Safety Hardware
      • 5.2.3 Austroads Safety Barrier Assessment Panel
    • 5.3 Barrier Flexibility
      • 5.3.1 Establishing the Concept of Barrier Flexibility
      • 5.3.2 Operation of Different Barrier Types
    • 5.4 Barrier Configurations
      • 5.4.1 Barrier System Components
      • 5.4.2 General Configurations and Ground Anchorages
    • 5.5 Barrier System Performance Measures
      • 5.5.1 Test Levels
      • 5.5.2 Working Width, Deflection and System Width
      • 5.5.3 Working Widths for Concrete Barriers
      • 5.5.4 Points of Redirection
    • 5.6 Terminals and Crash Cushions
      • 5.6.1 General
      • 5.6.2 Classification of Terminals and Crash Cushions
      • 5.6.3 Run Out Areas for Terminals and Crash Cushions
    • 5.7 Transitions and Overlaps
      • 5.7.1 Transitions
      • 5.7.2 Overlaps
    • 5.8 Barriers for Heavy Vehicles
    • 5.9 Barriers for Motorcyclists
    • 5.10 Barriers for Pedestrians and Cyclists
    • 5.11 Barriers in Narrow Medians
    • 5.12 Continuous Barriers
    • 5.13 Road or Route Containment Level
      • 5.13.1 Choosing an Appropriate Minimum Containment Level
      • 5.13.2 Containment Levels at High Risk Sites
    • 5.14 Choosing an Appropriate Barrier
      • 5.14.1 Preferred Safety Barrier Systems for a Road Stereotype
  • 6. Road Safety Barriers
    • 6.1 Introduction
      • 6.1.1 Design Philosophy
    • 6.2 Road Safety Barrier Design Process
    • 6.3 Collect Site Information (Step 1)
    • 6.4 Determine the Objectives of the Proposed Safety Barrier (Step 2)
    • 6.5 Determine the Containment Level for the Proposed Barrier (Step 3)
      • 6.5.1 Increasing the Containment Level at Higher Risk Sites
    • 6.6 Identify Barriers that Meet the Objectives and the Containment Level (Step 4)
      • 6.6.1 Containment Level and a Barrier’s Test Level
      • 6.6.2 Other Barrier Selection Considerations
    • 6.7 Select a Barrier System and Define its Working Width (Step 5)
    • 6.8 Define the Constraints on the Lateral Position of the Barrier (Step 6)
      • 6.8.1 Offset from the Traffic Lane
      • 6.8.2 Minimum Lateral Distance of a Barrier from a Hazard
      • 6.8.3 Minimum Lateral Distance of a Barrier from an Embankment Hinge Point
      • 6.8.4 Barrier Setback from Kerbs
      • 6.8.5 Lateral Location of Barriers in Medians
      • 6.8.6 Number of Median Barriers Runs
      • 6.8.7 Location of Barriers in Narrow Medians
      • 6.8.8 Flaring of Barriers and Terminals
      • 6.8.9 Barriers in Constrained Locations
    • 6.9 Determine the Longitudinal Location of a Barrier (Step 7)
      • 6.9.1 Determine the Length of Need
      • 6.9.2 Length of Need for Hazards that Extend Long Distances Perpendicular to the Road
      • 6.9.3 Length of Need on Curved Roads
      • 6.9.4 Continuous Barriers and the Length of Need Concept
      • 6.9.5 Length of Need for TL-5 and TL-6 Concrete Barriers at High Risk Sites
    • 6.10 Evaluation of the Selected Barrier (Step 8)
    • 6.11 Evaluate the Strength of the Soil at the Proposed Barrier Location (Step 9)
    • 6.12 Structural Design of the Proposed Barrier (Step 10)
    • 6.13 Detailed Installation Refinements (Step 11)
      • 6.13.1 Modification of the Working Width
      • 6.13.2 Minimum Length of Barrier System
      • 6.13.3 Maximum Barrier Length
      • 6.13.4 Sight Distance Requirements
    • 6.14 Select End Treatments to Longitudinal Barriers (Step 12)
      • 6.14.1 Terminal Selection
      • 6.14.2 Crash Cushion Selection
      • 6.14.3 Run Out Areas
      • 6.14.4 Transitions and Overlaps
      • 6.14.5 Transitions
      • 6.14.6 Overlaps
      • 6.14.7 Transition in Barrier Heights
    • 6.15 Access Through Barriers
      • 6.15.1 Access Through Barriers in the Verge
      • 6.15.2 Median Barrier Openings
      • 6.15.3 Barriers at Intersections and Property Accesses
    • 6.16 Continuous Barriers on the Verge
      • 6.16.1 Barrier Offsets
      • 6.16.2 Continuous Barrier Lengths
      • 6.16.3 Provision for Roadside Stops
    • 6.17 Vulnerable Road Users
      • 6.17.1 Motorcyclists
      • 6.17.2 Pedestrians and Cyclists
    • 6.18 Two-stage Shielding
      • 6.18.1 Layout
      • 6.18.2 Points of Need for Two-stage Shielding
    • 6.19 Barriers Across Drainage Structures and to Avoid Underground Conflicts
    • 6.20 Protecting Critical Infrastructure Close to Barriers
      • 6.20.1 Sign Supports
      • 6.20.2 Gantries and Bridge Piers
      • 6.20.3 Tunnels
      • 6.20.4 Noise Barriers
      • 6.20.5 Poles and Masts with a Breakaway Footing
    • 6.21 Fauna Crossings
    • 6.22 Installation of Concrete Barriers on Superelevated Roads and Stepped Medians
    • 6.23 Aesthetic Road Safety Barriers
    • 6.24 Additional Barrier Design Considerations
      • 6.24.1 Stepped Offset
      • 6.24.2 Excessive Offset
      • 6.24.3 Delineation
      • 6.24.4 System Height
      • 6.24.5 Sub-Standard Curves
      • 6.24.6 W-beam Barriers Close to or on Embankment Slopes
      • 6.24.7 Barriers in Floodplains
      • 6.24.8 Barriers in a Road-rail Interface
      • 6.24.9 Maintenance of Barriers
      • 6.24.10 Bullnose Treatments for Medians and Short Radius Treatments for Intersections
      • 6.24.11 Location Additional Hazards in the Area Shielded by a Barrier
    • 6.25 Develop a Plan to Maintain the Barrier (Step 14)
    • 6.26 Confirm that the Barrier Meets the Objectives (Step 15)
    • 6.27 Documentation of the Design (Step 16)
  • 7. Installation of Other Roadside Safety Devices
    • 7.1 Introduction
    • 7.2 Frangible Poles and Masts
      • 7.2.1 General
      • 7.2.2 Slip-base Poles
      • 7.2.3 Energy Absorbing Poles
      • 7.2.4 Slip Base Masts for Larger Signs
      • 7.2.5 Utility Poles
    • 7.3 Frangible Sign Posts
    • 7.4 Permanent Bollards
    • 7.5 Security Bollards
    • 7.6 High Profile Kerbs and Low Profile Barriers
    • 7.7 Traversable Culvert End Treatments
    • 7.8 Audio Tactile Line Marking
  • 8. Roadside Design for Steep Downgrades
    • 8.1 Purpose and Need
    • 8.2 Containment Facilities
      • 8.2.1 Gravity Safety Ramps
      • 8.2.2 Arrester Beds
      • 8.2.3 Vehicle Catch Net Systems
    • 8.3 Warrants for Investigation
    • 8.4 Location and Spacing
    • 8.5 Key Design Considerations
    • 8.6 Design Process
      • 8.6.1 Outline of Process
      • 8.6.2 Step S1 – Determine Vehicle Entry Speed
      • 8.6.3 Step S2 – Evaluate Truck Stability on Approach
      • 8.6.4 Step S3 – Design Entry Alignment
      • 8.6.5 Step S4 – Determine Type of Facility
      • 8.6.6 Step S5 – Determine Pavement Surface of Facility
      • 8.6.7 Step S6 – Design Facility Length
      • 8.6.8 Step S7 – Design the Facility
      • 8.6.9 Step S8 – Design End Treatment
      • 8.6.10 Step S9 – Design Vehicle Recovery Facilities
      • 8.6.11 Step S10 – Design Delineation
      • 8.6.12 Step S11 – Design Truck Parking Areas
  • 9. Work Zone Safety Barrier Systems
  • References
  • Appendix A Terminology
    • A.1 Vehicle Movement Terminology
    • A.2 Road Safety Barrier Terminology
  • Appendix B Detailed Risk Evaluation Procedure
    • B.1 Exposure
      • B.1.1 Determine the Future Traffic Flow
    • B.2 Likelihood
    • B.3 Likelihood of Colliding with a Point Hazard and a Length of Road Safety Barrier
    • B.4 Severity
      • B.4.1 Consistent Background Hazards
      • B.4.2 Isolated Hazards
      • B.4.3 Roadside Barriers
      • B.4.4 Oncoming Vehicles
      • B.4.5 Trauma Indices for Roadside Features on Roads with Other Operating Speeds
    • B.5 Evaluation of Risk Associated with Vehicle Rollovers
    • B.6 Risk Score
      • B.6.1 Collective Risk
      • B.6.2 Individual Risk
      • B.6.3 Risk of Short Lengths of Roadside
    • B.7 Limitations of the Risk Assessment Process
    • B.8 Worksheets
    • B.9 Example 1 – Culvert Headwall
    • B.10 Example 2 – Centreline Treatments on a Rural Two-lane Road
    • B.11 Number of Fatal and Serious injuries
  • Appendix C Treatment of Roads Based on Jurisdictional Policies
    • C.1 Installation of Barriers on Particular Road Segments
    • C.2 Installation of Barriers at Sites with High Consequence Infrastructure and Land
    • C.3 Installation of Barriers Between Adjacent Carriageways
    • C.4 Installation of Barriers or Other Safety Measures on Other Defined Road Types and Locations
  • Appendix D Risk Score Charts
  • Appendix E Cost of Impacts
    • E.1 Determine Crash Costs
  • Appendix F Likely Impact Conditions and Consequences
    • F.1 Errant Vehicle Trajectories
    • F.2 The Relationship Between Impact Conditions and Vehicle Occupant Safety
      • F.2.1 Application to the Design of Barrier Installations
    • F.3 Trajectories Over Kerbs and Embankments
  • Appendix G Length of Need
    • G.1 Length of Need for a Straight Installation
      • G.1.1 Leading Point of Need
      • G.1.2 Trailing Point of Need for Roads with Two-way Traffic
      • G.1.3 Length of Need for Hazards that Extend Long Distances Perpendicular to the Road
      • G.1.4 Length of Need for Roads with Two-way Traffic
      • G.1.5 Trailing Point of Need for Roads with One-way Traffic
      • G.1.6 Length of Need for Roads with One-Way Traffic
    • G.2 Length of Need for a Flared Installation
      • G.2.1 Leading Point of Need
      • G.2.2 Trailing Point of Need for Roads with Two-way Traffic
      • G.2.3 Trailing Point of Need for Roads with One-way Traffic
      • G.2.4 Length of Need
    • G.3 Location of the Points of Need with Hazards on the Outside of a Horizontal Curve
      • G.3.1 Leading Points of Need
      • G.3.2 Trailing Points of Need for Roads with Two-way Traffic
      • G.3.3 Trailing Points of Need for Roads with One-way Traffic
      • G.3.4 Leading and Trailing Points of Need on Small Radii Curves
      • G.3.5 Length of Need
    • G.4 Location of the Points of Need with the Hazards on the Inside of a Horizontal Curve
      • G.4.1 Leading Point of Need
      • G.4.2 Trailing Point of Need for Roads with Two-way Traffic
      • G.4.3 Trailing Point of Need for Roads with One-way Traffic
      • G.4.4 Length of Need
    • G.5 Worked Examples to Determine Road Safety Barrier Length of Need
      • G.5.1 Example 1: Straight Installations
      • G.5.2 Example 2
  • Commentary 1 Design Parameters and Environment
    • C1.1 Combinations of Design Parameters
    • C1.2 Consistent Design Environment
    • C1.3 Vehicle Mix Considerations
  • Commentary 2 Run-off-road Crashes
  • Commentary 3 Background to Clear Zone Width
  • Commentary 4 Vehicle Escape Ramps
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AP-R670-22
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