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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: AGRD06-20
  • ISBN: 978-1-922382-44-3
  • Published: 26 November 2020
  • Edition: 3.1
  • Superseded

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

Edition 3.1 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 a NRRIT Based on Two-lane Undivided Rural Roads
      • 2.4.4 Setting a NRRIT Based on Urban Roads
    • 2.5 Example of Setting a 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 Types of Treatments
      • 4.4.1 Treatments for Trees
      • 4.4.2 Treatments for Steep Downgrades
      • 4.4.3 Treatments for Medians
      • 4.4.4 Treatments for Drains
      • 4.4.5 Treatments for Drainage Features
      • 4.4.6 Treatments for Rock Face Cuttings
      • 4.4.7 Treatments for Minor Roadside Hazards
      • 4.4.8 Treatments for Road Furniture
      • 4.4.9 Treatments for Poles
      • 4.4.10 Treatments at Active Controlled Level Crossings
      • 4.4.11 Weather Warning Systems
  • 5. Road Safety Barriers
    • 5.1 Introduction
      • 5.1.1 General
      • 5.1.2 General Requirements for Road Safety Barrier Systems
      • 5.1.3 Road Safety Barriers for Vulnerable Road Users
    • 5.2 Factors Considered in Barrier Selection
      • 5.2.1 Site Conditions
    • 5.3 Road Safety Barrier Design Process
      • 5.3.1 Outline of Process
      • 5.3.2 Collect Site Information (Step B1)
      • 5.3.3 Determine the Objectives of the Safety Barrier (Step B2)
      • 5.3.4 Determine the Lateral Position of the Barrier (Step B3)
      • 5.3.5 Offset to Traffic Lane
      • 5.3.6 Support Width
      • 5.3.7 Deflection Width
      • 5.3.8 System Width
      • 5.3.9 Barrier Location in Medians
      • 5.3.10 Narrow Medians
      • 5.3.11 Wider Medians
      • 5.3.12 Barrier-to-hazard Clearance (Step B4)
      • 5.3.13 Barrier Containment Level Required (Step B5)
      • 5.3.14 Barrier Type (Step B6)
      • 5.3.17 Working Width (Steps B9 and 10)
      • 5.3.18 Barrier Length of Need (Step B11)
      • 5.3.19 Minimum Length of Barrier (Step B12)
      • 5.3.20 Sight Distance (Step B13)
      • 5.3.21 Terminal Treatments (Step B14)
      • 5.3.22 Transitions between Barriers (Step B15)
      • 5.3.23 Confirm that the Barrier Meets the Objectives (Step B16)
    • 5.4 General Access Through Road Safety Barriers
    • 5.5 Aesthetic Road Safety Barriers
    • 5.6 Other Road Safety Barrier Design Considerations
      • 5.6.1 Barriers at Intersections
      • 5.6.2 Stepped Offset
      • 5.6.3 Excessive Offset
      • 5.6.4 Delineation
      • 5.6.5 System Height
  • 6. Roadside Design for Steep Downgrades
    • 6.1 Purpose and Need
    • 6.2 Containment Facilities
      • 6.2.1 Gravity Safety Ramps
      • 6.2.2 Arrester Beds
      • 6.2.3 Dragnets
    • 6.3 Warrants for Investigation
    • 6.4 Location and Spacing
    • 6.5 Key Design Considerations
    • 6.6 Design Process
      • 6.6.1 Outline of Process
      • 6.6.2 Step S1 – Determine Vehicle Entry Speed
      • 6.6.3 Step S2 – Evaluate Truck Stability on Approach
      • 6.6.4 Step S3 – Design Entry Alignment
      • 6.6.5 Step S4 – Determine Type of Facility
      • 6.6.6 Step S5 – Determine Pavement Surface of Facility
      • 6.6.7 Step S6 – Design Facility Length
      • 6.6.8 Step S7 – Design the Facility
      • 6.6.9 Step S8 – Design End Treatment
      • 6.6.10 Step S9 – Design Vehicle Recovery Facilities
      • 6.6.11 Step S10 – Design Delineation
      • 6.6.12 Step S11 – Design Truck Parking Areas
  • 7. 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 Treatments for Brownfield Sites
    • F.1 Treatments for Roads
      • F.1.1 Treatments for Pavement Edge Drop-off
      • F.1.2 Treatments for Opposing Vehicles
    • F.2 Treatments for Bridges
      • F.2.1 General
      • F.2.2 Treatments for Bridge Piers, Abutments, End Posts and Tunnel Portals
    • F.3 Barrier Placement in Constrained Situations
      • F.3.1 Location on Embankments
      • F.3.2 Location on Urban Footpath Corners
    • F.4 Wire Rope Barriers in Narrow Medians
  • Appendix G Angle of Departure Method
  • Appendix H Examples of Length of Need Calculations
    • H.1 General
    • H.2 Run-out Length Method
    • H.3 Angle of Departure Method
    • H.4 Worked Examples to Determine Road Safety Barrier Length of Need
      • H.4.1 Example 1
      • H.4.2 Example 2
  • Appendix I Types of Safety Barrier Terminals
    • I.1 General
      • I.1.1 Gating End Treatments
      • I.1.2 Non-gating End Treatments
      • I.1.3 Trailing Terminal
  • Appendix J Transitions between Barrier Types
    • J.1 General
    • J.2 Design Criteria – Physically Connected Barriers
    • J.3 Typical Interfaces between Barrier Types
      • J.3.1 General
    • J.4 W-beam to Thrie-beam
    • J.5 W-beam to Concrete
    • J.6 Thrie-beam to Concrete
    • J.7 Wire Rope Safety Barrier to Semi-rigid Barrier
    • J.8 Wire Rope Safety Barrier to Concrete Barrier
  • Commentary 1
    • C1.1 Combinations of Design Parameters
    • C1.2 Consistent Design Environment
    • C1.3 Vehicle Mix Considerations
    • C1.4 Other Factors Contributing to Errant Vehicles
  • Commentary 2
  • Commentary 3
    • C3.1 Background to Clear Zone Width
  • Commentary 4
    • C4.1 Embankment Slopes
  • Commentary 5
  • Commentary 6
    • C6.1 General
    • C6.2 Vehicle Trajectory Over Embankments
    • C6.3 Vehicle Trajectory Over Kerbs
    • C6.4 Vehicle Trajectory Over Cutting Slopes
    • C6.5 Summary of Limitations on Barrier Location
  • Commentary 7
  • Commentary 8
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