Road safety

Cover of Infrastructure Risk Rating Manual for Australian Roads
Infrastructure Risk Rating Manual for Australian Roads
  • Publication no: AP-R587A-19
  • ISBN: 978-1-925854-14-5
  • Published: 4 March 2019

Infrastructure Risk Rating (IRR) is a road safety risk assessment methodology that is calculated by coding the following road and roadside features:

  • Land  use
  • Road  stereotype
  • Lane  and shoulder width
  • Horizontal  alignment
  • Roadside  hazards
  • Intersection  density
  • Access  density
  • Traffic  volume – rural roads only
  • Speed  limit – rural roads only.

This manual sets out the steps for undertaking an IRR assessment. It is divided into four parts:

  1. Identify  supporting data sources
  2. Identify  homogenous road sections
  3. Code  road and roadside features
  4. Calculate IRR score and risk band.

An online map-based tool for calculating IRR can be accessed via

A quick user guide is available in the supporting documents tab after logging in.

  • Summary
  • Step 1: Identify Supporting Data Sources
  • Step 2: Identify Homogenous Sections
    • Split roads by land use
    • Split roads by road stereotype
    • On rural roads, break sections where there is significant change in horizontal alignment
    • Consider significant changes in traffic volume
    • Consider other factors
    • Cluster urban roads with similar IRR attributes
  • Step 3: Code IRR attributes
    • Land use
    • Road stereotype
    • Lane and shoulder width
    • Horizontal alignment
    • Roadside hazards
    • Intersection density and access density
    • Traffic volume (rural roads only)
    • Speed limit (rural roads only)
  • Step 4: Calculate IRR Score and Risk Band
    • IRR category scores
    • Operating Speed Factor (rural only)
  • Appendix A IRR Attribute Coding Examples
    • A.1 Land use
    • A.2 Road Stereotype
    • A.3 Roadside Hazards
    • A.4 Horizontal Alignment