MRWA Supplement to Austroads Guide to Road Design - Part 1

Document No:  D17#491950
Revision:  2A
Date amended:  07-Feb-2019

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The information below is intended to reflect the preferred practice of Main Roads Western Australia ("Main Roads"). Main Roads reserves the right to update this information at any time without notice. If you have any questions or comments please contact Albert Wong by e-mail or on (08) 9323 4153.

To the extent permitted by law, Main Roads, its employees, agents, authors and contributors are not liable for any loss resulting from any action taken or reliance made by you on the information herein displayed.

Revision Register


Ed/Version Number Clause Number Description of Revision Date



Guideline Developed. 09-Dec-2011 
​1A​All​Contact person changed to Albert Wong.​12-Jul-2016
​2​All​Guideline Amended.​26-Jun-2017
​2A​AllDocument hierarchy clarified.​07-Feb-2019

Table of Content

MRWA Supplement to Austroads Guide to Road Design

Part 1: Introduction to Road Design


This Supplement has been developed to be read in conjunction with Austroads Guide to Road Design (GRD) Part 1: Introduction to Road Design (2015), a copy of which can be purchased via the Austroads website.

In Western Australia, Main Roads' policies, guidelines and standards take precedence over Austroads Guides and Standards Australia Standards. National Guides and Standards take precedence over International Guides and Standards, unless specifically stated otherwise.

This Supplement has the same structure as the equivalent Austroads Guide and only additional requirements, clarifications, or practices different from Austroads appear. Where appropriate, this Supplement may also contain additional sections and figures not covered by Austroads, but the numbering sequence found in the Austroads Guide remains. Figures and tables in this Supplement replace those with the same figure or table number in the equivalent Austroads Guide.



Main Roads has no supplementary comments for this section.



2.3 Road Safety and Road Design

Main Roads has adopted ROSMA Road Safety Management System. The ROSMA Policy document sets out Main Roads' requirements for implementing a management system based on Safe System principles. This system has been designed to enable Main Roads to meet its corporate, state and national road safety targets and commitments.



3.1 Introduction

The philosophy and principles set out in the suite of Austroads Guides, and Main Roads Supplementary Information, underpin the creation of a successful, site-specific design solution.

Designers choose the features of the road and dimensions of its elements based on technical guides, calculations and their own experience and judgement. However, a very important principle in choosing these dimensions is to avoid combinations of minimum or limiting values of different design elements as this has the potential to quickly reduce the inherent safety of the overall solution.

The practice of good road design, especially under constraints, involves judgement as well as calculation.  It involves compromises between conflicting goals. Experience assists the Designer to arrive at an appropriate balance that cannot be met by a system of mathematical rules alone.  The Austroads Guides and the Main Roads Supplementary Information give ranges of values within which the Designer has reasonable flexibility to produce an appropriate design solution for a specific problem, whilst retaining a reasonable overall level of uniformity.

3.3 Context-Sensitive Design

Context-Sensitive Design is explained in greater detail in Austroads Part 2: Design Considerations where there is reference to the Design Domain and Extended Design Domain. A value outside the Normal Design Domain may only be used with the explicit approval of the Manager Road & Traffic Engineering, supported by a documented risk assessment that fully justifies the use of that value.



The impact of climate change needs to be considered in Main Roads projects. 'A Guide to Flood Estimation' published by ARR (Australian Rainfall and Runoff) in 2016 provides practitioners, designers and decision makers with an approach to address the risks from climate change in projects. CSIRO and the Bureau of Meteorology have developed an approach based on temperature scaling using temperature projections for the target years of 2030 and 2090. Further details can be found at the 'Climate Change in Australia' website. In general, CSIRO and BOM suggest that a 5% increase in rainfall correlates with every 1.0 degree Celsius increase in temperature. However, it is recommended that Intensity Frequency Duration (IFD) rainfall data be adjusted for future climate using the method outlined in Book1, Chapter 6 of ARR 'A Guide to Flood Estimation 2016'. 



Project Managers and Designers are referred to Austroads Part 8: Process and Documentation (2009) for expanded information relating to this subject.



Main Roads has no supplementary comments for this section.