Extended Design Domain

Document No:  D19#965054
 
Revision:  1A
 
Date amended:  27-Nov-2019

​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 regarding these Extended Design Domain Guidelines, please contact Dave Landmark by e-mail or on (08) 9323 5441.

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​

​1All​Guideline Developed.​14-Nov-2019​
​1A3​Guidelines and EDD RRA Tool spreadsheet updated.​27-Nov-2019​

 


Table of Content


​MRWA Supplement to Austroads Guide to Road Design

 

This document should be considered as a Main Roads WA supplement to the Austroads Guide to Road Design (GRD) series of documents, copies of which can be obtained via the Austroads website. The document shall be used by Consultants seeking to apply EDD and DE standards and principles for geometric road design parameters on roads controlled by Main Roads WA.

 

1. DEPARTURES FROM STANDARDS, EXTENDED DESIGN DOMAIN & DESIGN EXCEPTIONS

The processes detailed in the guideline documents relate specifically to design values that are outside of the Normal Design Domain. i.e. they fall within the Extended Design Domain or are of a lower standard and are considered as Design Exceptions.

 

Sometimes designers may choose to use design values that fall within the Normal Design Domain as defined by Austroads, but they do not meet Main Roads desirable requirements.  For example, the desirable stopping sight distance requirements for rural roads in WA are based on a reaction time of 2.5 seconds and a coefficient of deceleration rate of 0.36.  However, the absolute minimum stopping sight distances (for specific road types and situations) may be based on a reaction time of 2.0 seconds and a coefficient of deceleration rate of 0.46.  These values are considered by Austroads to be within the Normal Design Domain.

 

In WA, the use of any design parameter from absolute minimum to desirable is treated as a “Departure from the Standards".  Approval for the use of these values is outside of the Extended Design Domain and Design Exception process.  Approval for “Departure from the Standards" is required from the Manager Road and Traffic Engineering and resolution is generally given via e-mail.

 

2. GUIDELINES FOR THE EXTENDED DESIGN DOMAIN & DESIGN EXCEPTION PROCESS

The Guidelines for the Extended Design Domain & Design Exception Process give an overview of the Design Domain Concept and discuss the principles directing the EDD and DE process. The EDD and DE process is given in detail including required documentation for submission to Main Roads for approval.

 

The above process requires the use of the Main Roads “Risk Assessment Process for EDD & DE Design Values - Excel Spreadsheet".

 

To document the process a report template has been created.

 

3. GUIDELINES FOR THE DETAILED ASSESSMENT OF EXISTING RURAL ROAD SECTIONS

 Where it is necessary to assess existing lengths of rural road with potentially multitudes of geometric features, which require the EDD or DE process to be applied, separate guidelines have been created.  Refer to Guidelines for the Detailed Assessment of Existing Rural Road Section. This guideline includes an example report, which utilises information, tools and software located in the links below: