The Introduction of a Rural Enhanced Auxiliary Left-turn (EAUL) Treatment at Geometrically Constrained Locations in NSW

Drake, Michael (2017) The Introduction of a Rural Enhanced Auxiliary Left-turn (EAUL) Treatment at Geometrically Constrained Locations in NSW. [USQ Project]


Some rural intersection arrangements incorporating a left-turn treatment can result in a blind spot. The consequence of this is the potential for an incident resulting in death or serious injury. The aim of the project is to introduce and investigate the effectiveness of an intersection arrangement that eliminates the existing blind spot experienced by the road user.

Based on observation, there is blind spots at intersections which can occur due to a combination of factors including the obstruction of a smaller vehicle behind a larger turning vehicle in combination with the curve radius, curve direction and longitudinal grade. A consequence of this blind spot is the potential for incidents which result in death or serious injury. These incidents are occurring on intersection arrangements used in current design guidelines and therefore a solution is required which can be incorporated in to existing intersection arrangements, as well as current guidelines used by road authorities for new construction.

The intersection treatment under investigation is the Rural Enhanced Auxiliary Left-turn (EAUL) treatment. The EAUL was developed in response to a continued occurrence of the Road User Movement (RUM) 13 (right near or T-bone) crash type at rural intersections incorporating an Auxiliary Left-turn (AUL) treatment. The intention of the arrangement is to create a separation of the major road approaching vehicles from those turning in the left-turn auxiliary lane using a painted chevron treatment.

To investigate the proposed intersection configuration, analysis of crash data at test locations where the design had been applied was undertaken to verify the effectiveness of the design implementation. The identification of an existing black spot in need of the proposed treatment was completed through crash data analysis, identifying where there is a high occurrence of the targeted crash type RUM 13. The undertaking of a site inspection and Road Safety Audit (RSA) also confirmed the blind spot issue was present.

A technical analysis was conducted which compared the technical aspects of the EAUL treatment with current industry guideline treatments. From this, a set of figures and guidelines was produced using the format adopted by Austroads Guide to Road Design and with the aid of computer-aided design and drafting software.

There were five key outcomes from the project:
• The highlight of a typical blind spot present on intersection treatments found in current guidelines, • Verification of the EAUL’s effectiveness in mitigating the targeted crash type,
• The identification of particular road geometry which can influence the recognised blind spot,
• The identification of an existing black spot that would benefit from an EAUL arrangement, and
• The production of a set of guidelines and figures based on investigations for use by road authorities. The conclusions drawn from investigations show the EAUL is mitigating the targeted crash type and is indeed effective in eliminating the existing blind spot experienced by the road user.

This has enabled the necessary proposal to introduce the arrangement in to the Roads and Maritime Services (RMS) design supplement for Austroads used by the road authority. This subsequent addition could lead to the potential inclusion in the Austroads Guide to Road Design. Further trials of the EAUL may be undertaken at black spot locations to further investigate the effectiveness of the treatment over time and in different application situations.

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Item Type: USQ Project
Item Status: Live Archive
Additional Information: Bachelor of Engineering (Honours)(Civil Engineering)
Faculty/School / Institute/Centre: Historic - Faculty of Health, Engineering and Sciences - School of Civil Engineering and Surveying (1 Jul 2013 - 31 Dec 2021)
Date Deposited: 09 Sep 2021 03:50
Last Modified: 09 Sep 2021 03:50

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