The effect of wide centreline treatments on run-off-road left incidents on rural Queensland highways and potential for a review of road shoulder width guidelines

McNamara, Peter (2019) The effect of wide centreline treatments on run-off-road left incidents on rural Queensland highways and potential for a review of road shoulder width guidelines. [USQ Project]

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Head-on/Cross centreline (HOCL) crashes are one of the most severe crash types and a disproportionate number of these occur on Australia’s rural highways. Wide centreline treatments (WCLT) have been introduced to several major Queensland highways since 2011 to reduce the likelihood of these crashes by providing up to 1m of lateral separation between opposing traffic flows. The effectiveness of this treatment has been the focus of several Bruce Highway studies in Queensland. All studies indicated reduced HOCL crash rates suggesting the more rural highways WCLT can be applied to, the greater the number of severe crashes can be prevented. Notably, these studies also determined a large reduction in the rate of run off the road left (RORL) crash types despite hypothesising that this crash type may increase.

This study aimed to determine if the significantly reduced rate of RORL crashes could be verified on other rural highways across south-east Queensland. If so, subsequent investigations into the effect of WCLT on driver behaviour and vehicle position could be supported which may lead to further investigations into the potential use of narrower sealed road shoulders with WCLT.

The empirical Bayes (EB) approach was identified as suitably robust and able to account for component effects. The analysis used crash data from both reference and treatment sites. Reference data was used to develop safety performance functions that enabled ‘predicted’ crash numbers at treatment sites to be calculated. These were compared with the actual crash figures to quantify the effect of WCLT on low volume rural highway crashes, particularly on RORL events.

This study found no support to verify that WCLT reduces the RORL rate on low volume rural highways when all overtaking types are considered. Additionally, low statistical significance due to variance in the data resulted in no support for a review of associated road shoulder width guidelines. While not statistically significant, an increase in the rates of all crash types in the postWCLT period was determined. Additionally, higher than predicted observed crash numbers were also found during both the pre- and post-treatment periods, suggesting the low volume highways studied may have a crash problem in comparison to the reference highways. As this study included all overtaking types of WCLT, the crash reduction effect of WCLT may not be influenced by low traffic volume alone but it is possible it may be influenced by a combination of contributing factors such as overtaking type and segment length. This research builds on the existing knowledge of WCLT effectiveness, indicating there may be limitations to the treatment’s use.

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Item Type: USQ Project
Item Status: Live Archive
Faculty/School / Institute/Centre: Historic - Faculty of Health, Engineering and Sciences - School of Civil Engineering and Surveying (1 Jul 2013 - 31 Dec 2021)
Supervisors: Somasundaraswaran, Soma
Qualification: Bachelor of Engineering (Honours) (Civil)
Date Deposited: 18 Aug 2021 06:18
Last Modified: 26 Jun 2023 22:53

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