Safety Benefits of Narrow Median Wire Rope Safety Barriers on Rural Highways

Nash, Joseph (2018) Safety Benefits of Narrow Median Wire Rope Safety Barriers on Rural Highways. [USQ Project]


Minimal studies have been undertaken on the safety benefits of narrow median wire rope safety barrier (NMWRSB) in Australia. The purpose of this research is to quantify through analysis the safety benefits of NMWRSB on New South Wales (NSW) rural highways. Since 2007 NMWRSB is being increasingly used on higher volume rural roads in NSW to act as a severity reduction safety treatment to reduce the prevalence of fatalities and serious injuries for cross-centreline crashes. At the time of this research the Pacific Highway and New England Highway were the only two highways in NSW that contained a significant amount of NMWRSB on an undivided rural road. As a result of this both highways have been analysed.

Rural roads in New South Wales are identified as being 90 km/h or higher posted speed limits outside of Newcastle, Sydney and Wollongong metropolitan areas. They can be characterised by high operating speeds, traffic volumes containing greater than 25% heavy vehicles and poor geometry. It was found that two-thirds of fatalities in NSW occur on rural roads and that the fatality rate in rural NSW is four times the rate in metropolitan areas. Two of the most common high severity crash types that occur on rural roads in NSW are run-off-road and head-on crashes. A literature review of NMWRSB use in Sweden found that there was an 82% and 76% reduction in fatalities for 90 km/h and 110 km/h posted speed limits respectively.

The Empirical Bayes (EB) methodology was used for this research to conduct a before-and-after study. To determine the change in safety of a treatment, the EB method calculates the difference between the expected number of crashes and observed number of crashes after a treatment has been installed. The EB method is used in crash analysis research since it as able to account for the effects of treatment, changes in traffic volumes, trends and regression-to-the-mean bias.

In this research various crash types and severities were analysed. These crash types included cross-centreline, run-off-road-left and other crashes and were based on road user movement (RUM) codes. The crash severities considered included fatalities, all injuries, serious injuries, moderate + minor injuries and non-casualty crashes. The analysis for each crash type and severity consisted of developing a safety performance function (SPF) using SPSS, calculating the change in crashes, and the composition of a cost-benefit analysis (CBA) for both highways.

The results of this study were very different for the Pacific Highway and New England Highway. On the Pacific Highway there was an increase in all crash types and severities except for fatalities. Fatalities had a reduction of 17.4%, however all other crash types and severity crashes increased between 27.3% and 154.5%. Since wire rope safety barrier is a hazard when placed near the road it was expected that crashes would increase based on nuisance strikes however being a severity reduction device it was also expected that fatalities and serious injuries would decrease. This has not been the case for serious injuries, which have seen an 80% increase. A CBA of the Pacific Highway yielded a benefit cost ratio (BCR) of -0.004. A negative BCR occurred because the increase in crashes were not offset by a decrease in crash severity. Based on the five years analysed there has been a net cost of $17,054,466.20. This would indicate that the treatment has had no economic benefit. Alternatively, the New England Highway has had an elimination of recorded crashes in the two years in the sections analysed since the NMWRSB was installed. This elimination of crashes has resulted in a BCR of 1.485 and a net saving of $2,229,568.05. This BCR and net cost saving indicates that the treatment has been a success on the New England Highway treatment sites.

Based on the research and the difference in results for the two analysed highways it is recommended that further studies be undertaken on NMWRSB to determine its safety and economic benefit. It is hoped that this research is beneficial to those considering research into the safety benefits of NMWRSB and rural crashes in crashes in NSW and Australia.

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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: Devine, Jo
Qualification: Bachelor of Engineering (Honours) (Civil)
Date Deposited: 09 Sep 2021 04:41
Last Modified: 29 Jun 2023 02:21

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