Following a sharp increase in road deaths, the Centre for Road Safety and Transport for NSW sought guidance on focussed implementation strategies to reverse the trend. One of their focus areas was reducing fatal and serious crashes on high speed roads outside of metropolitan areas, particularly on curves. To address, a strategy for prioritising and treating high risk curves was developed.
High-risk (out-of-context) curves were identified and assessed across the state using the Abley geospatial curve analysis model. This model, which is based on the Austroads Operating Speed Model, identifies and classifies high risk curves based on modelled approach speeds and curve radii.
Rather than prioritising individual curves for safety interventions, prioritisation was carried out at a corridor level to ensure consistency from a driver’s perspective. Corridors were prioritised based on the number of injury crashes on out-of-context curves, and the number of injury crashes on all curves normalised for traffic volume. Corridors were then prioritised into five priority bands.
It was found that corridors classified as “High” risk had 2.5 times the rate of loss-of-control injury crashes compared to corridors classified as “Medium-High”, and 90 times the rate compared to sections classified as “Low” when normalised by traffic exposure. These results showed that the prioritisation process is highly effective for targeting crash risk on curves.
Following prioritisation, a treatment hierarchy was developed for mass action curve investigation and improvement programs, considering the number of out-of-context curves, historic safety performance, traffic volumes, road classification and operating speeds. The potential crash savings that could be addressed through speed management interventions were also quantified.
The outputs of this project enabled Transport for NSW to target safety spending on projects that would yield the greatest safety benefit.