This report summarises research carried out in 2011–12 to quantify the effects of roadside barriers and clear zones on mitigation of run-off-road crash numbers and crash severity for New Zealand road and roadside characteristics through statistical and computer simulation modelling. The purpose of the research was to provide practitioners with information that would allow them to make safe, more appropriate and cost-effective treatments for specific conditions.
The statistical modelling included extending an existing crash risk model to cover the available parameters relating to barriers and clear zones, eg offset from the road and barrier type. Limited computer simulation modelling of run-off-road scenarios on selected straight and corner road sections was used to confirm and supplement the findings of the statistical modelling.
The key finding was that the roadside condition, whether comprising clear zones of varying widths, or different barrier types, had an impact on the crash rate that was statistically significant. However, the results of both the statistical analysis and the computer simulation modelling showed that while the lateral distance offset to the nearest hazard or barrier was important, the type of hazard that was encountered at the far side of this offset distance was also important in determining the crash rate.