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Modelling and analysis of crash densities for Karangahake Gorge, New Zealand.
An 18 km length of New Zealand state highway located in tortuous terrain that displayed a poor safety level (11 injury crashes per year) was selected to trial the “safety improvement potential” approach to safety management of roads. This approach involves comparing the actual safety level over a section of road with the average safety level estimated from a crash prediction model.
This paper presents the results of applying a crash prediction model specifically developed for the New Zealand state highway network to analyse the safety performance of the 18 km route. The Poisson regression model is believed to be one of the first to successfully relate crash rates to road geometry and road condition. Therefore, the relative effectiveness of various engineering based countermeasures to bring about an improvement in the current safety level was also able to be assessed. The countermeasures investigated included realignment, high friction surfacing and road smoothing. It was determined from the modelling studies that a more consistent level of crash risk throughout the 18 km route could be achieved through either increasing friction levels or increasing the radius of the horizontal curves at specific locations.