Investigation of the relationship between speed and separation width for head-on crashes in New South Wales

Of all the types of crashes, head-on and crossover collisions are most severe and result in a higher percentage of deaths due to the physical forces at work when one vehicle is struck by another. Speeding is regarded as one of the principal contributing factors in road crashes. Once a crash occurs, the outcome of the crash upon the vehicle occupants is related to the amount of kinetic energy applied to them. Medians and/or separations between opposing carriageways aim to reduce the incidence and severity of head-on and crossover crashes. Data was obtained for crashes in the state of New South Wales (NSW). The data spanned from 2009 to 2013 and was analysed to determine the trends and common causes of head-on/crossover crashes in NSW. Road design information such as posted speed limits, road geometry and separation width were obtained using aerial photography and crash report records. The data was used to contextualise the crashes and determine the role that speed, separation width and other contributory factors played in the crashes and their severity. Crash data and review of the available literature indicated a significant increase in severity as the speed limit increased, however a reduction in crashes as the separation between opposing carriageways increased. Analysis of the data concluded that there was a 90% reduction in crash rates across all speed environments when providing a separation between opposing carriageways of 0-1m. A further reduction in crashes was seen when providing a separation of 1-2m; however there was an unexpected finding of increased crash rates at locations with a 2-3m median separation. More in-depth research is required into specific case study sites and crashes to explain these findings