Application of a network safety management tool in urban areas: Zurich, Switzerland, case study

Because of the economic and social cost of traffic accidents, it is essential for road administrators to evaluate where infrastructure investments are necessary to improve the system. Network safety management (NSM) is an analysis tool typically used on freeways and other interurban roads to identify the locations with the highest potential for infrastructure improvements from a safety perspective. A study was done on how this tool could also be used to identify such locations within an urban environment. The area of study was the city of Zurich, Switzerland, and the accident data were for the period 2009 to 2013. The aim was to investigate the application of NSM in urban environments, illustrate it with a real case study, evaluate the results obtained, and test robustness of the results for different input parameters. To do this, georeferenced data were required to have explicit distinctions between the three road network elements used: primary road segments, inter sections, and residential zones. On the basis of different accident cost rates, a prioritization of the individual network elements was made. Results show that mostly network elements with numerous conflict points have the highest safety potential. Further tests reveal that traffic volume is the most influential parameter within the model. Additionally, more differentiated cost rates are presented, and a comparison with the road safety tool Black Spot Management is employed to verify the detected accident clusters. The findings are used to make pragmatic recommendations on the use of NSM in an urban context.