A priori assessment of safety impacts of traffic management operations: Level of service based approach

The number of accidents that occur on a road is often linked to traffic flow whereas the severity is related to mean speed. The method developed in this paper links the level of service-described by both traffic mean flow and speed-to the number of accidents observed on a road section. The objective is to use this relationship in a priori assessment of traffic management strategies by using traffic simulation tools. Flows and speed represent the main outputs of such models and are assumed to be influenced by other parameters such as road geometry, Iighting, and weather conditions. Four levels of service are considered according to the classification used in several European countries. The levels define traffic conditions from free flow to congestion. The study uses accident and traffic data collected for a 9-year period on a 17-km stretch of the A 1 motorway in the Paris region. An accident rate is computed for ench level of service. The results confirm the existence of a relationship between accident rates and levels of service, with more accidents observed during congestion. An application example of a real case study illustrates the use of the proposed method for a priori assessment of traffic management strategies