Implementation of a Tool for Measuring ITS Impacts on Freeway Safety Performance

The research was undertaken to develop a tool for assessing the impacts of changes in freeway traffic flow on the level of traffic safety. Safety is measured in terms of the probability of a reportable accident, and the tool is so far restricted to urban freeway mainlines with substantial traffic levels. The tool will: (1) monitor the safety level of freeway operations (2) aid in freeway planning. The tool was calibrated by applying advanced statistical models to actual data combined from two sources: Vehicle Detector Station (VDS) data for freeways in Orange County (District 12), and data on all reported accidents in Orange County from the Traffic Surveillance and Analysis System (TASAS). The analytical engine that drives the safety tool is based on models that are highly effective in identifying those myriad aspects of traffic flow that are statistically related to accident probabilities. It is recommended that Caltrans invest in projects that will validate the current work, and subsequently: (1) improve the accuracy of the safety predictions; (2) extend the applicability of the modeling approach to other Caltrans districts; and (3) evaluate the dissemination of safety predictions in real time.