Abstract
In this paper, the authors investigate the relationship between traffic states on freeways and collision frequency. The authors first defined fourtraffic phases for road sections: free flow (FF), back of queue (BQ), bottleneck front (BN) and congestion (CT). Secondly, by integrating freeway collision data and traffic data from the California PeMS database, over a three year period the authors obtained the collision frequency for each traffic phase and compared for a 32 mile section of the I-880 freeway. The results show that collision frequencies in BN, BQ, and CT phase are approximately 5 times higher than the collisions in FF. Also, the proposed method shows potential for predicting collision frequencies on freeway sections.