Identification and Simulation of Common Freeway Accident Mechanisms
Gary Davis, Professor, Civil, Environmental and Geo-Engineering
Arguably, the main cause of non-recurring traffic congestion on urban freeways is capacity-reducing crashes and incidents. Since large-scale increases in freeway capacity appear unlikely, reducing the occurrence of crashes should help freeway managers make the best use of the existing investment in freeway capacity, and this in turn should help minimize the delays experienced by the travelling public. The main principle underlying this project was that one is more likely to identify effective strategies for reducing traffic crashes if one understands the mechanisms by which they occur.
Starting with video recordings of accidents on I-94, trajectory information on a platoon of vehicles involved in a crash was extracted from the video record and these trajectories were then used to estimate each driver's initial speed, following distance, reaction time, and braking rate. Using Brill's model of rear-end accidents it is then possible to simulate what would have happened had, other things equal, certain driver reactions been other than they were. In each of three accidents the researchers found evidence that: (1) short following headways by the colliding drivers were probable causal factors for the collisions, (2) for each collision at least one driver ahead of the colliding vehicles probably had a reaction time that was longer than his or her following headway, and (3) had this driver's reaction time been equal to his or her following headway, the rear-end collision probably would not have happened.