Development of Analysis Methods Using Recent Data

Abstract

This report documents the second phase of a two-phase project under Strategic Highway Research Program 2 (SHRP 2) Safety Project S01A. The primary objective of this work was to establish an analytic foundation for using conflicts and near crashes as surrogate measures. The project introduced a counterfactual analytic approach suggesting that a traffic event qualifies as a crash cause under two conditions: (a) both the event and the crash occurred and (b) had the event in question not occurred, then the crash also would not have occurred. Data from site-based field studies and vehicle studies were used to extend these ideas from a trajectory model to more complicated scenarios. The report introduces an approach to microscopic (i.e., individual event) modeling of crash-related events, where driver actions, initial speeds, and vehicle locations are treated as inputs to a physical model describing vehicle motion. This choice of modeling strategy reflects a need for such models if realistic crash processes are to be included in microscopic traffic simulation models. The simple trajectory model can be used to estimate features of crash and near-crash events—such as driver reaction times, following headways, and deceleration rates—from trajectory data produced from a site-based field study. Given sufficiently large samples of crash and near-crash events, this method can be used to compile distributions for these inputs for use in traffic simulation models. Finally, the report illustrates how a trajectory model, together with estimates of input variables, can quantify the degree to which a non-crash event could have been a crash event. The report describes how these ideas were extended to more complicated scenarios by using data from both vehicle- and site-based field studies, including data obtained from the 100-car vehicle-based field study, data from site-based video on Interstate 94 from the Minnesota Traffic Observatory, and site-based radar data from the Cooperative Intersection Collision Avoidance System (CICAS) intersection in North Carolina.