Perception response time and its misapplication: an historical and forensic perspective

Perception response time (PRT), the time required for drivers to respond to roadway events, is a concept that is derived from scientific psychology. The concept is now fundamental to human factors and ergonomics (HFE), to the design of transportation systems, and is often called upon in forensic analyses of traffic crashes. Yet the application of PRT is neither simple nor straightforward, especially when evaluating human performance under difficult conditions, which is typically the situation in forensic analysis of traffic crashes. This article revisits these fundamental limitations by reviewing the scientific history of PRT, highlighting its utility and evolution as well as important constraints on its application. Common violations of these constraints and their ramifications for providing accurate and defensible information in forensic practice are discussed. We conclude that driving behavior is both complex and variable, and no single PRT value, adjusted or not, will ever be universally applicable.