Age and Driver Time Requirements at Intersections

Abstract

Current highway design models for required sight distance at stop-sign controlled intersections assume that the perception-reaction time (PRT) required is 2.0 seconds. That is, a 2.0 second interval to perceive, evaluate, decide, and initiate a response, is adequate to cover the range of time it takes real drivers to do this. This experiment evaluated the adequacy of the 2.0 second PRT assumption, including specific consideration of older drivers, who are known to experience relatively greater difficulty at intersections. Subjects in three age groups (20–40; 65–69; and 70+ years old) drove their own vehicles (fitted with a computer-controlled video-based data collection system) over a route that included 14 stop-controlled intersections. At each stop sign, they were required to make ratings of “road quality;” this broke visual search, and provided an opportunity for the experimenter to precisely define the initiation of search and the initiation of forward movement (thus defining PRT). The 2.0 second PRT assumption was found to work reasonably well for all age groups, and corresponded to roughly the 85th percentile PRT for all subjects. PRTs for older subjects were slightly (but significantly) briefer than for younger drivers. Reasons for not observing a slowing of intersection PRT with advancing age are discussed. The findings are also compared to gap acceptance data from another experiment. Even though the present experiment did not find objective evidence of older drivers requiring longer decision times, older subjects nonetheless demanded longer gaps in traffic in order to judge it safe to enter traffic.