Brake Perception-Reaction Times of Older and Younger Drivers

The time drivers require to react in braking situations underlies many practices in highway design and operations. There is concern whether the perception-reaction time (PRT) values used in current practice adequately meet the requirements of many older drivers. This study compared on-the-road brake PRTs for unsuspecting drivers in three age groups: 20–40, 65–69, and 70-plus years old. The method included features to enhance the ecological validity of the observed reactions: subjects drove their own vehicles in their normal manner; driving was on actual roadways; extended preliminary driving put the driver at ease and without expectation of unusual events at the time of the braking incident; the incident occurred at a location lacking features that might enhance alertness (e.g., curves, crests, driveways). Subjects drove an extended route, under the guise that they were making periodic judgments about “road quality.” At one point, a large crash barrel was remotely released from behind brush on a berm and rolled toward the driver's path. Although most of the fastest observed PRTs were from the young group, there were no differences in central tendency (mean = 1.5 s) or upper percentile values (85th percentile = 1.9 s) among the age groups. Furthermore, the current highway design value of 2.5 seconds for brake PRT appears adequate to cover the full range of drivers.