Reaction Time of Drivers to Road Stimuli

Monash University Human Factors Group - Report HFR-12

Authors: T. Triggs & W. Harris

Full report in .pdf format [670KB]


The assumption of a reaction time value for drivers responding to road situations is fundamental for the design requirements involving sight distance, in particular for vertical and horizontal curves. This response time is frequently referred to as the "perception-reaction time" in traffic engineering literature. Previous attempts to estimate an appropriate value for this time are discussed, along with other relevant laboratory and field reaction time literature. It is suggested that the procedures used have generally been deficient on one of several grounds. The majority of studies have used briefed subjects in an experimental situation. The duration of various processing stages have generally been arrived at by a subtractive technique. Responses have usually been assumed to be the result of speeded processes. Within single studies, the stimulus situations examined have typically been limited.

The requirement for unobtrusive observational techniques is stressed so that reaction time estimates can be obtained that are representative of real world performance. This approach was used in the study reported here to obtain data for a range of eliciting stimuli. The salience of the stimulus type was estimated by the driver response rate and form of response distribution. Vehicle speed was observed for some situations, so as to allow an assessment to be made of whether driver response times depend on vehicle speed. The data showed generally that faster drivers had lower reaction times under otherwise similar conditions. The road situations that yielded the highest responding rates were railway level crossing signals, and the amphometer (pairs of cables across the road surface used by Victoria police to detect speeding drivers). The estimates obtained are discussed in terms of the commonly assumed design value of 2.5 a. Values of the 85th percentile reaction time were found that were both above and below this design value. However, the pattern of results overall suggests that the current standard may be inadequate in some circumstances, and a review of this standard is strongly recommended.