Perceptual Errors in Judging the Approach of Motor Vehicles

When drivers attempt to negotiate their way safely out of a road side junction and into the flow of traffic, the most dependable cues for judging whether an approaching vehicle poses an immediate threat are its optical size and its rate of expansion on the retina (Lee, 1976).

While this information may appear to be the most reliable, research has demonstrated that individuals gauge the time-to-passage (TTP) of smaller vehicles less accurately than larger vehicles (e.g. Caird & Hancock, 1994). This thesis investigated the perceptual mechanisms that underlie a driver’s ability to make judgements about the immediacy of the threat posed by approaching vehicles at roadside junctions. This is investigated in three areas; judgements of relative speed, detection of vehicle approach and the effect of conspicuity aids.

Overall, the thesis demonstrates the limitations of the human perceptual system in judging the relative speed of a motorcycle compared with a car stimulus, a problem which is exacerbated under low levels of luminance. However, the simple engineering solution of additional headlights is shown to vastly improve these speed judgement impairments under low levels of luminance.

The thesis provides evidence that individuals are less sensitive to the detection of motorcycle approach compared with a car stimulus. The effect of additional scenic motion is shown to negatively affect car detection sensitivity, while simulated self-motion is shown to impair detection thresholds for motor vehicles. Implications for road design are discussed. Lastly, the thesis demonstrates that high visibility garments do not significantly improve detection capabilities for motorcycles.