The effect of luminance on simulated driving speed.

Perceived speed is modulated by a range of stimulus attributes such as contrast, luminance and adaptation duration. It has been suggested that such changes in perceived speed may influence driving behaviour. In order to evaluate the effect of luminance on driving speed we have measured subjects' driving speed in a driving simulator for a range of luminance and speed over time. The results indicate that reducing luminance results in a decrease in driving speed for all speeds measured. This reduction in driving speed at low luminance is consistent with previous findings that perceived speed increases at low luminance. However, the results also indicated that driving speed remained stable over a 30s period. The stability of driving speed over time is inconsistent with previous findings that perceived speed reduces exponentially as a function of adaptation duration. The results are suggestive of a scheme whereby driving speed is consistent with the known effects of luminance upon perceived speed but may also be modulated by higher order processes that serve to maintain a constant speed over time.