‘Earwitness’: A comparison of auditory, visual and audio-visual judgements of vehicle speed

This investigation examined the accuracy of judgements of traffic speed by comparing audio, visual and audio-visual perception in two experiments. In the first study 60 adults estimated the approach speed of a car on video. Five speeds (10,20, 30,40 and 50m.p.h.) were presented. In the second study 37 adults were presented with videos of an approaching car travelling at either 30, 40 or 50m.p.h. and chose the actual speed from five given alternatives. Results indicated a low level of accuracy overall. For the first study extent of error increased in the order audio-visual, visual and auditory. In the second study, no significant effect of perceptual mode was observed for extent of error. In both studies an interaction between speed and perceptual mode was observed for extent of error. Speed was over-estimated in the auditory mode and under-estimated in the visual and audio-visual modes. Findings were discussed in relation to witness capabilities.