the instantaneous judgement of distance is frequently required during driving e.g. in judging the distance necessary to brake safely from a particular speed and in the estimation of distances which would allow safe overtaking. in some overtaking situations, it may be the perception of relative rather than absolute distances which is important. the present study investigated how capable drivers were at making absolute and relative distance judgements from a vehicle travelling at a range of speeds. drivers had to say when they were a particular distance (1000 ft) from various 'targets' along a specified route, they then had to either halve or quarter this distance. the range of values obtained for a specified distance indicate that drivers in general would be unable to estimate accurately distances given to them in feet. whilst many drivers overestimated absolute distances, in general the results showed that drivers underestimated absolute distances and this underestimation was greatest at lower speeds. it was found that in relative judgements, the shorter the overall distance the driver was required to fractionate the more accurate was his judgement; although in general, drivers did tend to overestimate distances relative to each other i.e. the fractions were always larger than required. estimates of relative distances unlike those of absolute distances, were unaffected by speed.(a)

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