Drivers' estimations of overtaking and passing distance were compared with actual overtaking distance. Drivers made estimates in a familiar car and in an unfamiliar car, at speeds of 18, 30, and 50mph. Conclusions were as follows: (1) drivers were unable to estimate overtaking and passing distances accurately. Mean error ranged from 20 to 52 percent of performance distance. Significantly larger errors were made in the unfamiliar vehicle than in the driver's own vehicle. (2) negative errors of underestimation, where the manoeuvre required more space than judged, increased with speed. At 50 mph, 60 percent of the estimates made by drivers in the unfamiliar car, and 78 percent of those made in own cars were under-estimations. (3) overtaking and passing required proportionally more distances as lead car speed increased. (4) vehicular differences affected passing distance more than did driver variance. /author/.
Abstract