Drivers' judgments in overtaking and passing.

Drivers' judgments in vehicular overtaking and passing were studied using familiar (drivers' own) cars and an unfamiliar government vehicle at speeds of 18, 30 and 50 mph. Drivers were not able to estimate passing distances accurately. Average errors of estimation for the different conditions varied from 20 to 50 % of the actual overtaking distance. Errors of underestimation, where the manoeuvre required more space than judged, increased with speed. At 18 mph. 15 % of the estimates made by drivers were underestimates: at 50 mph 68% were underestimates. There were no differences observed attributable to familiarity with the car.