A Field Study of the Effects of Drivers' Adaptation to Automobile Velocity

Abstract

A roadside survey of vehicle velocities was carried out by radar on a four lane, median divided highway with a 50 mile-per-hour (80 km/h) legal speed limit. Northbound traffic on the highway had been previously exposed to expressway conditions with vehicle speeds in excess of 96 km/h, whereas southbound traffic had been previously exposed to an urban highway with speeds of about 64 km/h. Northbound traffic velocities exceeded those of southbound traffic by an average of 6.9 km/h, which, it is argued, is the result of drivers of northbound vehicles being exposed to conditions under which velocity adaptation occurs. An analysis of the data by vehicle category indicates that while large cars are driven significantly faster than small cars under all conditions, the magnitude of the velocity adaptation effect is greater for drivers of small cars.