Although car-following is such a common driving task it has received relatively little study and the effects of alcohol upon it have received virtually no attention. In this study a closed-loop, direct view driving simulator was used to conduct tests of car-following performance and alcohol. The tests were conducted to simulate the conditions on a two-lane highway where passing is not permitted, and in which the lead car changes its speed by coasting and occasionally braking and the driver of the following-car attempts to maintain a constant, large spacing.

The subjects, six drivers who were familiar with the simulator, were administered a placebo or alcohol drinks. Three dose levels of alcohol were used:​ 0.0%, 0.05% and 0.10%, and monitored by breathalyzer. The subjects also performed the car-following tasks with and without a side-task.

Performance was measured by:​ the response times to the side-task lights, reaction times to the brake lights on the leading car, spectral analysis of car-following performance signals, and cross-correlation between the following car velocity and the relative velocity signals to obtain the gain and phase relations of each trial period.

No differences in the response times to the side-task signals or in the driver-vehicle transfer functions were obtained, attributable to alcohol. The mean response time to brake signals on the leading vehicle were significantly greater at 0.10% BAC, and the variability in the relative acceleration and the mean relative velocity bandwidth were greater under alcohol than the placebo condition.