Eight subjects were administered drugs (marihuana) and alcohol, and their driving was tested in an automatic, instrumented (potentiometer attached to the steering wheel, a wheel counter, real time clock, a secondary task periperal light on the dashboard) car on an 8.5 mile stretch of highway. Details are given of the equipment and the driving task. The following measures of driver performance were made: steering amplitude and frequency in the 60 mph region, steering amplituted in the 25 mph region, speed and speed variation in both the 60 and 25 mph zones, reaction time to the peripheral light on the dash board, number of pylons knocked down, and distance between the front tires and the white line adjacent to the traffic signal. The results indicated that alcohol alone and in combination with other drugs affects driving performance in different ways. Steering movement and average velocity were measures which most clearly differentiated between drug conditions.
Abstract