Citation

Moskowitz H, McGlothlin W, Hulbert S. U.S. DOT National Highway Traffic Safety Administration. Washington, D.C.: U.S. National Highway Traffic Safety Administration, 1973.

Copyright

(Copyright 1973, U.S. DOT National Highway Traffic Safety Administration)

The full document is available online.

Abstract

There are inadequate epidemiological data to establish whether using marihuana will increase the probability of driving accidents.

As a means of assessing the potential effects of marihuana upon driving safety, this study included two experiments involving administration of marihuana to subjects who were required to perform tasks assumed important for driving. The first experiment examined performance in a complex driving simulator, the second performance of a sensory signal detection task. In both studies 23 subjects were examined in replications of Latin square designs with marihuana treatments containing 0, 50, 100 or 200 micro­ grams delta-9 tetrahydrocannabinol per kilogram bodyweight.

The simulator study utilizes an actual car mounted on a chassis dyna­ mometer, facing a 160 degree screen on which is projected a filmed ride of 31 miles. The speed of the film projection is controlled by the accelerator and brake pedals. The subject must manipulate the steering wheel appropriately as the scene pivots laterally in response to a program describing the contours of the road.

While tracking the filmed scene the subject is also required to respond as rapidly as possible to a visual recognition subsidiary task within the car. This subsidiary task simulates the search-and-recognition component of the actual driving function.

Results suggest little effect of marihuana upon the car control aspects of the driving simulator. However, there was a statistically significant and clearly dose-related impairment of the subsidiary task with both an increase in errors of recognition and a delay in response to the visual. recognition task.

The results of the study are discussed in relation to the experimental literature on the effects of marihuana. In studies of the effects of marihuana upon tracking, inconsistent evidence for an impairment by marihuana has been reported. On the other hand, there is considerable evidence that marihuana does produce an impairment of sensory perceptual functions.

The second experiment examined an auditory signal detection task in s conditions of both concentrated and divided attention under marihuana. The technique employed permitted the use of signal detection theory. Again, a clearly dose-related significant impairment of performance under marihuana was found. The signal detection theory analysis made it clear that the performance deficit was related to a true change in discrimination sensitivity and was not merely a change in criterion. These results support the finding of the previous experiment that marihuana affects the perceptual functions in driving and may therefore constitute a danger to driving safety.