From: [a--e--r] at [kauri.vuw.ac.nz] (I. Aptekar)
Newsgroups: alt.drugs
Subject: MJ and Driving
Date: 17 Sep 1993 04:27:22 GMT

Copied from p.223 of 'Drugs and Behavior' by William A. McKim.
 
Marijuana and Driving

There have been numerous studies on the effects of marijuana on
driving. These have been plagued by the same difficulties as other
performance studies and subsequently, there are a great variety of
conclusions. Early studies generally found that marijuana smoking had
little effect on driving[1], but later studies have been able to
detect a slight detrimental effect. One experiment tested subjects
after a low and a high dose of marijuana on both a closed course and
on a crowded city street. The experiment was designed so that each
subject was tested several times and so some improvement with practice
was expected. In fact, in the placebo group, 38% showed a significant
improvement in their driving and 14% got worse. In the high-dose
marijuana group, only 14% improved significantly and 55% got worse.
The findings were similar on the crowded street. The elements of
driving that were most affected in this study were concentration and
judgment[2].

Driving studies in a driving simulator have shown that marijuana has
little effect on the ability to control a car, but impairs the
subject's ability to attend to peripheral stimuli. Thus,
marijuana-intoxicated drivers might be able to stop a car as fast as
they normally could, but they may not be as quick to notice things that
they should stop for. This is probably because they are attending to
internal events rather than what is happening on the road[3].

[1] Grinspoon, L. (1969). Marihuana, _Scientific American_, 221(6), 17-25

[2] Klonoff, H. (1974). Effects of marihuana on driving in a restricted
area and on city streets: Driving performance and physiological
changes. In L. L. Miller (Ed.), _Marijuana, Effects on human behavior_
(pp. 359-397). New York: Academic Press.

[3] Muskowitz, H., Hulbert, S., & McGlothlin, W. H. (1976). Marihuana:
Effects on simulated driving performance. _Accident Analysis and
Prevention_, 8(1), 45-50.