Saying ‘no study’ seems to be very bold.
I did a very quick search and found this.
druglibrary.org/schaffer/misc/driving/driving.htm
Seems the research community has repeatedly documented impairment brought on by marijuana use.
I guess the impact on a user’s ability to stay centered in a driving lane must really be brought on by ‘stimulated’ brain cells.
I’ll take my fellow drivers without marijuana usage, thank you very much.
Dan Grelinger
Did you read this report? I’d like to comment on it.
This research was conducted by the U.S. Department of Transportation,
National Highway Traffic Safety Administration.
This research consists of a group of three studies, examining impairment in driving of subjects, both male and female.
All were healthy.
Results of Study 1:
Figure 1 demonstrates that marijuana impairs driving performance as measured by an increase in lateral position variability…impairment after marijuana was the same in both trials…Other driving performance measures were not significantly affected by THC. Plasma concentrations of the drug were clearly related to the administered dose and time of blood sampling but unrelated to driving performance impairment.
Results of Study 2:
[P]erformance in the standard test was impaired in a dose- related manner by THC and confirmed the results obtained in the previous closed highway study. After marijuana smoking, subjects drove with an average speed that was only slightly lower than after placebo and very close to the prescribed level. In the car-following test, subjects maintained a distance of 45-50 m while driving in the successive placebo conditions. Our explanation for this observation is that the subjects’ caution was greatest the first time they undertook the test under the influence of THC and progressively less thereafter. As in the previous study, plasma concentrations of the drug were not related to driving impairment.
Results of Study 3:
Neither alcohol nor marijuana significantly affected driving performance measures obtained by the molecular approach, indicating that it may be relatively insensitive to drug-induced changes. … shows that a modest dose of alcohol (bac=0.034 g%) produced a significant impairment in city driving, relative to placebo. More specifically, alcohol impaired both vehicle handling and traffic maneuvers. Marijuana, administered in a dose of 100 g/kg THC, on the other hand, did not significantly change mean driving performance as measured by this approach.
Thus, there is evidence that subjects in the marijuana group were not only aware of their intoxicated condition, but were also attempting to compensate for it. These seem to be important findings. They support both the common belief that drivers become overconfident after drinking alcohol and investigators’ suspicions that they become more cautious and self- critical after consuming low doses of THC, as smoked marijuana.
Drug plasma concentrations were neither related to absolute driving performance scores nor to the changes that occurred from placebo to drug conditions.
Summary:
In summary, this program of research has shown that marijuana, when taken alone, produces a moderate degree of driving impairment which is related to the consumed THC dose. The impairment manifests itself mainly in the ability to maintain a steady lateral position on the road, but its magnitude is not exceptional in comparison with changes produced by many medicinal drugs and alcohol. Drivers under the influence of marijuana retain insight in their performance and will compensate where they can, for example, by slowing down or increasing effort. As a consequence, THC’s adverse effects on driving performance appear relatively small…the magnitude of marijuana’s, relative to many other drugs’, effects also justify Gieringer’s (1988) conclusion that “marijuana impairment presents a real, but secondary, safety risk; and that alcohol is the leading drug-related accident risk factor”.
Of the many psychotropic drugs, licit and illicit, that are available and used by people who subsequently drive, marijuana may well be among the least harmful. Campaigns to discourage the use of marijuana by drivers are certainly warranted. But concentrating a campaign on marijuana alone may not be in proportion to the safety problem it causes.
Discussion:
The results of the studies corroborate those of previous driving simulator and closed-course tests by indicating that THC in inhaled doses up to 300 g/kg has significant, yet not dramatic, dose-related impairing effects on driving performance (cf. Smiley, 1986).
THC’s effects on road-tracking after doses up to 300 g/kg never exceeded alcohol’s at bacs of 0.08 g%; and, were in no way unusual compared to many medicinal drugs. Evidence from the present and previous studies strongly suggests that alcohol encourages risky driving whereas THC encourages greater caution, at least in experiments. Another way THC seems to differ qualitatively from many other drugs is that the former’s users seem better able to compensate for its adverse effects while driving under the influence.
…[A]n important practical implications of the study is that is not possible to conclude anything about a driver’s impairment on the basis of his/her plasma concentrations of THC and THC-COOH determined in a single sample.
[T]he results of the present studies should not be considered as the final word. They should, however, serve as the point of departure for subsequent studies that will ultimately complete the picture of THC’s effects on driving performance.
-----continued in next post-----