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Marijuana And Actual Driving Performance

Posted in General, Politics, Pop Culture, Safety, Science, Traffic by Vito Rispo | December 17th, 2008 | 2 Responses |

Whenever the subject of reforming marijuana laws comes up, someone always brings up the issue of driving while high, which makes sense. It’s an established fact that alcohol increases a drivers accident risk – but does that same risk apply to marijuana? The scientific research out there shows that cannabis is rarely a factor in car accidents, and has much less of an impact on the psychomotor skills needed for driving than alcohol does.

In fact, when it comes to speed and focus, high and drunk drivers actually have the exact opposite reactions. Drivers under the influence of marijuana are aware of their impairment and compensate for it by slowing down and over-compensating their focus, while drunk drivers tend to drive in a more risky manner proportional to their intoxication.

There’s a large amount of research out there on the effects of marijuana on driving, and the results are fairly consistent: Marijuana has a measurable yet relatively mild effect on psychomotor skills, yet it does not appear to play a significant role in vehicle crashes, particularly when compared to alcohol. Check out the conclusions from the US Department of Transportation study:

* Current users of marijuana prefer THC doses of about 300 ug/kg to achieve their desired “high”.

* It is possible to safely study the effects of marijuana on driving on highways or city streets in the presence of other traffic.

* Marijuana smoking impairs fundamental road tracking ability with the degree if impairment increasing as a function of the consumed THC dose.

* Marijuana smoking which delivers THC up to a 300 ug/kg dose slightly impairs the ability to maintain a constant headway while following another car.

* A low THC dose (100 ug/kg) does not impair driving ability in urban traffic to the same extent as a blood alcohol concentration (BAC) of 0.04g%.

* Drivers under the influence of marijuana tend to over-estimate the adverse effects of the drug on their driving quality and compensate when they can; e.g. by increasing effort to accomplish the task, increasing headway or slowing down, or a combination of these.

* Drivers under the influence of alcohol tend to under-estimate the adverse effects of the drug on their driving quality and do not invest compensatory effort.

* The maximum road tracking impairment after the highest THC dose (300 ug/kg) was within a range of effects produced by many commonly used medicinal drugs and less than that associated with a blood alcohol concentration (BAC) of 0.08g% in previous studies employing the same test.

* It 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.

So stoners are safer because they’re paranoid?

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2 Responses

  1. yeah! says:

    I think the best way to combat the anti-marijuana fervor is through good scientific research. This article is an excellent example, by citing legitimate sources the author came up with a valid conclusion…you are a better driver when stoned then when you are drunk.

    I think scientific studies highlighting the positive effects of cannabis are the key to winning against the ignorant.

    Thank you so much for enlightening us!

  2. Sceptic says:

    When I was in 7th grade, in 1987, someone in my class did a report on how mosquitoes spread HIV/AIDS. I know, that comment seems unrelated to this article… but did anyone see when this “study” was originally conducted? 1993! Why would anyone site sources so old??

    Also, did anyone READ the actual study? It’s full of contradictions. The Abstract says the first test was performed 30 and 90 minutes after smoking and the Methods section says 40 minutes and an hour later.

    How can a study who’s Final Report date of November 1993 site sources from 1995?

    Does the U.S. Government measure in metric?