Thursday, June 22, 2017

Legalizing Pot and Car Crahes

Does driving while high have any impact on auto accident rates? Legalized recreational marijuana use in Colorado, Oregon and Washington correlates to about a 3 percent increase in auto collision claim frequencies compared to states without such legislation, according to a new Highway Loss Data Institute (HLDI) study. It's the first one the group has conducted since the drug went on sale legally.
"More drivers admit to using marijuana, and it is showing up more frequently among people involved in crashes," the study said.
It is an article of faith that legalizing pot reduces impaired driving because drunks drive, while pot smokers do not, and pot substitutes for alcohol.  It should be apparent that anything that increases the percentage of people intoxicated is likely to increase number of people driving while intoxicated.  Further, I have seen no evidence that pot replaces alcohol abuse; often it seems to be in addition to alcohol.


  1. now that it is not illegal more drivers admit to it . 3% could just sampling artifact. Also what about severity. Drunks crash catastrophically do pot smokers just driv so slow and absently that the slowly run into things?

  2. "often it seems to be in addition to alcohol. "

    Correct, and in a significant percentage.

    And, marijuana and alcohol combined produce synergistic impairment.

  3. This wasn't based on admissions, but accident rates. Admitting to an officer that you were smoking pot sounds like a good way to be charged with DUI, whether legal or not.

  4. Yet the only controlled studies (Give someone calibrated amounts of weed, make them drive an obstacle course), Done by US Govt, have shown either no significant impairment or slight improvement.

    This study you cite has so many holes in it as to make swiss cheese look solid.

    John Henry

  5. John, where is that study? It is hard to imagine any intoxicant helping driving skills. Care to identify the holes?

  6. I think this is the study I remember.


    It is commonly assumed that marijuana smoking in real-life social situations delivers THC doses that seriously degrade the ability to safely operate motor vehicles; and, that the drug's users frequently drive shortly after smoking. If these premises are correct, it would follow that marijuana users are, while intoxicated, at increased risk of traffic accident involvement and constitute a safety hazard for other road users. However, the. foremost impression one gains from reviewing the literature is that no clear relationship has ever been demonstrated between marijuana smoking and either seriously impaired driving performance or traffic safety. The
    epidemiological evidence, as limited as it is, shows that the combination of THC and alcohol is over-represented in injured and dead drivers and more so in those who actually caused the accidents. Yet there is little if any evidence to indicate that drivers who have used marijuana alone are any more likely to cause serious accidents than drug free drivers.

    Emph added

    I thought I remembered a second, similar study by NHTSA but can't find it. It's been 20-25 years since I read either. (I was still searching with Gopher and downloading via FTP. The Web was not yet existent)

    OTOH, while searching just now, I also found this article along with many others showing essentially no increased risk from MJ alone. My recollection is that there is extensive literature showing impairment when MJ and booze are combined but none of it has any way to tease out the effect of each.

    U.S.: Pot use doesn't increase crash risk
    David Shepardson , Detroit News Washington Bureau Published 5:34 p.m. ET Feb. 6, 2015 | Updated 12:08 a.m. ET Feb. 7, 2015

    Washington — A government study released late Friday found no evidence that marijuana use leads to a higher risk of getting into a traffic crash.

    But safety advocates believe it is still dangerous to drive after smoking significant amounts of marijuana, and the government plans more testing.

    The National Highway Traffic Safety Administration said a 20-month survey of drivers in 2013 and 2014 found that while drinking dramatically raises the chance of a crash, there was no evidence that marijuana use is statistically significant in boosting wreck rates.

    John Henry

  7. Re the holes in the study you mentioned, I have not read it. I did read some discussion about it pointing out a number of faults. Mostly with methodology of collecting the data, comparison of dissimilar geographic areas were the two I remember.

    If you like, we can both read the actual study and discuss. Not something I am that interested in but if you'll do it I will.

    John Henry