Study Examines Marijuana/Alcohol Impact on Driving

June 29, 2015

  • June 29, 2015 at 9:29 am
    Paul Pot says:
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    “Colorado has reported an increase in driving under the influence of cannabis cases and fatal motor vehicle crashes with cannabis-only positive drivers.”
    This is called lying by omission, this stat may be correct but the crucially omitted stat is the overall number of accidents and they have gone down and if you go back to the very beginning of medical marijuana in Colorado some 12 yrs ago you will find that fatal car accidents have declined by almost 50%.
    The presence of cannabis has nothing to do with traffic accidents and by replacing alcohol consumption which the community obviously prefers has actually helped reduce the number of fatalities and saved lives.

  • June 29, 2015 at 9:57 am
    Stel1776 says:
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    Cannabis does cause some impairment, however studies have shown that consumers tend to overestimate this impairment, and that they compensate for it with added caution. Alcohol tends to do the opposite, consumers perceive their impairment to be less that what it actually is and often become overconfident, aggressive, and careless. [Robbe and O’Hanlon. 1993; Robbe. 1995]

    To find out how cannabis use affects crash risk overall, in 2015 the U.S. government completed the largest case controlled study to date regarding DUI of cannabis and crash risk. It involved over 9,000 cases and controls spanning a 20-month period. It found that cannabis use while driving is not associated with increased crash risk once adjusted for confounding variables such as age, race, gender, and the presence of other drugs, including alcohol:

    “This analysis shows that the significant increased risk of crash involvement associated with THC and illegal drugs shown in Table 3 is not found after adjusting for these demographic variables.”

    Further, they found that cannabis did not add to the crash risk for drivers under the influence of alcohol:

    “As was described above, there was no difference in crash risk for marijuana (THC)-positive drivers who were also positive for alcohol than for marijuana (THC)-positive drivers with no alcohol, beyond the risk attributable to alcohol.”

    They found that alcohol significantly increased crash risk:

    “at moderate alcohol levels (0.05 BrAC) risk increases to double that of sober drivers, and at a higher level (0.10 BrAC) the risk increases to five and a half times. At a BrAC of 0.15, the risk is 12 times, and by BrACs of 0.20+ the risk is over 23 times higher.”

    Compton and Berning. DOT HS 812 117. Drug and Alcohol Crash Risk. U.S. Department of Transportation – National Highway Traffic Safety Administration. 2015.

    That said, at some point one could be high enough to significantly increase crash risk, something roughly the equivalent of 0.08% BAC, and DUI laws should reflect that, and be based on actual impairment, not “per se” limits. However it is rare for anyone that high to want to actually drive a car, whereas it is commonplace for someone very drunk to attempt to drive.

    SOURCES:

    –Robbe and O’Hanlon. DOT HS 808 078. Marijuana and actual driving performance. U.S. Department of Transportation – National Highway Traffic Safety Administration. 1993.
    –Robbe H. Marijuana’s effects on actual driving performance. HHMRC Road Research Unit, University of Adelaide. 1995.

    Colorado legalized recreational cannabis in Dec 2012 (Jan 2014 for retail sales) and did not see a statistically significant change in fatal traffic accidents:

    2012: 474 (Population: 5.19 million, 0.0091%)
    2013: 481 (Population: 5.27 million, 0.0091%)
    2014: 479 (Population: 5.36 million, 0.0089%)
    [SOURCE: Colorado DOT & “As Reported” to NHTSA by FARS]

    Recreational cannabis use was legalized in Washington state in Dec of 2012. Retail sales began in July, 2014. Fatal traffic accidents have not increased:

    2012 – 403 (Population: 6.90 million, 0.0058%)
    2013 – 401 (Population: 6.97 million, 0.0057%)
    [SOURCE: Washington State Department of Transportation – 2012, 2013 Annual Collision Summary]

  • June 29, 2015 at 10:32 am
    Freedom Fighter says:
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    2014 : During a congressional hearing on the threat posed by cannabis intoxicated drivers, representative Jeff Michael of the National Highway Traffic Safety Administration (NHTSA) was asked how many fatal crashes are caused by marijuana each year. “That’s difficult to say,” replied Michael, “We don’t have a precise estimate.” The most he was willing to affirm was that the number is “probably not” zero.
    If you take the spin off it what Jeff Michael of the NHTSA is saying, the translation comes out, there’s not enough fatal accidents related to cannabis to provide quantifiable data.
    If you go further in your thinking it’s clear the reason for the lack of data is because cannabis is safe by comparison to alcohol and pharmaceuticals which are easily quantifiable because of the massive numbers of victims killed. Nearly 60 traffic fatalities PER DAY in the US directly attributable to alcohol and pharmaceutical intoxication!!! Alcohol and pharmaceutical drugs kill over 21,000 people per year in the US in traffic deaths alone and over 500,000 in non automobile related deaths.
    I have searched high and low, talked to local law enforcement, Highway Patrol, State Police and get the same answer from every agency. Not one single law enforcement agency can show a single case of fatal accident caused by cannabis directly. They can show cases by the thousands where alcohol or pharmaceuticals were the direct cause of traffic fatalities. When cornered police officials hem and haw about cannabis probabilities, but when asked to show one single case of a traffic fatality solely caused by cannabis intoxication it’s always the same answer “there is currently no data is available.”
    Q. What does the Mothers Against Drunk Driving website say about cannabis and driving?
    A. Virtually nothing is the answer!
    The reason for that answer is that cannabis is safe by comparison to driving under the influence of pharmaceuticals and alcohol which are prominently featured at the MADD website.

  • June 29, 2015 at 11:39 am
    Krymsun says:
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    Why does most everyone jump to the automatic, knee-jerk, and FALSE assumption that cannabis impairs drivers much the same as does alcohol? Why let uninformed opinions be the basis of new laws? It took me very little time to do a search, and find actual scientific studies which indicate just how incorrect such an assumption is. Examples follow.

    Studies Show Marijuana Consumption Not Associated With Dangerous Driving, May Lead to Safer Drivers
    Anyone who consumes cannabis on a regular basis knows that it doesn’t make you a dangerous driver. Many people find that it makes them a safer, more focused driver; one that’s more aware of their surroundings and the dangers associated with controlling tons of gasoline-filled metal. Not only has this been an anecdotal truth for as long as cars and cannabis have been paired, science has also been clear that consuming marijuana doesn’t make you a dangerous driver, and may make some people safer drivers. More research is needed, but it’s hard to deny that of the research we have, marijuana hasn’t been found to increase a person’s risk of an accident. To back this claim up, here’s a list of studies and research conducted on this very topic, some of which were funded by national governments in hopes of different results.

    Marijuana and Driving: A Review of the Scientific Evidence
    “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. Below is a summary of some of the existing data.”

    The incidence and role of drugs in fatally injured drivers
    “There was no indication that cannabis by itself was a cause of fatal crashes.”
    REFERENCE: Washington, DC: US Department of Transportation, National Highway Traffic Safety Administration,
    Report No. DOT HS 808 065, K. Terhune. 1992.

    Marijuana’s effects on actual driving performance
    “Evidence from the present and previous studies strongly suggests that alcohol encourages risky driving whereas THC encourages greater caution. .. Drivers under the influence of marijuana retain insight in their performance and will compensate when they can, for example, by slowing down or increasing effort. As a consequence, THC’s adverse effects on driving performance appear relatively small.”
    REFERENCE: University of Adelaide study, 1995

    Role of cannabis in motor vehicle crashes
    “There is no evidence that consumption of cannabis alone increases the risk of culpability for traffic crash fatalities or injuries for which hospitalization occurs, and may reduce those risks.. The more cautious behavior of subjects who have received marijuana decreases the impact of the drug on performance, whereas the opposite holds true for alcohol.”
    REFERENCE: Marijuana: On-Road and Driving-Simulator Studies; Epidemiologic Reviews 21: 222-232, A. Smiley. 1999.

    “Both simulation and road trials generally find that driving behaviour shortly after consumption of larger doses of cannabis results in (i) a more cautious driving style; (ii) increased variability in lane position (and headway); and (iii) longer decision times. Whereas these results indicate a ‘change’ from normal conditions, they do not necessarily reflect ‘impairment’ in terms of performance effectiveness since few studies report increased accident risk.”
    REFERENCE: UK Department of Environment, Transport and the Regions (Road Safety Division). 2000.

    Cannabis And Cannabinoids – Pharmacology, Toxicology And Therapy
    “At the present time, the evidence to suggest an involvement of cannabis in road crashes is scientifically unproven”.
    REFERENCE: G. Chesher and M. Longo. 2002.

    Cannabis: Our position for a Canadian Public Policy
    “Cannabis alone, particularly in low doses, has little effect on the skills involved in automobile driving. Cannabis leads to a more cautious style of driving. However it has a negative impact on decision time and trajectory. This in itself does not mean that drivers under the influence of cannabis represent a traffic safety risk”
    REFERENCE: Canadian Senate Special Committee on Illegal Drugs. 2002.

    “The evidence to suggest an involvement of cannabis in road crashes is scientifically unproven.”
    REFERENCE: Cannabis and Cannabinoids: Pharmacology, Toxicology, and Therapeutic Potential, 2002
    Cannabis and Cannabinoids: Pharmacology, Toxicology, and Therapeutic Potential, edited by Franjo Grotenhermen, MD and Ethan Russo, MD (Haworth Press 2002).

    The Prevalence of Drug Use in Drivers, and Characteristics of the Drug-Positive Group
    “There was a clear relationship between alcohol and culpability. In contrast, there was no significant increase in culpability for cannabinoids alone.”
    REFERENCE: Accident Analysis and Prevention 32(5): 613-622. Longo, MC; Hunter, CE; Lokan, RJ; White, JM; and White, MA. (2000a).

    The Effect Of Cannabis Compared With Alcohol On Driving
    “Although cognitive studies suggest that cannabis use may lead to unsafe driving, experimental studies have suggested that it can have the opposite effect.” U.S. National Library of Medicine, 2009

    Why Medical Marijuana Laws Reduce Traffic Deaths
    “No differences were found during the baseline driving segment (and the) collision avoidance scenarios,”
    REFERENCE: Research published in the Journal of Psychoactive Drugs, 2010

    Top 10 Reasons Marijuana Users Are Safer Drivers
    “20 years of study has concluded that marijuana smokers may actually have fewer accidents than other drivers.”

    Risk of severe driver injury by driving with psychoactive substances
    “The study found that those with a blood alcohol level of 0.12% were over 30 times more likely to get into a serious accident than someone who’s consumed any amount of cannabis. .. The least risky drug seemed to be cannabis and benzodiazepines and Z-drugs.”
    REFERENCE: Accident Analysis & Prevention; Volume 59, October 2013, Pages 346–356

    Cannabis: Summary Report
    “Cannabis alone, particularly in low doses, has little effect on the skills involved in automobile driving.”
    REFERENCE: Canadian Senate Special Committee on Illegal Drugs

    Acute cannabis consumption and motor vehicle collision risk
    “There is no evidence that consumption of cannabis alone increases the risk of culpability for traffic crash fatalities or injuries for which hospitalization occurs, and may reduce those risks.”
    REFERENCE: British Medical Journal, 1999; M. Bates and T. Blakely

    Marijuana-DUI Case Tossed by Arizona Supreme Court in Metabolite Ruling
    “Because the legislature intended to prevent impaired driving, we hold that the ‘metabolite’ reference in [the law] is limited to any of a proscribed substance’s metabolites that are capable of causing impairment . . . Drivers cannot be convicted of the . . . offense based merely on the presence of a non-impairing metabolite that may reflect the prior usage of marijuana.”

    Landmark Study Finds Marijuana Is Not Linked to Car Crashes

    Stoned drivers are a lot safer than drunk ones, new federal data show

    “Stick all *that* in your pipe and smoke it!”



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