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Marijuana And Driving: A Review Of The Scientific Evidence


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#1 outsideinthecold

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Posted 24 August 2010 - 04:07 PM

It is well established that alcohol increases accident risk. Evidence of marijuana’s culpability in on-road driving accidents is much less convincing.
Although cannabis intoxication has been shown to mildly impair psychomotor skills, this impairment does not appear to be severe or long lasting. In driving simulator tests, this impairment is typically manifested by subjects decreasing their driving speed and requiring greater time to respond to emergency situations.

Nevertheless, this impairment does not appear to play a significant role in on-road traffic accidents. A 2002 review of seven separate studies involving 7,934 drivers reported, “Crash culpability studies have failed to demonstrate that drivers with cannabinoids in the blood are significantly more likely than drug-free drivers to be culpable in road crashes.”

This result is likely because subject under the influence of marijuana are aware of their impairment and compensate for it accordingly, such as by slowing down and by focusing their attention when they know a response will be required. This reaction is just the opposite of that exhibited by drivers under the influence of alcohol, who tend to drive in a more risky manner proportional to their intoxication.

Today, a large body of research exists exploring the impact of marijuana on psychomotor skills and actual driving performance. This research consists of driving simulator studies, on-road performance studies, crash culpability studies, and summary reviews of the existing evidence. To date, the result of this research is 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. Below is a summary of some of the existing data.

SUMMARY
At the present time, the evidence to suggest an involvement of cannabis in road crashes is scientifically unproven.

To date …, seven studies using culpability analysis have been reported, involving a total of 7,934 drivers. Alcohol was detected as the only drug in 1,785 drivers, and together with cannabis in 390 drivers. Cannabis was detected in 684 drivers, and in 294 of these it was the only drug detected.

The results to date of crash culpability studies have failed to demonstrate that drivers with cannabinoids in the blood are significantly more likely than drug-free drivers to be culpable in road crashes. [In] cases in which THC was the only drug present were analyzed, the culpability ratio was found to be not significantly different from the no-drug group.”

REFERENCE: G. Chesher and M. Longo. 2002. Cannabis and alcohol in motor vehicle accidents. In: F. Grotenhermen and E. Russo (Eds.) Cannabis and Cannabinoids: Pharmacology, Toxicology, and Therapeutic Potential. New York: Haworth Press. Pp. 313-323.


“Cannabis leads to a more cautious style of driving, [but] it has a negative impact on decision time and trajectory. [However,] this in itself does not mean that drivers under the influence of cannabis represent a traffic safety risk. Cannabis alone, particularly in low doses, has little effect on the skills involved in automobile driving.”


REFERENCE: Canadian Senate Special Committee on Illegal Drugs. 2002. Cannabis: Summary Report: Our Position for a Canadian Public Policy. Ottawa. Chapter 8: Driving Under the Influence of Cannabis.

This report has summarized available research on cannabis and driving.

Evidence of impairment from the consumption of cannabis has been reported by studies using laboratory tests, driving simulators and on-road observation. Both simulation and road trials generally find that driving behavior 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 Driving: A Review of the Literature and Commentary. Crowthorne, Berks: TRL Limited.


”Overall, we conclude that the weight of the evidence indicates that:

1) 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.
2) The evidence concerning the combined effect of cannabis and alcohol on the risk of traffic fatalities and injuries, relative to the risk of alcohol alone, is unclear.
3) It is not possible to exclude the possibility that the use of cannabis (with or without alcohol) leads to an increased risk of road traffic crashes causing less serious injuries and vehicle damage.”

REFERENCE: M. Bates and T. Blakely. 1999. “Role of cannabis in motor vehicle crashes.” Epidemiologic Reviews 21: 222-232.


“In conclusion, marijuana impairs driving behavior. However, this impairment is mitigated in that subjects under marijuana treatment appear to perceive that they are indeed impaired. Where they can compensate, they do, for example by not overtaking, by slowing down and by focusing their attention when they know a response will be required. Effects on driving behavior are present up to an hour after smoking but do not continue for extended periods.

With respect to comparisons between alcohol and marijuana effects, these substances tend to differ in their effects. In contrast to the compensatory behavior exhibited by subjects under marijuana treatment, subjects who have received alcohol tend to drive in a more risky manner. Both substances impair performance; however, 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: A. Smiley. 1999. Marijuana: On-Road and Driving-Simulator Studies. In: H. Kalant et al. (Eds) The Health Effects of Cannabis. Toronto: Center for Addiction and Mental Health. Pp. 173-191.


“Intoxication with cannabis leads to a slight impairment of psychomotor function. [However,] the impairment in driving skills does not appear to be severe, even immediately after taking cannabis, when subjects are tested in a driving simulator. This may be because people intoxicated by cannabis appear to compensate for their impairment by taking fewer risks and driving more slowly, whereas alcohol tends to encourage people to take great risks and drive more aggressively.”

REFERENCE: UK House of Lords Select Committee on Science and Technology. 1998. Ninth Report. London: United Kingdom. Chapter 4: Section 4.7.


“The evidence suggests that marijuana presents a real, but secondary safety risk; and that alcohol is the leading drug-related accident risk factor.”

REFERENCES: D. Gieringer. 1988. Marijuana, driving, and accident safety. Journal of Psychoactive Drugs 20: 93-101.



CRASH CULPABILITY STUDIES

“For each of 2,500 injured drivers presenting to a hospital, a blood sample was collected for later analysis.

There was a clear relationship between alcohol and culpability. In contrast, there was no significant increase in culpability for cannabinoids alone. While a relatively large number of injured drivers tested positive for cannabinoids, culpability rates were no higher than those for the drug free group. This is consistent with other findings.”

REFERENCE:
Logan, M.C., Hunter, C.E., Lokan, R.J., White, J.M., & White, M.A. (2000). The Prevalence of Alcohol, Cannabinoids, Benzodiazepines and Stimulants Amongst Injured Drivers and Their Role in Driver Culpability: Part II: The Relationship Between Drug Prevalence and Drug Concentration, and Driver Culpability. Accident Analysis and Prevention, 32, 623-32.

“Blood samples from 894 patients presenting to two Emergency Departments for treatment of motor vehicle injur[ies] … were tested for alcohol and other drugs.

Based on alcohol and drug testing of the full range of patients alcohol is clearly the major drug associated with serious crashes and greater injury. Patients testing positive for illicit drugs (marijuana, opiates, and cocaine), in the absence of alcohol, were in crashes very similar to those of patients with neither alcohol nor drugs. When other relevant variables were considered, these drugs were not associated with more severe crashes or greater injury.”

REFERENCE: P. Waller et al. 1997. Crash characteristics and injuries of victims impaired by alcohol versus illicit drugs. Accident Analysis and Prevention 29: 817-827.

“Blood specimens were collected from a sample of 1,882 drivers from 7 states, during 14 months in the years 1990 and 1991. The sample comprised operators of passenger cars, trucks, and motorcycles who died within 4 hours of their crash.

While cannabinoids were detected in 7 percent of the drivers, the psychoactive agent THC was found in only 4 percent. The THC-only drivers had a responsibility rate below that of the drug-free drivers. While the difference was not statistically significant, there was no indication that cannabis by itself was a cause of fatal crashes.”

REFERENCE: K. Terhune. 1992. The incidence and role of drugs in fatally injured drivers. Washington, DC: US Department of Transportation National Highway Traffic Safety Administration, Report No. DOT HS 808 065.

ON-ROAD PERFORMANCE STUDIES
“Marijuana's effects on actual driving performance were assessed in a series of three studies wherein dose-effect relationships were measured in actual driving situations that progressively approached reality.

THC's effects on road-tracking after doses up to 300 µg/kg never exceeded alcohol's at bacs of 0.08%; and, were in no way unusual compared to many medicinal drugs. Yet, THC's effects differ qualitatively from many other drugs, especially alcohol. 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 formers users seem better able to compensate for its adverse effects while driving under the influence.”

REFERENCE: H. Robbe. 1995. Marijuana’s effects on actual driving performance. In: C. Kloeden and A. McLean (Eds) Alcohol, Drugs and Traffic Safety T-95. Adelaide: Australia: HHMRC Road Research Unit, University of Adelaide. Pp. 11-20.

“This report concerns the effects of marijuana smoking on actual driving performance. … This program of research has shown that marijuana, when taken alone, produces a moderate degree of driving impairment which is related to consumed THC dose. The impairment manifests itself mainly in the ability to maintain a 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 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: W. Hindrik and J. Robbe and J. O’Hanlon. 1993. Marijuana and actual driving performance. Washington, DC: US Department of Transportation National Highway Traffic Safety Administration, Report No. DOT HS 808 078.

DRIVING SIMULATOR STUDIES

“Overall, it is possible to conclude that cannabis has a measurable effect on psychomotor performance, particularly tracking ability. Its effect on higher cognitive functions, for example divided attention tasks associated with driving, appear not to be as critical. Drivers under the influence of cannabis seem aware that they are impaired, and attempt to compensate for this impairment by reducing the difficulty of the driving task, for example by driving more slowly.

In terms of road safety, it cannot be concluded that driving under the influence of cannabis is not a hazard, as the effects of various aspects of driver performance are unpredictable. However, in comparison with alcohol, the severe effects of alcohol on the higher cognitive processes of driving are likely to make this more of a hazard, particularly at higher blood alcohol levels.”
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#2 Phil78

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Posted 24 August 2010 - 09:12 PM

no, sorry. driving while intoxicated with ANYTHING is wrong and DANGEROUS! to suggest otherwise is ignorant, and backing it up with studies also degrades the integrity of all other studies used to support mj legalization (makes EVERY pro-mj argument look like a farce)

what you do with your life is your own right, however, don't put my family's lives and my life in danger. i've driven altered, and it was a stupid, stupid thing to do. i thank the Lord that I didn't die, and more importantly, that I didn't kill anyone!!

#3 peanutbutter

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Posted 24 August 2010 - 09:51 PM

no, sorry. driving while intoxicated with ANYTHING is wrong and DANGEROUS! to suggest otherwise is ignorant, and backing it up with studies also degrades the integrity of all other studies used to support mj legalization (makes EVERY pro-mj argument look like a farce)

what you do with your life is your own right, however, don't put my family's lives and my life in danger. i've driven altered, and it was a stupid, stupid thing to do. i thank the Lord that I didn't die, and more importantly, that I didn't kill anyone!!


I understand that you feel strongly about this.

Please double check that Federal Government report that was quoted.

Culpability in traffic deaths? Zero.

The main reason? That feeling of extra caution that you felt.

#4 Wild Bill

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Posted 25 August 2010 - 08:59 AM





mod fixed post
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#5 outsideinthecold

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Posted 25 August 2010 - 09:26 AM

The original information was posted NOT to condone any behavior.

It was posted to make folks aware that any claim by a Sheriff or other LEO/PA that marijuana's effects increase traffic accident risks is simply malarky.

For the record, marijuana use does not correlate with increased frequency of injury or damage accidents for most motor vehicle operators who use cannabis by itself.
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#6 vial

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Posted 26 August 2010 - 04:33 AM

"I think we're parked man."



best post on the entire MMMA forums :) + rep
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#7 LedFloyd

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Posted 30 August 2010 - 04:30 AM

i treat smoking and driving like drinking and driving
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#8 dutch&Dutchess

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Posted 30 August 2010 - 11:55 AM

I have a few more for you as well.

#9 Phil78

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Posted 30 August 2010 - 12:38 PM

i think it's pretty sh*tty, whomever gave me a neg rep. it's not that it hurts my feelings, but really? there are people out there who feel it is okay to drive around without all your faculties? seriously?

i've done it, guys. i'm not just saying "don't do it," because i think i might have a clue about what it must feel like. i've got experience doing it, and from that experience can confidently say that you are putting other people's (including children) lives at stake, because you cannot resist the urge to drive stoned. it's irresponsible.

how much support would i get if i supported drunk driving? i should start a pro-drunk-driving campaign. yeah, that would be ignorant, wouldn't it. but yet, driving stoned is okay? i am pro mj (not just medical) all the way, but losing sensibility is going to get us no where. to suggest driving under the influence of anything is okay, is wrong.

#10 boroboro

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Posted 30 August 2010 - 01:56 PM

Phil78, do you think most people drive around "without all their faculties"? I do. What do you think about this list of things that reduce a driver's attention or ability to drive at peak performance:
  • Cell Phone Usage
  • Fiddling with the radio
  • Talking with passengers
  • Talking with kids in the back seat
  • many kinds of medications
  • fatigue
  • mechanical problems with the car's brakes, tires, suspension, etc.
  • headlights out, faded, misaligned, dim
  • being very angry at your boss, spouse, the driver of that slow car in front of you, etc.
  • being a rural driver and suddenly finding yourself in a busy urban driving environment
  • being a slow-thinking person
  • old age
I argue that all of the above are real-world factors that do reduce the safety of driving, and do measurably increase the likelihood of an accident. If you want to include cannabis use as a factor contributing to dangerous driving, and include it on a list of prohibited actions, it seems to me that some or all of the above list should be included also, or there won't be any real logical consistency.

Phil78, It seems like you're seeing this in black and white, and disagreeing with people who are talking about different shades of gray.
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#11 Phil78

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Posted 30 August 2010 - 07:03 PM

yes, i am seeing this as black and white. you don't drink and drive, and you don't smoke and drive. there are enough idiots on the road, we don't need to add to the dangers. driving is a privilege, not a right. working in a hospital, i know that it's never the drunk f**k who gets killed, it's the mom driving their kids to soccer practice (or whatever).

i swear to the Lord above, if anyone ever killed my wife and daughter due to the fact they couldn't wait 5 minutes to smoke a jay, there is nothing on this earth that would keep me from taking their life. you may have nothing to lose, and can afford to take risks. those of us that have something to lose do not appreciate your risks.
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#12 Rashore

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Posted 01 September 2010 - 03:04 PM

There are for sure grey areas in this.
If someone takes their MM as a heavy duty pain killer or muscle relaxant, then they probably shouldn't be driving, just like if they were taking a pill like vicodin. If they are taking it as a light mood leveler or appetite stimulant it might not matter so much because none of their driving skills have been impaired in any way.
If they get into an accident because they are paying attention to lighting a j instead of driving.. that's not stoner stupid, that's flat out stupid, same way texting while driving is.

#13 the green leaf farmacy

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Posted 01 September 2010 - 03:14 PM

if you smoke and drive you are impard. its up to the goverment or sociaty to set the limits never before has this potent of pot been around for so many people let me tell you when i smoke this high potent pot i get riped and so do you so if you drive you are impared.
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#14 peanutbutter

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Posted 01 September 2010 - 03:36 PM

yes, i am seeing this as black and white. you don't drink and drive, and you don't smoke and drive. there are enough idiots on the road, we don't need to add to the dangers. driving is a privilege, not a right. working in a hospital, i know that it's never the drunk f**k who gets killed, it's the mom driving their kids to soccer practice (or whatever).

i swear to the Lord above, if anyone ever killed my wife and daughter due to the fact they couldn't wait 5 minutes to smoke a jay, there is nothing on this earth that would keep me from taking their life. you may have nothing to lose, and can afford to take risks. those of us that have something to lose do not appreciate your risks.


Here is the standard warning on pharmaceutical THC:

Patients should avoid driving or operating machinery until Marinol’s affect is known.
http://www.drugwatch...ide-effects.php



#15 1337Gr33n

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Posted 01 September 2010 - 09:53 PM

"I think we're parked man."


best
quote
ever

i was about to say "You don't need a study that costs thousands of dollars to find out that you drive slower when you're high!" ask ANYONE that has ever driven high! (not that i condone this behavior - i do not.)

#16 lawyercaregiver

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Posted 09 November 2010 - 09:47 PM

Oh please. Smoking and driving is NOT like drinking and driving. The studies and personal experience clearly show that there is some mild delayed reaction time with people really, really stoned.

The milder effects, that is, a nice little buzz where you feel you are OK to talk to the cops if that becomes necessary is not going to impair your driving because you compensate.

This is not like a nice little alcohol buzz which is another word for drunk driving.

Way to stick to your guns and defend against the negative rep btw even though I disagree with you.

#17 Wayne'sWorld

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Posted 11 November 2010 - 02:58 PM

i treat smoking and driving like drinking and driving

I treat consuming cannabis and driving, like nicotine and driving, or caffeine and driving, or Vicodin and driving, or LedFloyd and driving! LOL
No comparison!!!

#18 Wayne'sWorld

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Posted 11 November 2010 - 03:02 PM

I remember every single leg of everywhere I've ever driven while consuming cannabis. Alcohol! Well perhaps, ages ago.............perhaps! If only I could remember. Blacked out? Alcohol? Is that even possible? Naw............Always a safe driver!




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