Driving, Drinking, and Drug Use

41. Cannabis Use and Motor Vehicle Accident Risk

"A review of over a dozen of these [laboratory] experiments reveals three findings. First, after using marijuana, people drive more slowly. In addition, they increase the distance between their cars and the car in front of them. Third, they are less likely to attempt to pass other vehicles on the road. All of these practices can decrease the chance of crashes and certainly limit the probability of injury or death if an accident does occur. These three habits may explain the slightly lower risk of accidents that appears in the epidemiological studies. These results contrast dramatically to those found for alcohol. Alcohol intoxication often increases speed and passing while decreasing following distance, and markedly raises the chance of crashes.(632)"

"Rulemaking petition to reclassify cannabis for medical use from a Schedule I controlled substance to a Schedule II, Exhibit B: Statement of Grounds," Prepared by Carter, Gregory T.; Earleywine, Mitchell; and McGill, Jason T. (Office of Lincoln D. Chafee, Governor Rhode Island and Office of Christine O. Gregoire, Governor of Washington, November 30, 2011), Filed With US Drug Enforcement Administration on November 30, 2011, p. 37.

42. Cannabis Use and Driving Impairment

"There is considerable evidence from laboratory studies that cannabis (marijuana) impairs reaction time, attention, tracking, hand-eye coordination, and concentration, although not all of these impairments were equally detected by all studies (Couper & Logan, 2004a; Heishman, Stitzer, & Yingling, 1989; Gieringer, 1988; Moskowitz, 1985). In reviewing the literature on marijuana, Smiley (1998) concluded that marijuana impairs performance in divided attention tasks (i.e., a poorer performance on subsidiary tasks). Jones et al. (2003) adds that Smiley’s finding is relevant to the multitasking essence of driving, in particular by making marijuana impaired drivers perhaps less able to handle unexpected events. Interestingly, there is also evidence showing that, unlike alcohol, marijuana enhances rather than mitigates the individual’s perception of impairment (Lamers & Ramaekers, 1999; Robbe & O'Hanlon, 1993; Perez-Reyes, Hicks, Bumberry, Jeffcoat, & Cook, 1988). Robbe and O'Hanlon (1993) reported that in laboratory conditions, drivers under the influence of marijuana were aware of their impairment, which led them to decrease speed, avoid passing other vehicles, and reduce other risk-taking behaviors. Such was not the case with alcohol; for the authors reported that alcohol-impaired drivers were generally not aware of impairment, and therefore did not adjust their driving accordingly."

Lacey, John H.; Kelley-Baker, Tara; Furr-Holden, Debra; Voas, Robert B.; Romano, Eduardo; Ramirez, Anthony; Brainard, Katharine; Moore, Christine; Torres, Pedro; and Berning, Amy , "2007 National Roadside Survey of Alcohol and Drug Use by Drivers," Pacific Institute for Research and Evaluation (Calverton, MD: National Highway Traffic Safety Administration, December 2009), p. 9.

43. Driving After Cannabis Consumption

"Cannabis is only considered a risk factor for traffic accidents if drivers operate vehicles after consuming the drug. Robbe (1994) found that 30% to 90% of his participants were willing to drive after consuming a typical dose of cannabis. This is consistent with a recent Australian survey in which more than 50% of users drove after consuming cannabis (Lenne, Fry, Dietze, & Rumbold, 2000). A self administered questionnaire given to 508 students in grades 10 to 13 in Ontario, Canada, found that 19.7% reported driving within an hour after using cannabis (Adlaf, Mann, & Paglia, 2003)."

Laberge, Jason C., Nicholas J. Ward, "Research Note: Cannabis and Driving -- Research Needs and Issues for Transportation Policy," Journal of Drug Issues (Tallahassee, FL: School of Criminology & Criminal Justice, Florida State University, 2004) Volume 34, Number 4, pp. 974-5.

44. Cannabis and Driving Impairment

"Participants receiving active marijuana decreased their speed more so than those receiving the placebo cigarette during a distracted section of the drive, An overall effect of marijuana was seen for the mean speed during the distracted driving (PASAT [Paced Auditory Serial-Addition Test] section), While no other changes in driving performance were found, marijuana appeared to hinder practice effects on the PASAT task, suggesting individuals may not be able to adequately use information and experience previously acquired while under the influence of marijuana, While only minimal differences in driving performance were found, this failure to benefit from prior practice may be detrimental to driving performance. Research has shown that graduated driver's licensing programs in which participants receive more on the road training results in a decrease in fatal crashes in 16-year-olds (Baker, Chen & Li 2006), If marijuana indeed impairs one's ability to use prior experience to improve performance, this will likely impair driving under pretrained conditions (e,g,, steering into a skid, allowing increased stopping time on slippery roads, etc)."

Anderson, Beth M.; Rizzo, Matthew; Block, Robert I.; Pearlson, Godfrey D.; O'Leary, Daniel S., "Sex differences in the effects of marijuana on simulated driving performance," Journal of Psychoactive Drugs (San Francisco, CA: Haight Ashbury Publications, March 1, 2010), Vol. 42, No. 1.

45. Cannabis and Driving Impairment

"The present study's subtle finding of decreased speed under the influence of acute marijuana is generally consistent with the literature, which has found that marijuana's effects on driving can be subtle. In Berghaus's review of the literature prior to 1995, 45% of driving simulator studies showed no impairment from marijuana within the first hour after use (Berghaus, Scheer & Schmidt 1995), More cautious driving behaviors were found in several studies (Lamers & Ramaekers 2001; Stein et al, 1983; Ellingstad, McFarling & Struckman 1973; Rafaelsen, Bech & Rafaelsen 1973; Dott 1972), while an increased reaction time for stopping was the most common finding (Liguori, Gatto & Robinson 1998; Rafaelsen, Bech & Rafaelsen 1973), Moskowitz, Ziedman and Sharma (1976) also found slowed reaction times for a visual choice-reaction time task administered while driving and Smiley, Moskowitz and Zeidman (1981) found increased variability in velocity and lateral position while following curves and while controlling the car in gusts of wind with a high dose of marijuana (200 mcg/kg THC) but not with a lower dose (100 mcg/kg THC), They also found an increase in variability of headway and lateral position while following other cars."

Anderson, Beth M.; Rizzo, Matthew; Block, Robert I.; Pearlson, Godfrey D.; O'Leary, Daniel S., "Sex differences in the effects of marijuana on simulated driving performance," Journal of Psychoactive Drugs (San Francisco, CA: Haight Ashbury Publications, March 1, 2010), Vol. 42, No. 1.