The following articles may cast great doubt on the claims that cannabis use severely detrimentally effects driving skills. It seems that the Dutch Government are correct in not regarding cannabis driving as a serious problem after all.

STUDIES had found it impossible to prove cannabis adversely affected driving, an Adelaide University researcher said yesterday.

Professor Jack Maclean, director of the road accident research unit, said, while there was no doubt alcohol affected driving adversely, that was not the case with marijuana.

"It has been impossible to prove marijuana affects driving adversely," he told the Australian Driver Fatigue Conference in Sydney.

"There is no doubt marijuana affects performance but it may be it affects it in a favourable way by reducing risk-taking."

Professor Maclean said a study of blood samples taken by SA hospitals from people injured in road accidents found marijuana was the second most common drug, after alcohol, in the bloodstream.

Those with marijuana in their blood, however, were at fault in less than half of the accidents.

"Alcohol was by far the most common drug and 80 per cent of those with alcohol on board were judged to be responsible (for accidents)," he said.

"The next most common drug, but much less, was marijuana and about 48 per cent of the people with marijuana were judged to have been responsible for their crash."

He said the lack of proof that marijuana was detrimental to driving was not because of a lack of effort by researchers.

"I can say that there are some quite distinguished researchers who are going through incredible contortions to try and prove that marijuana has to be a problem," he said.

Professor Maclean said some researchers also found the risk of crashing while driving at the speed limit in a metropolitan area actually decreased if a driver had been drinking but was under the 0.05 blood alcohol limit.

"Perhaps for some people one or two glasses of alcohol may steady them down," he said.

As speed and alcohol concentration rose, however, the risk of accidents rose exponentially.

RESEARCH for a computer game company has found a small amount of cannabis could help players' performance, making them drive faster and safer.

The experiment was carried out for Acclaim Entertainment to see how cannabis would affect people playing its new game, Burnout. A group of 20 experienced games enthusiasts and drivers between 21 and 40 took part in the test to study reaction times, speed, concentration levels and road safety.

Ten of them then smoked about 0.15 milligrams of cannabis, or about half a "joint", while the other ten had had no stimulant for at least 72 hours prior to the test. They were then given a demonstration of Burnout and asked to take the controls.

The researchers say 80 per cent of those who had smoked cannabis demonstrated superior reaction times to those who had not. About 60 per cent finished a lap faster, while 70 per cent experienced a lower number of collisions, and more than half reached a higher level in the game.

When playing in competition with each other, the drivers who had smoked cannabis won eight out of the ten matches. The company claims drivers under the influence of cannabis appeared to have more confidence in their ability and be much calmer.

Simon Smith-Wright, Burnout's communications director, admitted the findings do not translate into real life, but insisted small amounts of the drug helped driving.

He said: "The results of our tests clearly indicate that a small or moderate amount of cannabis is actually quite beneficial to someone's driving performance.



If you're going to smoke a joint, don't drive home

IT'S official: smoking dope makes you a worse driver. But cannabis has less effect on driving ability than alcohol, according to a study by the Transport Research Laboratory (TRL) in Crowthorne, Berkshire.

The Department of Environment, Transport and the Regions asked the TRL Safety Department to investigate the effect of cannabis intoxication on driving ability. Cannabis is by far the most common illegal drug found in the bloodstream of road accident victims, and THC-the active ingredient in cannabis-can remain in the body for more than a month.

Barry Sexton and his colleagues at the TRL recruited 15 volunteers to complete driving tests while under the influence of low or high doses of cannabis, or no drug at all. The volunteers either smoked readyrolled cannabis joints or rolled their own with resin supplied under government licence. They were then put through their paces on a sophisticated driving simulator.

The researchers measured their accuracy at steering the car, known as "tracking ability", and other psychomotor responses, such as hazard perception and braking responses. They took blood and saliva samples at regular intervals and also tested the subjects' coordination, balance and timing.

The first thing the researchers noticed was that the subjects drove more slowly under the influence of dope, compensating for their intoxication by driving more cautiously. Tracking ability was the only test criterion that was adversely affected: the volunteers found it very difficult to follow a figure-of-eight loop of road when given a high dose. Reaction times to motorway hazards and performance on cognitive tests in the lab were not significantly affected.

Trials previously completed under similar test conditions at the TRL have shown that alcohol and tiredness have a more adverse effect on driving ability, affecting higher cognitive processes. The results of the cannabis and driving study agree with similar research carried out in Australia, the US and Holland.

The Technical Officer of the Legalise Cannabis Alliance, which is a British political party, comments that "any person who is not in full control of their body should not drive, be it through tiredness, alcohol, cannabis or drugs ... but everything must be seen in proportion. We need to legalise and regulate cannabis in a similar way to alcohol to be able to see the size of the problem."

Jane Eason of the Royal Society for the Prevention of Accidents favours the roadside tests to spot cannabis intoxication now being tried by British police. "We would welcome any measure that might make the roads of Britain safer."

Cannabis may make you a safer driver by Jonathon Carr-Brown, Sunday Times, 13 August 2000

TAKING the high road may not be so dangerous after all. Ministers are set to be embarrassed by government-funded research which shows that driving under the influence of drugs makes motorists more cautious and has a limited impact on their risk of crashing.

In the study, conducted by the Transport Research Laboratory, "grade A" cannabis specially imported from America was given to 15 regular users. The doped- up drivers were then put through four weeks of tests on driving simulators to gauge reaction times and awareness.

Regular smokers were used because previous tests in America using first- timers resulted in the volunteers falling over and feeling ill. The laboratory found its guinea pigs through what it described as a "snowballing technique" - one known user was asked to find another after being promised anonymity and exemption from prosecution agreed with the Home Office.

Instead of proving that drug-taking while driving increased the risk of accidents, researchers found that the mellowing effects of cannabis made drivers more cautious and so less likely to drive dangerously.

Although the cannabis affected reaction time in regular users, its effects appear to be substantially less dangerous than fatigue or drinking. Research by the Australian Drugs Foundation found that cannabis was the only drug tested that decreased the relative risk of having an accident.

The findings will embarrass ministers at the Department of the Environment, Transport and the Regions (DETR) who commissioned the study after pressure from motoring organisations and anti-drug campaigners. Lord Whitty, the transport minister, will receive the report later this month.

Last week police revealed details of new drug-driving tests to be administered by the roadside, which were received with some amusement. They require suspected drug- drivers to stand on one leg, lean back and touch their nose with their eyes closed, and to count to 30 silently with their eyes shut. This is apparently difficult for those on a drug trip.

However, if the findings are less than frightening on the effects of marijuana, they may convince ministers to put more money into raising driver awareness of fatigue. Tiredness is now blamed for causing 10% of all fatal accidents, compared with 6% for alcohol and 3% for drugs.

A low-key radio campaign will be launched tomorrow warning drivers to take breaks.

The report's surprising conclusions will not sway organisations such as the RAC, which believes there is incontrovertible evidence that drug-driving is a growing menace. DETR statistics published in January showed a six-fold increase in the number of people found to be driving with drugs in their system after fatal road accidents. The figure jumped from 3% in 1989 to 18%.

Dr Rob Tunbridge, the report's author, refused to reveal his findings before they were published but said: "If you were to ask me to rank them in order of priority, fatigue is the worst killer, followed by alcohol, and drugs follow way behind in third."

Tunbridge admitted that the effect of drugs differed with the individual, the amount taken, the environment they were taken in and the point at which you tested reactions.

Zimmer and Jones (Lindesmith)


Cannabis makes you a better driver - more evidence

"Simulated driving scores for subjects experiencing a normal social 'high' and the same subjects under control conditions are not significantly different. However, there are significantly more errors for alcohol intoxicated than for control subjects"....... Crancer Study, Washington Department of Motor Vehicles

Professor Olaf Drummer, a forensic scientist the Royal College of Surgeons in Melbourne in 1996 "Compared to alcohol, which makes people take more risks on the road, marijuana made drivers slow down and drive more carefully.... Cannabis is good for driving skills, as people tend to overcompensate for a perceived impairment."



U.S. Department of Transportation,
National Highway Traffic Safety Administration
(DOT HS 808 078), Final Report, November 1993:

"This program of research has shown that marijuana, when taken alone, produces a moderate degree of driving impairment which is related to the consumed THC dose. The impairment manifests itself mainly in the ability to maintain a steady 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, where they can, for example, by slowing down or increasing effort. As a consequence, THC's adverse effects on driving performance appear relatively small."

The study used actual, stoned Dutch drivers (in Holland) and it was paid for by our government.


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. The first was conducted on a highway closed to other traffic. Subjects (24) were treated on separate occasions with THC 100, 200 and 300 g/kg, and placebo. They performed a 22-km road tracking test beginning 30 and 90 minutes after smoking. Their lateral position variability increased significantly after each THC dose relative to placebo in a dose-dependent manner for two hours after smoking. The second study was conducted on a highway in the presence of other traffic. Subjects (16) were treated with the same THC doses as before. They performed a 64-km road tracking test preceded and followed by 16-km car following tests. Results confirmed those of the previous study. Car following performance was only slightly impaired. The third study was conducted in high-density urban traffic. Separate groups of 16 subjects were treated with 100 g/kg THC and placebo; and, ethanol (mean BAC .034 g%) and placebo. Alcohol impaired performance relative to placebo but subjects did not perceive it. THC did not impair driving performance yet the subjects thought it had. These studies show that THC in single inhaled doses up to 300 g/kg has significant, yet not dramatic, dose-related impairing effects on driving performance.


This article describes the results of a research program that was set up to determine the dose-response relationship between marijuana and objectively and subjectively measured aspects of real world driving; and to determine whether it is possible to correlate driving performance impairment with plasma concentrations of the drug or a metabolite. The program consisted of three driving studies in which a variety of driving tasks were employed, including: maintenance of a constant speed and lateral position during uninterrupted highway travel, following a leading car with varying speed on a highway, and city driving. A laboratory study preceded the driving studies for identifying the highest THC dose to be administered in the subsequent studies.


Subjects in all studies were recreational users of marijuana or hashish, i.e., smoking the drug more than once a month, but not daily. They were all healthy, between 21 and 40 years of age, had normal weight and binocular acuity, and were licensed to drive an automobile. Furthermore, law enforcement authorities were contacted, with the volunteers' consent, to verify that they had no previous arrests or convictions for drunken driving or drug trafficking.
Each subject was required to submit a urine sample immediately upon arrival at the test site. Samples were assayed qualitatively for the following common 'street drugs' (or metabolites): cannabinoids, benzodiazepines, opiates, cocaine, amphetamines and barbiturates. In addition a breath sample was analyzed for the presence of alcohol. Blood samples were repeatedly taken after smoking by venepuncture. Quantitative analysis of THC and THC-COOH in plasma was performed by gas chromatography/mass spectrometry (gc/ms) using deuterated cannabinoids as internal standards.

Marijuana and placebo marijuana cigarettes were supplied by the U.S. National Institute on Drug Abuse. The lowest and highest THC concentrations in the marijuana cigarettes used in the studies were 1.75% and 3.57%, respectively. Subjects smoked the administered cigarettes through a plastic holder in their customary fashion.
Subjects were accompanied during every driving test by a licensed driving instructor. A redundant control system in the test vehicle was available for controlling the car, should emergency situations arise.
In each study, subjects repeatedly performed certain simple laboratory tests (e.g. critical instability tracking, hand and posture stability), estimated their levels of intoxication and indicated their willingness to drive under several specified conditions of urgency. In addition, heart rate and blood pressure were measured. Results of these measurements are reported elsewhere (Robbe, 1994).



Twenty-four subjects, equally comprised of men and women, participated in this study. They were allowed to smoke part or all of the THC content in three cigarettes until achieving the desired psychological effect. The only requirement was to smoke for a period not exceeding 15 minutes. When subjects voluntarily stopped smoking, cigarettes were carefully extinguished and retained for subsequent gravimetric estimation of the amount of THC consumed.


Six subjects consumed one cigarette, thirteen smoked two and four smoked three (data from one male subject were excluded from the results because no drug was found in his plasma after smoking). The average amount of THC consumed was 20.8 mg, after adjustment for body weight, 308 g/kg. It should be noted that these amounts of THC represent both the inhaled dose and the portion that was lost through pyrolysis and side-stream smoke during the smoking process. There were no significant differences between males and females, nor between frequent and infrequent users, with respect to the weight adjusted preferred dose. It was decided that the maximum dose for subsequent driving studies would be 300 g/kg.



The first driving study was conducted on a highway closed to other traffic. The same twelve men and twelve women who participated in the laboratory study served again as the subjects. They were treated on separate occasions with marijuana cigarettes containing THC doses of 0 (placebo), 100, 200, and 300 g/kg. Treatments were administered double-blind and in a counterbalanced order. On each occasion, subjects performed a road-tracking test beginning 40 minutes after initiation of smoking and repeated one hour later. The test involved maintaining a constant speed at 90 km/h and a steady lateral position between the delineated boundaries of the traffic lane. Subjects drove 22 km on a primary highway and were accompanied by a licensed driving instructor. The primary dependent variable was the standard deviation of lateral position (sdlp), which has been shown to be both highly reliable and very sensitive to the influence of sedative medicinal drugs and alcohol. Other dependent variables were mean speed, and standard deviations of speed and steering wheel angle. Blood samples were taken 10 minutes before the driving tests (i.e. 30 and 90 minutes after initiation of smoking, respectively).


All subjects were willing and able to finish the driving tests without great difficulty. Data from one male subject were excluded from the results because no drug was found in his plasma after smoking.
Figure 1 [absent here] demonstrates that marijuana impairs driving performance as measured by an increase in lateral position variability: all three THC doses significantly affected sdlp relative to placebo<.012, .001 & .001, for the 100, 200 & 300 g/kg conditions, respectively. The Dose by Time effect was not significant indicating that impairment after marijuana was the same in both trials. Marijuana's effects on sdlp were compared to those of alcohol obtained in a very similar study by Louwerens et al. (1987). It appeared that the effects of the various administered THC doses (100-300 g/kg) on sdlp were equivalent to those associated with bacs in the range of 0.03-0.07 g%. Other driving performance measures were not significantly affected by THC. Plasma concentrations of the drug were clearly related to the administered dose and time of blood sampling but unrelated to driving performance impairment. STUDY 2: DRIVING ON A NORMAL HIGHWAY IN TRAFFIC Methods The second driving study was conducted on a highway in the presence of other traffic and involved both a road-tracking and a car-following test. A new group of sixteen subjects, equally comprised of men and women, participated in this study. A conservative approach was chosen in designing the present study in order to satisfy the strictest safety requirements. That is, the study was conducted according to an ascending dose series design where both active drug and placebo conditions were administered, double-blind, at each of three THC dose levels. THC doses were the same as those used in the previous study, namely 100, 200, and 300 g/kg. Cigarettes appeared identical at each level of treatment conditions. If any subject would have reacted in an unacceptable manner to a lower dose, he/she would not have been permitted to receive a higher dose. The subjects began the car-following test 45 minutes after smoking. The test was performed on a 16 km segment of the highway and lasted about 15 minutes. After the conclusion of this test, subjects performed a 64-km road-tracking test on the same highway which lasted about 50 minutes. At the conclusion of this test, they participated again in the car-following test. Blood samples were taken both before the first and after the last driving test (i.e. 35 and 190 minutes after initiation of smoking, respectively). The road-tracking test was the same as in the previous study except for its duration and the presence of other traffic. The car-following test involved attempting to match velocity with, and maintain a constant distance from a preceding vehicle as it executed a series of deceleration/acceleration maneuvers. The preceding vehicle's speed would vary between 80 and 100 km/h and the subject was instructed to maintain a 50 m distance however the preceding vehicle's speed might vary. The duration of one deceleration and acceleration maneuver was approximately 50 seconds and six to eight of these maneuvers were executed during one test, depending upon traffic density. The subject's average reaction time to the movements of the preceding vehicle, mean distance and coefficient of variation of distance during maneuvers were taken as the dependent variables from this. Results All subjects were able to complete the series without suffering any untoward reaction while driving. Data from one female subject were excluded from the results because no drug was found in her plasma after smoking. Road-tracking performance in the standard test was impaired in a dose-related manner by THC and confirmed the results obtained in the previous closed highway study (Figure 2). The 100 g/kg dose produced a slight elevation in mean sdlp, albeit not statistically significant (p.13). The 200 g/kg dose produced a significant (p.023) elevation, of dubious practical relevance. The 300 g/kg dose produced a highly significant (p<.007) elevation which may be viewed as practically relevant. After marijuana smoking, subjects drove with an average speed that was only slightly lower than after placebo and very close to the prescribed level. In the car-following test, subjects maintained a distance of 45-50 m while driving in the successive placebo conditions. They lengthened mean distance by 8, 6 and 2 m in the corresponding THC conditions after 100, 200 and 300 g/kg, respectively. The initially large drug-placebo difference and its subsequent decline is a surprising result. Our explanation for this observation is that the subjects' caution was greatest the first time they undertook the test under the influence of THC and progressively less thereafter. The reaction time of the subjects to changes in the preceding vehicle's speed increased following THC treatment, relative to placebo. The administered THC dose was inversely related to the change in reaction time, as it was to distance. However, increased reaction times were partly due to longer distance (i.e. the longer the distance to the preceding vehicle, the more difficult it is to perceive changes in its speed). Statistical adjustment for this confounding variable resulted in smaller and non-significant increases in reaction time following marijuana treatment, the greatest impairment (0.32 s) being observed in the first test following the lowest THC dose (Figure 3). Distance variability followed a similar pattern as mean distance and reaction time; the greatest impairment was found following the lowest dose. As in the previous study, plasma concentrations of the drug were not related to driving impairment. STUDY 3: DRIVING IN URBAN TRAFFIC Methods The program proceeded into the third driving study, which involved tests conducted in high-density urban traffic. There were logical and safety reasons for restricting the THC dose to 100 g/kg. It was given to a new group of 16 regular marijuana (or hashish) users, along with a placebo. For comparative purposes, another group of 16 regular users of alcohol, but not marijuana, were treated with a modest dose of their preferred recreational drug, ethanol, and again placebo, before undertaking the same city driving test. Both groups were equally comprised of men and women. Marijuana was administered to deliver 100 g/kg THC. The driving test commenced 30 minutes after smoking. The alcohol dose was chosen to yield a bac approaching 0.05 g% when the driving test commenced 45 minutes after onset of drinking. Active drug and placebo conditions were administered double-blind and in a counterbalanced order in each group. Blood samples were taken immediately prior to and following all placebo and drug driving tests (i.e. 20 and 80 minutes after initiation of smoking, or 35 and 95 minutes after initiation of drinking). Driving tests were conducted in daylight over a constant 17.5 km route within the city limits of Maastricht. Subjects drove their placebo and active-drug rides through heavy, medium and low density traffic on the same day of the week, and at the same time of day. Two scoring methods were employed in the present study. The first, a 'molecular' approach adopted from Jones (1978), involved the employment of a specially trained observer who applied simple and strict criteria for recording when the driver made or failed to make each in a series of observable responses at predetermined points along a chosen route. The second, a 'molar' approach, required the driving instructor acting as the safety controller during the tests to retrospectively rate the driver's performance using a shortened version of the Royal Dutch Tourist Association's Driving Proficiency Test. In total, 108 items were dichotomously scored, as either pass or fail. Total test performance was measured by the percentage items scored as 'pass'. Subscores were calculated for vehicle checks, vehicle handling, traffic maneuvers, observation and understanding of traffic, and turning'. This method has been applied previously to show the impairing effects of alcohol and diazepam (De Gier, 1979; De Gier et al., 1981). Results Data from two male subjects in the marijuana group were excluded from the results because neither THC nor THC-COOH was found in their plasma after smoking. Neither alcohol nor marijuana significantly affected driving performance measures obtained by the molecular approach, indicating that it may be relatively insensitive to drug-induced changes. The molar approach was more sensitive. Table 1 shows that a modest dose of alcohol (bac=0.034 g%) produced a significant impairment in city driving, relative to placebo. More specifically, alcohol impaired both vehicle handling and traffic maneuvers. Marijuana, administered in a dose of 100 g/kg THC, on the other hand, did not significantly change mean driving performance as measured by this approach. Subjects' ratings of driving quality and effort to accomplish the task were strikingly different from the driving instructor's ratings. Both groups rated their driving performance following placebo as somewhat better than 'normal'. Following the active drug, ratings were significantly lower (35%, p.009) in the marijuana, but not (5%, ns) in the alcohol group. Perceived effort to accomplish the driving test was about the same in both groups following placebo. Following the active drug, a significant (p.033) increase in perceived effort was reported by the marijuana, but not the alcohol group. Thus, there is evidence that subjects in the marijuana group were not only aware of their intoxicated condition, but were also attempting to compensate for it. These seem to be important findings. They support both the common belief that drivers become overconfident after drinking alcohol and investigators' suspicions that they become more cautious and self-critical after consuming low doses of THC, as smoked marijuana. Drug plasma concentrations were neither related to absolute driving performance scores nor to the changes that occurred from placebo to drug conditions. With respect to THC, these results confirm the findings in previous studies. They are somewhat surprising for alcohol but may be due to the restricted range of ethanol concentrations in the plasma of different subjects. DISCUSSION The results of the studies corroborate those of previous driving simulator and closed-course tests by indicating that THC in inhaled doses up to 300 g/kg has significant, yet not dramatic, dose-related impairing effects on driving performance (cf. Smiley, 1986). Standard deviation of lateral position in the road-tracking test was the most sensitive measure for revealing THC's adverse effects. This is because road-tracking is primarily controlled by an automatic information processing system which operates outside of conscious control. The process is relatively impervious to environmental changes but highly vulnerable to internal factors that retard the flow of information through the system. THC and many other drugs are among these factors. When they interfere with the process that restricts road-tracking error, there is little the afflicted individual can do by way of compensation to restore the situation. Car-following and, to a greater extent, city driving performance depend more on controlled information processing and are therefore more accessible for compensatory mechanisms that reduce the decrements or abolish them entirely. THC's effects on road-tracking after doses up to 300 g/kg never exceeded alcohol's at bacs of 0.08 g%; and, were in no way unusual compared to many medicinal drugs' (Robbe, 1994; Robbe and O'Hanlon, 1995; O'Hanlon et al., 1995). 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 former's users seem better able to compensate for its adverse effects while driving under the influence. Inter-subject correlation's between plasma concentrations of the drug and driving performance after every dose were essentially nil, partly due to the peculiar kinetics of THC. It enters the brain relatively rapidly, although with a perceptible delay relative to plasma concentrations. Once there, it remains even at a time when plasma concentrations approach or reach zero. As a result, performance may still be impaired at the time that plasma concentrations of the drug are near the detection limit. This is exactly what happened in the first driving study. Therefore an important practical implications of the study is that 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. Although THC's adverse effects on driving performance appeared relatively small in the tests employed in this program, one can still easily imagine situations where the influence of marijuana smoking might have a dangerous effect; i.e., emergency situations which put high demands on the driver's information processing capacity, prolonged monotonous driving, and after THC has been taken with other drugs, especially alcohol. Because these possibilities are real, the results of the present studies should not be considered as the final word. They should, however, serve as the point of departure for subsequent studies that will ultimately complete the picture of THC's effects on driving performance. REFERENCES De Gier JJ (1979) A subjective measurement of the influence of ethyl/alcohol in moderate doses on real driving performances. Blutalkohol, 16, 363-370. De Gier JJ, 't Hart BJ, Nelemans FA and Bergman H (1981) Psychomotor performance and real driving performance of outpatients receiving diazepam. Psychopharmacology, 73, 340-347. Jones MH (1978) Driver Performance Measures for the Safe Performance Curriculum. Traffic Safety Center, Institute of Safety and Systems Management, University of South California, Los Angeles, CA (DOT HS 803 461). Louwerens JW, Gloerich ABM, de Vries G, Brookhuis KA and O'Hanlon JF (1987). The relationship between drivers' blood alcohol concentration (bac) and actual driving performance during high speed travel. Pages 183-192 in PC Noordzij and R Roszbach, eds., Alcohol, Drugs and Traffic Safety. Proceedings of the 10th International Conference on Alcohol, Drugs and Traffic Safety. Excerpta Medica, Amsterdam. O'Hanlon JF, Vermeeren A, Uiterwijk MMC, van Veggel LMA and Swijgman HF (1995) Anxiolytics' effects on the actual driving performance of patients and healthy volunteers in a standardized test: an integration of three studies. Neuropsychobiology, 31:81-88. Robbe HWJ (1994). Influence of Marijuana on Driving. PhD thesis,Institute for Human Psychopharmacology, University of Limburg, Maastricht. Robbe HWJ and O'Hanlon JF (1995) Acute and subchronic effects of paroxetine and amitriptyline on actual driving, psychomotor performance and subjective assessments in healthy volunteers. European Neuropsychopharmacology, 5:35-42 Smiley AM (1986). Marijuana: On-road and driving simulator studies. Alcohol, Drugs and Driving: Abstracts and Reviews 2: 121-134. Exposing Marijuana Myths Claim #12 : Marijuana is a Major Cause of Highway Accidents: By Lynn Zimmer, Associate Professor of Sociology, Queens College, & John P Morgan, Professor of Pharmacology, City University of New York Medical School: The Lindesmith Center, 1995 The detrimental impact of alcohol on highway safety has been well documented. Marijuana's opponents claim that it, too, causes significant impairment and that any increase in use will lead to increased highway accidents and fatalities. THE FACTS In high doses marijuana probably produces driving impairment in most people. However, there is no evidence that marijuana, in current consumption patters, contributes substantially to the rate of vehicular accidents in America. A number of studies have looked for evidence of drugs in blood or urine of drivers involved in fatal crashes. All have found alcohol present in 50 percent or more. Marijuana has been found much less often. Furthermore, in the majority of cases where marijuana has been detected, alcohol has been detected as well. (*1) For example, a recent study sponsored by the US National Highway Traffic Safety Administration (NHTSA) involving analysis of nearly 2000 fatal accident cases, found 6.7 percent of drivers positive for marijuana. In more than two-thirds of those, alcohol was present and may have been the primary contributor to the fatal outcome (*2) To accurately access marijuana's contribution to fatal crashed, the positive rate among deceased drivers would have to be compared to the positive rate from a random sample of drivers not involved in fatal accidents. Since the rate of the past-month marijuana use for Americans above the legal driving age is about 12 percent, on any given day a substantial proportion of all drivers would test positive, particularly since marijuana's metabolites remain in blood and urine long after its psychoactive effects are finished. A recent study found that one-third of those stopped for "bad driving" between the hours of 7 p.m and 2 a.m - mostly young males - tested positive for marijuana only. (*3). To be meaningful, these test results would have to be compared to those from a matched control group of drivers. A number of driving simulator studies have shown that marijuana does not produce the kind of psychomotor impairment evident with moderate doses of alcohol (*4). In fact, in a recent NHTSA study, the only statistically significant outcome associated with marijuana was speed reduction. (*5) A recent study of actual driving ability under the influence of cannabis - employing the same protocol used to test impairment-potential of medicinal drugs - evaluated the impact of placebo and three active THC doses in three driving trials, including one in high-density urban traffic. Dose-related impairment was observed in drivers' ability to maintain steady lateral position. However, even with the highest dose of THC, impairment was relatively minor - similar to that observed with blood-alcohol concentrations between 0.03 and 0.07 percent and many legal medications. Drivers under the influence of marijuana also tended to drive more slowly and approach other cars more cautiously While recognising some limitations of this study, the authors conclude that "THC is not a profoundly impairing drug." (*6) Refs: *1 : McBay AJ and Owens SM., "Marijuana and Driving", pp 257-63 in L.S.Harris (ed) Problems of Drug Dependence 1980, Washington, DC: U.S. Government Printing Office (1981): Teale, JD et al., "The Incidmnece of Cannabinoids in Fatally Impaired Drivers: An Investigation by Radioimmunoassay and High Pressure Liquid Chromatography," Journal of the Forensic Science Society 17: 177-83 (1978) *2 Terhune, KW et al., The Incidence and Role of Drugs in Fatally Injured Drivers, Washington DC: Department of Transportation (1994) *3 Brookoff, D et al., "Testing Reckless Drivers for Cocaine and Marijuana", New England Journal of Medicine 331: 518-22 (1994) *4 Kv'alseth, TO, "Effects of Marijuana on Human Reaction Time and Motor Control", Perceptual and Motor Skills 45: 935-39 (1977): Hansteen, RW, et al, "Effects of Cannabis and Alcohol on Automobile Driving and Psychomotor Tracking," Annals of New York Academy of Science 282: 240-56 (1976): Moskowitz, H et al., " Marijuana: Effects on Simulated Driving Performance," Accident Analysis and Prevention 8: 45-50 (1976); Moskowitz H et al., "Visual Search Behaviour While Viewing Driving Scenes Under the Influence of Alcohol and Marijuana", Human Factors 18: 417-31 (1976) *5 Stein, AC et al., A Simulator Study of the Combined Effects of Alcohol and Marijuana on Driving Behavior-Phase II, Washington DC: Department of Transportation (1983) Cannabis makes you a better driver - more evidence Source: 1 The AGE 21 October 1998 pA5; 2. CANBERRA TIMES 21 October 1998 p4 The largest study ever done linking road accidents with drugs and alcohol has found drivers with cannabis in their blood were no more at risk than those who were drug-free. In fact, the findings by a pharmacology team from the University of Adelaide and Transport SA showed drivers who had smoked marijuana were marginally less likely to have an accident than those who were drug-free. A study spokesman, Dr Jason White, said the difference was not great enough to be statistically significant but could be explained by anecdotal evidence that marijuana smokers were more cautious and drove more slowly because of altered time perception. The study of 2,500 accidents, which matched the blood alcohol levels of injured drivers with details from police reports, found drug-free drivers caused the accidents in 53.5 per cent of cases. Injured drivers with a blood-alcohol concentration of more than 0.05 per cent were culpable in nearly 90 per cent of accidents they were involved in. Drivers with cannabis in their blood were less likely to cause an accident, with a culpability rate of 50.6 per cent. The study has policy implications for those who argue drug detection should be a new focus for road safety. Dr White said the study showed the importance of concentrating efforts on alcohol rather than other drugs. This information was posted by the library of The Alcohol and other Drugs Council of Australia (ADCA). Requests for copies of newsclips can be directed to the library by phone 02 62811002, fax 02 6282 7364 or e-mail To subscribe to this listserv, send the message "subscribe update" (without the inverted commas) in the text field to with the subject field left empty.

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