Communiqué 05.07.2002

Publié par : ASAC.
TSR ‘Mise au point’ du 16 juin 2002
VIOLATION DE LA CONCESSION

Une plainte contre la TSR a été déposée auprès de l’ombudsman par l’Association Suisse des Amis/es du Chanvre (ASAC).  Il est reproché à la TSR d’avoir violé la concession, laquelle exige que les données et affirmations portées à l’antenne correspondent à la vérité. Or, tel n’est pas le cas pour l’émission objet de la présente.

En effet, l’émission ‘Mise au point’ du 16 juin 2002 fait dire tant par le présentateur Patrick Fischer que par la journaliste menant enquête, Eva Ceccaroli, que « la drogue est présente dans un accident mortel sur quatre ». Suit une image montrant en gros plan un objet qu’il convient d’appeler une cigarette de chanvre, ce qui ne laisse aucun doute quant à la marchandise dont il est question. Cela donne à croire que le cannabis est la cause, ou une des causes d’un accident  mortel sur quatre. La primauté du cannabis dans les accidents mortels dont il est question est soulignée par l’affirmation suivante: « On retrouve des traces de stupéfiants, le plus souvent du cannabis et de la cocaïne, chez les personnes impliquées dans des accidents mortels ». D’autres affirmations, telles que « Drogue au volant, mort au tournant » et « La drogue au volant fait toujours plus de ravages» renforcent l’impression de danger inhérent au cannabis en relation avec la circulation routière.

Or, il n’y a eu en Suisse, depuis ces trente dernières années qu’une large frange de la population suisse consomme du chanvre (cannabis) et conduit, aucun accident, ni mortel ni de conséquences sérieuses, qui ait de façon avérée été causé par la consommation de chanvre. La conduite sous l’effet du chanvre, au contraire, réduit les risques d’accident, puisque le conducteur circule alors plus lentement que d’habitude. C’est ce que démontrent toutes les études effectuées à ce jour  (voir ci-dessous). L’émission en question ne fait d’ailleurs état concrètement d’aucun accident dû au chanvre, à bonne raison, puisqu’il n’en existe aucun.

L’émission en question prolonge une campagne apparue depuis deux ou trois mois dans la presse écrite, inspirée par une poignée de personnes en Suisse, celles justement interviewées en l’émission en question, et qui font croire à un danger, par ailleurs inexistant, de la consommation de chanvre au volant. L’émission est un appel à l’hostilité envers les consommateurs de chanvre et comme elle n’a aucun fondement objectivement vrai, elle est à considérer comme une mise à disposition du service public qu’est la TSR pour une action de propagande mensongère en tous points de vue contre le chanvre.

ASAC





1) L’étude  -commandée par le ministère nord-américain des transports et réalisée sur routes normales aux Pays-Bas- démontre de façon irréfutable que la conduite sous l’influence du chanvre n’est en aucune façon source de risques, car les réflexes ne sont que peu affectés. Le chanvre, au contraire de l’alcool qui augmente l’agressivité et porte l’automobiliste à augmenter la vitesse, fait prendre conscience d’une (légère) diminution des réflexes, de sorte que l’automobiliste se montre prudent et réduit sa vitesse.


 


Marijuana use and driving


Hindrik W.J. Robbe


Institute for Human Psychopharmacology, University of Limburg,
P.O. Box 616, 6200 MD Maastricht, The Netherlands





Robbe, Hindrik W.J. , 1994. Marijuana use and driving. Journal of the International Hemp Association 1: 44-48.


This article concerns the effects of marijuana smoking on actual driving performance. It presents the major results of one laboratory and three on-road driving studies. The latter were conducted on a closed section of a primary highway, on a highway in the presence of other traffic and in urban traffic, respectively. This program of research has shown that marijuana produces only 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 into their performance and will compensate where they can (e.g., by increasing distance between vehicles or increasing effort).  As a consequence, THC’s adverse effects on driving performance appeared relatively small in the tests employed in this program.





Introduction


After alcohol, delta-9-tetrahydrocannabinol (THC), marijuana’s major psychoactive constituent, is the drug which is found most often in the blood of drivers involved in road accidents. With some exceptions, epidemiological studies indicate the presence of THC in roughly 4-12% of drivers injured or killed in traffic accidents: for example, 10% in New York (Terhune 1982), 7% in New South Wales (Chesher and Starmer 1983), 8% in North Carolina (Mason and McBay 1984), 11% in DŸsseldorf (Daldrup et al. 1987), 10% in Tasmania (McLean 1987) and 11% in Ontario (Cimbura et al. 1990). The most recent data regarding the incidence of drugs in fatally injured drivers in the United States are available from a nationwide study conducted in 1990 and 1991 (Terhune et al. 1992): THC was found in only 4% of the drivers. This relatively low percentage may indicate a declining trend in the incidence rate of THC in fatally injured drivers in the United States, explainable by the declining prevalence of marijuana use throughout the 1980s (Johnston et al. 1992).


These numbers are, however, inconclusive regarding THC’s contribution to accidents because alcohol has been a severe confounding factor in all surveys of injured or killed drivers: generally 60-80% of drivers who were found positive for THC also showed the presence of alcohol. Another problem of these surveys is the common lack of sound control groups. To determine whether drivers under the influence of THC are overrepresented in accidents, the THC incidence in accident victims should be compared to the THC incidence in randomly selected drivers passing the same accident site at the same times and days of the week. This has been done for alcohol (Borkenstein et al. 1974), but not for THC.


The lack of separate control groups has been circumvented by the use of a ‘culpability index’. This index is the ratio of the percentage of drivers with detectable drug levels and deemed responsible for a traffic accident to that of drug-free drivers from the same sample who were likewise culpable. But results from this approach have not been consistent: three studies yielded a culpability index of about 1.7 (Warren et al. 1981, Terhune 1982, Donelson et al. 1985), two other studies failed to find a significantly elevated culpability index for marijuana users (Williams et al. 1985, Terhune et al. 1992). For this and other reasons given above, the independent contribution of THC to accidents remains exceedingly obscure. Several literature reviews, the most recent by Robbe (1994), have shown that the results from driving simulator and closed-course tests indicate that THC in inhaled doses up to 250 µg/kg has relatively minor effects on driving performance, certainly less than blood alcohol concentrations (BACs) in the range 0.08-0.10 g%. In contrast to this, laboratory studies have repeatedly shown performance impairment occurring after inhaled doses as low as about 40 µg/kg. These became large and persistent after 100-200 µg/kg doses. Tracking, divided attention and vigilance test performance were particularly vulnerable to THC’s effects. Assuming that both sets of results are valid for the particular circumstances under which they were obtained, they demonstrate that performance decrements obtained under the artificial and non-life threatening conditions in the laboratory do not automatically predict similar decrements in driving simulations that are closer to real-world driving. These conflicting results led, however, to opposing opinions regarding marijuana’s effects on driving performance. Real-world driving studies were therefore warranted.


Only one study (Klonoff 1974) had been conducted in actual traffic before the present research program started. In a city driving study, Klonoff assessed the effects of two THC doses, 4.9 and 8.4 mg, which are equivalent to 70 and 120 µg/kg for a 70 kg person. Aspects of subjects’ driving performance were scored by a professional examiner. The results showed that subjects performed less competently when under the influence of the highest, but not the lowest dose. In particular, they scored lower on judgment and concentration scales. Several investigators, however, criticized the method used by Klonoff for measuring driving performance on the grounds that the examiners’ reliability was never determined and that the scoring instrument had never been shown to provide measures related to driving safety (Moskowitz 1985, Smiley 1986). Furthermore, Klonoff administered relatively low THC doses to his subjects. The effects of high doses of THC on driving in real traffic still needed to be determined.


The studies reported in this article were conducted to escape these limitations. First, the effects of low, moderate and high THC doses on highway driving were determined, both in the absence and presence of other traffic. Second, Klonoff’s city driving study was replicated, with some modifications with regards to the employed procedures and with the addition of another group of subjects who undertook the same driving test but then under the influence of a low dose of alcohol.


An important practical objective of the program was to determine whether degrees of driving impairment can be accurately predicted from either measured concentrations of THC in plasma or performance measured in potential roadside ‘sobriety’ tests of tracking ability or hand and posture stability. The results (Robbe 1994), like many reported before, indicate that none of these measures accurately predicts changes in actual driving performance under the influence of THC.


General procedures


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 using a Lion-SD3 breath-analyzer.


Subjects were accompanied during every driving test by an licensed driving instructor. A redundant control system in the test vehicle was available for controlling the car, should emergency situations arise.


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.


Pilot study


Methods


The pilot study was conducted in a hospital under strict medical supervision to identify THC doses that recreational marijuana users were likely to consume before driving. Twenty-four subjects, twelve males and twelve females, participated. They were allowed to smoke part or all of the THC content in three cigarettes until achieving the desired psychological effect. Cigarettes were smoked through a plastic holder in a manner determined by the subjects. 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.


Results


Six subjects consumed one cigarette, thirteen smoked two and four smoked three. The average amount of THC consumed was 20.8 mg, after adjustment for body weight, 308 µg/kg. It should be noted that the amounts of THC consumed 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 µg/kg. This is considerably higher than doses that have usually been administered to subjects in experimental studies (typically, 100­200 µg/kg THC).


Study 1: Driving on a restricted highway


Methods


The first driving study was conducted on a highway closed to other traffic. One objective of this study was to determine whether it would be safe to repeat the study on a normal highway in the presence of other traffic. The second objective was to define the dose-effect relationship between inhaled THC dose and driving performance. 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 µg/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, developed and standardized by O’Hanlon et al. (1982, 1986), 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 drugs and alcohol. Other dependent variables were mean speed, and standard deviation of speed and steering wheel angle.


Results


All subjects were willing and able to finish the driving tests without great difficulty. The study demonstrated that marijuana impairs driving performance as measured by an increase in SDLP; all three THC doses significantly affected SDLP relative to placebo. The driving performance decrement after smoking marijuana persisted almost undiminished for two hours after smoking. Marijuana’s effects on SDLP were compared to those of alcohol obtained in a very similar study by Louwerens et al. (1985, 1987). It appeared that the effects of the various administered doses of THC (100­300 µg/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. Both the observed degree of driving impairment, and what subjects said and did, indicated that normal safeguards would be sufficient for ensuring safety in further testing. Hence, the final conclusion was to repeat this study on a normal highway in the presence of other traffic.


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 µg/kg. Cigarettes appeared identical at each level of treatment conditions. If any subject had 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 16Êkm stretch 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.


The road-tracking test was the same as in the previous study except for its duration and the presence of other traffic. Subjects were instructed to maintain a constant speed of 95Êkm/h and a steady lateral position between lane boundaries in the right traffic lane. They were allowed to deviate from this only if it became necessary to pass a slower vehicle in the same lane. Data from the standard test were analyzed to yield the same performance measures as in the previous study.


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. 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. The 100 µg/kg dose produced a slight elevation in mean SDLP, albeit not statistically significant. The 200 µg/kg dose produced a significant elevation, of dubious practical relevance. The 300 µg/kg dose produced a highly significant elevation which may be viewed as practically relevant but unexceptional in comparison with similarly measured effects of many medicinal drugs. After marijuana smoking, subjects drove with an average speed that was only slightly lower than after a placebo and very close to the prescribed level.


In the car-following test, subjects maintained a distance of 45­50 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 µg/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. 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. Distance variability followed a similar pattern as mean distance and reaction time; the greatest impairment was found following the lowest dose.


Study 3: Driving in urban traffic


Methods


The program proceeded to 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 µg/kg. It was given to a group of regular marijuana (or hashish) users, along with a placebo. For comparative purposes, another group of regular alcohol users was treated with a modest dose of its members’ preferred recreational drug, ethanol, or a placebo, before undertaking the same city driving test. Two groups participated, each composed of sixteen new subjects comprising equal numbers of men and women. Subjects in the alcohol group were regular users of alcohol, but not marijuana. Both groups were treated on separate occasions with the active drug and a placebo. Marijuana was administered to deliver 100ʵg/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.


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 ‘molar’ approach, required the driving instructor acting as the safety controller during the tests to rate the driver’s performance retrospectively using a standard scale. The second, a more ‘molecular’ approach, 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.


Results


The study showed that a modest dose of alcohol (BAC = 0.034 g%) produced a significant impairment in city driving, as measured by the molar approach, relative to a placebo. More specifically, alcohol impaired both vehicle handling and traffic maneuvers. Marijuana, administered in a dose of 100ʵg/kg THC, on the other hand, did not significantly change mean driving performance as measured by this approach. 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.


Driving quality, as rated by the subjects, contrasted with observer ratings. Alcohol impaired driving performance according to the driving instructor, but subjects did not perceive it; marijuana did not impair driving performance, but the subjects themselves perceived their driving performance as such. Both groups reported about the same amount of effort in accomplishing the driving test following a placebo. Yet only subjects in the marijuana group reported significantly higher levels of invested effort following the active drug. 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.


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 µg/kg has significant, yet not dramatic, dose-related impairing effects on driving performance. 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 SDLP, 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 after doses up to 300 µg/kg never exceeded alcohol’s at BACs of 0.08 g% and were in no way unusual compared to many medicinal drugs (Robbe 1994). 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.


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.

                                         




2) L’étude australienne dit que la consommation de chanvre (indien)augmente le sens de la responsabilité du conducteur  et peut donc être considéré comme un facteur de sécurité accrue dans le trafic automobile. 


 


Drugs and Accident Risk in Fatally-Injured Drivers


Olaf H. Drummer, Ph.D.


Victorian Institute of Forensic Pathology, Department of Forensic Medicine, Monash University, 57-83 Kavanagh Street, South Melbourne 3205, Australia


ABSTRACT


Risk analysis studies to investigate the contribution of drugs to accident causation are limited. We have used a method based on establishing the responsibility of a driver to investigate the involvement of drugs other than alcohol in 1052 fatally injured drivers. The proportion of drivers deemed to be responsible in a drug-free group were compared to drivers with target drugs found in their blood stream.


Drugs (including alcohol) were detected in 49% of the drivers. Alcohol was detected in 36% of the cases, whilst drugs were detected in 22%. 13% had only drugs detected. The remaining 9% of the population involved a combination of drugs and alcohol. The order of prevalence of drugs were marijuana (112 cases), amphetamines and related stimulants (35), benzodiazepines (34) and opiates (34).


Drivers in whom only opiates were detected had an odd’s ratio of 2.4, whilst marijuana cases provided a relative risk of 0.6. Drivers in whom stimulants were detected gave an odd’s ratio of 1.4 whilst benzodiazepines gave an odd’s ratio of 1.0. By contrast the odd’s ratio for alcohol was 6.8.


Drivers with higher than therapeutic concentrations detected represented 22 drivers (2.1%). Most of these drivers were found to be culpable. Multiple drug cases also tended to be culpable. The culpability rate in this group was 89% compared to 70% in drug-free drivers.


These data show that only a small proportion of impaired drivers are drug effected, the remainder being impaired by alcohol. The relative risk for psychoactive drugs is also not uniform, with marijuana use providing the least effect on risk, whilst opiate use seems to provide the largest increase in risk compared to the other drug groups studied.


INTRODUCTION


While certain psychoactive drugs other than alcohol can adversely affect driving skills in simulated studies, epidemiological risk analysis data which provides an assessment of the contribution, of specific drugs or drug classes to accident causation is limited. The effect of benzodiazepines and minor tranquillisers on accident risk are uncertain [Skegg et al, 1979; Jick et al, 1981; Lagier et al, 1993], while the effects of THC appears to be slight or even protective [Terhune et al, 1992; Williams et al, 1985]. Assessment of risk for other drugs or drug groups has not been studied in any detail.


We have used a method based on establishing the responsibility of a driver using strict scoring guidelines [Robertson & Drummer, 1994]. We have used this


DISCUSSION


The use of responsibility rates of drivers has been used to establish that alcohol increases accident risk [Terhune et al, 1992; Williams et al, 1985]. This is again confirmed in this study. The prevalence of alcohol at over 30% in the Australian fatally-injured driver population reinforces the magnitude of alcohol-related trauma which still exist on Australian roads.


The contribution of drug use on road trauma and accident risk is less well defined. While most common drug type detected were the illegal drugs, marijuana, certain stimulants and certain opiates, their effect individually and collectively were small compared to alcohol.


Drivers with higher than therapeutic drug concentrations and drivers involving multiple drug use tended to be responsible. If cases involving alcohol were excluded, then such cases represented 2.6% of the driving population. This contrasts to ~30% of the population involving alcohol over 0.05 gram/100 mL (general legal limit in Australia).


It was of some interest that cannabis tended to show a negative effect on relative risk when other drug groups showed an increase. This phenomenon has also been seen elsewhere [Terhune et al, 1992; Williams et al, 1985]. The most likley reason probably relates to the over compensation of marijuana-using drivers on their driving skills. Over compensation may be caused simply by slowing down and avoiding adverse driving situations. These observations do not seem to be related to whether delta-9-THC or 11-carboxy-THC are measured in blood [Terhune et al, 1992; Williams et al, 1985].


In conclusion, these findings show that the contribution of drugs to accident causation is much lower than for alcohol. While more cases are required before any definitive conclusions can be made on the effect of specific drug types on driving risk, cases involving multiple drug use and higher than therapeutic drug concentrations tended to be culpable in fatal accidents.


ACKNOWLEDGMENTS


There were many persons and/or organisations who provided valuable assistance to various parts of this project;. Ms. Lynette Kornmehl; Ms Maryanne Maisey; the staff of the Victorian Institute of Forensic Pathology and the State Coroners Office; Dr. Phillip Swann of Vic Roads; members of the Advisory Group on Drugs and Driving (AGODD); Dr. Peter Vulcan of the Accident Research Centre, Monash University; NSW State Coroners; staff of the NSW Institute of Forensic Medicine; staff of the NSW Division of Analytical Laboratories; Dr. David Saffron of the Road Safety Unit of the NSW Roads and Traffic Authority; the Federal Office of Road Safety; WA Police; the WA Coroner; staff of the Toxicology Section of the Western Australian Department of Mines, and Professor John McNeil and Dr. Andrew Forbes of the Department of Social and Preventative Medicine, Monash University.





                                  


3) L’étude commandée par le ministère britannique des transports démontre que les automobiliste sous l’influence de la ‘marijuana’ (chanvre indien) savent très bien compenser la (légère) diminution de réaction par une conduite moins rapide et plus concentrée, ce qui élimine les risques d’accident.


 


Department for Transport


The Influence of Cannabis on Driving






by

B F Sexton, TRL
R J Tunbridge, TRL
N Brook-Carter, TRL
P G Jackson, DETR Road Safety Division
K Wright, University of Birmingham
M M Stark, St George’s Hospital Medical School
K Englehart, Principal Police Surgeon, Surrey.


Executive Summary


Introduction


Results from the study of the “Incidence of alcohol and drugs in road accident fatalities” have consistently shown a large increase in the incidence of drugs in fatal road casualties (drivers, riders, passengers and pedestrians) since the last comparable study in the mid-1980s. The latest results show that among all road users traces of illicit drugs were present in 18% of fatalities. These figures represent a six-fold increase in presence of illicit drugs when compared with the previous study. Cannabis constitutes around two thirds of the illegal drugs found.


Despite the increase in the incidence of drugs, it is not possible to say that drugs caused these deaths. There may be an association, but presence cannot be taken as evidence of causation – there is no way of telling how much was consumed and how long before the fatal accident. So far as cannabis is concerned, the prevalence in drivers was not significantly different from that of passengers, who can be taken as a (albeit imperfect) measure of the prevalence in the population as a whole. However, cannabis remains detectable in the body for up to four weeks after use – long after any impairment of driving.


In addition, in most surveys reported in Europe cannabis is the most frequently detected illicit drug. In a range of accident involved populations cannabis is found with an incidence between 2 and 12% with a mode incidence around 5-8%. This is certainly significantly above that of any other illicit drug.


Previous research studies on cannabis and driving have focussed largely on the effects of cannabinoids on driving performance. These studies have been almost exclusively experimental, involving laboratory tasks, driving simulator and on road ‘real driving’ experiments. A much smaller number of studies have attempted to gain broader sociological information about driving habits under the influence of cannabis and what factors influence the decision to drive. This research attempted to combine these two aspects, certainly for the first time in the UK, with a view to assessing the degree to which there may be a problem with cannabis in relation to driving. The research had three primary objectives:


·        To provide reliable data, under laboratory conditions, on the impairing effects of cannabis on driving.


·        To determine the duration and extent of any impairment under different degrees of intoxication (using different levels of cannabis).


·        To provide an overview of attitudes and habits of cannabis users in relation to driving and explore factors which may influence the decision to drive under its influence.


The research attempted to address these objectives using experienced cannabis users carrying out a variety of laboratory-based tasks and driving in a simulator under four cannabis conditions: placebo; low THC; high THC; and cannabis resin. The placebo, low and high dose THC conditions used herbal cannabis (‘grass’) cigarettes supplied by the National Institute on Drug Abuse (NIDA), while the cannabis resin condition used cannabis supplied by Customs and Excise from seized supplies.


In 1999 the DETR commissioned a review of the latest evidence of the impairment effects of cannabis. That report provided an overview of the effects of cannabis on driving and accident risk and identified key research questions for areas where current knowledge was deemed to be insufficient to guide road safety policy. These research questions have shaped and informed the current research project. In addition to the primary objectives outlined above, the research reported here sought to inform four key issues identified by the review.


These were: exposure; biological response; acute psychomotor response; and driving response.


i) Exposure
Prior to this research, few studies have attempted to gain broader sociological information about driving under the influence of cannabis. A comparison between the participants in the current study and a group of regular users in the West Midlands showed the trial group to be fairly typical. Both groups showed a reluctance to drive after consuming more than 4 units of alcohol, believing their driving to be significantly impaired. The majority of both groups again thought that cannabis impaired their driving, but only to a slight degree.


ii) Biological Response
In considering the results of the present study, the biological response of the participants to the consumption of cannabis is of fundamental importance. Urine was screened on arrival to check for and exclude multiple drug use.


Blood and saliva measurements were taken immediately prior to dosing and at 10 and 30 minutes post dosing. The subjective reports given by the participants of the effects of smoking the various strengths of cannabis cigarettes showed an extremely good correlation between what participants thought they had smoked and the THC dosage in the cigarettes. The maximum amounts of THC administered were around 10mg for the low dose and 20 mg for the high and the majority of participants were able to distinguish between the effects of these doses and placebo. The subjective feelings of the “highs” experienced were also closely correlated with the participants “liking” of the smoking effect as stated in the mood questionnaire. Making allowance for the experimental situation, the majority of participants also found the experience of smoking cannabis similar to their normal experience.


iii) Acute Psychomotor Response and Tests of Impairment
It is of the utmost importance to try to relate the observations derived from this experimental study to the situations likely to be encountered in real life drug driving cases. Part of the experimental procedures therefore included the formal sobriety testing of participants. Two registered medical practitioners (experienced Forensic Medical Examiners (FMEs)) examined the participants and carried out a comprehensive physical examination to see whether the suggested standard “impairment” tests currently used were effective in detecting impairment due to cannabis.


The results of the sobriety testing clearly show a strong correlation between cannabis dose received and whether impairment was judged to be present. In total, 56 assessments were performed on the 15 participants at the various dose levels. In 7 cases on high dose and 3 cases on low dose impairment was judged to be present, but no cases on placebo. In assessments where a condition was judged to be due to a drug 30 had received one of the three cannabis dose levels and only 2 were placebo conditions. On the basis of these observations, the general medical examination and standardised impairment testing applied by the FMEs were judged to be effective in determining both impairment and establishing condition due to a drug. There was also a strong relation between the FME’s decision regarding the participant’s impairment and the participant’s subjective rating, which formed part of the mood questionnaire.


These results are important for two reasons. First, they offer strong support for the validity of the FME’s decisions and for the effectiveness of the sobriety tests as detectors of impairment. Second, they offer further support for the view that, under the influence of cannabis, users are acutely aware of their impairment.


It is also interesting to note that, despite participants having smoked some form of cannabis before 42 of these examinations, on only 11 occasions did the FME consider the participant to be impaired. This finding could have implications for the number of cases that will be detected by the Field Impairment Testing recently launched in the UK by the police.


In addition to the general medical examination, pupil size was measured using a Pupillometer, supplied by Procyon Ltd. The Pupillometer showed a significant increase in pupil sizes 25-30 minutes after dosing. The difference was statistically significant for the placebo v high dose and the placebo v low dose. This suggests that this measure may be helpful in assessing if a person has recently smoked and may be impaired through cannabis, although this would require a baseline and an ‘impaired condition’ measure to be useful.


iv) Driving Response
The final key objective of the study was to consider the effects of cannabis on driving response. Statistically significant results, which have been found for the simulator-derived measures, are given in the report. There was a reduction of average speed on the motorway when participants had the high or low doses of cannabis. This confirms the results from many previous studies. It strongly suggests that the participants as drivers are aware of their impairment, but attempt to compensate by driving more cautiously. Participants did not know what strength of cannabis they had received, but knew there was a likelihood of having had something ‘active’ and so were perhaps being more careful. A post trial survey of participants showed that they were very good at guessing when they had taken the placebo dose and most participants even managed to correctly guess if they had the low dose or high dose.


In the simulator trials, participants reacted more slowly to a pulling-out event when they had taken the low dose of cannabis, suggesting a similar compensatory action for the effects of cannabis impairment. However, when taking the high dose this effect was not significant. This is probably due to the variability in the response data.


Similarly, there was no significant difference between braking reaction times. The mean response times increased slightly, but there was too much variability in the data for this to be statistically significant. This variability in the results when considering the impairing effects of cannabis has been observed by other researchers. The variability of drug effects on individuals is well recognised and this seems to be even more in evidence with cannabis than with other drugs.


When considering the simulator tracking tasks, participants tended to drive less accurately on the left and right loops of the ‘figure of eight’ when they had been on the high cannabis dose. There was also a significant increase in their Standard Deviation of Lateral Position (SDLP) on the right loop when on the high dose as compared to the low dose of cannabis. This suggests that they were unable to control their steering as well when under the influence of the high cannabis dose. This again confirms previous observations that cannabis adversely affects drivers’ tracking ability.


The mean time to move from stationary at a traffic light controlled junction once the lights had turned to red/amber on the driving simulator produced an interesting result. This was significantly reduced with high cannabis dose level, the reduction was in the order of ½ second between the placebo condition and high dose condition, and slightly less from the low dose to high dose. There are a number of possible explanations for this. It may suggest that in the “observational” conditions of the driving simulator participants were aware of missing the traffic light change and so reacted slightly more quickly. Alternatively, the effects on the participants’ internal clocks might have made them feel that they had been at the lights longer than they actually had and therefore heightened their attention to the imminent change in lights. It has been suggested that cannabis, in a similar way to alcohol at low doses, can have a stimulant effect on dopamine that may account for more risky behaviour in some circumstances. Other explanations are possible, however, and further assessment of this observation will be required.


The hazard perception (HP)[1] task did not produce any statistically significant results. Although reaction times were found to increase with dose level, there was too much variability in the data for statistical significance. An increase of 0.08 seconds between the placebo and low dose and an increase of 0.14 seconds between the placebo and high dose was observed. This suggests that there may be an effect on the reaction time of participants responding to hazards, but it is quite a small effect which would require a much larger sample to determine whether or not it was statistically significant. This would also seem to confirm earlier observations of the effects of cannabis on the various aspects of driver performance; the effect on reaction time being somewhat indeterminate.


The mean tracking accuracy on the Compensatory Tracking Task (CTT) decreased with increasing level of dose. The placebo tracking accuracy was higher than either the high dose or resin tracking accuracy. Thus tracking accuracy does change with dose. The proportion of correct trials also decreased with increasing dose level. All participants were still quite accurate, but the difference from 99.5% accuracy when on placebo was statistically significantly different from the 97.0% accuracy when on the high dose. The HP and CTT results are of particular interest because the HP test was taken at least 75 minutes post smoking the cannabis, and the CTT test at least 85 minutes post dosing. Some of the acute impairment effects may well have diminished by then.


In summary, the results of this study show a broad consistency with the effects of cannabis on driver performance observed by previous researchers. In addition, the habits and attitudes of cannabis users in relation to driving have been explored for the first time in the UK.


Conclusions


The research has demonstrated the practicability of assessing the influence of cannabis on driving performance in a controlled clinical trials experimental situation. Participants were recruited, medically screened and tested under conditions of a strict protocol that had local ethics committee approval.


The maximum amounts of THC administered in the cannabis cigarettes were shown to be typical of that available with ‘street’ cannabis. Participants were generally able to distinguish between the effects of cannabis with active THC and placebo conditions. The subjective reports of smokers on the effects of smoking the various strengths of cannabis cigarettes showed an extremely good correlation between what participants thought they had smoked and the THC dosage in the cigarettes.


The feelings of the “highs” experienced were also closely correlated with participants’ positive reactions as measured by a mood questionnaire. Given the controlled conditions of the experimental situation, the majority of participants also found the experience of smoking cannabis similar to their normal experience.


Previous studies have shown that simulated and actual driving and divided attention tasks which all require integrative mental processes are severely affected by alcohol. Simple attention / vigilance tasks are not so much affected and psychomotor skills, especially tracking, and simple reaction time tasks are only affected at relatively high blood alcohol levels. Alcohol may, therefore, be seen as first disturbing higher cognitive processes, especially those that require integrative performances. Compared to those effects, the losses in psychomotor skills and simple attentional processes are much smaller. In contrast, previous studies with cannabis show that it first seems to affect all tasks requiring psychomotor skills and continuous attention. Thus, tracking tasks, which are very sensitive to short term changes in attention, are very sensitive to cannabis impairment. On the other hand, integration processes and higher cognitive functions are not as time critical. A short attention lapse can be compensated for by increased activity later.


In the case of the overall driving task, it seems that the negative effects of these short-term distortions can be reduced by lowering the difficulty, and hence the time critical aspects, of the task. This would explain the frequently reported observation that drivers under the influence of cannabis drive at notably reduced speeds.


Results from the current study using the TRL driving simulator confirm the results from these previous studies. There was a reduction of average speed on simulated motorway driving when participants had the high or low doses of cannabis. This strongly suggests that the participants as drivers are aware of their impairment, but attempt to compensate by driving more cautiously.


When considering the simulator tracking tasks, participants tended to drive less accurately on the left and right loops of the ‘figure of eight’ when they had been on the high cannabis dose. This suggests that they were unable to control their steering as well when under the influence of the high cannabis dose. This again confirms previous observations that cannabis adversely affects drivers’ tracking ability.


There is variability in the results when considering the impairing effects of cannabis that has been observed by other researchers. The variability of drug effects on individuals is well recognised and this seems to be even more in evidence with cannabis than with other drugs. The failure to produce significant results on various driving performance measurements when compared to alcohol may be explained by the more variable effects of cannabis on participants.


The results of the driving related laboratory tests conducted in general did not produce statistically significant results. Although reaction times were found to increase with dose level, there was too much variability in the data for statistical significance. This suggests that there may be an effect on the reaction time of participants responding to hazards, but it is quite a small effect which would require a much larger sample to determine whether or not it was statistically significant. This again confirms earlier observations of the effects of cannabis on the various aspects of driver performance; the effect on reaction time being somewhat difficult to predict.


The general medical examination and standardised impairment testing applied by the FMEs were judged to be effective in determining both impairment and establishing condition due to a drug. Preliminary conclusions were drawn by the FMEs on the number and combination of impairment test failures which would allow a conclusion that the driver was “impaired”. Further refinement and calibration of these techniques in the field, for use by both police officers and FMEs, is however desirable and is planned.


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 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 on 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.


A copy of the full TRL Report, TRL477 (price at publication £50), may be obtained from: TRL Publications Sales by telephone on 01344 770783 or by writing to: TRL Limited, Publication Sales, PO Box 303, Wokingham, Berkshire RG45 6YX.m 


Published 15 December 2000






 


4)  La consommation de chanvre peut être un facteur de plus grande sécurité dans le trafic routier, tel est le message paru dans le quotidien australien “The Advertiser” du  31 octobre 2001


 


No Proof Cannabis Put Drivers At Risk