ReviewInternational approaches to driving under the influence of cannabis: A review of evidence on impact
Introduction
For decades, alcohol has been recognized as the psychoactive drug that is most associated with impaired driving. In recent years, increasing attention is being paid to other drugs and impaired driving, and accompanying legal and public health implications. Among illicit drugs, cannabis is the most commonly consumed in the world, although the prevalence of cannabis use is not evenly distributed as some regions, such as North America, report much higher usage rates than others (Degenhardt et al., 2008, UNODC, 2015, WHO, 2016). Furthermore, the legality of cannabis is shifting, as varied jurisdictions have legalized cannabis or are debating how to implement regulated cannabis markets, despite international drug treaties (Bewley-Taylor et al., 2016; Hall and Lynskey, in press). In the United States, for example, four states have legalized cannabis for recreational use, while 23 states have approved cannabis for medical use (Huestis, 2015). Given these shifts, legal and policy responses to driving under the influence of cannabis (DUIC) are also evolving and generating increasing public interest. Thus it is presently an important time to review literature on such responses, especially as there are gaps in our knowledge regarding the effectiveness of different approaches designed to prevent, deter, and reduce any potential harms associated with DUIC.
General deterrent approaches to impaired driving aim to dissuade the public or subgroups of people who may not have performed the behaviour, while specific deterrent approaches target those who have performed the behaviour or have been apprehended (Krismann et al., 2011). Efforts to prevent DUIC can reasonably be guided by and compared to approaches to prevent driving under the influence of alcohol (DUIA). Initial understanding of the effects of alcohol on basic driving skills and collision risk (e.g., Bjerver and Goldberg, 1950, Holcomb, 1938, Smith and Popham, 1951) led to the development of methods to assess the level of alcohol in the body, legal frameworks designed to achieve general deterrence, and educational and specific deterrent measures designed to reinforce the general deterrent impact of drinking-driving laws. Behavioural impairment laws, requiring assessment of behavioural symptoms of impairment, were implemented in many jurisdictions. However, it was not until the development and introduction of per se laws in the Scandinavian countries and subsequently in most other parts of the world − implemented through criminal or administrative law with the ability to make the probability of detection, apprehension, and sanctioning relatively swift and certain − that substantial reductions in rates of drinking-driving deaths (i.e., general deterrence) were observed (e.g., Byrne et al., 2016, Homel, 1994, Mann et al., 2001, Ross, 1973, Tippetts et al., 2005, Voas and Lacey, 1990). Per se laws that address DUIA set fixed limits for alcohol detected in the driver’s system (e.g., blood alcohol concentration [BAC] of 0.05%). Over the past few decades, per se laws, combined with public education and high-visibility enforcement, have been considered the cornerstones of effective general deterrence of DUIA, while behavioural impairment laws by themselves have been considered largely ineffective in achieving general deterrence (Mann et al., 2001, Voas and Lacey, 1990). Additionally, effective rehabilitative programs and incapacitative measures such as ignition interlock programs have added to the ability to reduce driver recidivism (i.e., specific deterrence) and thus to the overall impact of DUIA laws (Elder et al., 2011, Ma et al., 2015).
A central question for stakeholders and policymakers is the extent to which successful means to address DUIA are transferrable to DUIC. For example, can a per se or hybrid approach (e.g., behavioural impairment plus per se limits) similar to how many countries have addressed DUIA be effectively transferred to DUIC (e.g., Huestis, 2015, Solomon and Chamberlain, 2014)? Among many complicating factors is that cannabis has a very different pharmacological profile than alcohol. The main psychoactive component of cannabis is delta-9-tetrahydrocannabinol (THC) and, although it can have a shorter detection window, its metabolites (namely, carboxy THC or THC-COOH) can be detected in blood or urine for many days after cannabis use, long after any signs of impairment (Bergamaschi et al., 2013, Wolff et al., 2013).
As more jurisdictions consider legal initiatives to address DUIC, and also other drugs and driving, there is increasing interest in the relevant research and questions regarding the impact of cannabis use on collision risk, whether there should be a THC legal limit or per se level for drivers, and impact of DUIC laws on road safety. In this paper, we provide an overview of DUIC and international approaches to this issue, and contribute to the literature a comprehensive review of evaluations of the impact of varied countermeasures.
Section snippets
Methods
Systematic searches to identify literature on evaluations of DUIC countermeasures were performed using the following databases: Medline, Embase, PsycINFO, CINAHL, Sociological Abstracts, and Criminal Justice Abstracts. All databases were searched for literature published in English and from 1995 onward; no additional exclusion criteria were used. Various driving/driver-related terms were used and combined with cannabis/marijuana terms. (For complete search strategies, please contact the first
Prevalence of DUIC
Providing a global picture of DUIC prevalence is challenging given numerous factors, including regional differences in cannabis use and in data collection methods across studies (Walsh et al., 2008). Data from general population surveys suggest that the proportion of the population that reports DUIC is relatively low, and is lower than the proportion that reports DUIA. For example, Walsh and Mann (1999) observed that 1.9% of the adult population in Ontario, Canada reported driving within one
General deterrent approaches to DUIC
Less than 20 years ago, very few countries − Norway, a notable exception − had “established any systematic system to detect drugs other than alcohol among drivers suspected to be influenced” (Christophersen and Mørland, 1997, p. 126). Since then, numerous jurisdictions worldwide have introduced or are considering varied legal measures to prevent or deter drug-impaired driving and, in some places, DUIC specifically. Our comprehensive literature searches revealed that there are very few published
Specific deterrent and related approaches to DUIC
Relatively little evidence is available on the impact of specific deterrent measures on DUIC. A variety of punitive sanctions, including license suspensions, fines, and imprisonment are typically applied to those convicted of a DUIC offence. Several studies have described the number of cases processed for suspected DUIC, or characteristics of individuals apprehended when new drug-impaired driving laws are introduced (e.g., Davey et al., 2014, Jones, 2005, Steentoft et al., 2010, Vindenes et
Conclusions and future directions
Our understanding of and approaches to cannabis are, in some ways, changing rapidly. In recent years, evidence has emerged that cannabis use increases traffic collision risk. Governments are responding by considering or introducing legal measures to address DUIC at a time when some governments have legalized or decriminalized cannabis possession, or are considering doing so. This review of the literature, focusing on studies that have appeared since 1995, provides an overview of the road safety
Role of funding source
Nothing declared.
Contributors
Dr. Tara Marie Watson conceptualized the review, arranged the literature searches and reviewed new material, prepared the first full draft, and edited revised versions of the paper. Dr. Robert E. Mann conceptualized the review, and revised drafts of the paper and table. Both authors approved the final draft before submission.
Conflict of interest
No conflict declared.
Acknowledgement
Dr. Tara Marie Watson is funded by a Canadian Institutes of Health Research Postdoctoral Fellowship.
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