Cannabis is the illegal psychoactive substance most frequently used by the Canadian population (Adlaf, Begin, and Sawka 2005). A primary concern regarding cannabis use from a public health perspective is cannabis use and driving (CUD) (Hall and Babor 2000; Hall, Room, and Bondy 1999) due to the drug's impairment effects. Evidence suggests that cannabis use--mainly following a positive dose-response relationship--impairs crucial psycho-motor skills required for driving activities (Hadom 2004; Lenne, Triggs, and Regan 2004; Ramaekers, Berghaus, van Laar, and Drummer 2004). Epidemiological studies focusing on indicators of acute cannabis consumption (e.g., from use within 24 hours) have found that recent use significantly increases the odds of motor vehicle accident (MVA) involvement, including an increased culpability rate in fatal accidents (Bedard, Dubois, and Weaver 2007; Drummer, Gerostamoulos, Batziris, Chu, Caplehom, Robertson, and Swann 2003; O'Kane, Tutt, and Bauer 2002; Ramaekers, Berghaus, van Laar, and Drummer 2002). Cannabis-related impairment is further substantially amplified by the co-use of alcohol, a substance frequently consumed by cannabis users (Robbe 1998).
While attention has been given to the increasing prevalence of CUD in the Canadian population, the sub-populations for whom greatest concern exists on this issue are adolescents and young adults (i.e., the age group 16-25 years of age) for several reasons. First, cannabis use is by far most prevalent (i.e., as expressed in past year use) in this age group, ranging from 29% to 47% according to data from the most recent national survey (Adlaf et al. 2005). Similarly, the Canadian Campus Survey examining substance use among post-secondary students reported increasing levels of cannabis use in this population, with a prevalence level of 33% in 2004 (Adlaf, Demers, and Gliksman 2004). Second, young drivers--regardless of psychoactive substance-related impairment--are at elevated risk for MVA involvement, partly related to their lack of skill and experience as well as behavioural disposition (Doherty, Andrey, and MacGregor 1998; Jonah 1990; Williams 2003). Third, considerable proportions of young people perceive the effects of cannabis to be rather innocuous and of limited relevance for impairment related to driving (Davey, Davies, French, Williams, and Lang 2005; Duff 2003; Paglia and Room 1999; Terry and Wright 2005). Recent studies have drawn concrete attention to the phenomenon of CUD among young drivers in Canada, indicating that the prevalence of CUD is high in this group, ranging from 15% to 20%, and may be higher than the frequency of driving after drinking (Adlaf, Mann, and Paglia 2003; Asbridge, Poulin, and Donato 2005).
Evidence from studies on drug-impaired driving among young people suggests that such risk behaviour is typically associated with a variety of factors, including frequent drug use or dependence, previous traffic or legal infractions, conduct or attitude problems, as well as social or peer dynamics (Armstrong, Wills, and Watson 2005; Begg, Langley, and Stephenson 2003; Finken, Jacobs, and Laguna 1998; Lewis, Thombs, and Olds 2005). Fergusson and Horwood (2001) examined the prevalence of CUD and related accidents in a birth cohort age 18-21 years, in New Zealand, and found a significant relationship between cannabis use and accident rates. Specifically, those who had used cannabis on at least a weekly basis had an accident rate 1.6 times higher than that of non-users. Mann et al. observed a similar dose-response relationship between increasing frequency of cannabis use and increased likelihood of collision involvement in the past year in a representative sample of Ontario adult drivers (Mann, Adlaf, Zhao, Stoduto, Ialomiteanu, Smart, and Asbridge 2007).
Presently, interventions targeting CUD--especially among young drivers--occur in Canada only at rather limited levels. Recent preventive initiatives include the Canadian Public Health Association-sponsored nationwide "pot-and-driving" campaign ("Pot and Driving"); yet, general awareness of the issue and preventative efforts remain far behind those focusing on drinking and driving (Asbridge et al. 2005). Enforcement--and general deterrence effects--are constrained by the nature of current criminal law (Criminal Code, s 253) requiring driver consent for the collection of a fluid sample to test for the presence of cannabis as well as the limitations of reliable road-side testing methods (Barnett 2007; Janhevich, Gannon, and Morisset 2003; Mann, Brands, Macdonald, and Stoduto 2004). While the federal government has worked to provide stricter drug-impaired driving legislation as well as increased enforcement resources, this offence is rarely enforced at the present time.
An improved understanding of factors associated with CUD among the risk-population of young drivers is required to facilitate evidence-based intervention development. This study responds to this need by specifically exploring factors associated with frequent CUD in a multi-site sample of university students who had engaged in CUD in the past year.
Study participants were recruited by mass advertising and word-of-mouth methods, between April 2005 and March 2006, on the campuses of five universities located in Toronto and Ottawa, Ontario. Eligibility criteria for the study included (a) 18-28 years of age, (b) active university enrolment, and (c) having driven a motor vehicle within 4 hours of cannabis use in the last 12 months. Potential participants called a study phone line for screening. Assessments consisted of an interviewer-administered questionnaire, including closed and some open-ended items, and were conducted in confidential settings, based on written consent. Participants' anonymity was protected throughout the study; and they were given two movie vouchers for compensation. The study was approved by REBs in each of the participating universities.
The final study sample included N = 272 participants, resulting in a final analysis sample of n = 248 by list-wise deletion of cases with missing data. Deleted cases did not differ significantly from the analysis sample regarding sex, age, or CUD characteristics. The sample was divided into low frequency CUD (LFCUD; 12 or less incidents of CUD in the past year) and high-frequency CUD (HFCUD; 13 or more CUD incidents) analysis groups, based on a median split of the frequency of reported CUD incidents in the sample. Bivariate analyses (BVA) were performed to identify factors associated with LFCUD...