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Does Treatment for Substance Abuse Improve Driving Safety? A Preliminary Evaluation

Robert E. Mann, Lise Anglin, Sayeda Rahman, Lorie Ann Blessing, Evelyn R. Vingilis and Edward Larkin

Addiction Research Foundation, 33 Russell St., Toronto, Ontario, Canada M5S 2S1


There appears to be a growing consensus that rehabilative programs for convicted drivers can improve traffic safety outcomes. However, there is little evidence on the more general question of whether or not treatment for abuse of alcohol and other substances can reduce traffic safety risks. In order to provide some preliminary information on this question, we obtained driving record information on 137 males between the ages of 21 and 40 who underwent treatment for substance abuse at the Clinical Institute of the Addiction Research Foundation. These individuals were volunteers from the general clinical stream, that is, they were not specifically referred because of an impaired driving conviction. About 1/3 of the sample reported problems solely with alcohol, 1/3 reported problems with alcohol and one other substance (Cannabis, Stimulants), and 1/3 reported problems with one or two substances other than alcohol. Yearly rates of accidents, drinking-driving charges and moving violations were compared for the five years immediately preceding treatment entry and a post-treatment follow-up interval ranging from 6 to 36 months. The results demonstrated significant reductions on all three driving-related measures following treatment. Further analyses will explore whether different substances of abuse are associated with different outcomes.


A major health hazard posed by substance abuse is that of increased risk of death and injuries in traffic crashes. The contribution of alcohol to highway deaths has long been known (e.g., Borkenstein et al, 1964). Alcohol abusers are much more likely to die prematurely from accidental and violent causes, including motor vehicle accidents (Nicholls, Edwards and Kyle, 1974; Mann, Anglin, Wilkins, Vingilis and Macdonald, 1993). Until fairly recently, the role of other substance use in traffic crashes was less clear. However, it has been shown that substantial numbers of individuals killed or injured in traffic crashes test positive for one or more drugs in addition to alcohol (e.g., Cimburra, Lucas, Bennett, Warren and Simpson, 1982; Stoduto, Vingilis, Kapur, Sheu, McLellan and Liban, 1993). Abusers of at least some substances have higher accident rates than nonabusers or the general population (e.g., Mann, Anglin, Vingilis and Larkin, 1993).

Can treatment for substance abuse can reduce traffic safety risks in substance abusers? There is little direct evidence on this question, but the substantial literature on the effects of rehabilitation for convicted drinking drivers provides indirect evidence. Reviews of this literature suggest that rehabilitative measures have modest but significant beneficial effects on subsequent drinking-driving recidivism and alcohol-related accidents (Mann, Vingilis and Stewart, 1988; McKnight and Voas, 1991; Wells-Parker, Anderson, McMillen and Landrum, 1989). However, there is little or no evidence on the traffic safety impact of treatment for individuals seeking help for alcohol problems and in particular for problems with drugs other than alcohol.

This paper presents a preliminary evaluation of the effects of treatment for substance abuse on traffic safety measures. The sample includes individuals seeking treatment for alcohol, cannabis or stimulant use problems. The individuals were not referred to treatment for reasons related to traffic safety, e.g., because of a drinking-driving charge.


Subjects in the study were 137 clients (mean age = 31 years) at the Clinical Institute of the Addiction Research Foundation who volunteered for the research. Participants had to meet the following criteria: 1) male, 2) aged between 21 and 40, 3) must have first received a driver's licence at least five years previously, 4) must have driven at least 20,000 km in the past five years, and 5) must have a self-identified problem with one or two of alcohol, cannabis (e.g., hashish, marijuana) and/or stimulants (e.g., cocaine, amphetamines). Participants were administered an interview in which data on self-reported substance use and driving behaviour were obtained, and they also provided voluntary consent to obtain follow-up driving record information from the Ministry of Transportation.

At the time of interview administration, all participants were either involved in a treatment program or were undergoing assessment prior to entering treatment. None of the participants had specifically entered treatment as a result of an impaired driving conviction. Most were self-referred, or had been referred from their place of employment or by a probation officer. The treatment programs in which the clients were seen were a clinic for young people (under 25), an outpatient treatment program, and a program for employed substance abusers.

Driving record information was subsequently obtained from the Ministry of Transportation. We selected five driving-related measures for analysis: alcohol-related accidents, accidents not related to alcohol, total accidents, drinking-driving convictions, and moving offenses (e.g., speeding, failure to remain at the scene of an accident). The date of the interview was selected as defining the point of separation between pretreatment and post-treatment data. Five years of pretreatment data were available for all participants, while for the post-treatment interval the data available ranged from six months to three years. All data (pretreatment and post-treatment) were expressed as means per year.


Table 1 presents the mean pretreatment and post-treatment driving record data. Overall, there were declines in all measures of driving problems following treatment. T-tests for paired samples revealed that these declines were significant for total accidents, drinking-driving convictions and moving violations.

Table 1
Pretreatment and Post-treatment Driving Record Measures

Variable Pretreatment Mean Per Year (S.D.) Post-treatment Mean Per Year (S.D.) t p
Moving Violations .406 (.458) .217 (.552) 3.51 .001
Drinking-Driving Convictions .079 (.140) .018 (.096) 4.43 .000
Alcohol-Related Accidents .035 (.087) .015 (.115) 1.58 .116
Nonalcohol-Related Accidents .088 (.139) .052 (.195) 1.73 .086
Total Accidents .123 (.167) .068 (.223) 2.32 .022

We also attempted to determine whether the type of substance influenced the outcome. Using regression procedures (Ordinary Least Squares) the post-treatment driving record measures were regressed onto dummy variables indicating whether or not the individual's problem substance was alcohol, cannabis or stimulants, and whether the individual reported a problem with one or two substances. The corresponding pretreatment driving record measure and age were also included in the analyses. The results indicated that the problem substance, and whether the person reported a problem with one or two substances, were not significantly related to outcome on any of the driving record measures.


The simple pre-post design and the small sample size preclude a strong interpretation of the results. On the other hand, these data do provide an indication that treatment for substance abuse may have traffic safety benefits. Compared to pretreatment measures, following treatment a group of substance abusers had significantly fewer moving violations, drinking-driving convictions and total accidents.

These observations are consistent with other studies reporting that rehabilitation for convicted drinking drivers can have beneficial effects on traffic safety and general health measures (e.g., Mann et al., 1994; McKnight and Voas, 1991; Wells-Parker et al., 1989) and which report beneficial outcomes for alcohol-related interventions in general (e.g., Babor and Grant, 1994). Thus, it may be the case that not only can traffic safety be improved by providing treatment or rehabilitation to convicted drinking drivers, but also by providing treatment services for people with alcohol problems in general.

These effects were of similar magnitude for people treated for problems with cannabis and stimulants (at least, no statistically significant effect of drug was detected). Thus, treatment for problems with substances other than alcohol may have traffic safety benefits as well. At present, very few individuals are charged or convicted with driving offenses involving drugs. However, if detection technology improves and drug-impaired driving receives more recognition as a traffic safety problem, more people might be apprehended and convicted of these offenses in the future. These data suggest that treatment or rehabilitation may be an effective countermeasure for at least some of these individuals, in that the effects were comparable to those for treatment of an alcohol problem. However, when the possible effects of drugs other than alcohol on outcome were examined, the resulting subsamples were relatively small. Thus, the failure to find outcome differences among individuals reporting alcohol, cannabis and stimulant problems may have been due, at least in part, to the small sample size.


Babor, T., Grant, M. et al. (1994) Comments on the WHO report 'Brief Interventions for alcohol problems': A summary and some international comments. Addiction, 89, 657-678.

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Cimbura, G., Lucas, D.M., Bennett, R.C., Warren, R.A. and Simpson, H.M. (1982) Incidence and toxicological aspects of drugs detected in 484 fatally injured drivers and pedestrians in Ontario. J. Forensic Sci., 27, 855-867.

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Mann, R.E., Anglin, L., Wilkins, K., Vingilis, E.R. and Macdonald, S. (1993) Mortality in a sample of convicted drinking drivers. Addiction, 88, 643-647.

Mann, R.E., Vingilis, E.R. and Stewart, K. (1988) Programmes to change individual behaviour: Education and rehabilitation in the prevention of drinking and driving. In M.D. Laurence, J.R. Snortum and F.E. Zimring (eds.) The Social Control of Drinking and Driving, Chicago, University of Chicago Press, pp. 248-269.

McKnight, A.J. and Voas, R.B. (1991) The effects of license suspension upon DWI recidivism. Alcohol, Drugs and Driving, 7, 43-54.

Nicholls, P., Edwards, G. and Kyle, E. (1974) Alcoholics admitted to four hospitals in England II. General and cause-specific mortality. Quarterly Journal of Studies on Alcohol, 35, 841-855.

Stoduto, G., Vingilis, E.R., Kapur, B., McLellan, B. and Liban, C.B. (1993) Alcohol and drug use among motor vehicle collision victims admitted to a Regional Trauma Unit: Demographic, injury and crash characteristics. Accident Analysis and Prevention, 25, 411-420.

Wells-Parker, E.N., Anderson, B.J., McMillen, D.L. and Landrum, J.L. (1989) Interactions among DUI offender characteristics and traditional intervention modalities: A long-term recidivism follow-up. British Journal of Addiction, 84, 381-390.