Increased police patrols for preventing alcohol-impaired driving: Cochrane systematic review


Assessed as up to date: 2006/05/31


Road traffic injuries cause 1.2 million deaths worldwide each year. Alcohol consumption increases the risk of traffic crashes, especially fatal crashes. Increased police patrols aim to increase both the perceived and actual likelihood of being caught driving while alcohol-impaired, potentially reducing alcohol-related driving, crashes and injuries.


To assess the effects on injuries and crashes of increased police patrols that target alcohol-impaired driving.

Search strategy

We searched the Cochrane Injuries Group Specialised Register (5/2006), CENTRAL (The Cochrane Library 2006, Issue 2), MEDLINE (1966 to 5/2006), TRANSPORT (1968 to 5/2006), C2-SPECTR (2/2005), NCJRS (1/1951 to 5/2006), PsycINFO (1872 to 5/2006), Social Science Citation Index (1974 to 5/2006), SIGLE (1980 to 2/2006), Science Citation Index Expanded (1970 to 5/2006), Dissertation Abstracts (1870 to 5/2006), NTIS (1964 to 12/2004), conference proceedings, and reference lists. We contacted authors of eligible studies.

Selection criteria

Randomized controlled trials, controlled trials, controlled before and after studies, interrupted time series (ITS) studies, and controlled ITS studies evaluating increased police patrols, either alone or combined with other interventions, targeting alcohol-impaired motor vehicle drivers.

Data collection and analysis

Two investigators independently screened citations, extracted data, and assessed quality criteria. We compared intervention and no-intervention geographical areas or time periods. We re-analyzed study data as required. Results are presented narratively.

Main results

The 32 eligible studies included one randomized controlled trial, eight controlled before-after studies, 14 controlled ITS studies, six ITS studies, and three studies with both ITS and controlled before-after analyses. Most interventions targeted only alcohol-impaired driving (69%) and included additional interventions such as media campaigns or special training for police officers (91%). Only two studies reported sufficient information to assess study quality completely. Two-thirds of studies were scored 'not adequate' on at least one feature. Five of six studies evaluating traffic fatalities reported reductions with the intervention, but differences were statistically significant in only one study. Effects of intervention on traffic injuries were inconsistent in the six studies evaluating this outcome, and no results were statistically significant. All four controlled studies evaluating fatal crashes reported reductions with the intervention, which were statistically significant in one study. All 12 controlled studies assessing injury crashes reported greater reductions with the intervention, though effects were minimal or not significant in several studies. ITS studies showed less consistent effects on fatal crashes (three studies) and injury crashes (four studies), and effect estimates were typically imprecise. Thirteen of 20 studies showed reductions in total crashes and about two-thirds of these were statistically significant.

Authors' conclusions

Studies examining increased police patrol programs were generally consistent in reporting beneficial effects on traffic crashes and fatalities, but study quality and reporting were often poor. Methodological limitations included inadequate sample size, dissimilar baseline measures, contamination, and inadequate data analysis. Thus existing evidence, although supportive, does not firmly establish whether increased police patrols, implemented with or without other intervention elements, reduce the adverse consequences of alcohol-impaired driving.


Goss Cynthia W, Van Bramer Lisa D, Gliner Jeffrey A, Porter Todd R, Roberts Ian G, DiGuiseppi Carolyn


Increased police patrols for preventing alcohol-impaired driving

More than one million people are killed worldwide each year in traffic crashes. Driving after drinking alcohol increases the chance of a traffic crash. To reduce alcohol-impaired driving, some police agencies have increased the number of police patrols or the time the police spend patrolling. The aim of these increased patrols is to raise the perceived and actual likelihood that impaired drivers will be identified and stopped. Identification is based on observable behavioral cues, which include moving violations, erratic driving, and crash involvement. In response to these cues, police officers stop the driver and administer tests for alcohol impairment. We found 32 studies that tested the effects of increased police patrols on traffic deaths, injuries, and crashes. There was one randomized controlled trial and no quasi-randomized controlled trials. Almost all of the programs included additional interventions like community information programs, media campaigns, and special training for police officers. Most studies found that increased police patrols reduced traffic crashes and fatalities. Evidence for the effect on traffic injuries was less consistent. The detail provided on the methodology of included studies was almost uniformly poor. When this information was reported, the methodological quality was often weak. Therefore, the available evidence does not firmly establish that increased police patrols reduce the adverse consequences of alcohol-impaired driving. Good quality controlled studies with adequate sample size are needed to evaluate increased patrols. Also needed are studies assessing the cost-effectiveness of this intervention.

Reviewer's Conclusions

Implications for practice

We found many studies of increased police patrol programs, which in general showed at least some beneficial effect on fatalities and crashes although few results were statistically significant. The most consistent benefits were seen for total crashes, fatalities and fatal crashes. However, nearly three-quarters of the studies had at least one methodological limitation which could affect their results. Evidence about whether prevention of alcohol-impaired driving is a mechanism for the decrease in crashes and injuries that is observed with increased police patrols is also inconclusive. Thus, existing evidence, although suggestive, does not establish whether increased police patrols, implemented with or without other intervention elements, has an important effect on the adverse consequences of alcohol-impaired driving.

Implications for research

Although increased police patrols appeared to reduce alcohol-related crashes and traffic fatalities in the identified studies, the quality and reporting of these studies was often poor. Methodologically rigorous research is still needed to evaluate whether increased police patrols are an effective intervention for targeting alcohol-impaired driving. The identification of one relatively good quality randomized controlled trial suggests that studies of better design and quality can and should be implemented to evaluate increased police patrols, even though the studies must occur in a natural setting. The need for high quality evaluation is particularly vital in the context of the substantial resources currently being expended to implement this intervention, despite its unproven efficacy. 

Additional directions for future research might include the following.

  • Direct comparisons of enforcement strategies (sobriety checkpoints, increased patrols, random breath testing or behavior-based versus chemistry-based enforcement).
  • Examination of specific additional interventional elements that may influence the effectiveness of increased police patrols.
  • Evaluation of objective measurements of alcohol-impaired driving during increased police patrol interventions using controlled study designs.
  • Determination of the cost-effectiveness of increased police patrol programs relative to other programs shown to reduce alcohol-impaired driving or its consequences.

Updates to this review will incorporate studies identified but not yet assessed and attempt to identify additional relevant literature.

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