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How the Number and Location of Alcohol Sales Outlets Affects Traffic Crashes

How does the number and location of bars and restaurants that serve alcohol affect traffic crashes?  A new study by the Prevention Research Center in Oakland, California along with partners at the University of Pennsylvania and Ambulance Victoria in Melbourne, Australia helps to answer that question.  There is now substantial evidence that geographic areas with fewer alcohol outlets have fewer incidents of alcohol-related problems (e.g., assault, child abuse, crime).  This study investigates the association between alcohol-related road crashes and the availability of alcohol through retail outlets within very small geographic units.

The larger the geographic unit studied, the more likely it is that outlets, origins, destinations and crashes will be co-located within that area, washing out the effects of outlet density. For this study, crash data and alcohol outlet data were used from within Statistical Area level 1 (SA1) units from the city of Melbourne, Australia. These units have an average resident population of 415.3 and cover a land area of less than one third of a square mile. In such small areas, the authors predicted that greater density of on-premise outlets, such as bars and restaurants, would be positively associated with alcohol-related crash rates in local and adjacent areas, but that there would be no similar effect for off-premise outlets (such as liquor stores).

As predicted, there was no evidence that greater bar density was associated with greater rates of alcohol-related crashes within these very small local areas.  There was, however, a positive relationship with crashes in the areas adjacent to the zones with many bars. In contrast, greater off-premise outlet density was associated with fewer alcohol-related crashes in local areas.

The study authors point out that alcohol-affected drivers are at increased risk of crashing after leaving an on-premise outlet where they have been drinking. But since people driving cars travel beyond the very small area where the bars are located, the risk of crashes is likely to be dispersed over a wider geographic area. A 10% increase in bar density was associated with 0.3% increased crash risk in adjacent SA1 units. By contrast, drivers who consume alcohol purchased in off-premise outlets are likely to be affected while driving in areas much farther away.  In fact, there was a negative relationship between the location of off-premise outlets and alcohol related crashes.  This negative relationship does not suggest that these outlets in some way protect against alcohol-related crashes, rather it may support the hypothesis that alcohol-related crashes related to alcohol purchases when the alcohol is consumed elsewhere are likely to lead to crashes in completely different geographic areas.

The authors conclude that this study provides more evidence that allowing a high density of alcohol outlets in an area contributes to a greater incidence of alcohol problems, including impaired driving crashes.

Drug and Alcohol Dependence, Spatial Relationships between Alcohol-Related Road Crashes and Retail Alcohol Availability, http://dx.doi.org/10.1016/j.drugalcdep.2016.02.033

Christopher Morrison, Perelman School of Medicine, University of Pennsylvania
William R. Ponicki, Prevention Research Center, Pacific Institute for Research & Evaluation
Paul J. Gruenewald, Prevention Research Center, Pacific Institute for Research & Evaluation
Douglas J. Wiebe, Perelman School of Medicine, University of Pennsylvania
Karen Smith, Research and Evaluation Department, Ambulance Victoria