Trends in Blood Alcohol Concentration Levels of Drivers at Night: A Comparison of BAC Levels Determined in the First Two Roadside Surveys of the Fairfax Alcohol Safety Action Project

Report No: 73-R26

Published in 1973

About the report:

As part of the Fairfax Alcohol Safety Action Project (ASAP), staff members of the Virginia Highway Research Council, acting in their role as evaluators of the project, have conducted two roadside surveys in Fairfax, Virginia. A baseline survey was conducted in January 1972 prior to the start of ASAP operations in February 1972 and a second survey was conducted in October 1972. These two surveys were part of the series of four annual surveys to be conducted throughout the duration of the project. The ASAP concept recognizes the major role that alcohol plays in fatal and serious highway crashes, and the project consists of countermeasures designed to identify drunken drivers, remove them from the road, and refer them to proper educational or rehabilitation programs. The ultimate objective of the ASAP is to reduce the number of fatalities, personal injuries and property damage accidents caused by the drinking driver. The purpose of the nighttime roadside surveys of randomly selected drivers is to provide a secondary measure of the project's effectiveness in reducing the incidence of driving while under the influence of alcohol. This paper compares the BAC's (blood alcohol concentrations) of drivers in the baseline survey with the BAC's of drivers tested near the end of the first year of the ASAP. The findings can be summarized as follows: 1. There was a significantly greater percentage of drinking drivers in the second survey compared with the baseline survey. This difference was significant at the 99% confidence level. 2. There was a slight reduction in the percentage of drivers with BAC's above 10%, but this difference was not statistically significant. 3. Even though there was a greater percentage of drivers who were drinking on the second survey, the relative probability of accidents was 1.9% lower for the second survey as calculated by the Index of Accident Probability (IAP). 4. On weeknights, there was no apparent difference in the risk of accidents from the baseline survey to the second survey. However, there was a dramatic reduction in the IAP for the later time periods on weekends. This reduction cannot be proven to be a result of the ASAP, but it is a very encouraging sign that the ASAP patrols are succeeding in altering the late-night drinking and driving patterns on weekends in Fairfax.

Disclaimer Statement:The contents of this report reflect the views of the author(s), who is responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Virginia Department of Transportation, the Commonwealth Transportation Board, or the Federal Highway Administration. This report does not constitute a standard, specification, or regulation. Any inclusion of manufacturer names, trade names, or trademarks is for identification purposes only and is not to be considered an endorsement.


  • Thomas J. Smith

Last updated: February 6, 2024

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