1 - Introduction

This document is the final report of a project entitled “Evaluation of Lower BAC Limits for Convicted DWI Offenders.” The general objective of the project was to determine the effectiveness of establishing lower BAC limits for convicted DWI offenders in one State.


Convicted DWI offenders have been identified as a special target group for DWI countermeasures. A recent review of the scientific literature about drivers who have been convicted more than once of driving while impaired by alcohol (DWI) found that repeat DWI offenders comprise a small, but not negligible, percentage of drivers involved in traffic crashes (Jones and Lacey, 2000). Unfortunately, there are very little data on the actual magnitude of that percentage, but data from California suggest it could be in the 26% range for alcohol-related fatal crashes, and data from Minnesota suggest it could be even higher when administrative violations are counted as convictions. FARS data for 2001 suggest a figure of some 9% for alcohol-related fatal crashes and a figure of about 3½% for all fatal crashes when only court convictions in the previous three years are counted as a prior DWI.

The amount of evaluative literature on repeat offender countermeasures has grown considerably in the last several years, nearly all of which is concerned with the specific deterrent effect of various sanctions. Sanctions classified as alternative sanctions appeared especially effective, offering potential reductions in recidivism in the 15% to 90% range. License suspension or revocation combined with treatment continues to look effective, with the potential for reducing recidivism by as much as 50%. Several evaluations also indicate strongly that certain vehicle-based sanctions can also be effective in reducing the recidivism of repeat DWI offenders.

An evaluation of another legal-system countermeasure for alcohol-related crashes involving convicted DWI offenders has created interest recently in the highway safety community. The evaluation (Hingson, Heeren, and Winter, 1998) examined the effect of a 1988 Maine law lowering the BAC limit from .10 to .05 for convicted DWI offenders. The law mandated an administrative license suspension for violators, but did not establish a .05 limit for the criminal offense of DWI (called operating under the influence of in-toxicants or OUI in Maine). The evaluation found the proportion of fatal crashes involving drivers with recorded prior OUI convictions declined 25 percent following passage of the .05 OUI law, while the proportion rose in the rest of New England during the same years. This evaluation, while useful for indicating the potential of such a law, must be considered as preliminary, since (1) it did not consider important process-related questions (that is, the extent to which the law was implemented and its effect on the implementing agencies), and (2) involved a before-and-after treatment-and-control experimental design for the impact evaluation. Further, the law has since been changed to reduce the limit to .00, and the Maine law applies only to administrative sanctions, requiring license suspension for a period of one year for first time convicted offenders and 10 years for multiple repeat offenders who commit the violation after reinstatement following an OUI conviction or administrative action.

The mandatory nature of the lower limit provision in Maine’s law required further examination. Many judges across the nation include a prohibition of drinking or driving after drinking in their standard OUI sentences. However, because there is no statutory sanction attached and officers on the street are unlikely to know of the prohibition from checks of computerized records, this violation of probation is in practice seldom reported and thus action is infrequently taken on low BACs.

Study Approach

Our approach to the project started with the State selection process which involved developing State selection criteria, identifying potential case-study States that best met those criteria, and recommending a case-study State for NHTSA consideration.

After the study State (Maine) was selected, we prepared a plan for collecting and analyzing the data needed for the evaluation. The plan addressed both a process evaluation and an impact evaluation. The impact evaluation preceded along two lines, (1) an analysis of the general deterrent effect on alcohol-related fatal crashes, and (2) an analysis of the specific deterrent effect on OUI recidivism. Execution of the data collection and analysis plan followed, and the final technical report (this document) was prepared.

This report is presented in five major sections. Section 2 describes the research method and the evaluation design, and Section 3 presents the results of the evaluation. Overall conclusions are contained in Section 4, and a bibliography of cited references is presented in Section 5. Appendix A contains the Maine statute setting forth the current version of its lower BAC law.