Arrests and convictions for drunken driving in Virginia before and after adoption of a per se offense.

Stoke, Charles B; Byler, Patricia M · 1988 · ROSA P / Virginia Transportation Research Council (VTRC)

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Summary

This study investigates the impact of legislative changes to Virginia’s drunken driving laws on enforcement outcomes, specifically arrest and conviction rates. The research was motivated by concerns that the initial implementation of a "per se" offense in July 1984, which set the blood alcohol concentration (BAC) limit at 0.15% while retaining a lower presumptive intoxication level of 0.10%, created confusion and discouraged police enforcement. Critics argued this discrepancy legitimized BACs below 0.15% and reduced conviction likelihoods. In April 1986, the per se limit was lowered to 0.10% to align with the presumptive level. The study aimed to determine if these statutory variations significantly affected the number of arrests and convictions. The methodology involved a comparative analysis of three distinct time periods: Period I (prior to July 1984, no per se law), Period II (July 1984–April 1986, 0.15% per se limit), and Period III (post-April 1986, 0.10% per se limit). Due to inconsistencies in data collection systems prior to 1984, the researchers utilized Uniform Crime Report data for arrests and Department of Motor Vehicles records for convictions. To control for monthly seasonal variations and transition periods, the analysis sampled full calendar years for arrests (1983, 1985, and 1987) and the first six months of those respective years for convictions. The study employed Analysis of Variance (ANOVA) to test for statistical significance among the groups, using a rigorous significance level of p < .05. A broader survey of state laws was conducted but ultimately limited to Virginia data due to inconsistencies in other states' statutory interpretations. The results indicated no statistically significant difference in arrest or conviction numbers across the three time periods. For arrests, the ANOVA yielded a significance level of .184, failing to reject the null hypothesis. Although the mean number of arrests was lowest in 1985 (Period II), the variation was attributed to normal fluctuations rather than the law's definition. Similarly, conviction data showed no significant difference at the p < .05 level, with a significance level of .078. While conviction numbers were highest in 1987 (Period III), the small sample size and data limitations prevented definitive conclusions about trends. The study concludes that the variations in Virginia’s per se and presumptive BAC limits did not produce statistically significant changes in enforcement or adjudication rates. The data do not support the claim that the initial 0.15% per se limit negatively impacted arrests or convictions, nor do they confirm that lowering the limit to 0.10% improved outcomes. The findings suggest that the lowering of the per se level to 0.10% had no negative impact, indicating that enforcement levels remained stable regardless of the specific statutory definition during the studied period.

Key finding

There was no statistically significant difference in the number of arrests or convictions for drunken driving in Virginia when comparing periods with no per se offense, a 0.15% per se limit, and a 0.10% per se limit.

Methodology

dataset

Provenance

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Topics

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• dui enforcement
• drowsy as impairment