Charge combinations and conviction rates among alcohol-influenced drivers involved in motor vehicle crashes in Iowa

Alcohol impairment is a major contributor to road traffic crashes and has increased across the United States in recent years. In 2022, over 13,000 people were killed in drunk driving crashes. Enforcement of impaired driving laws is an essential strategy to reduce alcohol-impaired driving and subsequent crashes. However, little is known about conviction outcomes related to alcohol-involved crashes. The aim of this study is to examine the association between charge combinations and conviction rates among alcohol-influenced drivers involved in crashes.

Data for this study included 2016-2019 Iowa Department of Transportation crash data linked to charges and convictions from the Iowa Court Information System. The study sample included drivers with reported BAC ≥ 0.08 g/dl and/or driver condition reported as under influence of alcohol. Charges were divided into three categories: alcohol, moving, and administrative/miscellaneous. Two logistic regression models were built with any conviction and alcohol conviction as the outcomes. The main predictor was charge combination.

The study sample included 8,238 alcohol-impaired drivers, of whom 6,846 (83.1%) were charged with any type of traffic offense and 6,253 (75.8%) were charged with alcohol-related traffic offenses. Among charged drivers, 96.2% were convicted on any traffic charge and 87.7% were convicted on an alcohol charge. Drivers with a combination of alcohol, administrative, and moving violation charges had higher odds of any conviction (OR = 2.6, 95% CI = 1.7-4.3) compared to drivers with only alcohol charges.

Charging impaired drivers with multiple types of charges was associated with increased odds of conviction on any charge but not on alcohol charges, which had high conviction rates overall.

Results from this study can help guide law enforcement to ensure appropriate charges are made in all relevant categories and optimal combinations of charges are administered to impaired drivers to increase odds of conviction.