Association for Public Policy Analysis & Management

Impaired driving is a major public safety concern within the United States as impaired drivers increase the risk of traffic accidents for both themselves and other drivers.  For example, in 2013 over 10,000 individuals were killed in alcohol-impaired traffic accidents, representing nearly one third of all traffic related deaths.  In the same time period illicit drugs were involved in nearly 20% of all fatal traffic accidents.  These statistics suggest that the social costs of impaired driving are high.  In response, governments of all levels have taken steps to address impaired driving by setting maximum allowable levels of alcohol drivers may legally consume, prohibiting driving while under the influence of illicit drugs, instituting roadside check points, and so forth. 

A potential policy approach to impaired driving is to reduce the level of substance use disorders (SUDs) within the population through effective and affordable treatment.  Reducing SUDs should reduce the number of impaired drivers on roadways, and hence traffic accidents.  Although treatment has been shown to reduce SUDs and associated harms, many individuals who could benefit from such treatment do not receive it.  A commonly cited barrier to treatment is cost.  Indeed, within the U.S. health insurance plans (public and private) have historically covered SUD treatment less generously than medical/surgical treatment.  For example, patient cost-sharing (e.g., copayments, deductibles) has historically been higher for SUD treatment than medical/surgical treatment. 

In this study we explore how state parity, or equal coverage, mandates for substance use treatment impact fatal traffic accidents attributable to impaired driving.  State parity mandates regulate private insurance markets and expand affordable coverage for alcohol and illicit drug treatment by requiring insurers to cover SUD treatment services at parity with medical/surgical services in terms of cost sharing and service limitations.  Previous research documents that state parity mandates increase utilization of SUD treatment. 

To explore the effect of state parity laws on traffic fatalities, we use data from the Fatal Accident Reporting System between 1988 and 2009.  During this period, 22 states passed parity mandates, offering a novel quasi experiment with which to study the effects of these mandates on traffic fatalities.  We apply differences-in-differences methods and control for a wide range of time-varying state factors and state-specific linear time trends.  We explore heterogeneity across states in how they choose to regulate the private insurance market.  In an extension, we examine the extent to which state parity mandates impact levels of substance misuse as reduced substance use is the key channel through which we expect mandates to impact traffic accidents. 

Our findings suggest that the passage of a state parity mandate reduces the number of fatal traffic accidents and the level of substance misuse within the population.  These findings suggest that government regulations, such as those codified within the Affordable Care Act, that require insurance companies to cover substance use treatment at parity with medical/surgical services can improve traffic safety by reducing the number of impaired drivers, in addition to reducing the level of substance misuse within the population.