There are three different types of interlock laws. Are there different effects? What type of law had the greatest impact?

Alcohol-impaired driving results in thousands of deaths annually. Alcohol ignition interlocks require a negative breath test for the presence of alcohol to start a vehicle’s engine, and as of 2014, some 44 states had mandated some form of interlock law for drivers convicted of driving while intoxicated (DWI).

There is strong evidence that interlocks reduce DWI recidivism, but is there also a general deterrent effect of the laws on impaired driving? The objective of this study was to estimate the association between interlock laws and fatal impaired-driving crashes.

Dive into the data: The Year Interlock Law Adopted by State and Impaired Driving Fatal Crashes by State by Year.

Legal research was conducted to determine the kind of ignition interlock law that was adopted and the year the law went into effect. The Fatality Analysis Reporting System was used in the analysis of impaired driving fatal crashes in the state. Differences in three interlock laws were evaluated by comparing alcohol-impaired passenger vehicle drivers involved in fatal crashes between 2001 and 2019 in the United States across state and time. State/time differences unrelated to interlock laws were controlled for by fitting a Poisson model. The exposure measure was the number of passenger vehicle drivers in fatal crashes that did not involve impaired drivers. Laws requiring interlocks for drivers convicted of DWI covered: repeat offenders, repeat offenders and high-BAC offenders, all offenders, or none.