This study is sponsored by the Insurance Institute for Highway Safety. Evaluation studies of alcohol ignition interlock device (IID) laws have been limited to individual states with the effectiveness assessed primarily in terms of reduced driving while intoxicated (DWI) recidivism. We will assess IID safety benefits at the national level based on the extent to which they reduce impaired driving fatal crashes. We will determine the relationship of two types of state IID laws on the involvement of drivers with prior convictions for DWI in fatal crashes as a measure of the specific deterrent effect of IID laws (Have these IID laws affected offenders who have experienced the sanction?). We will also determine the relationship of the two different types of IID laws on the involvement of drivers without prior convictions for DWI in fatal crashes as a measure of the general deterrent effect of the laws (Have the adoption of these IID laws deterred drivers in general from drinking and driving?).