This paper is an expansion of a previously presented paper “Ignition Interlocks for Intoxicated Drivers,” with additional data analysis which exposed the basic problems resulting from the operation of automobiles by intoxicated drivers in the United States. Several approaches to the development of ignition interlock systems are discussed. The Phystester,* an ignition interlock developed by General Motors and based on a predriving performance test of short duration, is discussed. Plans for evaluation of its effectiveness are presented, and available data from experiments involving both sober and intoxicated subjects are included. Integration of the Phystester in the operation of the vehicle and additional functional uses of the device are also discussed. Results of the Michigan Breath Testing Program, 1970-1971, are provided as an Appendix.