There are a number of situations in which judgments of a driver's BAC is important for practical decisions that people make which influence the incidence of impaired driving. In addition to the use of evidential breath tests to provide BAC data for use in court, there are other times when individuals must estimate their own or another's BAC in order to take appropriate action. Partygoers want to know if they are within the legal limits, bartenders need to know when to stop serving patrons, police need a basis for requesting an evidential breath test, physicians need information to counsel their patients on estimating BACs, etc.

This paper (a) identifies the various situations in which such information is needed, noting the differences in accuracy for types of information required in the various situations, (b) identifies the types of approaches for providing impairment or BAC information to people and (c) presents data on a variety of different techniques that have been tested recently.