Enforcement of zero tolerance laws in the United States
By 1998 all states had enacted zero tolerance laws, which prohibit people younger than 21 from driving with any positive blood alcohol concentration (BAC). A review of the law was undertaken to determine whether variations in zero tolerance laws might affect their enforcement. Five states were selected (California, Michigan, New Mexico, New York, and Virginia) that appeared to differ in the ease with which the laws could be enforced. Detailed information on enforcement practices was collected in interviews with police officers and motor vehicle officials. The zero tolerance laws in these states have done little to change the way police identify underage drinking drivers. Consequently, these laws rarely are being enforced independently of the laws against impaired driving aimed at all ages. However, if an officer stops an underage drinking driver, some provisions of the laws can make it easier to issue a zero tolerance citation. For example, in most states an evidentiary test for BAC is required to prove a zero tolerance violation, but in a number of states the implied consent law requires either an arrest for driving while impaired (DWI) or probably cause for an arrest before such a test can be administered. Thus, underage offenders with low BACs cannot be arrested for zero tolerance. By contrast, in California officers can use results from preliminary breath test (PBT) units at the roadside as evidence of zero tolerance if an underage driver is suspected of drinking. Factors that reduce the likelihood of enforcement are discussed.