The net result is a BAC closer to 0.09 percent is needed in Great Britain for a violation, whereas a measured BAC of 0.10 is sufficient for arrest in the United States. Although police cannot stop and test individual drivers without cause, they can investigate any driver who, based on established criteria, appears to have been driving while impaired by alcohol. Most alcohol-impaired driving arrests are made by officers on routine patrol who discern signs of impairment after stopping a driver for an ordinary traffic violation. In some jurisdictions, specialized patrols work exclusively on alcohol-impaired driving enforcement. Plus, police can stop drivers at roadblocks known as sobriety checkpoints.
Police can use checkpoints to stop drivers at specified locations to identify impaired drivers.
All drivers, or a predetermined proportion of them, are stopped based on rules that prevent police from arbitrarily selecting drivers to stop. Checkpoints are a very visible enforcement method intended to deter potential offenders as well as to catch violators. Annotated bibliography of research reports on the effectiveness of sobriety checkpoints. The U.S. Supreme Court held in 1990 that properly conducted sobriety checkpoints are legal under the federal Constitution. Most state courts that have addressed the issue have upheld checkpoints, too, but some have interpreted state law to prohibit checkpoints.