Nighttime observations of safety belt use: an evaluation of California's primary law.

OBJECTIVES: An analysis was conducted to determine what effect California's change to a primary safety belt law had on safety belt use among nighttime weekend drivers. METHODS: Observations of 18,469 drivers in 2 California communities were made during voluntary roadside surveys conducted every other Friday and Saturday night from 9 PM to 2 AM for 4 years. RESULTS: Rates of safety belt use rose from 73.0% to 95.6% (P < .0005). For drivers with blood alcohol concentrations of 0.10 or higher, rates rose from 53.4% to 92.1% (P < .0005). CONCLUSIONS: Because substantial improvement in safety belt use was seen even in a group of high-risk drivers, the injury reduction benefits of this law may be high.