How intoxicated are drivers in the United States? Estimating the extent, risks and costs per kilometer of driving by blood alcohol level.

This study develops and applies an algorithm with international applicability for estimating vehicle kilometers (kms) driven by blood alcohol level (BAL) from police crash report data. In the United States, an estimated one in 120 kms was driven with BAL > or = 0.10% in 1992-1993. The ratio increased to 1 in 7 kms driven on weekend evenings. The estimated cost per vehicle km driven with BAL > or = 0.08% was $3.40 compared to $0.07 per sober km. Males, those age 21-29 and those driving between 22:00 and 04:00 had the greatest percentage of driving with BAL > or = 0.08%. These estimates are computed, in part, from early 1960s data on crash odds by driver BAL and assume crash odds by BAL relative to sober do not vary with driver age and sex. Preliminary investigation indicates that the method provides reliable estimates of alcohol-positive kms from roadside surveys at night, but seems to over-estimate high-BAL kms. Direct field validation is highly desirable.