Is a crash 3.93× as likely at .08?
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How much does crash risk climb with each step in breath alcohol?
In a US government study, researchers breath-tested drivers at 2,682 crashes in Virginia Beach over 20 months. A week later they tested drivers who hadn't crashed, at the same spot, day and time.
Adjusted for age and sex, crash risk vs no alcohol was 2.07× at a breath level of .05, 3.93× at .08, 5.64× at .10 and 12.18× at .15.
One US city, any police-reported crash, and every figure comes from one fitted curve; the top readings rest on few drivers (113 crash drivers at .05 or more).
Sources
Lacey JH, Kelley-Baker T, Berning A, Romano E, Ramirez A, Yao J, Moore C, Brainard K, Carr K, Pell K, Compton R. Drug and Alcohol Crash Risk: A Case-Control Study (Report No. DOT HS 812 355). Washington, DC: National Highway Traffic Safety Administration, December 2016.
What the study says
- “This study used a “case-control” design to estimate the risk of crashes involving drivers using drugs, alcohol or both. Data was collected in Virginia Beach, Virginia, for 20 months.”
- “When adjusted for age and gender, drivers with BrACs of.05 g/210L are 2.07 times more likely to crash than drivers with no alcohol. The adjusted crash risk for drivers at.08 g/210L is 3.93 times that of drivers with no alcohol.”
- “Teams responded to 2,682 crashes, of which approximately16% (n = 431) were single- vehicle crashes, and 84% (n = 2,251) were multiple-vehicle crashes.”
- “Approximately 66% (n = 1,781) were property-damage only crashes, and 34% were crashes involving an injury (n = 886) or fatality (n = 15). The small number of fatal crashes precluded separate analyses of crash risk.”
- “Because of sample size concerns and the relatively small number of drivers at very high BrAC levels (e.g., at AC =.08 and above), the statisticians collapsed all ACs ≥.05 into a single level.”
Where it falls short
These are relative risks, not a rule for when it's OK to drive.
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