On Blood Alcohol Content

Candace Lightner, founder of Mothers Against Drunk Drivers recently published a counter-intuitive op-ed against lowering the blood alcohol content (BAC).

Hopefully everyone agrees that if there were fewer drunk drivers on the road, there would be fewer deaths from drunk driving. Hopefully everyone also agrees that BAC is correlated with impairment. The blood alcohol content limit, currently 0.08 in the US, is 0.05 in many other countries of the world. Should the US lower the BAC?1280px-Ljubljana_car_crash_2013

The argument against is that pulling over safe drivers (say in a police screenline, where all drivers on a road are pulled over and briefly tested) takes police resources that could be better spent pulling over observed dangerous drivers. Lightner writes: “Every dollar spent enforcing DUI laws against sober drivers is one not spent on getting the worst offenders off our roads.” Perhaps 2 drivers at 0.05 BAC are less dangerous than 1 driver at 0.10, so spend the time finding that driver.

But such police screenlines have the effect not just immediately about arresting people in violation of the law, and also as warning, reminder, and deterrent against future alcohol (and drug) impaired driving. To say the resources are a waste misses a major point.

International experience shows most other developed countries have significantly lower crash and fatality rates than the US, and they have 0.05 or lower BAC. Perhaps the US should just copy their traffic laws lock, stock, and barrel. Researchers have estimated ‘an additional 538 lives could be saved each year if the United States reduced the limit to 0.05,’ (Wagenaar et al. 2007)

Casual drinkers are a problem. Social drinking is a problem. I don’t care if you drink at home and don’t bother anyone (aside from the health insurance claims you impose on society from the damage you do to yourself), but when you drive a car, you endanger others. And because you are impaired, you don’t have the reasoning abilities to realise this.

The rules of the road should not only punish, but also provide a strong deterrent, which includes arrest and punishment even if you didn’t actually kill someone this time. Until robots fully rule the roads in 25 years, possibly another million Americans will be killed in car crashes. We can avoid tens of thousands of them with lower BAC limits.

The scientific evidence on this is fairly clear: Fell and Voas (2006) write:


This scientific review provides a summary of the evidence regarding the benefits of reducing the illegal blood alcohol concentration (BAC) limit for driving and providing a case for enacting a .05 BAC limit.


Fourteen independent studies in the United States indicate that lowering the illegal BAC limit from .10 to .08 has resulted in 5–16% reductions in alcohol-related crashes, fatalities, or injuries. However, the illegal limit is .05 BAC in numerous countries around the world. Several studies indicate that lowering the illegal per se limit from .08 to .05 BAC also reduces alcohol-related fatalities. Laboratory studies indicate that impairment in critical driving functions begins at low BACs and that most subjects are significantly impaired at .05 BAC. The relative risk of being involved in a fatal crash as a driver is 4 to 10 times greater for drivers with BACs between .05 and .07 compared to drivers with .00 BACs.


There is strong evidence in the literature that lowering the BAC limit from .10 to .08 is effective, that lowering the BAC limit from .08 to .05 is effective, and that lowering the BAC limit for youth to .02 or lower is effective. These law changes serve as a general deterrent to drinking and driving and ultimately save lives.