Effect of Lower Legal BAC on Traffic Crashes

I. Impact of BAC on Traffic Crashes.

What’s the effect of BAC on traffic crashes? (BAC = blood alcohol concentration.) Most drivers who have any alcohol in their bodies have a low and legal BAC. As a result, they have few alcohol-related crashes.


I.   Impact of BAC on Traffic Crashes

II.  The Study

III. Resources

The chart below shows BAC in relation to risk of crach. Clearly, the chances of a crash rise sharply as the BAC goes beyond 0.11 or 0.12. In fact, over two-thirds of alcohol-related traffic deaths involve a driver with a BAC over 0.15.

BAC on trafficAs a result, many states have laws either permitting or requiring stronger punishments for drivers with high BACs. These sanctions may include longer imprisonment, higher fines, use of interlocks, longer license suspensions, etc. These often begin with BACs of 0.10 or higher.

Fortunately, alcohol related traffic deaths have dropped dramatically. The deaths drunk drivers cause is now half of what it was in 1982. It’s hard-core drunk drivers who now cause most traffic deaths. Therefore, many states use DUI Courts to address the problem of hard-core drunk drivers. Ther’s good evidence that such courts are effective in reducing intoxicated driving.

BAC on traffic
Krystil Kincaid

Although alcohol-related traffic deaths have dropped greatly, even a single death is a tragedy. Therefore, this page is dedicated to the memory of a randomly selected victim of a drunk driver. It’s Krystil Kincaid. Her grieving children, husband, and other family members mourn her death. Learn more in the Resources section below.

II. The Study

Scotland reduced the maximum legal BAC from 0.08 to 0.05 in 2016. England and Wales kept their BAC levels at 0.08.

This provided a natural experiment to test the effects of a lower BAC on traffic crashes. Researchers studied both crashes and alcohol purchases after the change. To do this, they compared these in Scotland, England, and Wales.

Here’s what they found after the reduction in Scotland.

    1. There was a 7% increase in traffic crashes.
    2. Sales of alcohol for drinking at home didn’t change.
    3. Sale of alcohol consumed on premises dropped seven-tenths of one percent (0.7).

The National (UK) Institute for Health Research Public Health Research Programme funded the study. Lancet published the article reporting it.

Mothers Against Drunk Driving (MADD) strongly supports lowering the legal BAC. It insists that lowering it from 0.10 to 0.08 would cause a dramatic drop in traffic deaths. But it did not. Yet arrests for DWI and DWI did increase greatly.

III. Resources: Effects of BAC on Traffic Deaths

Web Pages

Drinking and Driving Facts & Solutions.

Help Police Stop Drunken Drivers. 

DWI and DUI Courts are Effective  

Inaccuracy of Breathalyzers.  


Haghpanahan, H., et al. An evaluation of the effects of lowering blood alcohol concentration limits for drivers on the rates of road traffic accidents and alcohol consumption. A natural experiment. The Lancet.


Krystil Kincaid’s husband and son. The driver of the other vehicle was arrested and charged with gross vehicular manslaughter while intoxicated.

BAC on traffic
Son strains to get one last look as his mother.
BAC on alcohol
It’s so hard to let go.

Please don’t drive while impaired by any substance.