What you need to know about drinking and driving

Even a small amount of alcohol can affect your judgment and reaction time. This makes driving a motor vehicle after you’ve been drinking a potential danger to your own life and the lives of your passengers, fellow drivers and pedestrians.

To reduce this risk, governments around the world have put in place legal limits for how much you can drink and still drive a vehicle ⁽¹⁾. Not complying with these limits can result in fines, losing your license or even jail time.

As the alcohol you drink is absorbed by the body, some will cross into your brain and affect how it processes information and how you respond to the world around you ⁽²⁾. The more you drink, the higher your blood alcohol content, or BAC ⁽³⁾, and the more alcohol reaches your brain. This, in turn, slows down your reaction time and coordination, and impairs your judgment. BAC is expressed as milligrams of alcohol per liter of blood and is a reliable indicator of how impaired you are that’s used for legal and enforcement purposes.

Virtually all countries in the world have set legal limits on the maximum blood alcohol content allowed when driving a car ⁽¹⁾. However, these limits vary. In some countries, no blood alcohol is permitted if you’re driving; in others, a BAC of up to 0.08 is allowed. A zero-tolerance policy is often in place for novice drivers and those learning to drive.

BAC limits are enforced by police, either through roadside breath testing or from blood samples. If you exceed the limit, you’re breaking the law. In certain jurisdictions, people who have repeatedly been caught with excessive BAC may have to use an alcohol interlock device before driving, which requires them to blow into a mouthpiece to start their vehicle and can prevent the engine from running if they’ve been drinking.

There’s a direct relationship between the amount of alcohol you drink and your BAC ⁽³⁾, but how quickly your BAC rises depends on who you are and, of course, how much and how quickly you’ve been drinking. The only reliable way to test your BAC is through a breath or blood test. Whatever the legal limit, the safest option is not to drive impaired.