DUI and drunk driving laws are written by the state legislators in each state, so there are fifty-one different sets of laws, including the District of Columbia's. Every U.S. jurisdiction has a 0.08 percent blood alcohol content (BAC) limit for adults operating a motor vehicle. The amount of alcohol that's safe to drink before driving really depends on how alcohol affects you. That will vary based on your age, weight, metabolism, (how your body breaks down alcohol), how much you've eaten, and the type of alcohol you've consumed. If you drive with a BAC above 0.08 percent, you are considered in violation of the law and subject to punishments such as loss of driving privileges, fines, and jail time.

Zero tolerance laws

The zero tolerance laws say that since it is illegal for anyone under age 21 to drink alcoholic beverages, alcohol is an illegal drug for any person under the age of 21. All U.S. states have a zero tolerance policy and DUI laws to match, with a limit of 0.00-0.02 percent, depending on the state.

Drivers under age 21 in many states are in violation of the law even if they have a BAC as low as 0.01 percent. A driver under age 21 who is arrested for DUI and has a reading of 0.02 percent or more will be charged with DUI-alcohol per se(as a matter of law). Some states have even extended the loss of driving privileges to any underage passengers riding in a motor vehicle driven by an underage driver who is under the influence of an impairing substance.

Administrative License Revocation Laws

Administrative License Revocation (ALR) laws, also called Administrative License Suspension (ALS) laws serve to suspend or revoke a suspected drunk driver's license even before the case goes to trial on the charges of DUI.

As of 2008, forty-one states and the District of Columbia adopted some form of administrative license revocation (or suspension) laws. States that currently do not have any form of ALR/ALS laws are Kentucky, Michigan, Montana, New Jersey, New York, Pennsylvania, Rhode Island, South Dakota, and Tennessee.

In states with ALR/ALS laws, DUI detainees who refuse to give blood, breath, or urine samples, as well as anyone who submits to the testing and exceeds the legal limit, will suffer some sort of additional administrative legal action against his or her driving privileges.

Other impairing substances

Alcohol is not the only impairing substance that drivers are prohibited from being under the influence of while operating a motor vehicle. All states prohibit driving under the influence of most impairing drugs-including illegal, prescribed, or over-the-counter medications. Taking medication prescribed by a doctor, or even that which you may get in a grocery store, can constitute the basis for intoxication. Even some herbs and health formulas can reduce a person's cognitive ability and lead to a DUI arrest and conviction.

Additional resources:

OHS: Blood Alcohol Concentration ("BAC") Chart

NHS Direct: How much alcohol is safe to drink before driving?

Motortorque.com: Drunk Driving FAQ

Related Legal Guides:

Driving under the Influence

What to Do If You Are Stopped for Drunk Driving in Washington State

Consequences of a DUI Conviction in Washington State

If You Are Accused of DUI/OUI in Massachusetts