All States have now established low blood alcohol content limits of .00 to .02 for drivers under 21 years old. These "zero tolerance" laws are an extremely important tool for reducing impaired driving by youth. Such laws have resulted in decreases of about 20 percent in alcohol-related crashes among youth. When these laws are accompanied by a vigorous public awareness campaign, a reduction of 50 percent in alcohol-related crashes was found. In enforcement efforts, this guide recommends that in any stop of a young driver for any traffic violation, the officer should be alert for the presence of alcohol and keep in mind that any amount of alcohol is a violation for drivers under 21 years old. Further, where permitted by law, officers should use passive alcohol sensors to detect the presence of alcohol. Sobriety checkpoints should be used as a means of identifying young drivers who have been drinking, as well as to enforce the zero tolerance laws. Police agencies should work with community leaders to identify problems with the laws or policies that implement the law; they should work to reduce or eliminate those problems with legal or procedural changes. This guide also discusses some of the barriers to enforcing laws against youth drinking and driving and suggests possible techniques for overcoming these barriers. 4 references and 14 other resources