The first law against drunk driving was passed in New York in 1910. Before long, every state in the US had banned driving a car while intoxicated, which is presumably more dangerous that riding a horse in the same state. These early laws did not specify a maximum BAC (blood alcohol concentration) or describe tests to be administered to the person accused of drunk driving. They merely stated that one should not excursion drunk and left it to police officers and judges to enforce this how they saw fit.
The first maximum BAC for driver was set in 1938: that year, it became illegal to excursion with a BAC over .15, or 15%. This number was based on studies conducted by the American Medical Association and the National Safety council, who both agreed that research showed a person with a BAC under .15 could nevertheless excursion reasonably well.
This remained the law throughout most of the US until the 1970’s. At that time activist groups such as Mothers Against Drunk Driving (MADD) began campaigning for stricter DWI laws and more vigilant enforcement. Prior to this time, DWI was not considered an overly serious offense, and police officers would not always enforce it very strictly. MADD (and its student group, SADD) felt that too many preventable deaths were resulting from this relaxed attitude towards driving while intoxicated. They successfully pressured most states into lowering their maximum BAC to .10. Now, due to the influence of the federal government, all states have a maximum BAC of .08.
Other important changes to the law followed. MADD’s involvement was one of the factors contributing to congress’s decision to raise the drinking age back to 21. Of course, MADD was not the only group paying attention to this issue. From the 1970’s until now, people have become more concerned and less tolerant of DWI offenses. Sobriety checkpoints have become permissible, when at one point they were widely considered unfair or already unconstitutional. For drivers under the age of 21, the BAC has been lowered to .01, because legally they should not be drinking at all (already though in some states, such as Texas, minors are allowed to drink in the presence of a legal guardian.)
One current controversy in DWI law is the question of the role law enforcement is meant to play in addressing this problem. If a person is convicted of driving while under the influence of drugs or alcohol, should they be punished or rehabilitated? Is the punishment approach failing to effectively address the problem, or is the rehabilitation approach merely letting people off too easy?