DUI laws have changed significantly over the years. Prior to prohibition, the law simply stated that a driver could not operate a motor vehicle while intoxicated. However, the word “intoxication” was not defined. In the ‘30s, the American Medical Association and the National Safety Council decided that a legal limit should be imposed and placed that limit at 0.15 percent. This is nearly twice the limit today.
Mothers Against Drunk Driving (MADD) was founded in 1980 by Candace Lightner. Her organizations’ efforts led to federal pressure to lower the limit to 0.08 percent. All 50 states have this 0.08 standard. However, Colorado adopted a still stricter standard. Colorado does have the 0.08 per se standard for DUI but also has a 0.05 standard for Driving While Ability Impaired. "Driving while ability impaired" means driving a motor vehicle when a person has consumed alcohol or drugs that affects the person to the slightest degree so that the person is less able than the person ordinarily would have been, either mentally or physically, or both mentally and physically, to exercise clear judgment, sufficient physical control, or due care in the safe operation of a vehicle.
This lower 0.05 standard is being proposed nationally and is actually opposed by MADD’s founder. "I don't believe it is a practical long-term solution," Lightner told U.S. News. "You could go to 0.0 and that would save lives. You could go to a 40 mph speed limit and that would save lives, but you have to look at what's realistic."