Better public transportation, walkable streets, and non car-centric urban planning in general has done far more to prevent drunk driving than harsher laws. Data shows that the incidence of DUIs are more or less proportional to the need for residents in a city to drive in general. DUIs are rarely premeditated, purposeful crimes. Very few people are at the bar rubbing their hands together as they down their fourth shot, anticipating the moment when they get behind the wheel. The vast majority of DUIs are the result of poor planning and poor decisions when you just want to get home, and in situations like that the threat of punishment or simply the voice of their conscience is also a lot more likely to be ignored. Providing easy alternatives to droving goes a long way to preventing DUIs. People are way less likely to be in a position to DUI when the metro is the most convenient way to and from the bar.