I used to be a cop. (No kidding! Really!)
In my experience, after 10 pm, every third car on the road has an impaired driver (now, this was in a fairly small town--about 50,000--so I'd expect the ratio to be higher in a bigger town. More folks just going out for milk, you know). And on weekends--Friday, Saturday, Sunday--generally one out of two cars had an impaired driver.
Pull someone over for anything--seat belt, failure to use a turn signal, missing tail-light--and odds were, you'd be smelling booze and pulling them out of the vehicle to take a sobriety test. Catching drunk drivers was like shooting fish in a barrel.
What's worse, rare was the fellow who'd admit to being impaired. The worst part of drinking and driving is that people who are the most dangerous--those in the .05 to .10 range--don't think they're impaired. But their reaction time, vision and judgment have all declined significantly.
If you drink, DON'T DRIVE. Period. Take a cab. Call a friend. Sleep over. Don't get behind the wheel.