You're right, I was probably too harsh on the seatbelt point. If you have to be in a car, you should wear a seatbelt. But, the first line of defense is to not be in a car, and the second line of defense is to be on well-designed roads.
American cities lack these two lines of defense. This is probably why crashes are such a big problem here.
This seems strange to me. Why do you doubt this? Even if bus / truck drivers drive drunk at the same rates as car drivers, there would be less drunk bus / truck drivers due to the numbers.
The absolute number is whats important because each drunk driver you add is extremely dangerous to society.
Also if society moved away from car driving, the loss in car vehicle miles traveled would not be compensated for by equal increases in truck / bus vehicle miles traveled because trucks and busses aggregate many trips together.