Another difference I observed is San Francisco vs. Zurich (both urban areas). While in Zurich very few people I know would drink and drive, people in SF don't seem to really care about being a little tipsy. Of course, this is anecdotale.
Commonly in parts of the midwest, people will pop a roadie while they're driving, to the point that it is part of the culture in places like Wisconsin and Minnesota.
When I was visiting friends in the US, a totally different picture. Almost everyone was happy to drive after a few drinks and noone did care.