It probably depends on the location in the US, but every time I go there I find Americans amazingly relaxed when driving. Swiss are probably some of the more careful drivers in continental Europe (which is to say they're slow), but I think it's still way more nervous than in the US. However, one of the issues is probably the sheer size of US roads, it's just much harder to cross I think. And from my own experience, kids who are tasked to look after themselves, after a certain age will actually learn to be careful very quickly. Plus, near school there's lots of warning signs and drivers are generally careful there. Generally it's not an issue, but I can see how US suburbia could be ill fitted for such a system.