European cars have to live up to strict safety standards and pass regular thorough inspections
European drivers have to go through more driving education and pass stricter theoretical and practical driving tests to get a license than their US counterparts.
European car culture is different from American. Drunk driving seems to be significantly more frowned upon than in the US and there is a cultural norm of keeping eyes on the road at all time
Distances in Europe are shorter so drivers doesn't experience the same levels of fatigue.
In contrast to poorly maintained car-centric US roads European roads are generally in good shape and most places have infrastructure in place to protect cyclists and pedestrians
Some reasons for this