'mass * velocity' means it's a truism that heavier cars are more dangerous if they hit you. All factors being equal the question of car mass is indeed a significant issue. But if you compare road deaths in (for instance) Britain (about 21 per million) and Romania (about 93 per million) it's clear that priorities in this case at least, should be a focus on driver behaviour unless someone wants to suggest there's some other factor I've missed. That's my experience having driven extensively in both countries. I gather EU average is around 44 deaths per million.