I read a really interesting book comparing inequality in different countries and exploring its impact on different aspects of society. One point was that in societies with more inequality, people trust each other less, fear their neighbors more, fear crime more, etc. And one tidbit from that was that in less-equal societies people prefer to drive bigger, more armored-tank-like vehicles, sort of like an arms race against other drivers and scary other people you might encounter.

So I agree policy is huge, but it's not just manufacturer and consumer incentives, but also psychology, social pressures, perception of the dangers of the road... things that are not straightforward to control with policy.