Selt belt wearing is rarely enforced anywhere (especially in Europe, in Italy nobody wears one even though it is illegal).
As for autonomous cars. If they ever work, one of the first mods people will do is to add a steering wheel.
> Stopping selling of knives: Yes, once we have a safer way of cutting things.
Knives are a safe way of cutting things. Billions of people use them everyday without issue.
> Though the real problem is probably people cutting each other on purpose, rather than themselves by accident.
How are you going to stop people from making knives? Humans have been making them for several 1000s of years, IIRC Chimps can make them now. In prisons they literally make shives out of toilet paper.
In the UK carrying knives is banned and their sale is heavily restricted. However in our capital city we still have a lot of knife violence. Guns are also heavily restricted but people still have those illegally and people do get shot. My uncle is a convicted bank robber, he had plenty of guns.
You are solving the wrong problem. You must solve the problem of why people are being violent to one another. That will actually make people safer.