How to design a city?

not really.

'shared space' people are pushing users to mix but i feel that cars and people really don't mix. one is in a steel box and the other is not.

but you need to provide access for both. unless you're living in some fantasy land people are going to need cars for a variety of common purposes, and there's no point planning a city without adequately catering for that.

not everyone has the same ability to replace cars with bicycles as I do.