You'd have to build 3x as many extra roads, because cars take up a lot more space than bicycles.

Cheaper perahps, but better long-term? Doubtful.

I don't want to live in a concrete jungle. Have you seen what two level roads are like? It's MISERABLE at street level, all shadow and columns.

Well I would counter that that would serve as a great incentive for people to prefer riding their bikes over driving — so that they can enjoy the sunshine. When you think about it though, chances are these raised roads will be much narrower than the roads themselves, as bikes require much less space than cars. So it won't be like a full ceiling on the roadway.

You don't raise the people, you drop the cars. Boring Company style - a sublevel for vehicle traffic.

Are there any good examples of that besides that one Paris district?

maybe with the a bit of help from mirrors (reflecting the sun) the street level would look better.