[justincormack]

London tried to have a form of that, where pedestrians could go on raised walkways, while the cars owned the roads underneath. Fragments remain around the Barbican in the City of London, and you can see blocked off unfinished walkways.

Underground roads are being suggested in many places as they free up land for buildings.

[vidarh]

Toronto is a better example of separating cars and pedestrians, though it's underground rather than raised:

http://www1.toronto.ca/wps/portal/contentonly?vgnextoid=f537...