Streets in the center of the city with only bicycles, metro, trams a few busses. This would eliminate congestion and pollution. Cars are only used to go to places that dont have this type of transport.
Taking Jasmine´s feedback i would like to add that there would still be roads for service cars, or trucks to do there business. for example a construction truck, or a grocery truck or buss could use the service lane to full fill its service.
this lane would also be used for hospitals, police and firemen.