You know those moving walkways (Trav O lators?) that they have in airports to speed up travelers?
I'd place those everywhere.
Want to go to the grocery store? Walk there in 5 minutes. Living in LA and need to visit SF for the weekend? Get off your ass and walk there.
The thing that bugs me most about cars, in addition to wasting gas, is that they're isolating devices. They prevent me from admiring scenery, meeting interesting people, and walking more often.
(This idea is more a revolution than a reinvention.)