[chuckm]

This could be done with non-electric cars as well, but I think this would be VERY cool and good for saving power or gas:
Basically, equip cars with a GPS with an up-link to a city traffic grid. You put in your destination and the GPS uploads your route to the traffic computers, which then communicates back to you the optimum route and speed. In turn, it times the lights on your path. Equip enough cars with the system (and compliant drivers!) and you can reach a critical mass, essentially forcing most people to drive more efficiently.