Shanghai already employs supercapacitor buses in its regular Metro system. Supercapacitors have the advantage of incredibly fast charging compared to a standard lithium-ion battery, which allows Shanghai's super-cap buses to quickly top off every time they coast into a stop. A special electrical connector extends from the roof, making contact with an awning to recharge. It takes about 30 seconds, ideal for a vehicle making frequent and regular stops. Sunwin, the maker of the buses, is a partner of Volvo in China--more info on the super-cap buses can be found here.