On the Go Electric Bus Recharging

Korean transit company is installing inductive charging system.  Batteries on the bus are recharged as the bus drives over a particular segment of pavement.

http://spectrum.ieee.org/tech-talk/green-tech/advanced-cars/korean-bus-charges-itself-while-driving

Would seem to work just as well for trams, with recharging at stations. 
Probably means the buses/trams would be heavier (because they have to carry some batteries), but the battery systems are getting lighter all the time.