Light rail efficiency advantage

Great to see some pressure for trams/light rail in Bristol (see here). Some of the ensuing online debate mentioned only the disadvantages of trams/light rail but all technologies have both pros and cons to be weighed up. Trams and light rail have some significant factors in their favour and should be deployed where they are viable - they are up to twice as energy efficient as buses and therefore use much less fuel and produce much less carbon pollution. This could prove to be a major cost advantage in times of high fuel prices. The key is to use this technology in the best locations, after full and proper assessment - I dont think this has this has been done in Bristol.