What is a Trolleybus?
A Trolleybus is an electrically powered bus which collects its electricity supply from two overhead wires through a pair of trolley booms mounted on the roof. This is similar to a Tram, but as the latter run on rails, they do not need a second overhead wire; they return the electric current through their rails, whereas a Trolleybus has to use the second wire. Like a Motorbus, a Trolleybus runs on rubber tyres on normal roads, but does need the roads to be equipped with the necessary wiring. However, they are more flexible than a Tram, being able to diverge from the overhead wires by several yards to avoid obstacles or broken down vehicles, where a Tram would be stuck.
Some modern trolleybuses have an auxiliary means of providing traction power, either from a small diesel engine or a bank of batteries to allow operation away from the overhead wires.