A trolleybus (also known as trolley bus, trolley coach, trackless trolley, trackless tram or simply trolley) is a bus, which gets its power for the electric motor from a pair of powerlines, which is above the street. Trolleybuses get the power though 2 poles called "trolley poles".
A trolleybus does not have a normal engine which uses oil. So trolleybuses are much clearner and quieter than "normal" buses. Trolleybuses do not use tracks, so they are more flexible than trams. There are not many companies which built such types of buses. Some of these companies are:
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