A trolleybus normally uses two trolley poles.
A trolleybus draws electricity from two parallel overhead wires rather than from rails. One wire supplies current and the other provides the return circuit, so the vehicle needs two separate trolley poles—one contacting each wire. Spring-loaded or pneumatically raised poles keep the connection while the bus moves along the road.
This distinguishes a trolleybus from a conventional tram or streetcar. A tram generally uses the metal rails as the electrical return path, so it normally needs only one overhead contact wire and one pole or pantograph. Battery-electric buses, by contrast, do not require trolley poles while driving.
The poles are mounted at the rear of the bus and can come off the wires if the vehicle turns too sharply or moves outside the overhead alignment. Drivers may then have to reconnect them manually using poles or ropes. Modern trolleybuses may also carry batteries for short off-wire sections, but their ordinary overhead operation still uses two poles.