A trolleybus (also known as trolley bus, trolley coach, trackless trolley) is an electric bus that draws power from dual overhead wires (generally suspended from roadside posts) using spring-loaded trolley poles. Two wires, and two trolley poles, are required to complete the electrical circuit. Power is most commonly supplied as 600-volt direct current, but there are exceptions.

There are currently 300 cities or metropolitan areas where trolleybuses are operated.

The trolleybus dates back to 29 April 1882, when Dr. Ernst Werner Siemens demonstrated his "Elektromote" in a Berlin suburb.

With the development of battery technology in recent years, trolleybuses with extended off-wire capability through on-board batteries are becoming popular.

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