A trolleybus ( also known as trolley bus , trolley coach , trackless trolley , trackless tram or simply trolley ) is a bus , which get its power for the electric engine from a pair of powerlines , which is above the street . A trolleybus ( also known as trolley bus , trolley coach , trackless trolley , trackless tram or trolley ) is an electric bus that draws its electricity from overhead wires ( generally suspended from roadside posts ) using spring-loaded trolley poles .