The article Trolleybus gives a description of the electric trolley bus (trackless trolley; trolley coach) including technical details. As of 2012 there were around 300 cities or metropolitan areas where trolleybuses were operated, and more than 500 additional trolleybus systems have existed in the past. For complete lists of trolleybus systems by location, with dates of opening and (where applicable) closure, see List of trolleybus systems and the related lists indexed there.