 The vehicles had auxiliary diesel engines and steering wheels and were able to operate away from the guide rail, but only in diesel mode, and under normal operating conditions they ran only in electric mode when carrying passengers along the route, using their diesel engines only when travelling to and from the depot (garage).The use of pantographs for current collection meant the Caen vehicles could not move laterally away from the overhead wire when operating in electric mode, and for this reason they were not considered to be trolleybuses, under the English language meaning of that word, and the system is sometimes referred to as a "rubber-tyred tramway".It was in 1988 that the SMTCAC ("Syndicat Mixte des Transports en Commun de l'Agglomération Caennaise") first considered developing public transport on a large scale.