Modern Tramway and Light Railway Review, June 1962 carried an article based on notes by H.J. Bertschmann, G.A. Meier and M. Frei about then new articulated trams in these two Swiss cities.
Both the Basler Verkehrs-Betriebe and the Verkehrsbetriebe der Stadt Zürich had taken delivery, in the months prior to the article being written, of the first prototypes of a new design of articulated tramcar. The design was a new departure, a double-articulated tram on three trucks. Earlier models of articulated cars had two sections on two or three trucks, or three sections on two or four trucks, but never before three sections on three trucks.
http://rogerfarnworth.com/2023/08/03...way-june-1962/