Three-car trains of PCCs were a common rush hour sight on the MBTA's Boston College/Commonwealth Avenue line (now the MBTA B Line) in the late 60s/early 70s. The lead car on this train wears a short-lived experimental gray paint scheme. It's outbound approaching the BC terminal.
The MBTA is very dear to me. The first trains I ever rode as a toddle to teenager were those of the "T" Here is a collection of MBTA Subway and trolley I have found on RP from the 60's thru today.