Boston's trackless trolley-bus service will end on Saturday March 12th

[Willbridge]

The reason for the timing of eliminating the TT operation before electric buses are available is that the route is undergoing significant street work which would require removal of the wires so since the long range plan was to go to battery electric the MBTA decided to pull the plug on overhead wire operation now. Also the overhead infrastructure would require significant updates anyway and they figured battery electric was more cost effective.

This looks like the normal procedure -- trolley coach line/s discontinued with promise of something better, with motor coach temporarily -- then something better is unworkable, so Diesels roll on.