They have now phased out the SL operation via overhead wire. MBTA seems to have an aversion to trolley buses. They are instead going with the current fad of battery electric. How this will work out we will see. I think they are using CNG buses in the meantime.
I didn't know they had dumped the articulated trolley buses on the Silver Line. It always seemed so stupid that they ran diesel through the Williams Tunnel. One of the drivers told me it was because they didn't want to get stuck in traffic jams in the tunnel, but that made no sense. They could have run off the overhead wires normally, and then if stuck, retracted the trolley poles, started the diesel engine and driven around any traffic jams or accidents on the rare occasions it was an issue. I suspect they didn't leave enough overhead clearance for the wires when they built the new tunnels, which would have been sheer stupidity.
(Long rant about stupid decisions by the MBTA)
I suspect there are some middle managers at the T who hate electric buses of any kind. 3 of the 4 nearest bus lines to me are (or were until 2 years ago) trackless trolleys. The nearest line (75) is diesel, but though it passes two blocks from my house, had no stops for half a mile in either direction. When all the other recent inept actions went down, they did add an inbound stop at the corner nearest me, which is great, and did increase the frequency during rush hours, but there is no outbound stop (you have to get off a half mile away.)
The next closest lines were all trackless trolleys (aka trolley buses.) About 6 years ago, they rebuilt the road used by the closest line (73). During construction, they took down the overhead wires and some of the poles, replacing the buses with diesels. When they finished, just before Covid, they had put the wires back up and seemed to have upgraded the wiring considerably, adding many more connections between the power supply wires (strung pole-to-pole along the route) to the cat wires. You can see the difference between the new section and the older sections that are still up.
At about the same time, they rebuilt the last section of the 72 line, taking down the wires and then putting them back up when done. This was the last section of the 72 line, which terminates at Mt Auburn St in Cambridge, where it joins the combined 71 and 73 lines. (The buses can loop around and return on their original route or turn left or right on the 71/73 routes.)
Also at about the same time, they rebuilt the bus tunnels at Harvard Sq, terminus of all 4 trackless trolley routes, replacing them with diesels but eventually restoring them.
Then when Covid started, the T drastically cut back the schedules and replaced ALL the trackless trolleys with diesels. They were supposed to return when they restored full pre-Covid service but never did. About 3 years ago, in the midst of Covid, Cambridge (not the T) rebuilt the western section of Mt Auburn St (route of the combined 71/73) and the western most part of Huron Ave (72). They took down most of the poles, apparently for road construction. Then about a year later, the MBTA announced that the trolleys would not be restored, instead they are buying plugin electric buses (none of which have been delivered and possibly not even ordered yet), and eventually the diesels would be replaced by the totally unproven battery buses, and our local lines would get them AFTER everyone else. They said the trolley buses would need replacement soon, which might have been true, but they weren't that old, and seemed to work fine.
Most of the trolley wires are still up, in disjoint sections, and in lots of places, the power wires are still up, strung from pole-to-pole along one side of the road, but the the cross-street wires, which support the trolley wires have been removed.
Trolley buses are less flexible than other buses, because they are restricted to running under wires, but they are by far the most efficient type of bus, since they don't need to haul extremely heavy batteries everywhere. They could be made even more efficient by adding a small (50-100 lb) modern battery and using it to bridge short gaps and to get around traffic jams and detours. They should be adding trolley buses and extending the trolley network, not removing it. (All these decisions were made before hiring Philip Eng as GM, but I haven't heard one word about revisiting those decisions.)
