SLR #100 was once one of a large fleet of express motors that were intended to through operate onto the BERY, but when that business started to dry up under the pressure of trucks, paved roads, and the BERY’s desire to get wooden cars off their elevated system, , the fleet started to shrink (either via retirements, sale, or cutting down units to make them into MOW trailers) and #100, once an anonymous Brill express motor, found itself as the last wooden motor on the SLR, even if it was no longer being used for anything other than carrying tools & hauling MOW trailers around.

As a MOW vehicle, it worked pretty well. It had come with fairly beefy motors, and was able to produce a continuous 500hp. In MOW service, this meant that it could pick up and move a MOW train if it had to get out of the way of a regular freight move.

So when the PV&T took over the railroad, not very much changed; the old road number was painted over with black patches, which then had the new number on top of that, and that’s how it ran from 1950 up until the end of 1957, when the new 3000vdc electrification was done and the SLR could turn off the third rail for the last time.

319 was retired after this, but not scrapped; it was instead loaded onto a flatcar and donated to the Seashore Trolley Museum, along with a handful of money to build a new carbarn to store it in. And there it lives now, painted back into SLR colors, occasionally running, and theoretically available if the MBTA ever has a screaming desire to run express freight on their subway lines.