[quote="dth9269"]Engine #3247 outbound at West Cambridge just now (~9:50AM EDT), hauling a black tanker ("Water Only" stenciled on the side) and a yellow vehicle with various types of equipment (including perhaps a generator?).
UPDATE: The locomotive returned inbound, alone, at ~10:35.
That sounds like the "Slippery Rail" train that they run in the Fall. They fill the tanker with water and then the generator is basically hooked up to high-pressure washer which is then sprayed on the rails and knocks leaves and other gunk off of the rails, thereby improving traction for the locomotive. Somebody uploaded a video of it last year. The "Water Only" tanker spent most of last summer at the West Cambridge maintenance facility. I haven't seen it recently, so maybe it is being prepped for service again this year.