From J.Dinsdale: I think it may be a generator car, judging from the plug-ins on the side... either that or a hydraulic power pack for running auxilary hydraulic tools such as a drill and saw. It doesn't look like an air compressor because there's no tank. From me: I'd note there is a mechanical device on the right. It's out of focus in this picture, but can be clearly seen in the picture on the (previous) Track Monsters page. From W.L.Dunham, ex-machine operator, GTRR: It's obviously hydraulic, but lacking a work station suggests a power supply. May also be an old track liner. They were used to line the track before the technology of tampers improved to the point that they took over the role. From Railways -(at symbol)- Uniserve.Com: I note there is a rail head clamp assumably in the mid section of the unit as seen here. The hydraulic pump unit looks like it has a fair amount of power. There are what appears to be joint power bolting unit, maybe a rail drill. The mast could house a hyd.ram,with all the hydraulics noted it would be helpful to see the rest of the attached (?) cart. Best guess (and assumed) that this unit possible may be used by a spot lifting or by a destressing crew. It might be used also for tie anchor insertion. From a San Diego reader: It's a Rail Lifter for inserting tie plates.