However, when I saw them this morning in the yard outside of Oceanside, they had an Amtrak locomotive hooked up at either end. (The second one is a baggage car of some sort).
Do FRA employees criss cross the country doing inspections? What do they inspect?
The windows were pulled so I couldn't see anything inside.
Update from Anonymous in the comments:
[T]hey visit on average twice a year or so. I've worked the trains twice, it's actually very boring once you get past all the interesting gizmos in the car. The car is equipped with scanners which check the cross section of the track, x-ray it for fractures, and generally make sure it's balanced and everything is within tolerance. Usually the railroads have a gang ready, and as the car buzzes over the railroad they'll spot defects which are quickly reported to management and addressed.
This year they came down the Coast from the Bay area via San Luis Obispo, then went to San Diego, spent a night inspecting the San Diego Trolley lines (I believe under their own power, as a matter of fact, since there are different operating rules in place), they then went up to Oceanside where they made a round trip to Escondido on the Sprinter Line, then went back to LA where they traveled around the LA Basin before heading East.
The current generation of cars are capable of being self-powered, and initially were when they first came out, however for several reasons they stopped doing this (The week before the first time I worked one of these it had struck a pickup truck in the Bay area, The second time it had blown the transmission two months earlier and their schedule didn't allow time for repair. They also have problems defining whether the cars qualify as a train, or "On-Track-Equipment" when they operate on their own power, so there have been arguments over who is supposed to operate the controls, and how the dispatcher is supposed to dispatch it, so it's become operationally easier just to attach a locomotive and call it a train.)