Smallest rolling stock?

This has got to be one of the smallest modern rolling stock on the rails? This ballast car, on a track in San Diego, CA, has only 2 axles and doesn’t look very long either. I assume it’s on standard guage track, and not narrow guage. This yellow-painted car has no visible reporting marks either.

Just curious, where in San Diego is this?

Wow! That’s some “light rail” that is under the car. Got to be an industrial spur or something. It looks like there is a transition joint or something to the right, too. I can’t place the area, but then again, I don’t get around the industrial spurs a whole heck of a lot.

It looks like M/W equipment for a transit operation, probably the San Diego Trolley in this case.

It looks like Herzog owns it.

It was made by this company-
http://www.ballastcar.com/ballastcar.htm

I would guess the trolley owns it as well, notice it doesn’t have any couplers… A full size railroad is more likely to use old hoppers rather than buy new; especially with something that small!