Builder: State Belt Railroad (Originally Union Oil Tank). Year Built: circa 1915

Idler Flatcar #3 is one of four idler flatcars used by the State Belt Railroad of California (later known as the San Francisco Belt Railroad). Flatcars 1, 2 and 3 are identical, with the exception that #1 has the addition of end steps for the brakeman. These cars were rebuilt from turn-of-the-century oil tank cars. Curved tank braces still exist underneath the cars just over the truck bolsters. State Belt #3 was converted from Union Oil tank car UOX #88 (renumbered UOCX #907).

These cars still retain their original arch-bar trucks, even though these were prohibited in the 1930's for interchange to other railroads. Since these cars were not intended for interchange, there was no need to change the trucks to a more modern type.

Idler flatcars had a very specific purpose in life - they were used as spacers between the locomotive and freight cars that were being pushed onto barges. This was done to prevent the heavy locomotive from running onto the barge and accidentally sinking it. Since the freight cars were now several idler cars away from the locomotive, two idler cars had steps at the ends for the brakeman to stand on.

The State Belt Railroad serviced several ferry slips along San Francisco's Embarcadero waterfront, the most famous being pier 43 near Fisherman's wharf. This ferry slip still stands today just a short walk from Pier 39, although it is now disconnected from the railroad tracks. (If you look carefully, you can still see tracks underneath the lawn in front.) The State Belt Railroad received freight cars here from the NorthWestern Pacific R.R. (from Marin County), the Santa Fe (from Richmond), and the Western Pacific (from Alameda).

All four State Belt Railroad idler flatcars are preserved at the Golden Gate Railroad Museum in San Francisco. The GGRM considers these cars to be an important part of San Francisco's railroad heritage.