The GN used their one RDC-3 to serve two routes, Billings-Great Falls and Great Falls-Butte, at the same time. These were rural, secondary mainline runs of several hours each, and it made both round trips every day. The NP used their RDC-2s and 3s on branch lines in eastern Washington and the Midwest. Several roads used theirs in suburban/urban commuter service. So they could be found in almost any service and region. If you want them, there's bound to be a job for them.
The GN and NP bought the RDC-3 for the RPO space. If you don't need that, but can get an RDC-3 at a good price, the room could always be converted to extra baggage or LCL freight space.
