Amtrak developed their non-powered Control Units (NPCUs) by removing the prime mover, main alternator, and traction motors from surplus F40 locomotives. The control stand was left in place, as were equipment allowing horn, bell & headlight operation. A floor and roll-up side-doors were then installed to allow for baggage service leading to the nickname "cab-baggage cars" or "cabbages". The F40s rebuilt into NPCUs are identified by their former three-digit road number with the number 90 added.
