HO-Scale Scale Motor Car & Supply House for Signal Maintainers. The Motor Car & Supply House for Signal Maintainers were NP standard structures, dedicated to the personnel maintaining the critical signal equipment along the railroad. This tall shed is unique in its height, and really stands TALL in historical photos of line-side structures. The floor plan included a motor car compartment, a small workbench and tool storage area heated by a coal stove, and interior ladder access to an attic storage area. Once found at many points along the NP mainline, an intact prototype of the structure, as originally modified with an extension shed at the rear of the motor car compartment, still exists at Plateau, Montana (end of Plateau Road).