In order to sell to customers whose requirements (and electrical and track structure capacity) would not support a Class D, Baldwin-Westinghouse downwardly engineered this design in order to replace the Class A in its catalog. The better built steam road subsidiaries and those lines that delivered considerable tonnage per train could order larger Class D motors (and even operate them in multiple), while B-W could offer a smaller unit to potential customers with less demanding requirements. The Class B locomotives were better suited than the D's for use on lightly built interurban lines, due to their reduced weight and power draw.

One of the reasons there was a Baldwin-Westinghouse at all was because Baldwin Locomotive Works was so successful as an integrated manufacturer. Baldwin had sufficient capacity in its tender shop in downtown Philadelphia that it could easily underbid any proposed assembly by Westinghouse's own forces out in East Pittsburgh. Baldwin built the structure of each locomotive, riveting together an empty box with trucks and couplers (and at least rudimentary train air brakes), based on the familiar technology of locomotive tenders. The frame itself was assembled from standard steel shapes, with heavy Baldwin castings at each end to tie everything together. Even the trucks themselves were adapted from tender trucks used beneath thousands of Baldwin-built steam locomotive tenders. Windows and a host of additional appurtenances would be installed, then the locomotive-to-be would be shunted out to the interchange track. It would be handed off to a line-haul railroad and waybilled (as if it were a freight car) across Pennsylvania to the East Pittsburgh Works of Westinghouse Electric & Manufacturing. Westinghouse installed and tested electrical gear at East Pittsburgh. The locomotive would be finish painted, tested and otherwise prepared for delivery. A short stretch of adjustable-voltage overhead behind the Works allowed road testing (and publicity photographs) when the locomotive was complete. The track was historically 'pantograph country' so locomotives destined for customers who used only trolley poles or third rail were often pictured at this site fitted with pantographs, which would be removed prior to shipment. In the early years the consortium delivered interurban freight locomotives to specific order, rather than producing them on speculation for stock. However, Westinghouse occasionally ordered freight locomotives from Baldwin for stock, or in anticipation of orders not yet in hand. This practice tied up capital, but as the market for new locomotives dwindled (and credit grew tighter) during the late 1920's, Westinghouse decided to keep at least one or two new locomotives (with generic equipment) on the back lot in East Pittsburgh.

This appears to be a location to change over from 3rd rail to trolley wire.