Dr. Elmer A. Sperry undertook construction of a second detector car even before the ARA accepted the initial car ( accepted on October 2, 1928 ) and then established Sperry Rail Service Company in Chicago during 1929 to provide rail flaw detection service to the nation's railroads with a small fleet of cars owned by his company - a profitable business that continues to this day. The ARA acquired the original car under terms of its development contract with Sperry, ultimately paying an additional $15,000 to cover extra costs of the development project. On the ARA, the car was numbered X-101.

Sperry's contract with the ARA provided that member roads could purchase cars from Sperry at a stipulated sum or build them themselves according to Sperry's plans and specifications. But Sperry balked at this, so a group of six Western railroads, known as the Western Group, and including the Burlington, Great Northern and Northern Pacific, plus Santa Fe, Southern Pacific, and Union Pacific, banded together in 1929 and successfully fought Sperry, forcing the company to sell them his plans and specifications.

Over the next several years the Burlington undertook construction of six of the little cars on their short ( 8 feet 5½ inch wheelbase ) Kalamazoo Railway Supply Company chassis, one for each member of the Western Group. The Burlington, GN, and NP cars were jointly owned by a detector car pool established by the three roads and carried reporting marks of all three roads, with the Q car numbered 1, the NP car 2, and the GN car 3. Tow cars were provided by the individual railroads, The Burlington and NP cars were completed in 1933, and the GN car followed in 1941. The little four-wheel power unit for Burlington detector car 1 was lettered only for the Q and, in the inspection/internal combustion motive power tradition of 9000 number series, carried the number 9030. The power unit was constructed on a steel channel underframe, and both units featured vertical tongue-and-groove wooden siding. The two cars were painted Safety Yellow, a light, almost pastel shade that made them hard to miss. Underbodies, doors, window frames, and roofs were black.

By 1939 the homemade tow car had been modified somewhat from its original appearance. It now featured a pair of lower windows in the front and a box on the roof up front, on which the reporting marks and number were stenciled. The canvas cover seem to always cover the unidentified equipment mounted on the roof at the rear end. By 1942 Burlington's original detector car 1 was re-stenciled with just the CB&Q reporting marks following the dissolution of the Q/GN/NP detector pool for cars 1, 2, and 3.