In 1927, the D&RG's Burnham? Shops took combination baggage-coach car 392 (previously DRG 784, built as Rio Grande Western coach #216) and converted it into an experimental motorcar using two 6-cylinder, 100hp Continental diesel engines. Power was delivered to the wheels via generators and traction motors. The car was tried in numerous places across the system, including the Leadville Branch and Creede Branch, but never found acceptance. According to limited reports, the electrical gear was prone to failure.
Burnham removed the engines and electrical gear from the car in 1938 and returned it to just being a combine. It continued in service as a regular passenger car until 1951.
M1 and M2 - each a two car, stainless steel, self-propelled passenger train - were built by Budd in November of 1941. Each set was powered by a pair of 6-cylinder 192hp Hercules diesel engines. Unlike a Budd RDC, however, the wheels were driven electrically through a generator-traction motor setup.
M1's cars were named "John Evans" and "David H. Moffat", and M2's cars were named "Brigham Young" and "Heber C. Kimball", referencing prominent figures from Colorado and Utah sides of the railroad.
The cars were used to launch the new "Prospector?" service from Denver? to Salt Lake City? on 17 Nov 1941. The tiny engines and drive train were not up to dealing with the Rio Grande's mountainous route, however, and often suffered failures en route. As a result, they were often pulled by a steam engine coupled to the front. The cars were rather quickly deemed a failure and the train was discontinued on 5 Jul 1942. (The Prospector? would be relaunched three years later in 1945, using conventional heavyweight equipment and diesel locomotives.)
Both car sets were returned to Budd after being withdrawn from service, and were subsequently scrapped.
Images of M1 and M2
DPL images of M1:
DPL images of M2: