There is a N scale BART model out there.
http://www.wurlington-bros.com/DC/BartTrain.htmlFor HO scale and the history of Athearn (parts)/Walthers models.
From Trainorders; "I don't think it was actually made by Athearn, it was just "Athearn Powered" by using the RDC drive. Looks like the original price $38.95. I doubt many were ever sold."
and
"Not the same product. These were much earlier than the Walther's ones. These are actual extruded aluminum while the Walther's were plastic. And yes, I believe that the Walther's model was also offered in a WAMATA (Washington DC) version."
Followed by.
"Also, the Walther's model had an underfloor power truck, not a motor and drive shaft arrangement like in the photo."
To see the original model.
https://www.worthpoint.com/worthopedia/athearn-bart-train-car-set-ho-scale-1833714620