An Budd SPV-2000 Car #629 sits on the Grapevine Vintage Railroad turntable awaiting its future.

Below is an excerpt from Wikipedia

The Budd SPV-2000 is a self-propelled diesel multiple unit railcar built by the Budd Company between 1978 and 1981 for use on North American commuter railroads. The design was a successor to Budd's popular Rail Diesel Car (RDC) but based on the body of the Amfleet passenger car. It did not prove a success: Budd built 31 cars and they proved mechanically unreliable.

The Connecticut Department of Transportation purchased 13 SPV-2000s at roughly $1 million apiece in 1980; 12 for use on the New Haven–Springfield Line and one for commuter service on the Danbury Branch.The New Haven–Springfield Line cars were leased to Amtrak (numbered 988–999) and painted in Amtrak's Phase III livery. The cars were designed to be interoperable with Amfleet cars; for a brief period, Springfield shuttles were coupled to the rear of Boston trains at New Haven to provide through service to Washington, D.C.

The cars proved mechanically unreliable and were often pulled by locomotives, leading to the derisive sobriquet "Seldom Powered Vehicles". Amtrak withdrew them on January 12, 1986 and placed conventional locomotive-hauled Amfleet trains on the route. The cars saw some use on the Metro-North Railroad; most were stored in New Haven. In 1994, the remaining 11 were de-powered and converted to coaches for use on Shore Line East commuter service. Dubbed "Constitution Liners", they were the primary coaches for Shore Line East until replaced by Mafersa coaches in 2004.