Automobile traffic is threatening to overwhelm the cities of the San Francisco Bay Area, and an advanced mass transit system is being built by the Bay Area Rapid Transit District (BARTD) to help alleviate this problem. This article describes the design and development of the passenger vehicle for this system. BARTD system requirements and car design criteria are discussed, and the conceptual design and detailed development of passenger accommodations, environmental control provisions, lighting, ingress/egress, visibility and appearance design featurea are presented. The requirements for and the detailed design of the train attendant's pod are also discussed. A prototype car has been designed with primary emphasis on those human factors considerations that are expected to induce 200,000 commuters to use the system in preference to private automobiles. Public reactions to the prototype vehicle will be employed to refine and improve upon the design prior to its introduction into service in 1971.