 Dumbarton Rail Corridor would provide service between Union City in the East Bay (where passengers could connect with BART, ACE and Capitol Corridor trains) and Menlo Park on the Peninsula, with train service continuing to both San Francisco and San José along the existing Caltrain tracks.It has been in the planning stages since 1988, and would be the first above-ground transbay rail line since Key System electric trains stopped running on the lower deck of the Bay Bridge in 1958, and the first new transbay crossing of any kind since the completion of the Transbay Tube in 1974.The Dumbarton Rail Corridor service, as proposed in 2006, would provide six westbound trains originating from the Union City BART station, rebuilt as an intermodal station; after crossing the rebuilt Dumbarton Cut-off bridges, the trains would join the existing Peninsula Corridor (Caltrain) line south of the existing Redwood City station.