The 1999 Dumbarton Rail Corridor study by the San Mateo County Transportation Authority proposed that six trains originate in Union City during the AM commute and return in the PM. Under this proposal, half of these trains would serve the Redwood City-Millbrae portion of the Caltrain line, and half would serve the Atherton-San Jose portion. Some officials recently have recommended that Dumbarton-north Peninsula trains continue all the way to San Francisco.
In early 2000 a bill sponsored by State Senators Jackie Speier (D-San Mateo) and Byron Sher (D-Palo Alto), included funding for proposed Dumbarton commuter rail from the Stockton-Pleasanton ACE route. The bill's sponsors suggested that these trains could be running as early as 2003. This legislative action led to the establishment of Caltrain's Baby Bullet service in 2004. However, funding for Dumbarton rail was removed from the bill before the bill was approved by the Transportation Committee.