Passenger services on the 8.7km one-station extension from Fremont to Warm Springs began on March 25, with trains running to Daly City via Oakland and San Francisco.
The extension seeks to provide commuters with an alternative to the congested interstate highways 680 and 880, and the park-and ride station at Warm Springs has 2082 parking spaces, with 42 solar-powered electric vehicle charging stations.
Construction began in 2011 and the extension was originally due to open in 2014, but the project has suffered repeated delays.
Construction started on the 16.1km second phase of the Silicon Valley extension to Milpitas and Berryessa in 2012 and this section is due to open in 2018.
The 9.7km third phase will extend Bart services to Alum Rock, Downtown San Jose and Santa Clara, with an 8km tunnel under San Jose. Major construction is scheduled to start in 2018, with passenger services due to begin running in 2026.