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The station is in the Mission Bay/China Basin area, bordered on the north by Townsend Street, east by 4th Street, and south by King Street. All 13 tracks approaching from the west presently terminate here, just short of 4th Street. The facility opened on June 21, 1975, replacing a station built in 1914 at 3rd and Townsend, one block away to the east.
The Muni light-rail extension to the station was opened in 1998.
Future
The Portal project (formerly the Downtown Rail Extension) to the rebuilt Salesforce Transit Center includes the construction of an underground 4th and King station. The underground portion will be adjacent to the current station on the Townsend Street side, but Caltrain will continue using the surface platforms. Until that time, California High-Speed Rail trains are planned to utilize the existing station with modifications for that service.
Following the opening of the Portal project, California High-Speed Rail service will be extended to the new Transbay Terminal, though most trains are intended to stop at the underground 4th and Townsend as an additional, secondary stop for San Francisco.
The N Judah station platform is located on the median of King Street immediately southwest of the 4th and King intersection, while the T Third Street station platform is located on the median of 4th Street immediately southeast of the intersection. The nearest BART access is the Powell Street station, a 1-mile (1.6 km) walk up 4th Street then left on Market Street, or a nine minute T ride and a five minute walk from Union Square/Market Street station.
The station is also served by Muni bus routes 10, 30, 31, 45, and 47, along with special express routes 81X, 82X and 83X which provide service to or from business areas near Market Street during peak periods. Additionally, the N Bus, N Owl, T Bus and 91 Owl bus routes provide service along the N Judah and T Third Street lines during the early morning and late night hours when trains do not operate.