Purple Line (BART)

SFO–Millbrae line

Company type	Shuttle service
Industry	Public transportation
Founded	2003
Defunct	2021
Area served	San Francisco Bay Area
Products	Rapid transit shuttle service

The SFO–Millbrae line—also known as the SFO–Millbrae shuttle—was a Bay Area Rapid Transit (BART) service connecting Millbrae station and San Francisco International Airport station (SFO) within the San Francisco Bay Area. Identified by the color purple on transit maps and occasionally referred to as the Purple Line, this shuttle operated nonstop between its two endpoints, sharing the same tracks used by other primary BART routes. Its operation occurred during two distinct intervals: from June 2003 through February 2004, and later from February 2019 until August 2021.

2003–2004 service

At the time of the BART-SFO Extension inauguration on June 22, 2003, the Pittsburg/Bay Point line was extended to reach Millbrae station, while the Dublin/Pleasanton line began serving San Francisco International Airport station. The Blue Line operated a shuttle service between SFO and Millbrae at 20-minute intervals; however, this shuttle was discontinued on February 9, 2004 as part of early operational adjustments aimed at improving ridership efficiency.

Between 2004 and 2005, weekday service connecting SFO and Millbrae was provided by the Richmond line, with the Yellow Line taking over during nights and weekends. From 2005 until 2008, direct connections between these stations were maintained consistently by the Blue Line.

On January 1, 2008, continuous direct service between SFO and Millbrae was halted, necessitating transfers at San Bruno station. Direct service was reinstated on September 14, 2009 during evenings and weekends as an extension of the Pittsburg/Bay Point line, enhancing off-peak travel options.

On June 24, 2018, SamTrans introduced route SFO—a bus route providing a direct link between Millbrae and SFO stations with variable schedules aligned to select Caltrain departures at Millbrae.

BART restored uninterrupted SFO–Millbrae service on February 11, 2019. During weekdays until 9 pm and on Sundays, a dedicated shuttle train operated with coordinated transfers to the Antioch line at SFO. On weeknights and Saturdays, Antioch line trains ran directly between SFO and Millbrae. By February 10, 2020, BART's schedule showed the SFO–Millbrae shuttle running continuously with Antioch line trains terminating at SFO. The shuttle ran on weekdays and Saturdays requiring transfers to Antioch line services; meanwhile, weeknight and Sunday operations were interlined without transfer requirements.

Beginning March 22, 2021, shuttle operations were interlined with the Richmond line on weekdays and with the Antioch line during weekends. This shuttle service ceased on August 2, 2021, replaced by Richmond line extensions to SFO for weekdays and Saturdays, along with Antioch line extensions reaching Millbrae during evenings and Sundays.

Following a power cable failure near Berkeley on March 6, 2022 that disrupted SFO–Richmond operations, a shuttle between SFO and Millbrae commenced on March 8. Red Line services resumed on March 22, resulting in discontinuation of the shuttle. A similar cable fault near Richmond on June 17 prompted reinstatement of the SFO–Millbrae shuttle starting June 20 to supplement limited Red Line trains.

On January 13, 2025, a shuttle train will run between SFO and Millbrae from 9 pm until midnight due to installation work for Communications Based Train Control equipment near Millbrae. This temporary service will be classified under the Yellow Line.