The new Warm Springs Extension alignment will parallel portions of the Union Pacific (UP) railroad corridor, which contains the former Western Pacific (WP) and Southern Pacific (SP) railroad tracks, and Interstates 680 and 880 in southern Alameda County.

The initial segment will begin on an embankment at the southern end of the existing elevated Fremont BART Station, pass over Walnut Avenue on an aerial structure, and descend into a cut-and-cover subway north of Stevenson Boulevard. The alignment will continue southward in a subway under Fremont Central Park and the eastern lobe of Lake Elizabeth, and surface to at-grade between the former WP and SP alignments north of Paseo Padre Parkway.

Paseo Padre Parkway has been reconfigured as a vehicular underpass as part of the City of Fremont's Grade Separation Project. The Warm Springs Extension alignment will pass over Paseo Padre Parkway on a bridge structure, and continue southward at-grade, passing under a grade-separated Washington Boulevard. Additionally, Washington Boulevard has been reconfigured as a vehicular overpass as part of the City's Grade Separation project. From Washington Boulevard, the alignment will continue at-grade along the former WP alignment south at the new Warm Springs / South Fremont Station at Warm Springs and South Grimmer Boulevards in the Warm Springs District.

In 2007, BART devised an implementation strategy whereby the project would be constructed via two large contracts: The Fremont Central Park Subway Contract and the Line, Track, Station and Systems Contract. This approach is intended to minimize overall escalation costs and most appropriately deal with the special needs associated with the underground portion of the project in Fremont Central Park.

Fremont Central Park Subway Construction Contract (Subway) – This contract constructed the trackway embankment south of Walnut Avenue and the BART subway from just north of Stevenson Boulevard, through Fremont Central Park, under the eastern lobe of Lake Elizabeth, and beneath the UPRR freight track to just north of Paseo Padre Parkway. The contract included construction of two ventilation structures and relocation of a number of amenities within Fremont Central Park, including the Dog Park, Basketball Courts, and related parking. Construction began in the summer of 2009 and concluded on schedule in the spring of 2013.

Line, Track, Station and Systems Contract (LTSS) – Under this design-build contract, the contractor is responsible for completing the design, as well as constructing the trackway, systems, and the new Warm Springs/South Fremont Station. This contract was awarded in the fall of 2011 and final design is presently underway. The Warm Springs Extension is expected to open for revenue service in the fall of 2015.

BART also worked closely with the City of Fremont to ensure its Washington Boulevard/Paseo Padre Parkway Grade Separation project was designed and constructed to facilitate the WSX project. The City's Grade Separation project was completed in 2010.

Last Updated: April 9, 2014