Dumbarton Rail Corridor would provide service between Union City in the East Bay (where passengers could connect with BART, ACE and Capitol Corridor trains) and Menlo Park on the Peninsula, with train service continuing to both San Francisco and San José along the existing Caltrain tracks.

The initial service offering would not include reverse commute (west-to-east in the mornings and east-to-west in the afternoons), mid-day, evening, or weekend trains.

Trains originating in Union City would enter the Shinn connection, turning right from southbound to westbound, and pass under the BART tracks before joining the Centerville line.

The layover yard was proposed to be north of Whipple Road in Hayward, and would provide overnight storage for trains entering the Union City station, rebuilt for intermodal service.

[1] The two swing bridges and their timber trestle approaches were known to be in poor shape since 1996,[5] and a subsequent 2008 engineering investigation found the concrete foundations were also degraded, possibly since they were constructed in 1910.

[7] Separately, Capitol Corridor has been considering moving trains on to the Mulford/Coast subdivision, the westernmost railroad in Alameda County, partially sharing the route for the Coast Starlight, which would discontinue service to Hayward and Fremont Centerville, and bypass Union City entirely.

Phase II focused on improving the east side of the BART station and preparing it for intermodal service with commuter rail.

[1] A new station would be constructed in the Belle Haven neighborhood of Menlo Park, just west of Willow Road and south of State Route 84 (the Bayfront Expressway).

[1] The Central California Railway Company, a subsidiary of Southern Pacific, completed the Dumbarton Cut-off in 1910, reducing the rail route distance between Oakland and San Francisco by 26.1 miles (42.0 km).

[6] However, San Francisco gradually became a less important hub for rail transportation, and the Port of Oakland was better-suited to handle containerized shipping.

[5][20] In 2000, Santa Clara County voters approved Measure A, which set aside a portion of the funds generated from a half-cent sales tax increase for the Dumbarton Rail Corridor.

[20] California State Senator Jackie Speier introduced a bill in February 2000 that would devote US$90,000,000 (equivalent to $159,200,000 in 2023) to rehabilitating the Dumbarton Rail Bridge to add Altamont Corridor Express (ACE) service from Newark to San Jose;[23] however, ACE officials rebuffed the offer, saying the bill added no money for purchasing new trains or funding operating costs.

DRC was identified as one of the nineteen high-priority rail and bus projects for transit expansion in the Bay Area as part of MTC's adoption of Resolution 3434 in December 2001.

[25][26] In 2001, MTC estimated the total capital cost for DRC was US$129,000,000 (equivalent to $222,000,000 in 2023); of that, 91% had been secured or was pending via local sales taxes in San Mateo, Alameda, and Santa Clara Counties.

[27] In November 2004, MTC released a draft plan for spending over the next twenty-five years, entitled Transportation 2030, which included full funding to rehabilitate and reactivate the Dumbarton Rail Corridor.

[29] However, Regional Measure 2, which had been passed by voters earlier in March 2004, set aside an additional US$135,000,000 (equivalent to $217,800,000 in 2023) for the Dumbarton Rail Corridor project from increased toll bridge revenues.

[30] Much of the cost increase was driven by the 2003 Dumbarton Rail Corridor Project Study Report,[1] which identified several deficiencies in the existing infrastructure.

[31] A May 2005 community meeting attracted overwhelming opposition from Fremont residents living near the proposed new routing of Capitol Corridor and Dumbarton Rail trains.

Based on projected ridership, a blend of both alternatives was proposed, retaining the low-level single-track drawbridge as marine traffic was expected to remain light.

[42] The draft Strategic Plan amending Resolution 3434[43] was presented in June 2008, placing projects in four tiers, depending on their state of readiness.

[46] DRC would be repaid in Alameda County Regional Transportation Improvement Program funds over eight years, from FY 2019–20 to 2026–27, without accounting for inflation.

[47] In September 2008, MTC Vice Chair Scott Haggerty defended the shift, arguing that "The bottom line is that the Warm Springs BART extension is ready to go and the Dumbarton Rail project is not.

[49] California Streets and Highways Code Section 30914(f) gives MTC the authority to reallocate funds "to another project within the same bridge corridor,"[49] and the WSX does not provide the same transbay service as DRC.

[55] The February presentation also redefined the $91 million loan as an "investment in BART to Warm Springs" with "No future repayment from Alameda County" necessary.

[58] In the response to public comments, the MTC staff response stated "the Dumbarton Rail Bridge connects north–south corridors on both sides of the San Francisco Bay [...] Therefore, staff considers the investment in the Warm Springs Extension (and the Caltrain Electrification Program) to be appropriate investments of these bridge toll funds.

Recognizing these issues, the March 2011 Dumbarton Rail Corridor Alternatives Study (Wilbur Smith Associates)[64] set out to redefine the project to increase cost-effectiveness and boost ridership.

[66] The Federal Transit Administration (FTA) declined to review it, since "reasonable funding sources" were not available, and the project was placed on indefinite hold.

[69] Facebook headquarters are within walking distance of the proposed Willow Road station and could be a potential source of new ridership that was not accounted in the prior studies.

[72] This combined phasing contrasts with earlier DRC studies, which assumed that enhanced bus or rail service as mutually exclusive alternatives.

[77][78][79] On June 2, 2019, a brush fire that authorities suspected was arson spread to the wooden trestle on the eastern approach near the Newark Slough Bridge.