SAN CARLOS — For roughly two decades, transportation planners and local leaders have advocated for a rail crossing along the Dumbarton Bridge corridor that would connect Caltrain in the South Bay to the Altamont Corridor Express and Capitol Corridor in the East Bay.

And for roughly two decades, the idea has gathered dust.

But a Facebook-funded and SamTrans-led study set to be released Tuesday is again floating the idea of a southern rail crossing, and local leaders are hopeful that this time, the project’s fate will be different.

That’s because over the past decade or so jobs have become increasingly concentrated in the mid-Peninsula with housing increasingly moving further east from the Tri-Valley into places like Tracy, Stockton and Modesto, said Michael Cunningham, a public policy expert for the Bay Area Council.

“So, the result is, we have more and more people coming from further and further away, but we don’t have the transportation infrastructure and services to support that,” he said.

And, traffic along that corridor, says San Mateo County Supervisor Warren Slocum, “is a nightmare.”

SamTrans, the bus service operator in San Mateo County, owns the Dumbarton rail bridge, which runs parallel to and lies just south of Highway 84. Built in 1910, the single-track rail bridge was actually the first to span the San Francisco Bay and was used mostly for freight, with limited passenger service, said Melissa Reggiardo, a principal planner for SamTrans. It fell out of service and was then damaged in a fire in the 1990s, she said.

But interest in rehabbing the bridge persisted, and an environmental analysis looking at restoring rail service was partially completed in 2011, she said. But, with the economy still reeling from the Great Recession, the idea was shelved.

Then, Facebook expanded its campus abutting the bridge, and a conversation in 2015 ultimately led to the company contributing $1.2 million to fund the new study, said Dan Lieberman, a spokesman for SamTrans. Representatives from Facebook declined to comment on recommendations from the study.

Ultimately, Reggiardo said the transit agency envisions a multimodal corridor for the Dumbarton that includes not only a new railroad crossing but also improvements to the highway bridge. If approved, interchange improvement and expanded express bus service, along with two new express routes would come first, she said, with the latter connecting Union City with Menlo Park, Redwood City, Mountain View and Sunnyvale by 2020. HOV lanes could follow as an intermediary step to speed up bus service, she said.

Ultimately, the agency would embark on rebuilding the railroad connection along the Dumbarton rail bridge that would be phased in over time, first connecting Newark to Redwood City with diesel trains, followed by an extension to Union City by around 2030, with a combined estimated cost of nearly $1.3 billion.

The rail bridge would be electrified to allow Caltrain’s new electric trains to cross the bridge and connect to the Altamont Corridor Express and Capitol Corridor by 2035, for an additional $327 million.

More details will be available when the study is published on Tuesday, but both Cunningham and Slocum said the project is an ideal one to serve as a test case for a private investment, making it one of roughly a dozen transportation projects in the state to take that approach.

Even without private investment, Slocum said funds from the recently-approved gas tax hike and transportation funding bill, SB1, and the proposed $3 bridge toll hike, along with a proposed transportation sales tax ballot initiative in San Mateo County, could be combined to fund the project.

“The Dumbarton rail bridge is the missing link in our mega-regional transportation network,” Slocum said. “And this is a once-in-a-generation opportunity.”

Learn more

SamTrans is soliciting comments from the public about the proposed new services before the transit agency’s governing board accepts the final report and its recommendations later this year. The meeting times and locations are as follows:

Tuesday, 6:30 p.m. to 7:30 p.m., Union City Library, 34007 Alvarado-Niles Road, Union City.

Wednesday, 6:30 p.m. to 7:30 p.m., East Palo Alto Library/City Hall Community Room, 2415 University Avenue, East Palo Alto.