I-280 near Mission Bay would be razed in Caltrain tunnel plan

Interstate 280 as seen from Potrero Hill. Interstate 280 as seen from Potrero Hill. Photo: Michael Macor / Michael Macor / The Chronicle Buy photo Photo: Michael Macor / Michael Macor / The Chronicle Image 1 of / 10 Caption Close I-280 near Mission Bay would be razed in Caltrain tunnel plan 1 / 10 Back to Gallery

San Francisco Mayor Ed Lee is quietly shopping plans to tear down Interstate 280 at Mission Bay and build an underground rail tunnel through the area — complete with a station between the proposed Warriors arena and AT&T Park.

It’s all part of a revised effort to bring Caltrain — and, one day, high-speed rail — into downtown and the new Transbay Terminal while opening up a whole new area of the city for development.

As an added bonus, moving Caltrain’s current station a couple of blocks to the southeast — from Fourth and King streets to a site roughly opposite Pier 50 on Third Street — would help Lee sell the argument that he can keep a Warriors arena from creating huge traffic problems. The new station would be just a block or two from the 18,000-seat arena.

“A big game changer” is how one city official described the plan, which planners unveiled last week at a closed-door meeting with representatives of Caltrans, Caltrain, the Metropolitan Transportation Commission and other transportation agencies.

New neighborhood

The plan would cost billions, but Lee figures the payoff could be equally huge: a new neighborhood on land now taken up by the freeway and the rail yard at Fourth and King streets.

“It’s very attractive — the problem is, it’s also very expensive,’’ said Randy Rentschler, spokesman for the Metropolitan Transportation Commission. “But doing nothing is not an option.”

Costs aside, the plan also raises big questions for Caltrain — its station at Fourth and King would be bulldozed, and a major portion of its already-approved route for running trains downtown would be junked and redrawn.

Nonetheless, the mayor is moving fast, figuring that San Francisco’s development window won’t stay wide open forever. City officials plan to go public with their ideas next month, and there is already talk of a ballot measure down the road to seek public backing for whatever emerges as the final scheme.

Lee spokeswoman Christine Falvey called Mission Bay and the southeastern waterfront “exciting areas for growth and new housing,” and said the mayor believes the track-realignment plan could make for “a key transit link for the neighborhood and the region for the future.”

Lee first floated the idea two years ago of knocking down I-280 north of Mariposa Street and replacing it with a street-level boulevard like those built after the Embarcadero and Central freeways were torn down.

Since then, the city has been awarded $1.7 million in grants from the Metropolitan Transportation Commission and others to study the idea.

Until now, the plan has been to extend Caltrain and envisioned high-speed rail service from the Fourth and King station to the new Transbay Transit Center at First and Mission streets. The Lee administration’s plan is to reroute the tracks closer to the waterfront, running underground along Third Street starting at about 22nd Street.

Tunnel through landfill

That would require tunneling through landfill for an extra 2 to 3 miles — cutting under both the Warriors’ arena at 16th Street and AT&T Park.

From there, the tunnel would extend another mile to the Transbay Transit Center.

Supporters say moving the tracks would open wide swaths for development and knit together the Mission Bay and South of Market neighborhoods. It would also eliminate the need for a pair of $400 million grade separations that would include an underpass directing both 16th Street and Mission Bay Drive beneath the tracks.

Caltrain’s first reaction to the idea was tepid at best. The rail agency said it was “difficult to evaluate in the absence of any meaningful and in-depth technical review,” and that officials were “disappointed” the city had omitted any discussion of keeping the Fourth and King rail yard.

“This seems to be advancing rapidly without proper concern for their impact on Caltrain’s operations and our riders, a large segment of which are San Franciscans,” said Caltrain spokesman Mark Simon.

Adam Alberti, spokesman for the Transbay Transit Authority that is building the new downtown terminal, said that “our focus continues to be on bringing the rail into the new transit center as soon as possible after it opens in late 2017” — a not-so-subtle hint that they’re worried the track reconfiguration could result in costly delays.

San Francisco Supervisor Scott Wiener, who has been the point man on transportation issues on the board, said the city was looking at spending billions of dollars to extend Caltrain and high-speed rail downtown and “we need to make sure ... we get it right.”

“It’s definitely a big plan,” Wiener said of the Lee administration’s scheme, “but it’s definitely worth studying.”