With high-speed rail a distant dream and its mall space still a shell, officials at the newly opened Transbay Transit Center are scrambling to come up with the $27.5 million a year needed to run the three-block-long mega-bus station and rooftop park.

And from the looks of things, it will be drivers crossing the bay’s seven state-owned bridges who will be shelling out as much as $17 million a year in toll money to maintain the center — at least in the short term.

That’s more than three times the amount allocated from tolls for either the temporary or the old Transbay Terminal that the new center replaced.

“That’s just the way it is,” says regional Metropolitan Transportation Commission spokesman Randy Rentschler, who points out that tolls have been used to subsidize transbay operations since the Bay Bridge was built in the 1930s.

“Nothing is for free,” he said.

The $2.2 billion terminal, officially known as the Salesforce Transit Center, was initially envisioned as a hub for buses from multiple transit agencies, Caltrain and high-speed rail that would draw more than 100,000 passengers a day.

But without high-speed rail, there will be only about 13,000 AC Transit trips in and out of the “Grand Central Terminal of the West” on weekdays. There will be only about half that number on Muni.

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The lower-than-expected ridership numbers mean less foot traffic to support the center’s still unfinished, 100,000-square-foot mall, a hoped-for source of operating revenue.

Mark Zabaneh, executive director of the Transbay Joint Powers Authority, which operates the building, said retail interest in the mall is strong now, but “if the economy takes a downturn, we have some risks.”

In the meantime, the authority needs about $8 million a year for police and private security patrols to keep the park and station from becoming an ad-hoc homeless shelter, like the old terminal was.

Another $19 million is needed to keep the lights and power on and to keep the place clean, including maintaining the 5.4-acre park.

The biggest chunk of money — about $11 million — will come directly from bridge tolls, including money from Regional Measure 3, the recently approved toll increase for transit projects.

The rest of the operating budget comes from sources such as the Salesforce naming rights, development fees from nearby towers and revenue from special events.

Nevertheless, the transit center is looking at an $8 million hole next year — so Muni and AC Transit have agreed “to fund whatever the gap is,” Zabaneh said. From what we hear, AC Transit may use its own cut of toll money to help cover its $5.9 million obligation — so those drivers crossing Bay Area bridges are looking at paying a total of $17 million toward the center’s operations.

“It’s a large amount of money,” said AC Transit spokesman Robert Lyles. “We are working with (regional transportation planners) to figure out our options.”

State Assemblywoman Catharine Baker, whose 16th District covers commuter-heavy central and southern Contra Costa County, said the latest bridge toll increase was sold with the promise of “bridge maintenance, road construction and congestion relief.”

“To me, this is another example of voters being told one thing to extract more money from them, and then after it has passed, the dollars going to different place,” said Baker, R-San Ramon. “It’s frustrating ... and I’m disappointed to hear that.”

About the ceremony: Interesting to note who was — and who wasn’t — at Friday’s big ribbon-cutting ceremony for the $2.16 billion Transbay Transit Center.

Steve Heminger, the longtime head of the regional Metropolitan Transportation Commission, which has poured more than $500 million into the project — including a $150 million bailout — was on vacation. (We’re told he’s always off in August.)

Former transbay director Maria Ayerdi — the initial force behind the project who was pushed out of her job two years ago over soaring costs — was onstage, front and center. Dressed all in white, she told the crowd, “Immigrants can achieve great things when given the opportunity.”

As part of Ayerdi’s severance agreement, Transbay Joint Powers Authority officials agreed to give her a speaking role at the opening and include her name on the official plaque inside the terminal.

Lt. Gov. Gavin Newsom, who a couple of months back RSVPd that he couldn’t attend, showed up at the last minute for a quick tour of the rooftop park and to say hello, but didn’t stick around for all the speeches and the ceremonial ribbon cutting.

A decade ago, then-Mayor Newsom had insisted he wouldn’t allow the terminal to be built without funding for high-speed rail, declaring: “We’re not going to build a $2 billion bus station under my watch.”

And we didn’t build a $2 billion bus station. Instead, we built a $2.16 billion bus station.

San Francisco Chronicle columnists Phillip Matier and Andrew Ross appear Sundays, Mondays and Wednesdays. Matier can be seen on the KPIX-TV morning and evening news. He can also be heard on KCBS radio Monday through Friday at 7:50 a.m. and 5:50 p.m. Got a tip? Call 415-777-8815, or email matierandross@ sfchronicle.com. Twitter: @matierandross