When San Francisco reopens its $2.2 billion Transbay transit center on July 1, buses won’t be rolling through — but yoga mats may be rolling out.

That’s because the three-block-long structure isn’t quite ready for transportation. Instead, after the center opens at 6 a.m. July 1, people can once again stroll through the 5.4-acre rooftop park and join knitting circles, yoga classes and fitness boot camps. Food trucks will line the surrounding streets, and visitors may enter the art-bedecked terrazzo floor. The buses, however, will come later.

Muni and Golden Gate Transit buses will start rolling out of the plaza at Beale and First streets sometime in early July. Greyhound, Westcat Lynx and AC Transit’s bus lines will start service from the bus deck — which connects to the Bay Bridge — in late summer.

Restoring bus service is complicated: Crews that pulled ceiling panels and column covers apart during a lengthy inspection process are now putting them back together. Buses that drop passengers off at a temporary terminal on Folsom Street now have to be rerouted. Bus drivers have to be retrained.

But even though the transit center’s revival is slow, it moves the city past a period of embarrassment, when a project that symbolized so many aspirations started crumbling.

“In order to be a world-class city, you have to have a multi-modal transportation hub,” said Nathan Ballard, a political consultant to several former San Francisco mayors who now advises the chief contractor on high-speed rail. He hopes the reopening will put to rest all “the troubles that have dogged the project until recently.”

The decision to reopen the hub comes eight months after engineers discovered cracks in the transit center’s steel girders and shut it down. Meanwhile, city officials are pursuing long-term plans to bring rail into the building’s basement.

“Otherwise, we will have built the most expensive bus terminal in the history of humankind, rivaling the pyramids in Egypt,” said Supervisor Aaron Peskin, who chairs the county Transportation Authority board that’s helped fund and manage the project, sometimes while deriding it.

The transit center went through a gamut of inspections that required it to be stripped, sampled and perused to a degree that many buildings in San Francisco couldn’t withstand, one transportation official joked. A laboratory in New York analyzed metal samples from the failed girders, determining that they started as tiny cracks where workers cut holes in the steel. A five-member panel appointed by the Metropolitan Transportation Commission pored through thousands of inspection documents before finally approving the building’s reopening.

The testing and review process cost $6 million, and the city paid $2.5 million a month for security and maintenance while the center was closed. But elected leaders demanded that level of scrutiny: San Francisco Mayor London Breed and Oakland Mayor Libby Schaaf told MTC to put together the panel, hoping that independent experts would instill more public confidence in the building.

It’s otherwise under the thumb of the Transbay Joint Powers Authority, the independent government agency in charge of the building’s construction and operation, as well as the downtown railroad extension into its basement. Politicians and boosters hope the now-empty concrete box will eventually hold bullet trains that zip in from Southern California and commuter Caltrains from the Peninsula.

Some officials, including Peskin, fear that if the trains never arrive, the structure will merely represent government overspending and hubris. Politicians in City Hall have squabbled over the transit center for years, and some of those conflicts escalated after the discovery of cracks forced its closure; city supervisors flogged the Joint Powers Authority in public meetings and froze millions of dollars in sales tax funding for the next phase of the project.

“There’s obviously the lingering questions going on in political circles regarding governance, (the extension of) Caltrain, and who is in charge for the next 50 years,” said Ron Miguel, a former San Francisco Planning Commission president who participated in a citizen working group to help plan the downtown route for Caltrain.

“But putting all that aside, I really want to see it open,” he said.

Rachel Swan is a San Francisco Chronicle staff writer. Email: rswan@sfchronicle.com Twitter: @rachelswan