For 10 months, including most of 2019, the Transbay transit center sat empty, a wounded white ghost of a building hovering above three blocks of San Francisco’s South of Market neighborhood.

But now, six months since a set of cracked support beams were repaired and the $2.3 billion transit center finally reopened, the commuter hub is springing to life.

Hundreds of buses flow off the Bay Bridge onto the bus deck, disgorging tens of thousands of passengers in the morning and taking them home in the evening. People who live or work in towering glass buildings nearby stroll through the lush gardens of the rooftop park or eat lunch from food trucks that park on the street-level plaza.

Soon those trucks will be joined by sandwich, empanada and coffee shops, as well as a big fitness center to burn off the calories. Activities in the park already have people stretching, attending Zumba classes or Toddler Tuesdays, reading books or playing games available from stocked carts.

December saw Salesforce Plaza and the Grand Hall, the transit center’s main entrance, filled with food stands, a couple of bars, concerts and local vendors selling handcrafted items like belts and wallets, patches and caps and jewelry. Known as Emperor Norton’s Holiday Bazaar, officials hope to make the event an annual affair.

It’s been a long journey from a year ago, when the Transbay transit center was surrounded by controversy and uncertainty. On Sept. 25, six weeks after the center opened to much acclaim, a construction worker helping with the finishing touches noticed a crack in a steel girder. The center was hurriedly evacuated and buses were redirected to a temporary terminal blocks away. A crack in a second girder was soon discovered.

Last December, metallurgists and engineers started to narrow in on the cause of the breakdown — holes improperly cut in the large beams caused tiny cracks that grew into large fractures. But it wasn’t until January that officials devised a plan to repair the girders. Exhaustive inspections to ensure the safety of the structure lasted through the spring.

But now, with no signs of cracks or other damage since the center reopened six months ago, the transit hub, retail center and park are becoming fixtures finding their place in a rapidly changing neighborhood.

“There was a doom and gloom at this time last year, and now the center is coming back to life,” said Andrew Robinson, executive director for the East Cut Community Benefit District, a group of businesses and neighbors in the area.

While the four-level structure’s main purpose is to serve buses and eventually trains, the 5.4-acre rooftop park remains its most popular — and a unique — feature. In addition to drawing thousands of visitors a day, including some tourists and many more workers and neighbors, the park has also attracted the attention of the East Coast architecture and culture critics media. Earlier this month, both the New Yorker and New York magazines published somewhat snarky features about the gilded garden.

Everyday visitors, however, seem more appreciative. They rave about the abundance of greenery and activities, and tend to overlook the corporate logos on surrounding modern high-rises.

Jonathan Calero Sanchez, a preschool teacher who lives nearby in the Avery complex, visits the park often, sometimes reading or playing a game but often simply enjoying being in nature while surrounded by urbanity.

“We enjoy the birds that come over here and getting to be in greenery,” Sanchez said. “There’s even an area where hummingbirds hang out.”

Ted Ver Valen, a location sound recordist from San Rafael, took a break from a gig inside Salesforce Tower and took his first stroll around the park.

“I love the variety,” Ver Valen said.” It’s amazing. It’s a great sanctuary because there’s so much greenery. It’s a nice combination of nature and downtown.”

The Bay Area’s bus systems have also settled into the transit center, with AC Transit, Greyhound and others situated on the third-floor bus deck, which has a direct connection to and from the Bay Bridge. Muni and Golden Gate Transit are at street level and SamTrans and Amtrak buses stop on Mission Street.

Ridership on AC Transit’s transbay buses is up about 10% year over year, said Robert Lyles, a spokesman, perhaps because the bus ramp to and from Interstate 80 cuts travel times by 10 minutes or more.

“AC Transit increasingly became the transportation of choice from the East Bay into San Francisco,” he said. “BART is over its capacity and that has translated into increased ridership for AC Transit service.”

Robinson said the bus ramp not only benefits bus riders but also neighbors, cyclists and pedestrians.

“Having buses off the streets, not queuing up on Fremont Street, not traveling on Folsom, is a big improvement in the quality of life of people living in the area,” Robinson said.

Another improvement could happen within the next several days and weeks, when the transit center’s shops and restaurants start opening.

Fitness SF expects to open a large fitness center on Dec. 27. Philz Coffee plans to open two outlets in January and Verizon is likely to open a store in February. A handful of restaurants and a bar are under construction and scheduled to open within months, said Mark Zabaneh, executive director of the Transbay Joint Powers Authority, which operates the center.

As one might expect, the morning and evening commutes are the center’s busiest moments each day, but a burst of activity occurs around noon each weekday when people grab lunch and head to the park.

Zabaneh said he’s “very satisfied with the amount of activity,” and he’s looking forward to having more retailers open for business.

The biggest boost to the center won’t come until rail service arrives with an extension from the Caltrain station at Fourth and King streets to the Transbay terminal basement, which already has a concourse and platforms to allow for commuter and high-speed rail service.

Until then, the transit center will remain a big, fancy bus depot.

“It becomes a real beacon for the neighborhood once we get (the downtown extension) into the station,” Robinson said.

That could take at least 10 years to find the estimated $4 billion to $6 billion needed to build the 1.3-mile underground rail extension and complete construction, Zabaneh said.

“Funding is the biggest obstacle on big projects like this, “ he said. “It’s really not the design or any other factors, it’s finding the funding.”

Michael Cabanatuan is a San Francisco Chronicle staff writer. Email: mcabanatuan@sfchronicle.com Twitter: @ctuan