The $120 million Silver Spring Transit Center. (Sarah L. Voisin/The Washington Post)

The public will be at increased risk from falling chunks of concrete unless interior beams and girders supporting the Silver Spring Transit Center are strengthened before the facility is opened, according to a new report on the troubled, long-delayed project.

The extra work would add at least $7 million to the center’s $120 million price tag and could delay the opening — already more than two years behind schedule — until early 2015, said the report from an independent working group headed by former Lockheed Martin chairman and chief executive Norman Augustine.

The report, commissioned late last year by Montgomery County Executive Isiah Leggett, raises new questions about the condition of the three-level, 259,000-square-foot concrete structure, which is plagued by design and construction problems that have produced serious cracking.

On the basis of a 2013 study by KCE, their engineering consultant, county officials have repeatedly asserted that concerns over cracking are related to the building’s long-term durability and maintenance costs, not safety.

But Augustine’s report strikes a markedly different tone, calling the problem “a structural integrity issue as well as a potential local safety issue for the general public.”

Concrete issues at the Silver Spring Transit Center

While a major structural collapse would be “unlikely,” the report says, isolated instances of falling concrete could pose a danger to some of the estimated 30,000 commuters who are expected to use the bus-and-train hub each day.

“Any dislodged pieces of concrete could pose a potential safety hazard to pedestrians walking below an area where [falling concrete] occurs,” the report says.

In an interview, Augustine said that his engineering and construction experts “are probably a bit more conservative” in their analysis than KCE and the county.

“But we do see a safety issue,” he said. He added that the beam and girder reinforcement, combined with a rigorous inspection program after the center opens, should keep the facility safe.

The Augustine report is the latest development in what amounts to an impasse among the major players in the transit center project over how to complete repairs.

The county and KCE contend that the reinforcement is necessary to protect the building against the stresses generated by the estimated 240 buses an hour that will roll through the center. Specifically, KCE said, the center must be strengthened against torsion — the twisting force exerted when concrete is under pressure — and shearing, the vertical force that can cause concrete to crack or fail.

Parsons Brinckerhoff, the engineering firm that designed the structure, disagrees, maintaining that industry standards do not require that torsion and shearing be taken into account in a building like the transit center.

Firm vice president Jerry Jannetti said in a recent e-mail that the transit center was designed to withstand “the equivalent of several fully loaded 18-wheel tractor trailer trucks driving at Interstate highway speeds — loads far in excess of normal operation for this garage.” Jannetti said there is also concern that reinforcement of the beam and girders, which involves the embedding of additional steel supports, could further damage the building.

Metro, which is supposed to take possession of the center and operate it when repairs have been completed, has not taken a public position. But in correspondence with the county, it has shared Parsons Brinckerhoff’s concern about possible damage from the reinforcement work. A Metro spokesman did not respond Tuesday to questions about Augustine’s review.

Leggett said Tuesday that he’d reviewed the report but that ultimately it was up to Metro, as the county’s “customer,” to decide what to do. He said he was prepared to pursue one of two options.

If Metro decides the beam and girder issues are not urgent, the county will complete the remaining scheduled work this spring. That involves placing a new layer of latex-modified concrete on all three levels of the center to address cracks. Under that scenario, the county would turn the building over to Metro this summer for a possible early-fall opening.

The county is negotiating a surety bond — a form of binding financial assurance — from Parsons Brinckerhoff to guarantee that it will pay for any shear and torsion issues that might arise in the future.

The other option is for Metro to decide to go ahead with beam and girder reinforcement prior to opening the facility. That would push the opening into late 2014 and possibly early 2015.

“I’m prepared to go forward. We’ll do whatever they want,” Leggett said.

Council member Roger Berliner (D-Potomac-Bethesda), chairman of the council’s transportation and environment committee, said it is time for Metro to make a decision.

“I think we’re at a fork in the road,” he said. “It is time for them to tell us which of these two paths to go,” he said.