Cars in BART'S so-called "fleet of the future" are as much as a ton overweight, NBC Bay Area has learned, and the transit agency has hired outside engineers to inspect 30 key aerial structures to assure they can handle the load.

The weight problem comes as the first of BART's new 775-car fleet are expected to go into service later this year, once ongoing testing is complete.

Last spring, officials beamed as they showed off the first car in a fleet billed as sleeker, quieter and with an extra set of doors to better handle crowds.

But the fleet is more than a year behind schedule, and problems have marred early tests. Now, just as BART prepares to put the new fleet into service, engineers face another glitch.

"They’re overweight," admits Paul Oversier, BART’s operations manager.

He blames all the "bells and whistles" on the new cars, including bike racks, six video display screens and state-of-the-art crash safety gear.

"A lot of stuff that I think the customers are really going to appreciate," is on board the new fleet, he told NBC Bay Area. "Some of which has contributed to the weight issue."

The train cars are a half-ton to 1 ton heavier than specified under BART’s contract. As new cars approach BART’s design limit of 55 tons for trains fully loaded with passengers, there will be more strain on its aging infrastructure.

But the issue of BART’s aerial structures is not new. In fact, it was flagged as early as 1980. Back then, an outside engineering firm notified the agency that 5 percent of BART’s aerial structures failed to meet nationally accepted standards established to limit the risk of steel components cracking from the stress of millions of crossings.

Among the at-risk structures the Tudor Engineering Co. identified in its report were two overcrossings near Highway 24 in Oakland. Both were under greater stress than permitted by the national standard, Tudor warned.

After recommending that these and others on the Pittsburg/Bay Point line be checked, Tudor endorsed boosting the ultimate limit of fully loaded train cars from 50 tons to 55 tons. But no higher, they said.

Three decades later, BART engineers apparently had hopes they could rely on still heavier cars. But the agency’s consultants, Jacobs Engineers in Walnut Creek, refused to go along. They again cited the risk of overtaxing aging structures.

In its January 2011 report, Jacobs sounded the alarm about two rusting structures near Highway 24 in Oakland as particularly vulnerable to the repeated stress of trains crossing them.

"Stress corrosion coupled with fatigue is a definite cause for concern," Jacobs concluded in its report after inspecting the structures crossing Chabot Road and Golden Gate Avenue.

The engineers complained about apparent flaws and gaps in another key part of the Pittsburg/Bay Point line, where trains cross over both Interstate 680 and Highway 24 in Walnut Creek.

Despite BART’s promised regular inspections of the structures, they had actually not gone through a detailed inspection for a decade, according to the Jacobs report. The last time that happened was in 2000, when they were painted.

"Due to its inaccessibility, the structure is not being inspected to the degree that is required," the firm warned.

All this left Bob Bea, a UC Berkeley engineering professor emeritus who studies how major structures fail, concerned about what was being done to account for the apparently at-risk structures.

"So we’ve got a particularly challenging problem," Bea said. "Running heavier trains is simply putting more demand on the system, which is not a good thing. That’s escalating the risk again."

Bea reviewed the various studies and agreed that the two Oakland structures remain problematic. They are what engineers consider nonredundant.

"Which means if you break an important component, and all the components of these nonredundant structures are important, the system is then potentially at the point of collapse," Bea said. "Which means you don’t have backup."

BART engineers told NBC Bay Area the system’s structures are regularly inspected and meet state highway standards. They say despite outside engineers’ concerns back in 2011, they have confidence in the integrity of the 24/680 overcrossing.

As for the structures in Oakland, BART provided an engineer’s letter written just this month that acknowledged that while the structures may not meet some stress limits, they could last 144 years.

Still, to make sure, BART has hired an outside firm to inspect 30 of the aerial structures, including about two dozen flagged as problematic back in 1980. The Oakland and 680/24 crossings are on the list to be evaluated over the next year.

Joel Keller, a BART board member for the East Bay, expressed confidence that the agency’s engineers are on top of the situation.

"I have been assured by the engineering staff at BART that the structures are safe, and the train weight is appropriate for the system," Keller told NBC Bay Area.

Operations manager Oversier says BART is still negotiating with Bombardier, the maker of the new fleet, and is offering plenty of advice about how to cut the fat.

"There’s a lot of engineering behind those ideas," Oversier said, "and we’re working with them constantly to see which ones BART is willing to live with and which ones we feel aren’t worth it ... because there may be an impact on reliability, long-term maintainability, whatever."