BART is taking steps to slow down trains at more than three dozen hot spots where hazardous — and in some cases, deteriorating — track conditions could jeopardize the safety of thousands of riders.

That includes a location in Concord that has been the site of two derailments in the past five years — including a February 2014 incident that left the front end of an empty, 10-car train dangling off the edge of the elevated rails.

Track troubles on the 42-year-old system already prompted the shutdown beginning Sunday of the elevated stretch between the Oakland Coliseum and Fruitvale stations. It will be closed for an unprecedented 11 weekends spread out over the next few months while workers replace 1,000 degraded wooden ties and 3,000 feet of worn rail.

Trains have been limited to 50 mph along that stretch since January, after a track tie crumbled as an inspector stepped on it.

The Coliseum-Fruitvale work is only the beginning. In the coming months, partial or full shutdowns are planned near the Daly City, San Leandro and Bayfair stations — all on elevated crossover rails where the trains switch tracks, known as interlockings.

“They are afraid a tie could come loose, cause a derailment and send a train plunging off the tracks,” said a BART insider, speaking on condition of anonymity because he is not authorized to go on the record.

Worries over track conditions have already led the transit agency to reduce train speeds between the West Oakland station and the transbay tube, where repair work has begun, and between the Richmond Station and a nearby maintenance yard.

The derailment threat is very real, as the Concord accidents show. Train speeds at the spot where two trains jumped the tracks, just south of the Concord Station, have been capped at 18 mph, down from the previous 27 mph limit.

Officials traced the first derailment in March 2011 to uneven wear on a track section and flawed maintenance on a train wheel that slipped off the rails. Sixty-five people were safely evacuated from the train, and there were no serious injuries.

After last year’s accident at the same location, officials concluded that “a slight jog in the track” at the interlocking might have played a part in that derailment. It took more than a day for crews to haul away the dangling train cars after that incident, in which the operator escaped injury.

Now, according to BART officials, plans are in the works to slow speeds at 37 other interlockings because of concerns that trains might otherwise jump the tracks.

One member of BART’s Board of Directors, who asked not to be named for fear of upsetting management, said the agency faces an “awful dilemma” about how much information to disclose about the extent of its safety issues.

“If we put out everything that’s a problem, people are going to have second thoughts about riding the system,” the director said.

Assistant General Manager Paul Oversier said BART has made no secret of the need for repairs.

“We have been saying this for a couple of years now and have been trying to warn the board and tell them that we need to do maintenance in a different way,” Oversier said.

That “different way” means more extensive repairs than can be made during BART’s normal overnight shutdowns, Oversier said. The more far-reaching repairs unavoidably disrupt service.

At a board workshop in January, acting chief engineer Tamar Allen showed off a piece of rail whose head — the part where the train wheel sits — had been worn down by at least a half inch.

Only about 20 percent of BART’s track has been replaced since the system opened in 1972. A recent Federal Transit Administration-funded report says tracks’ normal life span is “assumed to be on the order of 25 years” for rapid transit agencies. BART says its rails are typically good for 20 to 35 years, depending on their location.

Officials say deferred maintenance is not unique to BART — rail upkeep is an issue nationwide. Chicago, for example, shut down its Red Line in the south part of the city for five months in 2013 for a $425 million track replacement project — the first time it has been closed for an overhaul in 44 years.

In BART’s case, the emphasis on expanding the system — including this year’s planned opening of a 5.4-mile extension to the Warm Springs section of Fremont — has come at the expense of maintenance to its core lines. Increased pressure from directors and the public to run the trains for longer hours — both on weeknights and weekends — threatens to put an even greater burden on the system.

BART officials say that what’s really needed is a complete overhaul, and they are quietly preparing to go to the ballot in November 2016 with a potentially multibillion-dollar bond measure to pay for at least some of it. The bond would go before voters in San Francisco, Alameda and Contra Costa counties.

“We know we need $4.8 billion,” said the BART director. “The bigger question is, how much will the public be willing to support?”

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 e-mail matierandross@sfchronicle.com. Twitter: @matierandross