Wheel problems similar to those that sidelined about half of Metro’s rail car fleet also occurred years earlier on older cars, partly stemming from a track issue Metro never addressed, the transit system’s regulatory agency said Tuesday while citing a years-old report that recently came to light.

The 2015 report by a Metro engineering consultant broadens the scope of the federal investigation into a defect that mainly affects 7000-series rail cars, most of which remain suspended nearly a year after a train derailed when wheels moved apart on an axle. The report, uncovered by Washington Metrorail Safety Commission investigators, says the wheel problem occurred enough times before 2015 that Metro hired the engineering consultant to study the problem.

The consultant’s report, the commission said, cited problems with the assembly of rail car wheels and axles, and with “restraining rails” in the Metro system.

The revelation from the safety commission raises questions about the overall safety of the rail system and whether its tracks are contributing to rail car wheels moving apart, making trains more vulnerable to derailments. It comes as the suspension of Metro’s latest train series has ushered in lengthy waits for commuters, hurting efforts to lure back riders amid a shift to telework.

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An investigation by the National Transportation Safety Board last fall found that the wheel problem appeared in about 50 of Metro’s 7000-series rail cars over four years, prompting the safety commission to order the series out of service. The cars are Metro’s most advanced model and previously had the fleet’s cleanest safety record. The transit system has 748 of the rail cars.

It’s not known why Metro’s track issues weren’t addressed, but internal reviews at the agency raised the matter as recently as last year, according to the safety commission. Metro declined to answer questions about the report or its findings but tweeted a statement assuring riders the transit system is safe.

“Our entire fleet is regularly inspected to deem our rail cars safe for passenger service,” the statement said. “We continue to work with the [safety commission] as part of the NTSB investigation on the 2021 Blue Line derailment.”

Our entire fleet is regularly inspected to deem our railcars safe for passenger service. We continue to work with the WMSC as part of the NTSB investigation on the 2021 Blue Line derailment. #wmata pic.twitter.com/ihdtYfKolr

While the discoveries bring a new dimension to the investigation into the derailment, safety commission spokesman Max Smith said the track issues don’t pose a new threat to riders. He called the issue with the restraining rail — located in track switches or turnouts that help trains maneuver on curves — one part of what could be causing wheel movements.

“The [rail] system is a complex interaction of systems,” he said. “It’s not like there’s one thing you would fix and that would fix the problems, necessarily.”

CEO Mayer: The 2015 Metrorail engineering report called for adjustments to the restraining rail flangeway widths; however, Metrorail did not make these changes.

It’s unclear how long wheel safety issues have been surfacing or what models have been cited for having unsafe wheels. Smith said the 2015 report cited more than 30 instances of wheel movements — cases that had not been publicly disclosed until Tuesday.

Previously, one other car outside the 7000 series was publicly known to have experienced wheel problems. In December, the safety commission reported that a 6000-series car — the 7000 series’s predecessor that was built by a different company — had a problem with wheelsets widening. Metro officials at the time said the issue was unrelated to the defect in the 7000 series.

Safety commission chief executive David L. Mayer said Tuesday that the 2015 report came to light during the investigation into the 7000-series cars. The safety commission had been unaware of the report, which was released three years before Congress created the commission to oversee safety on the rail system.

Mayer said current Metro track engineering leadership also learned of the report during the investigation.

The report, Mayer said, found problems in how car wheels and axles are put together and with the amount of force the tracks place on wheel flanges — the rims made of steel or other metal that keep cars on tracks.

Russell Quimby, a railroad accident consultant who worked as an NTSB investigator for more than two decades, said Metro’s turnouts or switches might have flangeways that are too narrow or more restrictive than they should be. Not only can the stress cause wheels to widen on their axles, he said, but it causes unnecessary wear on wheels and increases maintenance expenses.

“Those flangeways are putting stress on those wheels,” he said. “This sounds like a screw-up by the track department, to be honest with you.”

After the engineering report was released seven years ago, Mayer said, the transit agency ordered a change in car wheel specifications and to the force with which wheels are pressed onto axles. It asked for the changes from Kawasaki Rail Car, which was manufacturing the 7000 series at a plant in Lincoln, Neb.

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No alterations were made to cars that already were finished, Mayer said.

“This means that the new specifications applied to approximately the final one-third of the 7000 series cars Metrorail accepted, and not to the first two-thirds of the 748 cars,” he said. “Metrorail did not address the other identified item in its wheel migration report — a concern with flangeway width on restraining rails throughout the system.”

The 2015 report called for adjustments to the rail flangeway widths on the track, Mayer said. Setting the proper width “is critical to ensuring that no unnecessary force is placed on the wheel flange by a restraining or guard rail,” he said. The report, he said, indicated that the force applied to wheels from “these improperly placed restraining rails” can cause wheels to shift apart.

Metro officials did not respond to questions about why the adjustments weren’t made. An internal review in June of work performed in 2021 and 2020 found that quality assurance inspectors have questioned Metro’s standards for its restraining rails, calling for the agency to conduct an engineering study and update track-design criteria based on the results.

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Metro officials have said in recent months that a number of factors might be contributing to the wheel safety problem. That’s one reason the safety commission has limited which lines can host up to 20 of the returning 7000-series trains — a total of 160 rail cars — a measure designed to allow both agencies to study its effects on the cars.

“Available information continues to suggest there are multiple contributing factors to this wheel migration on 7000 series cars, including factors that could differ across similar elements of the Metrorail system,” Mayer said. “Line limitations are important to ensure that too many variables are not changed at the same time, so that data collected on wheel migration or lack thereof can be properly evaluated.”

The safety commission has permitted the returning 7000-series trains on the Green and Red lines, as well as on the Yellow Line, which is temporarily closed for a bridge and tunnel project. Mayer said Tuesday that the safety commission cited Metro on Sept. 7 for putting a 7000-series train on the Blue Line for more than an hour.

The defect that causes wheels to shift progresses slowly, investigators and experts say. It does not affect all cars and surfaces only after extended use.

The safety commission has allowed Metro to return some cars to service in phases under an agreement that Metro inspects the cars after four days of use. No cars have shown signs of the defect since Metro has returned them to service.

Metro General Manager Randy Clarke has said returning all 748 cars is one of Metro’s biggest priorities. He said transit engineers continue to work on installing and testing an automated wayside inspection system that Metro hopes will expedite wheel screenings now performed manually by Metro employees.

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Safety commission officials said Metro has not submitted plans to use the automated system, which must be approved by the commission.

The NTSB continues to investigate the cause, origin and circumstances surrounding the defect. Both Metro and the safety commission are participants in the probe.

NTSB spokesman Keith Holloway said Tuesday that the agency had nothing new to release about Metro’s track issues.

The WMSC has highlighted to WMATA the need for Metrorail to fully, seriously and with exigency consider and address engineering recommendations and suggestions previously identified by Metrorail, additional information obtained through the ongoing NTSB derailment investigation.

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