One of the Washington transit agency's most closely held secrets about its rail service in recent years is that the wheels have been coming off — literally. Since 2017, Metro, which served more than 600,000 rail passengers daily before the pandemic, has known that the wheels of some of its custom-built 7000-series trains had been shifting outward on their axles while moving on the tracks. Those cars, the newest in Metro's inventory, account for nearly two-thirds of the fleet and more than four-fifths of annual subway miles traveled. That problem, to put it in layman's terms, is absolutely not supposed to happen; it poses a risk of derailment, a dangerous and potentially fatal event. When a 7000-series car with precisely that issue derailed last week near Metro's Arlington Cemetery station in Northern Virginia, it was lucky indeed there were no injuries, although nearly 200 people aboard were evacuated to walk hundreds of yards underground on dark tracks to safety. It is disturbing that in the four years since the wheel troubles were detected — and even as Metro officials were in discussions about them with the manufacturer, Kawasaki Rail Car in Nebraska — the agency apparently said nothing either to its own board of directors or to the Washington Metrorail Safety Commission, an oversight panel that began work two years ago after it was established by Congress. Wheel assembly on Metro rail cars had failed repeatedly, NTSB says Do Metro officials regard their board and the safety commission as window dressing? Is transparency purely optional? Metro didn't mention the problem in its most recent annual performance report, covering the fiscal year ending June 30, either. To the contrary, the report's safety and reliability pages offer a litany of good news, including the conclusion that "railcar reliability improved throughout FY21 and ended at a record high, driven by strong performance in the 7000-series fleet." Railcar failures during the 12-month period, Metro reported, averaged fewer than half the number tallied just two years ago. Though the report mentions ongoing inspections to minimize the chance of derailments, not a word appears about the wheel issue, which, as Metro told the National Transportation Safety Board following the Oct. 12 derailment, has been recurring since 2017. That was three years before the agency took delivery of the last of its 748 7000-series trains. The fallout from the derailment is severe.