WASHINGTON: "Washington's regional Metro system abruptly pulled more than half its fleet of trains from service early Monday morning over a lingering problem with the wheels and axles that caused a dramatic derailing last week. The Metro authority's safety commission ordered the withdrawal of the entire 7000-series line of trains overnight. The Kawasaki-made 7000 series are the newest set of trains in service and the 748 cars comprise about 60% of the fleet. NTSB Chair Jennifer Homendy told reporters Monday that a design flaw had been identified which caused the trains' wheels to spread too wide on the axles, allowing the carriage to slip off the tracks. The incident promises to shine a potentially harsh light on WMATA, the regional transit authority which suffered a string of embarrassing and dangerous derailments and track fires, several years ago but claimed to have addressed its issues. Homendy revealed Monday that WMATA had been aware of the potential problem since 2017, but hadn't informed the NTSB, and that minor incidents with the wheels had been escalating since then. She said WMATA was aware of 18 such failures in 2021, and the current round of emergency inspections revealed an additional 21 failures, for a total of 39 this year alone."
https://www.timesunion.com/news/article/DC-suspends-most-of-its-Metro-trains-over-safety-16542563.php