On March 16, 2026, Region 1 entered into a Clean Air Act administrative order on consent requiring the Massachusetts Bay Transportation Authority ( MBTA ) and its commuter rail operator Keolis Commuter Services, LLC ( Keolis ) to both improve the reporting of and reduce locomotive idling at train layover facilities in the Greater Boston area. The order follows up on the Region's October 2025 Notice of Violation that found the two entities had violated federally-enforceable locomotive idling limits contained in the Massachusetts state implementation plan. The March 2026 administrative order specifically requires MBTA and Keolis to assess their reporting of locomotive idling, submit a data-quality assurance plan for EPA's review, produce a comprehensive idling control plan identifying specific corrective measures to implement, and submit quarterly progress reports. EPA previously brought an enforcement action against MBTA and its former commuter rail operator that resulted in a 2010 Consent Decree addressing locomotive idling. Both the order and preceding notice of violation were shared with the Massachusetts Department of Environmental Protection.