D.C. Subway
© Paul J. Richards/AFP/Getty ImagesA Washington Metropolitan Area Transit Authority worker walks past a new 7000 series train car in Washington on April 13, 2015.
Transportation Secretary Anthony Foxx threatened Tuesday to shut down the D.C. subway if the system fails to make immediate changes to fix dangerous safety lapses.

Foxx said he "would have no hesitation to shut down the system," the nation's second largest, if safety doesn't improve.

The Washington Metropolitan Area Transit Authority's subway system, known locally as the Metro, carries the second largest number of passengers in the nation. Metro's six lines serve 91 stations and traverse 117 miles of track.

Foxx's tough talk followed an incident Thursday during which Metro employees denied federal inspectors access to a tunnel after smoke closed two stations, Federal Center station and Capitol South, Foxx said. Metro restored rail service Friday on the affected Orange, Silver and Blue lines after installing new third-rail equipment at Federal Center station overnight.

But the Federal Transit Administration responded to Metro on Saturday with a directive threatening a shutdown or reduced funding unless the subway officials improve safety and give federal inspectors unfettered access.

"It's scary," Foxx said of video from the scene. "The culture of safety is not where we want to see it."

Smoke and fire in the tunnels is a long-running concern for the transit authority. A fire that filled a tunnel and the L'Enfant Plaza station with smoke in January 2015 killed one woman and sent 90 others to hospitals. A similar smoke incident atMcPherson Square station in March forced Metro to shut the entire system for a day so it could conduct emergency inspections and make repairs.

The National Transportation Safety Board, which investigated the fatal smoke incident from 2015, ruled May 3 that Metro ignored safety provisions for years.

Subway officials on Friday announced a massive program of repairs to begin in June. The repairs will cause major delays for riders, but won't entirely shut down lines. The plan concentrates on trouble spots and will close sections of the track until repairs are finished. In the past, the system made repairs at night and on weekends to avoid closing tracks during peak travel times.

Foxx said his safety concerns go beyond the maintenance issues Metro vowed to tackle last week. The system cannot handle the power demands made by the Metro trains, Foxx said. To avoid fires and other mishaps, the system must reduce the power, he said. Federal officials recommend the rail system run six-car trains instead of eight-car trains, and lower power use in stations so that trains start slower, Foxx said. Such measures would further inconvenience riders.

"We're not afraid to use the authority we have," Foxx said. "This is serious business."

Metro workers must also show they know how to evacuate riders when a station fills with smoke or fire, Foxx said. Workers don't always follow Metro's own protocols during an emergency, he said.

"I have great concerns," Foxx said. "There is an awful lot of work here to do to correct the problem."