Safety authorities in Maryland have cited Metro for violations in the January deaths of two workers.
Jeff Garrard, 49, and Sung Oh, 68, were replacing broken equipment on a track overnight.
A work truck designed to operate on the rails backed over them in the work zone.
Officials at the Maryland Occupational Safety and Health office said the deaths were caused in part because Metro ignored its own safety rules by failing to keep watch for the workers, operating a truck without a clear view behind it and without a working alarm for backing up.
Safety officials also discovered Metro workers used different radio frequencies and sometimes used their personal cell phones to communicate as shifts changed.
The agency did not fine Metro but is recommending improvements to its communication system.
Metro contested the safety citations, spokeswoman Lisa Farbstein said.
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The transit agency is also contesting a $7,000 fine for a "serious" violation of workplace safety in the August death of another worker, Michael Nash, who was hit by a machine spreading gravel on the Orange Line, said Virginia Department of Labor and Industry policy analyst Eric Delia.
The Virginia workplace safety watchdog found that the windshield on the equipment that killed him was covered in "significant amounts of dust," limiting visibility to less than 15 feet, records show.
The National Transportation Safety Board also has been investigating the three deaths as part of three ongoing investigations into Metro accidents.
The independent federal agency last week wrapped up a fourth probe into last summer's deadly Fort Totten crash, finding that the agency's "anemic" safety culture led to nine deaths in the Red Line train crash in June 2009.
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