According to preliminary findings from the National Transportation Safety Board, electrical arcing — essentially like static electricity escaping from the third rail that powers the system’s trains — happened about 1,100 feet in front of the train.

“The train stopped in the tunnel,” said Peter Knudson, a National Transportation Safety Board spokesman, “but we don’t know if that was because of a loss of power, or if the operator saw too much smoke” to proceed. Investigators concluded their initial work at the scene Tuesday.

The source of the smoke remained unclear Tuesday as there was no fire present, according to investigators. “Something had to create smoke,” said Augustine F. Ubaldi, a railroad engineering expert. “Arcing is not unusual; arcing with smoke is.”

The key, he said, will be to find “what caused it to burn, and is this a fluke or systematic and what can get done to prevent it in the future within reason.”

The agency that oversees the rail line was largely silent Monday. But on Tuesday, Tom Downs, the Metro Board chairman, released an open letter to customers in which he offered “my deepest condolences to the family of the passenger who died yesterday following the incident on the Yellow Line.” He also promised that “once the cause of this incident is understood, we are prepared to take the actions needed to prevent this from happening again.”

The Washington Metropolitan Area Transit Authority, which serves 3.4 million bus and train riders over a 1,500-square-mile region, was created in 1967 by an interstate compact serving Washington, suburban Maryland and Northern Virginia. Its board has eight voting directors appointed by the Northern Virginia Transportation Commission, the Washington City Council, the Washington Suburban Transit Commission and the federal government’s administrator of general services. Funding comes from all four.

“This is the sort of thing that makes people roll their eyes,” Charlie Bryant, who commutes between Washington and Rockville, Md., said as the Red Line was delayed at a station briefly Tuesday night. He said riding the Metro was better than sitting in traffic, but he added, “There is always stuff out of service.”

Ricardo Wright, who commutes to suburban Maryland, also expressed frustration. “You think they’d have it figured out by now, but they don’t,” he said. “They keep raising the prices to pay for more malfunctioning”