Sarah Trautwein, 19, lost control of her blue 2005 Chevrolet Cobalt on Interstate 95 near Charleston, S.C. as she headed home from visiting friends in June 2009. Her car began to run off the road, authorities said, causing her to overcorrect and hit a tree in the highway median. She died instantly.

Her family took small comfort in the idea that she had fallen asleep at the wheel. At least, they thought, she died in peace. So they were shaken in recent weeks when they learned about similar crashes tied to a faulty ignition switch that caused Cobalts and other small GM cars to switch off while in motion, stiffening their brakes and steering and disabling their air bags.

“This opens up a whole new thing. It is kind of crazy,” said Phil Trautwein, Sarah’s brother. Last week, the family learned after asking police that Sarah’s air bag had never deployed — as was the case for 13 people who died in accidents that GM has linked to the defect.

With Congress set to open hearings Tuesday into GM’s handling of the faulty ignition switches, Trautwein is among more than two dozen people who traveled to Washington in remembrance of relatives who died in GM cars. The family members met with GM’s chief executive, Mary T. Barra, at the automaker’s D.C. offices.

“There wasn’t a dry eye in the room,” said Bob Hilliard, a Corpus Christi, Tex., lawyer who sued GM on behalf of victims’ families.

First in the House and then in the Senate, lawmakers plan to grill Barra about why the defect went unaddressed despite a trail of red flags stretching back more than a decade. In written testimony submitted Monday to congressional investigators, Barra said she had the same question.

“I cannot tell you why it took years for a safety defect to be announced,” said Barra, who took over as GM’s CEO in mid-January. Apologizing again for GM’s actions, she added: “I can tell you that we will find out.”

Barra said she would use the results of an internal investigation being led by former federal prosecutor Anton Valukas to hold company executives accountable — and to “help assure that this does not happen again.”

Barra is expected to face tough questions from lawmakers alarmed that the company installed the ignition switches manufactured by a supplier, Delphi, even though they did not meet all of the automaker’s technical specifications.

“This information raises important new questions about what GM knew, when GM knew about the risks from this faulty ignition switch, and how the company has handled the recalls of affected vehicles,” wrote Democratic Reps. Henry A. Waxman (Calif.), Diana DeGette (Colo.) and Jan Schakowsky (Ill.), in a letter to Barra on Monday.

David Friedman, acting head of the National Highway Traffic Safety Administration, has also been summoned to testify. ­NHTSA is under fire for not doing more to recognize the defect and requiring GM to fix it, despite mounting accident reports, consumer complaints and a 2007 recommendation by a top staffer for a full-scale investigation. That recommendation was rejected after a review by a panel of NHTSA officials.

“This was a difficult case pursued by experts in the field of screening, investigations and technology involving air bags that are designed to deploy in some cases, but not in cases where they are not needed or would do more harm than good,” Friedman said in his prepared testimony. He added: “Advanced air bags are not intended to deploy in all crashes, even frontal crashes.”

Friedman said NHTSA suspects that GM did not provide regulators with timely information about the faulty ignition switch — a violation of federal law — complicating the agency’s handling of the problem.

As inquiries by GM engineers and NHTSA employees led nowhere, evidence of the defect mounted in private lawsuits. That prompted GM to assemble a team of engineers to review the problem, resulting in the first of several ignition-switch recalls in February. The recalled vehicles include 2.6 million Chevrolet Cobalts and five other small models.

Last month, Barra appointed a new vice president to oversee safety issues at the giant automaker; the company has since issued an unusual number of recall notices.

On Monday, GM released another one: The company said it will recall more than 1.3 million U.S. vehicles at risk of unexpectedly losing power steering. The latest announcement brings the total number of vehicles recalled this year by the automaker to more than 6 million.

For the survivors of accidents involving the faulty ignition switches, the recalls have come far too late.

Amber Marie Rose, 16, died in the predawn hours of July 29, 2005, when her new Cobalt crashed at the end of a cul-de-sac in Charles County, Md.

Rose had been drinking, and she was not wearing a seat belt. But a police officer noted that her air bag — which could have saved her life — had not deployed.

“He said it had to be an issue with the car,” said Rose’s mother, Terry DiBattista.

The family hired an investigator, who turned his findings over to GM. Within weeks, the automaker offered the family a financial settlement. But it was not until a few weeks ago that they learned that the air bags did not deploy because the car’s ignition switch had shifted into the accessory position.

“It is horrible that GM knew all of this and they allowed it to happen and all these people died because of this,” DiBattista said.

Susan Hayes, 49, of Ticonderoga, N.Y., said she received a recall notice in February for her son’s silver Chevrolet Cobalt. By then, her son, Ryan Quigley, 23, had been dead for more than two years. He and a friend were killed when Quigley’s Cobalt, purchased just four months earlier, veered off the road and plunged over an embankment, landing upside-down in a small stream not far from the family’s home. The force of the crash was so violent that it broke her son’s sternum.

After the accident, Hayes learned that her son had been drinking and that he was not wearing a seat belt. His 19-year-old passenger had fastened his belt but died anyway.

“My son was a very good human being who made a poor choice,” she said.

Hayes settled on that as an explanation for his death, until she learned about the ignition-switch problems. That prompted her to meet with the police officer who investigated her son’s accident. A little over a month ago, she learned that the air bags in the car had never deployed.

“I’ve read an awful lot recently about the knowledge that GM had about this problem, and how it was buried,” Hayes said, before reading words from a GM document that she had written down on a small pad. It said that GM had rejected an ignition-switch fix in 2005 because “none of the solutions represents an acceptable business case.”

“My son wasn’t a business case. He was a human being,” she said. “As were the other people who died because of this problem.”