Of course, other engineers, struck by projectiles in exactly the same place on the Northeast Corridor, managed to keep their trains from overturning — a point that Beall willingly concedes. “It happens, it’s violent and terrifying, but you move on,” he told me. Which brings up the second, and not mutually exclusive, possibility. This situation takes place in the same time frame but has Bostian lost, confusing Frankford Junction with the curve before it and realizing his mistake only at the last moment. Several people involved in the investigation offered the analogy of a driver on a long and darkened freeway, mesmerized by the unending roll of asphalt. A kind of hypnosis takes over. The driver, fatigued, looks up to see his exit, but it’s already starting to pass, and the car swerves off the road at a dangerous speed. If Bostian had been rocked earlier in the trip, they said, this might have only added to his confusion, putting him on edge.

It’s easy to see: a rattled young engineer finishing the second leg of a frustrating couplet, aboard a racehorse of a high-powered locomotive he was still growing accustomed to. A notoriously tricky piece of track. And a moment of distraction at precisely the worst time.

Perhaps the most tragic aspect of the wreck of 188 is that it could have been avoided, or at least mitigated, had the right safeguard — positive train control — been in place. Renewed pressure has been brought to bear on the industry by P.T.C. advocates like Robert Sumwalt of the N.T.S.B. and Sarah Feinberg of the Federal Railroad Administration. (The agencies have been pushing for the technology for decades.) “My hope,” Feinberg told me recently, “is that the derailment was our long-overdue wake-up call that we need P.T.C. — that we owe it to passengers and rail staff to have it online.”

In late May, Joseph Boardman, Amtrak’s C.E.O. and president, promised that the installation of P.T.C. on the Northeast Corridor would be completed by the end of 2015, a pledge he has kept: Today, the system is active on all routes, with the exception of substantial stretches of track owned by the State of Connecticut. (A spokesman for the Connecticut Department of Transportation said it hoped to have P.T.C. installed on all state-owned track by 2018.)

It will be some time before a national rollout is complete. In November, President Obama signed into law an extension to the Rail Safety Improvement Act of 2008, giving railroad companies — which had complained about the cost of implementation — until 2020 to bring the technology online. On sections of rail not protected by P.T.C., “there is absolutely nothing to prevent what happened to Amtrak 188 from happening again,” Richard Beall told me. “Nothing.”

For many survivors of the accident, and for the families of the dead, the public discussion about safety technology has come too late. “I spend my days thinking about how this could have happened,” Howard Zemser told me when I spoke to him by phone earlier this year. “But look, Justin was never lost like other young men are — he had this incredible focus. He didn’t need to count on other people. He counted on himself and his own strength. He would want us to do the same thing.”

In September, Howard and Susan filed their lawsuit against Amtrak, asking for a jury trial and claiming that the company’s “negligent, careless, reckless” actions led to Justin’s death. They are not alone: Dozens of other families and individuals, including the conductor onboard 188, Emilio Fonseca, are suing Amtrak, which said in July that it will not fight claims for compensatory damages. (Congress has capped the amount of money Amtrak can pay out in any single accident at $295 million.)