For the second time in two years, a passenger train traveling well above its speed limit has derailed, leaving a trail of death and injuries. And for the second time, existing technology that might have prevented the accident was missing.

Amtrak has installed the technology, known as positive train control, on parts of its rail network in the Northeast Corridor. But the technology, designed to automatically slow or stop a train to prevent accidents, was not available on a critical stretch of track in Philadelphia where Train No. 188 derailed on Tuesday night, killing at least seven and injuring more than 200.

Safety investigators said the technology might have prevented the derailment. The train from Washington to New York was traveling at 106 miles per hour just as it entered a curve limited to 50 m.p.h.

“We feel that had such a system been installed in this section of track, this accident would not have occurred,” Robert Sumwalt, a member of the National Transportation Safety Board, said during a news conference on Wednesday.