Train personel survey the NJ Transit train that crashed in to the platform at the Hoboken Terminal on Sept. 29, 2016 in Hoboken, New Jersey. (Photo by Pancho Bernasconi/Getty Images)

A commuter train that barreled into a Hoboken, N.J., rail terminal last month was going double the speed limit when it crashed, federal officials said Thursday.

The National Transportation Safety Board said the train was traveling at 21 mph, citing information downloaded from a data recorder in the train’s leading car.

In interviews with investigators over the weekend, engineer Thomas Gallagher, 48, who has no memory of the crash, recalled pulling into the station about 10 mph. The next thing he remembered was waking up on the floor of the train cab. Newly recovered data shows he made a last-second effort to brake before the train made impact.

The Sept. 29 crash killed 34-year-old Fabiola Bittar de Kroon, of Hoboken– who was struck by debris while standing on the platform– and left more than 100 injured.

Using data from the event recorder and a front-facing video camera, NTSB investigators reconstructed the moments before the crash.

A minute before the crash, the train’s horn sounded and a bell began to ring, signaling the train’s arrival. Twenty-two seconds later, as the train coasted into Hoboken terminal at 8 mph, the throttle moved from idle to an accelerating position, the NTSB said.

The train steadily gained speed and topped out at 21 mph. Less than one second before impact, Gallagher induced the emergency brake, NTSB said. The train crashed into a bumping post — a piece of rail equipment designed to halt a train’s movement — overrunning it and barreling into the terminal. Video showed a “large flash” as the train made impact, the NTSB said.

Over the weekend, NTSB investigators had trouble recovering the train’s speed and braking information because an event recorder aboard the the locomotive was not working. Debris had initially prevented investigators from accessing the other event recorder, aboard the train’s controlling car, but investigators managed to recover it early this week.

Vukan R. Vuchic, a professor emeritus of transportation engineering at the University of Pennsylvania, said the sequence of throttle movements — as described by the NTSB — seemed “totally irrational.”

“If he was awake and aware and normal, I cannot see how the engineer would perform these actions,” he said.

Vuchic added that he believed it was highly unlikely that a person would be able to increase the level of the throttle while incapacitated, by falling or slumping onto it.

Since the crash, New Jersey Transit officials have enacted new regulations for trains entering Hoboken Terminal, as well as Atlantic City Station. Conductors must walk to the front of the train as they approach the station and stand beside the operator as they move toward the platform at the end of the line.

Vuchic said he was not aware of any other rail agencies that had put in place similar regulations.

“It’s not a common practice. If it’s temporary, I understand,” Vuchic said, adding that he expects New Jersey Transit will come out with a more robust set of changes in procedures and regulations as they learn more about what led to the crash. “But having a second man in the cabin, that’s totally out of line with where the industry is going. It cannot be a permanent solution.”

NTSB officials have more tasks that they hope may be useful in their investigation into what caused the crash — including reviewing the engineer’s cell phones, conducting mechanical inspections, and performing a sight-distance test to establish what was visible to the engineer as he approached the station.