FILE PHOTO: Emergency responders are at the scene after an Amtrak passenger train collided with a freight train and derailed in Cayce, South Carolina, U.S., February 4, 2018. REUTERS/Randall Hill/File Photo (Randall Hill/Reuters)

The engineer of an Amtrak train sounded his horn for three seconds and eventually hit the emergency brake, slowing the train to 50 mph before it slammed head-on into a freight train near Columbia, S.C., federal investigators said Monday.

The impact of the crash early Sunday was so intense that it moved the empty CSX freight train 15 feet from where it was parked on tracks adjacent to the main rail line, according to Robert Sumwalt, chairman of the National Transportation Safety Board, which is investigating the crash. The Amtrak train's conductor and engineer were killed, and 116 others were hospitalized.

Sunday's crash in Cayce, S.C., about four miles south of Columbia, was the third high-profile incident involving an Amtrak train in less than two months. Last Wednesday, an Amtrak train carrying GOP lawmakers to their annual retreat in West Virginia hit a garbage truck outside Crozet, Va. No lawmakers were seriously injured, but a passenger in the truck was killed.

The crashes have renewed concern about whether enough is being done to equip railroads with an automatic braking system known as positive train control, which Sumwalt and others say could have prevented Sunday's fatal crash and one that occurred in December, just outside Seattle.

PTC originally was supposed to be in place by the end of 2015, but after a push by the rail industry, Congress postponed the deadline until the end of this year, with the possibility that it could be extended to the end of 2020.

Authorities investigate the scene of a fatal Amtrak train crash in Cayce, South Carolina, Sunday, Feb. 4, 2018. At least two were killed and dozens injured. (Tim Dominick/The State via AP)

Last month, however, Transportation Secretary Elaine Chao sent letters warning railroad industry leaders that they must meet the end-of-year deadline.

On Monday, members of the Association of American Railroads, which lobbies for the freight industry, said its members will meet the deadline.

"The railroads are very far along," said Michael J. Rush, senior vice president of the Association of American Railroads. "All of the (seven major railroads) are going to make it by (December) 2018."

What "making it" means will vary. The law passed by Congress puts a December deadline on hardware installation, acquisition of the mandated radio spectrum and training of employees in its use.

The law also requires that 50 percent of the system be switched on by December. If the railroads comply with that deadline they will then be required to complete the balance of the system by the end of 2020.

National Transportation Safety Board Chairman Robert Sumwalt presents the ongoing investigation to the media during a press conference at SC Emergency Management Division in Cayce, South Carolina, on February 4, 2018. Two Amtrak employees were killed and more than 100 other people were injured early Sunday when a passenger train carrying 147 people hit a CSX freight train in South Carolina, authorities said. / AFP PHOTO / Logan CyrusLOGAN CYRUS/AFP/Getty Images (Logan Cyrus/AFP/Getty Images)

In the briefing with reporters on Monday, Sumwalt said the information about the Amtrak train's speed and the engineer's actions comes from the data recorder, which was retrieved from the wreckage. Investigators were hopeful that the front-facing video camera retrieved from the train's locomotive Sunday would offer them more insight into what happened before the crash. However, it was discovered that the recording ended a few seconds before the crash. A forensics team in Washington is working on the footage, he said. The train hit a top speed of 57 mph before the engineer began to slow it; the speed limit in the corridor is 59.

About seven seconds before the end of the recording, the train's horn was activated for three seconds.

"A lot has been done, and a lot needs to be done," Sumwalt said. "But I'm confident that our investigator will be able to piece this together."

He said investigators are expected to remain in Cayce though the weekend.

Amtrak 91, traveling on tracks owned and maintained by freight railway giant CSX, was supposed to pass over the switch to continue onto the main-line tracks. Instead, it was directed onto a portion of track known as "siding," which was occupied by the parked CSX train, Sumwalt said.

Sumwalt said officials have confirmed that a signal outage along the rail corridor meant that trains had to be manually directed through the area. He said the outage occurred because of upgrades tied to the installation of PTC. Investigators also are focusing on why a railroad switch was locked in the wrong position, sending the Amtrak train off the main line and onto the side track.

Sumwalt said NTSB investigators have also been able to interview four CSX crew members, including the engineer, conductor and the dispatcher who would have been responsible for directing the Amtrak train because of a signal outage along the rail line.

Sumwalt could not say whether the Amtrak engineer's actions before the collision indicated that he knew the train had detoured off the main line and onto the side track.

Amtrak trains have PTC equipment, but the freight railroads on which Amtrak trains travel, including the one involved in Sunday's crash, must install and activate transponders along their rail beds for the system to work.

According to Sumwalt, the Amtrak train was headed south on the main track, as directed by dispatchers with CSX. The empty freight train, which had unloaded its cargo of automobiles, was parked on a side track adjacent to the main line. When the Amtrak train moved past the area, it hit a switch that moved it to the side track where it crashed into the freight train.

Installing PTC is an expensive challenge for the railroads, requiring that hardware be added in 25,000 locomotives and sensors be placed along the railway beds. The payoff, safety advocates say, is that it will help prevent collisions and derailments.

Rush said Monday, that PTC has been implemented on 56 percent of required route miles. He added that 78 percent of locomotives have been equipped with the technology. PTC has also been installed on 72 percent of the track segments required by law.

In addition, 87 percent of railroad employees have been trained in the system.

When the industry appealed to Congress for relief from the looming deadline in 2015, it said it had already invested more than $6.5 billion, anticipated a total price tag of $10.6 billion and needed additional time to put the system in place.

The NTSB says it has investigated 146 rail incidents since 1969 that positive train control could have prevented. The toll in those incidents is 291 people killed and 6,574 injured.

But industry groups have disputed the contention that PTC would prevent most rail crashes.

PTC could prevent only about 4 percent of incidents, said the Association of American Railroads' Rush. "There are lots and lots of other accidents that are not PTC preventable."