WASHINGTON/PHILADELPHIA (REUTERS/AFP) - Federal investigators said on Wednesday that preliminary data showed an Amtrak train in Philadelphia was travelling at more than 160kmh, or roughly twice the speed limit, when it derailed, killing seven people and injuring more than 200.
They added that the driver had slammed on the emergency brakes.
The driver engaged in a "full emergency brake application" moments before the derailment, but the train speed only decreased by a few miles per hour, Robert Sumwalt of the National Transportation Safety Board (NTSB) told reporters.
The NTSB's disclosure came as investigators pored over video footage and data from the black box aboard the train that crashed late Tuesday.
The NTSB has said it was also focusing on the condition of the tracks and equipment, crew training and the performance of the five-person crew, in addition to the train's speed.
Passenger rail service along Amtrak's Northeast Corridor, the country's busiest with 12 million passengers a year, was shut down immediately after the accident at about 9.30pm (9.30am Singapore time on Wednesday), leaving travellers scrambling for alternatives.
The derailment also snarled commuter rail services that share Amtrak tracks in the Philadelphia area and beyond.
About 15 hours after Amtrak No. 188 jumped the track, rescue workers sifted through the twisted metal and other debris. One of the seven cars landed upside down and three were tossed on their sides, while passengers and luggage were sent flying, survivors said.
Philadelphia Mayor Michael Nutter said at an afternoon news conference that seven people were confirmed dead, but authorities had not yet accounted for everyone aboard.
He said rescue teams expanded the search area out of fear that some victims may have been thrown from the train when it derailed.
"What we have to do today is make sure we're searching every car, every inch, every thousands of square feet to find or locate individuals who may have been on that train," Nutter said.
Hospitals in the area reported treating more than 200 people, city officials said.
Authorities believe 243 people, including a crew of five, were on board, but they were still trying to confirm the number.
Officials did not provide a figure on the number of injured, but Nutter said the train's engineer was among them. Nutter said the engineer was treated at a local hospital and later gave a statement to police.
He said he was mistaken when he said earlier that the train's conductor had given the statement to police.
The wreck was the latest in a series of rail accidents on heavily traveled passenger train routes over the past year, raising new concerns about the state of the country's ageing rail infrastructure.
The crash and Amtrak funding were likely to come up during a session of the House Appropriations Committee, which was meeting on Wednesday to discuss the transportation budget for the next fiscal year.
"LIKE A SECOND FAMILY"
Vice-President Joe Biden, who represented the state of Delaware - south of Philadelphia - in the US Senate for years, expressed shock and sorrow.
"Amtrak is like a second family to me, as it is for so many other passengers," Biden said in a statement.
He estimated taking some 8,000 Amtrak trips to and from Washington during his career.
One of the people killed was a midshipman on leave from the US Naval Academy in Annapolis, Maryland, an academy spokesman said.
He said the identity of the midshipman was being withheld for 24 hours until family was notified.
An Associated Press video software architect was also among those killed. Jim Gaines, a 48-year-old father of two, had attended meetings in Washington and was returning to his home in Plainsboro, New Jersey, when the train derailed Tuesday night. His death was confirmed by his wife, Jacqueline.
Dr Herbert Cushing, Temple University Hospital's chief medical officer, said the dead suffered massive chest injuries. Most of the injured at Temple suffered fractures, he said at a news conference.
In March, 21 people were injured in Los Angeles, when a commuter train collided with a car. A month earlier, 50 people were hurt and an engineer fatally injured when a Los Angeles-bound Metrolink train struck a pickup truck.
Also in February, six people were killed and a dozen injured when a commuter train hit a car stalled on the tracks north of New York City. The driver of the vehicle also died.
The train derailed in the city's Port Richmond neighborhood along the Delaware River, near the site of a 1943 rail accident that killed 79 people and injured 117 others, according to the National Railway Historical Society.
Tuesday's derailment left travelers along the Washington-to-New York corridor scrambling to find alternatives.
At New York's LaGuardia Airport, attorney Wayne Hess said he had planned to take the train back to Washington but instead booked a flight after hearing of the accident. "It made me feel lucky because I came up yesterday," Hess said.
NOT FITTED WITH LATEST SAFETY CONTROLS
The commuter rail route where an Amtrak train left the track was not governed by an advanced safety technology meant to prevent high-speed derailments, officials familiar with the investigation said.
Positive train control (PTC) automatically slows or even halts trains that are moving too fast or heading into a danger zone. Under current law, the rail industry must adopt the technology by year-end.
The cause of Tuesday's crash, in which seven people were killed, has only begun to be investigated.
Regulators are examining whether excessive speed led to the derailment on an Amtrak line in Philadelphia, said officials familiar with the investigation.
Amtrak has begun installing components of a PTC system but the network is not yet functioning, federal officials said.
An Amtrak official did not immediately respond to a call for comment.
"A functioning PTC system should prevent this," said Mr Joseph Szabo, who stepped down in January as administrator of the Federal Railroad Administration.
Federal rules require the national rail network to have an operating PTC system by the end of the year, though there has been a legislative push to extend that deadline by years.
In March, the Senate Commerce Committee voted to extend the deadline for implementing PTC until at least 2020.
Both Republicans and Democrats supported the measure which will now go to the Senate floor.
"This accident is exhibit A for ending the delays and getting positive train control in place," said Senator Richard Blumenthal, a Connecticut Democrat.
High-traffic areas like Amtrak's Northeast corridor should be early adopters of PTC, said Mr Szabo, though he did not know precisely what kind of technology is in place along that route.
Mr Szabo said PTC control would go as far as override a train conductor who was exceeding posted speed limits. "If there is a red signal you can't pass it. If there is a speed restriction, it will slow you down," he said of the override system.
The question of PTC, whether it was operating before the crash, would be an important one for investigators, Mr Szabo said.