The northbound Amtrak train that collided with a southbound MARC commuter train Monday evening near Penn Station received a signal to slow and stop before the accident, according to the National Transportation Safety Board.
But the train continued, and about 200 feet past the stop point, the operator attempted to merge onto the track occupied by the MARC train, sideswiping the commuter and causing cars on both trains to derail.
Although those facts emerged yesterday as significant details in the cause of the crash, NTSB spokeswoman Lauren Peduzzi said, "we haven't eliminated anything."
"There's more factual information that needs to be gathered before any conclusions can be drawn," she said.
Investigators said yesterday that the head locomotive of Amtrak's Miami-to-New York Palmetto train struck the fourth car in the seven-car MARC train and derailed cars five and six, which were not carrying passengers.
Of 60 MARC passengers, three reported minor injuries. The Amtrak train carried 147 people, and a passenger and engineer reported minor injuries.
The investigators continued to sort through information retrieved from the Amtrak train's data recorders, which document such things as braking, speed and throttle position, and which are the equivalent of an airplane's "black box."
They also have begun to review the mechanical histories of both trains and the records of the trains' operators.
The MARC train was traveling about 10 mph and the Amtrak train less than 15 mph, investigators concluded.
Peduzzi said preliminary tests of the track signals showed they were functioning properly.
The collision at 5:45 p.m. just south of Penn Station caused Amtrak to briefly halt service between Washington and Wilmington, Del., Monday evening. It also forced the cancellation of MARC service between Baltimore-Washington International Airport and Perryville.
MARC service resumed at 9:30 a.m. yesterday, according to the Maryland Transit Administration.
Amtrak, like MARC, used buses to transport passengers around the closed sections of rail.
An Amtrak official said they were experiencing 15-minute delays at 7 a.m. yesterday, but returned to a normal schedule by the afternoon.