Amtrak's Northeast Regional train #172 was headed from Washington to Boston when it hit the vehicle around 10 a.m. Thursday.
Amtrak spokesman Clifford Cole says there are no reports of injuries to the 278 passengers or crew members aboard.
Passengers will be transferred to other Amtrak trains.
Trains are running up to 30 minutes behind schedule in each direction around the area due to the investigation.
Two of the four northbound Northeast Corridor tracks are open.
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