A communication breakdown during a shift change may have kept an Amtrak engineer in the dark about workers on the tracks in Pennsylvania on Sunday morning, according to sources familiar with an investigation into a passenger train derailment that killed two workers and injured 37 passengers. Amtrak train 89 was traveling 106 mph in a 110 mph zone, en route from Savannah, Georgia, to NYC with 341 passengers on board when it crashed into a backhoe on the tracks in Chester, about 15 miles outside Philadelphia.

The crash killed backhoe operator Joseph Carter Jr., 61, of Wilmington, Delaware, and Peter Adamovich, 59, of Lincoln University, Pennsylvania. None of the passengers' injuries are described as life-threatening.

Investigators are trying to determine why the backhoe was on the tracks being used by train 89. According to a preliminary investigation, the engineer hit the emergency brakes five seconds before plowing into the backhoe, and the eight-car train traveled another mile before finally stopping.

"I believe without question it's a communication problem," says U.S. Rep. Bob Brady, who toured the crash scene Sunday. The backhoe was on one of four tracks when it was hit by train 89, and unnamed sources familiar with the investigation tell Philly.com that "problems with Amtrak's dispatch could have been a key factor in the crash. Information about the work crew's presence on the rails may not have been shared during a shift change."

Two are reported dead according to philly.com after an Amtrak train derails this morning in Chester. A Chester County...

Posted by WCHE 1520 AM Radio on Sunday, April 3, 2016

"Typically, the dispatcher has to give very specific permission for maintenance ... equipment, like a backhoe, to be on the track," professor Allan Zarembski, who teaches railroad engineering at the University of Delaware, tells ABC. "They have to take the track out of service for a defined distance and a defined time period. And then, they have to confirm that they understand it, repeat back the instructions, and only then can they get on the tracks."

In a statement released yesterday, Amtrak said, "Everyone at Amtrak is deeply saddened by the death of two Amtrak employees and injuries to our customers as a result of Train 89 hitting a piece of track equipment and derailing. We are working with the NTSB to identify the issues that led to this incident and will make any needed changes immediately.

"Amtrak has strict protocols that crews must follow when tracks are taken out of service for maintenance or when work is being performed along the right-of-way. These protocols help ensure safe operations - both for the crew performing the work, and for the trains traveling through the work area."

The union representing Carter tells ABC that a total of three workers have now been killed on the job in Amtrak's Northeast Corridor since March 1st. Sunday's derailment comes almost a year after a NYC-bound Amtrak derailment killed six and injured dozens more in Philadelphia.