The president of Amtrak, Joseph Boardman, said the railroad has had technical problems installing the system along that treacherous Philadelphia curve.
He vowed to have it up and running throughout the Northeast Corridor by the end of this year.
In 2008, the engineer of a Metrolink commuter train missed a warning signal while texting and collided with a freight train in Los Angeles. The 25 deaths prompted Congress to pass strict new safety guidelines.
The PTC safety system may have prevented that accident. It is now in use in Southern California and can stop or start the train by computer, avoiding human error.
"When you have a system like PTC in place, speed won't be an issue," Metrolink spokesman Jeff Lustsgarten tells CBS News. "The train will be able to operate safely at maximum speeds."
"GPS technology transmits signals from thousands of track sensors to a central computer system, according to R.T. McCarthy, director of operations for Metrolink.
"The system looks at the size of the train, the weight of the train and the speed of the train at all times," McCarthy said.
Using a simulator, he showed us how PTC relays crucial information to the train's engineer.
"What it is telling me is that you're going too fast for this curve, I won't let you take this curve," McCarthy described.
Warning lights and beeps tell the engineer how many seconds he has to brake before the computer takes over.
"If at any time I am unable to stop the train, positive train control then takes command, stops the train to prevent any kind of incident or accident," McCarthy said.
That was not the case in the Bronx, New York, where a 2013 crash left four passengers dead.
The NTSB says it was one of 29 rail disasters in the past decade that could have been avoided with PTC.
While positive train control offers safety, it is also costly -- $50,000 a mile.
The Association of American Railroads, an industry trade group, says more than $5 billion has already been spent, but that only 60 percent of trains have part or all of the system.