In light of Tuesday night's deadly tragedy around the Frankford curve, it is time to ask why Amtrak has failed to implement a comprehensive system — known as "positive train control" (PTC) — to minimize the risk of railroad accidents. What more will it take to make all our commuter railways safe?

The Rail Safety Improvement Act of 2008 mandated that railroads design a PTC system that would automatically slow or stop a train. The Chatsworth, Calif., train collision, in which 25 people were killed, was the impetus for this law. While Chatsworth garnered the attention and support necessary to kick-start the movement toward PTC, the momentum has slowed. Now it's time to fulfill the federal mandate before another tragedy strikes and more lives are lost.

PTC is a computer- and communications-based system that incorporates GPS tracking and a complex series of sensors and signals designed to prevent collisions, derailments due to excessive speed, and trains traveling on the wrong tracks.

Upon detecting a problem, PTC would both communicate with railroad employees to alert them to the danger, as well as serve as a backup system in case no other actions were taken to correct the problem. In other words, PTC alone could slow or stop a train when necessary.

PTC is not new technology. The systems have existed since the 1980s and have been successfully implemented in Europe for years. Yet, despite U.S. government support and seven years since the passage of the mandate, U.S. railroads have not yet fully implemented the system.

Tuesday night's Amtrak derailment occurred on the Northeast Corridor track, among the nation's busiest. More than 2,200 trains a day travel on it, from Washington to Philadelphia, New York City, and Boston. The mix of trains on these tracks ranges from high-speed passenger lines run by Amtrak to freight operations to local commuter trains such as those operated by SEPTA. With so many trains operating on limited tracks at speeds up to 125 m.p.h., a preventable error was almost inevitable.

The area involved in Tuesday's derailment has three distinct speed sections. While traveling from Philadelphia to the Frankford Junction, where the derailment occurred, trains are required to travel less than 70 m.p.h. While navigating the curve, trains must proceed at less than 50 m.p.h. Once through the curve, trains may travel as fast as 125 m.p.h. as they head toward New York City.

It has already been widely speculated that speed — as high as 100 m.p.h. — played a role in this week's derailment. If the PTC systems that had been mandated in 2008 had been in place, this accident might have been avoided.

Earlier this year, U.S. senators introduced the Railroad Safety and Positive Train Control Extension Act to grant railroads a five-year extension on the implementation of PTC. The Association of American Railroads supports this extension.

However, this delaying tactic is misguided. The nation's railroads, and the passengers who rely on them for safe transportation, need this system in place now.

America's railroads should stop dragging their feet and implement PTC in the Northeast Corridor now. Do it in memory of the passengers who were killed and their grieving families, for the sake of injured passengers and Amtrak crew members, and for the safety of all future rail travelers.

James J. McEldrew III is a Philadelphia-based attorney whose practice includes railroad litigation. He served as president of the Academy of Rail Labor Attorneys (http://arladepot.org) after serving seven years on the academy's board of directors.  jim@mceldrewyoung.com