In this May 13 photo, emergency personnel work at the scene of a deadly train derailment in Philadelphia. Federal regulators say positive-train-control technology could have prevented the crash. (Patrick Semansky/AP)

U.S. railroads that were granted a three-year delay to install a life-saving safety mechanism have been told by federal regulators that they will be held to a strict schedule to ensure that they get the job done.

The device — positive train control — has been called “arguably the single-most important rail safety development in more than a century” by federal regulators.

Safety experts say PTC could have prevented the deaths of eight people in a Philadelphia Amtrak derailment this year, and those of 288 other passengers and train crew members since 1969.

They consider implementation of PTC more important than ever since trains carrying volatile natural gas or oil have derailed nine times so far this year, and they fear one could cause catastrophic explosions as it passes through a city.

With the boom in domestic oil production, the number of rail tank cars carrying flammable material in the United States has grown from 9,500 seven years ago to 493,126 last year.

The railroads, most of which had fallen far behind schedule in meeting a Dec. 31 deadline for installation of PTC, petitioned Congress for relief and were given a three-year extension. Congress, whose members have received more than $24 million in campaign contributions from the powerful railroad industry since 2008, also said railroads could ask for up to two additional years after the 2018 deadline to complete the job.

But the legislation that granted the extension came with teeth, and Federal Railroad Administrator Sarah Feinberg has served notice that she intends to use them.

“The focus has to remain on getting PTC up and running and implemented as soon as possible,” she said in a speech to a railroad conference last week. “I recognize that the legislation allows 2018 to be the goal and there to be a potential extension beyond 2018 to 2020. But the deadline is 2018. If you need to get to 2020, there are certain boxes that have to be checked in order to get there.”

Warning against expecting another deadline extension, Feinberg sent a letter to the railroads outlining the “boxes” that must be checked in the coming months and years.

She said each railroad must submit a detailed plan before the end of January for PTC implementation, with justifications for the pace at which the railroad intends to proceed, and annual reports thereafter.

Feinberg wrote that extensions beyond the 2018 deadline would be considered only if a railroad had demonstrated a good-faith effort to comply with the mandate.

“What Feinberg was saying in her letter was ‘Don’t even send me a plan that says [you will complete installation by] 2020,’ ” said an FRA official who spoke on condition of anonymity in order to comment candidly. “Her main concern right now is that people are focused on 2020 and they’re not focused on 2018. She’s telling them, ‘If you happen to get to 2018 and you have met these criteria and benchmarks to be eligible [for an extension to 2020], then we’ll talk about it at that point.’ ”

It was the fear that the FRA might impose hundreds of millions of dollars in fines that sent the railroads to Congress seeking a reprieve from the Dec. 31 deadline that Congress established seven years ago.

The railroads long had argued that PTC technology was too complex to allow them to meet the December deadline and that the $14.7 billion cost to equip freight and commuter lines was prohibitive. They said they have devoted time, energy and billions of dollars for the installation of the systems and are firmly committed to proceeding as swiftly as possible.

But while some major railroads, notably the giant BNSF Railway and commuter rail lines such as Philadelphia’s SEPTA system, made substantial progress, others appeared to make minimal efforts to meet the deadline. Critics suggested that they were counting on a sympathetic Congress to extend the 2015 deadline.

In a Nov. 5 talk to the Railroad Safety Advisory Committee, Feinberg made clear that her agency would continue to press the railroads about PTC implementation.

“I know there were probably more than a few sighs of relief from the folks in this room last week when Congress passed the PTC extension,” Feinberg said. “The Amtrak accident in Philadelphia remains a stark reminder of both what can happen without PTC, and the sense of urgency required to prevent a similar accident in the future.”

Feinberg had been acting FRA administrator since January.

“Since she’s been here there’s been a different tone and posture on PTC,” said the FRA official who spoke on the condition of anonymity.

In what was seen as a message to the railroads, the Senate approved Feinberg’s nomination at the same time it passed the PTC extension.

“Over the last year, I am sure you have observed that FRA is in a much more aggressive posture on PTC,” Feinberg said in addressing the safety advisory committee, “and everyone should expect for that posture to continue.”