House and Senate negotiators are said to have reached a deal late Tuesday on extending the year-end deadline for U.S. railroads to install positive train control (PTC), the oft-praised safety system that slows or stops trains if their speed or location poses an imminent risk of accident. Congress set the original deadline in 2008, after a collision between two trains killed 25 people in Chatsworth, California.

The compromise language reportedly extends for three years the period in which freight and passenger railways may finish work on PTC. The deal also includes provisions that could push the deadline back even more, until the end of 2020.

The congressional action comes after a concerted lobbying effort on behalf of North American rail companies, which culminated in threats in the last few months that freight carriers would halt operations by year’s end rather than risk fines for not complying with the 2008 law.

A highway bill that included language on PTC — requiring submission of upgrade plans in exchange for the extension — passed the Senate in July. But the current compromise makes no such stipulations until 2018. If plans are submitted by the end of that year, railroads could be granted a two-year extension.

The House Transportation and Infrastructure Committee issued a statement Wednesday saying the deal is expected to be part of a stopgap highway spending bill scheduled for introduction within a week.

Neither the extension language nor the vehicle sits well with critics, however.

“This five-year extension of life-saving technology is way too long, with way too little guarantee that PTC implementation will get done,” Sen. Richard Blumenthal, D-Conn., said in a statement quoted in The Hill.

“A short-term patch of highway funding should not be the vehicle for such a profoundly important measure,” he said. He called for a bill requiring year by year reviews of railroad company progress.

Sen. Barbara Boxer, D-Calif., is among congressional leaders insisting that a full transportation bill — which has been languishing on the Hill — is urgent and that the approaching deadline on PTC should be used to encourage lawmakers to act on a broader bill.

“I think we need to pass a [long-term] bill, and I think [the PTC deal is] really going to help get it done,” she told Politico.

Republicans in the House and Senate, such as Rep. Jeff Denham, R-Calif., who chairs the House Subcommittee on Railroads, Pipelines and Hazardous Materials, and Sen. John Thune, R-S.D., the chairman of the Senate Commerce Committee, want to answer rail company calls sooner rather than later. They favor moving either a stand-alone extension or making deadline extensions part of the highway spending patch.

The GOP leaders echo statements from railroaders, like Edward Hamberger, the president of the Association of American Railroads, who told reporters on Monday, “It has to be done now. It cannot be business as usual in Washington, with Congress waiting until the day before the end of the fiscal year to pass legislation.”

PTC re-entered the public conversation in May when Al Jazeera discovered that the vital safety equipment was not operational at the site of a fatal Amtrak derailment near Philadelphia. That accident killed eight people and left over 200 injured.

Data showed that the train was traveling at 106 mph in a zone with a limit of 50 mph. PTC could have spotted the fast-moving locomotive, warned the engineer and automatically reduced the speed.

According to the National Transportation Safety Board, PTC — first proposed in 1970 — could have prevented 25 accidents in the last decade, saving 65 lives.

Still, seven years and an estimated $5.2 billion into the mandated installation of PTC, railroads insist the only answer is more time.

The deadline extension deal does not seem to heed the calls of safety watchdogs and rail experts who have argued that a simple blanket extension would not spur rail companies to complete the needed upgrades. Instead, as the likes of former Federal Railroad Administration head Joseph Szabo have advocated, extensions should be granted on a case-by-case basis.

Some in Congress, like Rep. Mike Quigley, D-Ill., have argued that new mandates should come with additional aid for strapped commuter systems still struggling to install safety systems.

“Commuter railroads have spent nearly $1 billion on PTC implementation and need $3 billion more to complete it,” he wrote in a letter to The Chicago Tribune. “Despite that, Congress has appropriated very little money for the railroads, and half of the country’s commuter railroads are deferring other safety and capital improvements to afford PTC.”

Still, it is the profitable freight carriers that have been loudest in calling for the deadline extension — a lobbying effort long in the making. According to a report in The Intercept, the Association of American Railroads began meeting with consultants in 2009 seeking ways to delay compliance with PTC requirements.

In the aftermath of the Philadelphia derailment, Amtrak — perennially low on funds — said it would meet the year-end deadline for its heavily traveled Northeast Corridor. But the passenger railroad eventually joined freight companies and other commuter lines in calling for the extension, saying that because passenger and freight trains share much of that track, liability issues would force Amtrak to also suspend service should Congress not extend the PTC deadline.

Blumenthal warned this summer that a blanket extension would not help with the goal of fully upgrading U.S. rails.

"It has been more than 45 years since the National Transportation Safety Board first urged railroads to implement positive train control,” he said in September. “Extensions should be granted only to railroads that have demonstrated diligent, good faith efforts to meet the mandate. Only by holding railroads’ feet to the fire will this critical, life-saving technology finally be implemented.”