Only a small number of U.S. railroads will meet the Dec. 31 deadline for implementing new train safety technology that experts say would have prevented the deadly May 12 Amtrak derailment in Philadelphia, officials said on Friday.

A report to Congress by the Federal Railroad Administration showed that just three out of 38 inter-city passenger, commuter and freight railroads have submitted the plans necessary for regulators to certify advanced technology systems known as positive train control, or PTC.

Barely four months before the congressionally mandated deadline, only 11 railroads have told regulators that they expect to begin demonstrating PTC systems in 2015. Others have said PTC demonstrations could start as late as 2020.

Meeting the deadline to install PTC, a complex system of sensors and automated controls that can slow or stop a train, poses a major challenge because of technological difficulties and its high costs, which run into the billions of dollars.

Regulators have long said that most railroads will not hit the year-end deadline that Congress imposed in 2008, while railroads face the possibility of fines or service suspension if lawmakers fail to extend the deadline this fall.

A six-year transportation bill that passed the Senate this month would allow the Obama administration to grant an extension of up to three years. But the measure is not expected to be taken up by the House of Representatives when lawmakers return from their summer break in September.

“It is difficult to reliably estimate a firm, network-wide PTC implementation date due to the varying degree of progress and incomplete data provided by the railroads,” the FRA report said.

The FRA did not say specifically which railroads can meet the December deadline. But it identified BNSF Railway Co , Southern California’s Metrolink service and Philadelphia’s Southeastern Pennsylvania Transportation Authority as the three rail services that have submitted PTC plans. None have been certified.

The 11 railroad companies that expect to demonstrate PTC technology this year include major freight handlers Canadian Pacific Railway Co, CSX Corp, Norfolk Southern Corp and Union Pacific Corp, the report said.

After the Philadelphia derailment that killed eight people and injured more than 200 others, Amtrak said it expects to have PTC technology operating along segments of the busy Northeast Corridor that it owns or controls.

The National Transportation Safety Board, which has been calling for PTC since the 1960s, says the technology would have prevented 300 deaths and more than 6,700 injuries over nearly five decades.