During this holiday season, millions of Americans will ride on passenger railroads to be with family and friends. It’s certainly a very safe way to make the trip. But if all had gone as planned, travel by rail could have been even safer.

That’s because a technology called positive train control (PTC) can detect imminent collisions and trains moving at excessive speeds. Humans can make errors, even on their best days, and PTC provides an extra safety net that slows or stops trains when their operators do not. The National Transportation Safety Board (NTSB) has been urging that railroads explore and implement such technology for more than 45 years.

In 2008, Congress enacted a law that required PTC to be implemented nationwide by Dec. 31, 2015. The law came after a deadly, PTC-preventable head-on collision between a commuter train and a freight train in Chatsworth, Calif. The collision killed 25 people and injured more than 100.

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In the more than seven years since the law passed, the NTSB has investigated PTC-preventable accidents that resulted in more loss of life, serious injuries, and significant property damages. Among them:

The June 24, 2012, head-on collision between two Union Pacific freight trains near Goodwell, Okla., which killed three crew members and injured a fourth.

The Dec. 1, 2013, Metro-North commuter train derailment in the Bronx, which killed four and injured dozens of others; the train was traveling more than 82 m.p.h. on a curve with a maximum authorized speed of 30 mph.

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The May 12 accident in which an Amtrak Northeast Regional train derailed in Philadelphia, traveling at 106 m.p.h. around a curve with a speed limitation of 50 mph. Eight passengers were killed and more than 200 others were injured.

Although the 2015 deadline would come too late for those who lost their lives or suffered serious injuries in these accidents, at least the law would have enabled us to depend on this life-saving technology coming online by the end of this year.

There have been legitimate hurdles along the way to implementation of PTC, and the railroads that have done the hard work to overcome these obstacles deserve our thanks. They have made railroad transportation safer. But most trains on most tracks remain unprotected by PTC.

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Simply put, railroads have not done what is needed to comply with the 2008 law. Instead, as the deadline approached, railroads threatened to discontinue service if the law were not changed. A seven-year implementation period had culminated in an ultimatum, a stark choice of safety or service. Congress relented, and extended the deadline to 2018 - with the possibility of future extensions through 2020.

So this holiday season, the public will continue to have access to service, but not the level of safety demanded by the 2008 law. The railroads will continue to run, but without full implementation of this life-saving technology.

This year, “Implement Positive Train Control in 2015” is on the NTSB’s most wanted list of transportation safety improvements. We included the date to emphasize the deadline in the law. As we pointed out in January, each death, each injury and each accident that PTC could have prevented testifies to the vital importance of implementing this technology now.

Federal Railroad Administrator (FRA) Sarah Feinberg took a courageous stand on enforcing the 2015 deadline. Now that Congress has changed the law, Feinberg has urged the railroads not to count on another extension - even though the law allows them to be granted by the Department of Transportation. So what’s to prevent railroads from issuing another safety-or-service ultimatum in 2018?

One tool can be found in recommendations the NTSB issued in 2013. At that time we asked that the railroads provide PTC update reports to the FRA every six months until all the trains and tracks covered by the law are protected. Additionally, we recommended that the FRA publish the reports on its website within 30 days of receipt.

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This information would enable the public to track the progress of railroads toward meeting the deadline, and policymakers could weigh the implications and take appropriate action.

We still think semi-annual reporting is a good idea, and we urge Feinberg to consider it anew. To avoid ever facing another safety-or-service ultimatum, the FRA and the public must know what progress the railroads are making.

As Feinberg recently told the RailTrends conference, “When we talk about PTC, we are really talking about saving lives.”

It is time for the conscientious stewards of safety throughout the railroad industry to make every day count, from now until the day that PTC is implemented nationwide. We hope that Feinberg will continue to stand firm, and demand that the public be kept frequently informed of the railroads’ progress toward the new 2018 PTC deadline.

Christopher Hart is chairman of the National Transportation Safety Board. He may be reached at correspondence@ntsb.gov