Positive Train Control is coming to a railroad near you — but perhaps not as soon as the government wants.

Emerging reports on the two recent train crashes in Europe suggest, ever so sadly, that they could have been avoided. In Spain, the engineer appears to have been talking on the phone and looking at documents while speeding. In Switzerland, one driver seems to have failed to stop at a signal and let another train pass, leading to their collision. Human errors are human nature, but these particular mistakes carried tragic consequences.

In the aftermath of a major train crash, let alone a pair in close succession, it's imperative to remember that train accidents are exceedingly rare. That's more or less true around the world, Yonah Freemark reminds us at, with high-speed rail in particular performing incredibly well. Writing here earlier this week, Emily Badger pointed out that Americans are less likely to die in a train crash than in a boating accident.

Indeed, in the past decade or so, the few U.S. accidents that have occurred have trended downward (via GAO):

Of course the sad exceptions are what stick most in our collective minds. Perhaps the worst during this period was the September 2008 collision in Los Angeles between a Metrolink commuter train and a freight train that killed 25 people and injured more than a hundred. That accident was the result of human error, too, with startling similarities to what occurred recently in Europe: an engineer who was texting at the controls and, likely as a result, missed a stop signal.

If there's anything good about these incidents it's that they often spark a conversation about safety that's easy to defer in brighter times. Less than a month after the Metrolink crash, Congress adopted the Rail Safety Improvement Act of 2008. The law's biggest measure was the mandatory implementation by intercity and commuter trains (as well as some large freight lines) of a billion-dollar technology called "positive train control."

The promise of PTC, according to the legislation, was to eliminate precisely the types of human errors responsible for the Metrolink and similar crashes: "train-to-train collisions, over-speed derailments, incursions into established work zone limits, and the movement of a train through a switch left in the wrong position."

PTC essentially creates a communication network connecting locomotives, central dispatchers, and wayside signals along the track — all continuously drawing information about speed limits, track configuration, and vital switches from a master database. In other words, the system not only knows where a train is located at all times, but how fast it should be going and whether there's a potential conflict ahead. If a problem does arise and an engineer fails to notice it in time, PTC then assumes the controls and hits the brakes.

Simply put, the PTC system is fantastic on paper, and very likely would have prevented the aforementioned accidents in Los Angeles, Spain, and Switzerland. That's a wonderful thing, but it's not to say that PTC will end the discussion of rail safety once and for all. On the contrary, its scope is limited, its cost is great, and its implementation has been beset by complications.

For starters, the benefits of positive train control are largely limited to accidents caused by human errors. In the United States these account for 35 percent of all crashes; that's a considerable share, to be sure, but far from an exhaustive one. Another third of accidents are caused by poor tracks, and many others come as a result of faulty equipment, grade crossings, or general track interference.

The Metro North crash that injured dozens of people this past May, for instance, occurred by way of a broken rail — a situation that falls outside PTC's domain.

Additionally, PTC is an unfunded mandate that stands to cost rail providers an enormous amount of money. The GAO recently estimated PTC implementation at somewhere between $6.7 billion and $22.5 billion [PDF]. A few operators have found the money — with Amtrak leading the way, and Metrolink nearly done, too — but others are struggling to keep up. The MTA (which runs Metro North and the Long Island Railroad) shelved all sorts of service plans to make room in the budget for PTC, despite having one of the best safety records in the country.

Some operators believe that money could be better spent in other ways. All sorts of technological upgrades are available at the moment: from new sensors that detect cracks in the rail (especially important for high-speed trains) to electronically controlled pneumatic brakes to smarter "crush zones" designed to absorb the impact of a collision. But according to the GAO, many railroads can't even afford to consider these options "because of the costs they are incurring to implement PTC."

For that matter, some industry experts aren't so sure PTC should be implemented at all. The CEO of Union Pacific called the PTC law a "terrible waste" back in 2011. More recently, one rail consultant told The Verge that it's "insane" to force railroads to spend billions on a technology considering the fact that so few people have died in train crashes in recent years. Another expert said PTC fails to satisfy both railroad operators and safety advocates alike.

In a recent piece for Bloomberg, rail historian Albert Churella outlines an even scarier scenario: the high cost of implementing PTC might lead railroads to raise their rates enough to push passengers and freight into cars and trucks — where of course they run a much higher risk of being involved in a crash. That would be a terrible irony, but not an unprecedented one. The same outcome has occurred in the aftermath of terrorist attacks around the world.

To top it all off, the one thing everyone agrees on is that there's no chance PTC will be implemented by the Congressional deadline of December 31, 2015. (One rail advocate called it "simply impossible.") Since the system relies on the ability of operators to communicate with each other, its full impact can't be realized until the upgrade is in place in every locomotive, central office, and wayside signal across the country.

The Federal Railroad Administration has recognized these hurdles and is searching for some middle ground. In a 2012 report, FRA recommended that Congress consider extending the PTC deadline and also allowing the agency to grant some leniency to systems that have adopted other safety measures. At a recent Congressional hearing, FRA chief Joseph Szabo said his agency could consider granting exemptions on a case-by-case basis, though whether or not lawmakers will go along with that plan remains to be seen.

The good news is that, at least to this point, no one seems to be suggesting that Congress rescind the positive train control mandate. That would be the bureaucratic equivalent of a train crash, and a bad one at that; without question, riding the rails in the United States will be safer with PTC in place. At some point quite soon, however, we will have to face very tough questions about whether the great cost of safety improvements is worth a small reduction in safety risk — and also the very tough truth that some accidents will happen no matter how much we want to stop them.

Top image: A passenger train drives past the site of a train crash, with the train engine (R) derailed from the track, in Santiago de Compostela, northwestern Spain. (Miguel Vidal/Reuters)

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