Death Rode the Rails, Indeed

The prospect of dying in a railroad accident is not something that too many Americans worry about these days.  But it was not ever thus.  In an excellent but little-known book entitled Death Rode the Rails:  American Railroad Accidents and Safety 1828-1965, economic historian Mark Aldrich reveals that in the earliest days of rail travel in the 1840s, passengers were sometimes surprised to see a thin strip of iron thrusting up through the floor of the carriage, threatening to impale them like bits of beef on a barbecue skewer.  Called "snakeheads" by the antebellum press, relatively few people were killed by these accidents, which occurred because some of the earliest railroads used a thin iron strap fastened to a wooden rail to save money, instead of a solid iron rail, and the strap would sometimes come loose from the wood, snaking its way up into the cars.  But the combination of surprise and powerlessness to avoid the accident made it particularly horrifying, and the novelty of rail travel was tarnished in the public mind by this vivid addition it made to the list of ways one could depart this earth.

While Aldrich has plenty of stories about the different ways that passengers, railroad employees, and trespassers on railroad property were injured and killed, his emphasis is on the economics of railroad safety and how economic considerations played a vital role.  He points out that even after wood-and-strap-iron rails were replaced with all-metal rails and many other safety improvements were made, traveling by U. S. rail in 1907 was still 110 times as dangerous as flying in a modern (2006) airliner.  Still, 22 fatalities per billion passenger miles did not mean that you were taking your life in your hands every time you climbed onto a train.

From the railroad companies' point of view, safety was an expense, and like every other expense, they wanted it to pay a return on investment.  Railroads were virtually unregulated by the federal government until the establishment of the Interstate Commerce Commission (ICC) in 1887, and for many years the ICC restricted itself to setting freight rates for interstate commerce.  Some safety ideas, such as the "block signal" system of controlling train movements, rather than sending out paper orders and hoping everyone would synchronize their watches and keep to the schedule, not only reduced accidents but increased traffic flow, leading to greater utilization of existing plant and higher profits.  The railroads liked this kind of safety measure.

On the other hand, in 1922 the ICC ordered all carriers (rail lines) with revenues over $25 million to install automatic train control on at least one passenger line.  The idea of automatic train control, which dates back to the 1800s, is that instead of relying on the engine driver to see a visual block signal and stop the train, the automatic system would directly receive the signal's command and apply the brakes.  The rail companies reluctantly complied, and by 1930 had spent $26 million to install the system on over 15,000 miles of track. 

But as Aldrich shows, automatic train control made essentially no difference in the rail safety record, did not improve productivity, and cost a great deal of money.  During the Great Depression, many carriers asked for and received permission to cut back or remove automatic train control, and the ICC relented.  However, the same technology turned out to be useful for activating signals in the driver's cab (so-called "cab signals"), which have since become a standard safety feature of great help in fog or rain where visibility of the track-side signals is obscured. 

I was unaware of all this when I blogged a few years ago about a "cornfield meet" (head-on collision) between two freight trains in Texas that killed three employees and did millions of dollars of damage.  At the time, the railroads were installing something called Positive Train Control (PTC), which is nothing but an updated electronic form of automatic train control.  So the idea has been around for more than a century, it turns out, and is just now being implemented.  But as Aldrich points out, the accidents in which PTC would have made a difference are a small percentage of all mishaps.

While Aldrich makes a great case that economics was a huge factor in railroad safety, he gives less emphasis to something that continues to drive debates about all kinds of transportation safety today:  public perception.  He does point out that the average citizen has an exaggerated horror of types of death that are grisly and out of one's control, such as the snakehead accidents.  All the statistics in the world will not comfort the lizard part of one's brain that is primally terrified by the prospect of a fiery or gory death inside some machine that you cannot influence.  But other factors, such as speed and convenience, can overcome such fears.  For example, early automobile travel (say around 1920 to 1940) was demonstrably many times as dangerous as rail travel, yet the rail lines lost most of their short-range passenger business to the automobile in that period.  Ah, but the driver of a car has at least the illusion of control, thinking that while accidents may happen to other drivers, his superior skills will enable him to avoid a crash.  Well, maybe, but the statistics said otherwise.

As you would expect, engineers come in for starring roles in Aldrich's saga.  The technical press, including editors of such publications as Railway Age, brought constructive criticism to egregious safety problems and coordinated cooperation among carriers, government institutions, and private and university researchers to bring about notable improvements in safety systems, devices, and training.  This included issues such as the quality of bridge construction.  Early U. S. railroad bridges were built with the "link-and-pin" method, and the failure of even one joint in the structure would make the whole thing fall down, which it often did.  Complex failure modes in steel rails baffled engineers and scientists for decades until a concerted effort involving inventor Elmer Sperry's electrical track inspection system and advances in metallurgy discovered how to prevent them. 

An old friend of mine summed up the goal of engineering ethics with the two-word phrase, "No headlines."  While U. S. railroads are doing pretty well today by that measure, it is the end result of many decades of improvements and safety efforts.  And Mark Aldrich has given us that history in a rewarding and highly readable volume.

Sources:  Death Rode the Rails (Johns Hopkins Univ. Press, 2006), by Mark Aldrich, is the source for most of my material.  I also drew on the following website for additional details about "snakeheads":  https://aaronwmarrs.com/blog/2012/02/snakeheads-on-antebellum-railroads.html.  My blog about the head-on collision in Texas is at https://engineeringethicsblog.blogspot.com/2018/08/some-answers-about-panhandle-cornfield.html.

The Latest Amtrak Crash: A Deadly Combination

Many accidents in complex systems happen when two or more failures align like tumbler pins in a lock, opening the way to tragedy.  That is apparently what happened around 2:45 AM on Sunday, Feb. 4, outside the central South Carolina town of Cayce.  Here's what led up to the crash.

For the last several years, U. S. railroads have been under the federal gun to complete installation of Positive Train Control (PTC), a complicated system involving GPS receivers on trains, transponders along the tracks, and coordinated data links that will automatically slow down trains that are going too fast and stop those heading toward disaster.  Lack of PTC has been cited in every recent fatal train wreck, and so at the time of this crash, installers were working on the South Carolina section of track in question to put in the necessary PTC equipment.  The only trouble was, as part of the process they had to shut down the safety block signals—the red-yellow-green lights beside the track that inform the engineer as to whether the track ahead is clear. 

Railroads have a way of dealing with the absence of block signals, which is to dispatch trains by means of documents called "track warrants."  Obviously, there has to be a special procedure for this, with good communications by radio to the dispatcher, because running through an area with no signals is a little like flying an airplane blind.  It can take more than a mile to stop an average train, so by the time the engineer sees an obstruction on the track it's usually too late to do anything more than set the brakes, blow the horn, and hope.

At this writing, it is unclear whether the track-warrant procedure was followed correctly.  But what is clear is that earlier in the evening, after a railroad employee set a switch to allow a freight train to pull off to a siding out of the main line that the Amtrak train was going to use later, the switch was locked in place,  still set to the siding.  In other words, any train coming down the main line in the same direction was going to head straight onto the siding, toward the sidelined freight.

Normally, this switch setting would cause the signals on the main line to change to yellow or red.  But due to the work going on to install PTC, the signals were inoperative.  So all that stood between the southbound Amtrak train that was coming along about 2:45 AM and disaster was good communications among the person who set the switch, the train dispatcher (many miles away in a CSX control center, CSX being the freight railroad that owns the track which Amtrak uses), and the Amtrak crew.

The third thing that is clear is that the communications broke down.  The last thing the Amtrak engineer saw was the end of the freight train, as his engine barreled off the main line at 56 MPH onto the siding and crashed.  He and the conductor were killed, and about 100 passengers were injured in the resulting Amtrak car derailments, some critically.

Amtrak officials were quick to throw blame to CSX, whose tracks they were using, as it was CSX's responsibility to ensure that any switches their crew used were set back to the proper direction.  Records indicate that the freight-train crew reported that they had set the switch correctly, so it is unclear at this point how the switch ended up in the wrong position anyway. 

While this is only the latest in a string of several fatal Amtrak accidents, each one has apparently had a different set of contributing factors, and accusations that Amtrak's safety culture is at fault are premature, to say the least.

The irony of this particular accident is that it was apparently caused at least partly by the rush to install PTC—a safety feature—which indirectly led to the accident.  It reminds me of the recent Takata air-bag-inflator fiasco, in which millions of cars had to be recalled, and many people were killed by defective inflators that shot shrapnel at them in accidents that would have otherwise merely bent a few fenders.

This is not to say we shouldn't have airbags, or we should call a halt to installing PTC.  And here is where we fall back on a philosophical method which engineers use almost without thinking—utilitarianism, otherwise known as the greatest good for the greatest number.  Utilitarianism is not the only way to decide ethical issues, by any means, but it has its uses.  Clearly, it makes sense to complete PTC installations even if it means shutting down signals temporarily here and there.  But the problem comes when those responsible for safety measures get too focused on the future good they will do, and neglect the present potential harms such installations can cause.  I don't know what went wrong with the track-warrant system in this case, but clearly something did.  And once a decision is made to install a safety feature, it is easy to allow too many temporary compromises in present safety in view of the greater good that the ultimate installation will lead to.

But that temptation has to be resisted.  Takata shouldn't have been as sloppy as they were in making crummy airbag inflators that would turn into bombs down the road a few years.  And everyone involved—train dispatchers, PTC installers, and above all, the freight train crew who apparently left the switch in the wrong position—should have been doing a better job communicating in the absence of the usual track signals. 

Sometimes people who work on safety features get careless because most of the time, the features don't see action.  But they are really like a standing army ready for battle.  When the crisis comes, the safety features rise to the top of the priority list.  Never mind the usual function of the system—transportation, communication, or whatever.  If the user is injured or killed, it would have been better not to have made the product at all.  So although Amtrak's safety culture alone may not be at fault, clearly something went wrong in Cayce that night.  And more work needs to be done to make sure that a complicated system like a railroad runs even more safely with PTC than it does without it.  Just installing PTC won't guarantee that, because PTC itself has the potential to cause trouble.  Let's hope that it doesn't, and that the recent flurry of fatal train mishaps are the last ones before PTC makes train-passenger fatalities as rare as airline-passenger fatalities are today.

Sources:  I referred to a thorough report on the accident carried by NPR on their website on Feb. 5 at https://www.npr.org/2018/02/05/583455540/ntsb-looks-at-disabled-signals-locked-switch-in-latest-deadly-amtrak-crash.

Too Fast and Too Slow: The Washington State Derailment and Positive Train Control

After more than a decade of planning and construction, a new section of track was opened for Amtrak passenger service south of Tacoma, Washington on Dec. 18, 2017.  The old route that Amtrak trains used to take went northwest from Tacoma along the coast of Puget Sound, around a peninsula named Point Defiance, and then down the coastline several miles until it crossed Interstate 5 south of the small town of DuPont and headed south inland.  The new shorter route uses a bypass track that goes southwest of Tacoma and hugs I-5 for the rest of the distance, crossing the interstate south of DuPont.  There is a long stretch of fairly straight track just north of I-5 past a golf course before the track makes a sharp left turn to the south to cross the bridge over the freeway.

The problem with the old route was that a number of sharp turns and single-track tunnels slowed the Amtrak passenger trains down, making the Point Defiance section something of a bottleneck.  The project map on the Washington State Department of Transportation website for the Point Defiance bypass bragged that the top speed allowed on the new route would be 79 miles per hour.

Rail fans and others interested in passenger rail transportation made plans to be on Amtrak 501 as it left the station in Tacoma on the new route.  The engineer, whose name has not yet been released, was training another railroad employee who rode with him in the cab. 

In most parts of the U. S., trains are not operated in a completely automatic mode, although in many regions a system called Positive Train Control (PTC) is in operation.  PTC is a kind of robotic supervisory system that, among other things, constantly monitors a train's speed and intervenes if the train goes too fast for a particular section of track.  About 60% of all Amtrak trains use PTC, but in order for PTC to work, the track has to have sensors installed along it, and the Point Defiance bypass was not one of those routes.  So the engineer was solely in charge.

Around 7:25 AM, the train was running on the long stretch of straight track before the turn to the bridge over I-5.  A properly trained engineer knows what speeds are safe for which parts of a route, and knows when to apply brakes in anticipation of a lower-speed area ahead, as passenger trains can take several miles to decelerate at a rate that doesn't unduly disturb the passengers.  A video exists of what was going on in the cab in the last few seconds before the train reached the I-5 bridge.  The train was still going at the maximum route speed of 78 MPH.  Six seconds before the bridge, the engineer commented about the excesssive speed of the train, but by then it was too late.  The engine and a dozen other cars left the tracks, killing three, injuring dozens, causing numerous highway-traffic crashes (none fatal), and closing Interstate 5 for many hours.  The maximum safe speed for negotiating the turn was posted as 30 MPH.

Although the National Transportation Safety Board (NTSB) will not issue its formal report on the investigation of this disaster for many months, the preliminary evidence is pretty clear that the accident was caused by human error.  Something—possibly distraction in conversing with the trainee, possibly plain forgetfulness—made the engineer neglect to slow the train before the I-5 curve.  As numerous reports emphasized after the wreck, if the train had been using PTC, it would have automatically slowed down for the curve if the engineer had done nothing, or even if he had tried to keep the speed high.  And we have no knowledge of how many wrecks of both freight and passenger trains have been prevented by PTC, because by definition such incidents that don't injure or kill anybody don't get reported.  But it is clear in this case that the absence of PTC was a contributory cause.

Congress mandated the installation of PTC after the worst train accident in the last thirty years, a 2008 wreck caused by operator error that killed 24 people.  The original deadline for all passenger trains to be using PTC was 2015.  But as the deadline approached and railroads were lagging behind in their rate of installations—in fairness to them, due to problems with government regulation of necessary radio frequencies as well as other causes—they told Congress that if the deadline wasn't extended, they would simply shut down.  How serious this threat was, we'll never know, because Congress caved and moved the deadline to the end of 2018.  And under the current business-friendly administration, we can expect if the railroads ask for another extension, they're likely to get it.

Statistically, rail passenger travel is very safe overall, with the number of fatalities most years hovering in the single digits.  Still, nobody wants to be one of the six or seven people who get killed in a train wreck or hit by lightning—dead is dead, no matter how you go. 

A utilitarian approach to the issue of PTC and passenger trains might conclude that, hey, given the low number of fatalities, let's just allow things to go the way they're going, and eventually we'll have PTC everywhere and we won't have to worry about it.  But the expense per life saved is so high with railroads that we'd be better off using political and monetary capital fighting automobile traffic accidents or promoting self-driving cars.

That's one approach.  But another approach says, "Look, here's this technological fix that will cost the railroads money and trouble, but will almost completely eliminate what is the last major remaining cause of railroad passenger fatalities:  human error.  Let's bite the bullet and make a special effort, even spend some extra money, to fix this thing once and for all."  Maybe that's the engineering approach, or even the perfectionist approach (many engineers have perfectionist tendencies).  Yes, the absolute numbers of fatalities are small.  But deaths in a train wreck share with deaths in plane crashes a peculiar horror, in that you are completely bereft of control of the situation.  And in the case of train fans who simply wanted to experience a new route for the first time and ended up paying for their hobby with their lives—well, some ironies are too much to contemplate.  I have a good friend who, if he was not otherwise engaged that day, might well have been on that train, because he simply likes to ride trains.

Better training (pardon the pun) of engineers and faster completion of the installation of PTC are needed.  And maybe if these things happen, this will be the last fatal accident involving train passengers for a long time.

Sources:  I referred to several news items on the accident, including CBS News at https://www.cbsnews.com/news/amtrak-derailment-dupont-washington-video-shows-crew-not-using-electronic-devices/, a government-run transportation statistics site at https://www.rita.dot.gov/bts/sites/rita.dot.gov.bts/files/publications/national_transportation_statistics/html/table_02_42.html, a Washington State Department of Transportation map of the bypass route at https://www.wsdot.wa.gov/Projects/Rail/PNWRC_PtDefiance/Map.htm, and a report giving the time of the crash at https://www.washingtonpost.com/news/dr-gridlock/wp/2017/12/18/amtrak-train-derails-in-washington-state-rail-cars-fall-onto-interstate-5/. 

Cornfield Meet Near Panhandle, Texas: How?

On Tuesday morning, June 28, the stretch of U. S. 60 leading east from Amarillo, Texas past the small town of Panhandle was quiet in the early morning sun.  The flat horizon was broken only by the spinning blades of a wind farm in the distance and a towering grain elevator near the double BNSF tracks, which run straight as an arrow from Amarillo east-northeast for many miles.  U. S. 60 parallels the tracks until the road nears the grain elevator, where it takes a bend southward for a quarter mile or so around the elevator and rejoins the tracks on the other side.

           

At about 8:25 AM, a BNSF intermodal freight train was heading west on one of the pair of tracks.  At the same time, a few miles west of that train, another train was heading east—on the same track. 

Railroads have faced this kind of problem ever since there were railroads.  In England, the main customers of an early form of electric telegraph were railroads, who saw in it a way of coordinating train movements on single tracks carrying two-way traffic.  Later, block signals were developed that turned red any time a train entered a section of track (or "block"), warning other trains to slow down or stop.  The main idea of double tracks is to allow only one-way traffic on each track, eliminating any chance of head-on collisions.  And most recently, a new communications and control system called Positive Train Control (PTC) has been adopted by most U. S. railways, but its implementation has been slowed by problems with radio-channel allocations and hardware issues.  On June 28, PTC was not implemented in the section of tracks that run past the grain elevator near Panhandle.

So it was that the two trains that morning, each with a crew of two, met in a fiery head-on collision that is known in railroad circles as a "cornfield meet."  One person managed to jump from the train before the collision.  Two bodies were recovered after the accident, and as of July 10, the fourth person's body had not yet been found. 

A passerby on nearby U. S. 60 made a phone video of the wreck even as it was occurring.  You can see cars flying off the track, and eyewitnesses testified to the horrific noise that seemed to go on forever.  A train running at speed can take up to a mile to stop after the brakes are applied, and it is not clear at this point when, if at all, the brakes were applied on either train.  Many trains, including those involved in the wreck, are equipped with digital video cameras and recorders at the front and rear, but the National Traffic Safety Board spokesman in charge of the NTSB investigation said that some of these were heavily damaged.  However, other data recorders on board the trains may have survived to help understand how this accident happened.

It will probably be some months before the NTSB has time to sift through the wreckage and other evidence that could show why, in 2016, it's still possible to have such an accident.  As in other railroad accidents involving fatalities in the last few years, PTC could very well have prevented this one.  If operating properly, the system calculates a safe maximum speed for the train at each point in its travels, and if another train is heading for yours, presumably it would put on the brakes in time to prevent a wreck. 

Trains are dispatched these days by means of centralized train-traffic control centers linked to the individual trains by microwave radio.  One of the dispatch centers for trains in Texas is in Fort Worth, so investigators will probably be reviewing all communications between the controllers and the two trains involved.  Like air-traffic controllers, the dispatcher's word is law as far as the in-train operator is concerned.  So if both trains were told they had a clear track ahead, and saw something that looked like a train in the distance, each might have thought the other one was on the other track instead of the same track.  With radio control, it's not clear to me how much significance the operators attach to block signals, which should have indicated a problem in this case soon enough to prevent the accident.

As train wrecks go in the last few years, this accident was not the worst in terms of fatalities.  In this space in 2013 I wrote about a commuter-train wreck in New York that killed four, and in Philadelphia in 2015 another commuter train derailed, killing eight passengers and injuring over 200.  But the Panhandle wreck is disturbing because it seems to reveal a systemic problem, either with the dispatching system or training or both.  Those trains never should have been on the same track heading toward each other in the first place.  And once they were, it sure seems like block signals should have let the drivers know something was seriously amiss.  It is likely that this accident was the product of a combination of unlikely events, each one of which by itself does not typically lead to a major tragedy. 

But to know for sure, we'll have to wait for the results of the investigation.  And hope that BNSF and the other railways can speed up their implementation of PTC, which promises to make cornfield meets as rare in the future as deaths due to runaway horse-drawn buggies. 

Sources:  I used reports on the accident from KFDA-TV in Amarillo at http://www.newschannel10.com/story/32408347/search-ends-for-body-of-conductor-killed-in-train-wreck and a video of the NTSB news conference held after the wreck at https://www.youtube.com/watch?v=mCBTmxKx2vA.  A video of the wreck itself can be viewed at https://www.youtube.com/watch?v=YiPE8e-fqKU.  I blogged about PTC and train wrecks at http://engineeringethicsblog.blogspot.com/2013/12/positive-train-control-and-commuter.html on Dec. 9, 2013 and at http://engineeringethicsblog.blogspot.com/2015/05/for-want-of-spectrum-allocation.html on May 25, 2015. 

For Want of a Spectrum Allocation: The Philadelphia Train Derailment

There's a proverb of uncertain origin that begins, "For want of a nail, the shoe was lost, for want of a shoe the horse was lost; and for want of a horse the rider was lost; being overtaken and slain by the enemy, all for want of care about a horse-shoe nail."  That particular version is attributed to Benjamin Franklin, but all the various versions make the same point:  lack of attention to apparently minor details can sometimes have major consequences.  As more information emerges about the tragic AMTRAK train derailment in Philadelphia on May 12, it looks like what began as a minor kerfuffle over frequency allocations may well have kept a new train-control system from preventing the deaths of eight passengers and the injuries of many more.

At this writing, no one seems to know for sure why the Northeast Regional train heading from Washington, DC to New York City sped up to 106 MPH (169 km/hr) as it entered a curve near a rail intersection called Frankford Junction.  The maximum recommended speed for the curve was 50 MPH (80 km/hr).  All the train's cars left the track, killing eight passengers and injuring at least 200 others.  There were some reports that an object might have hit the train's cab in the minutes before the wreck, but presently the reason for the train's excessive speed is not definitely known.  At the time of the wreck, the train was under the manual control of engineer Brandon Bostian, who was apparently knocked temporarily unconscious in the crash and claims to have no memory of the moments immediately before the derailment.

In many parts of the U. S. including the Northeast, railroads have installed an automatic system called Positive Train Control (PTC) that could well have prevented the May 12 tragedy.  A fully operational PTC system continuously monitors a train's position by means of radio links to trackside transmitters, and calculates the maximum speed that is allowed at each point along the route.  If the system notes that the train is going too fast, it will automatically apply the brakes to reduce speed. 

Why wasn't the Northeast Regional using PTC in Philadelphia?  Because AMTRAK hasn't been able to purchase a 220-MHz radio-frequency allocation (channel, essentially) to put it into operation there yet.  And thereby hangs a rather tortuous bureaucratic tale.

On their own over the past decade or more, railroads have developed pieces of what amounts to PTC using various existing equipment, and the most popular type of train-control radio systems use the 220-MHz frequency band.  For most of its existence since the 1930s, the U. S. Federal Communications Commission (FCC) allocated the limited resource called the radio-frequency spectrum through a purely administrative process, and in principle at least, money had nothing to do with it.  In practice, political pull and other arbitrary factors influenced the FCC's decisions.  Partly in response to accusations of unfairness, in 1994 the FCC began auctioning spectrum slots to the highest bidder, and most observers say that auctions have led to a fairer and more efficient set of allocations.  But in the case of the railroad's need for 220-MHz slots for its PTC system, the market method of frequency allocations may have failed.

The legal requirement for railroads to use PTC originated with a Congressional mandate passed in 2008 mainly to improve safety.  In that legislation, Congress told the railroads to finish the job by December of 2015.  Most railroads have largely complied by now, despite problems with interoperability of different systems developed by different lines and the fact that one railroad may operate on tracks owned by several other railroads.  When PTC was passed into law, the most common frequency band used for these types of train control and monitoring operations was 220 MHz, so the railroads decided to use their existing 220-MHz hardware and to require all PTC equipment to use that band.  If more bands were used, a single train might have to carry equipment that works with three different bands, for example, and as PTC was already costing billions of dollars to implement, they stuck with 220 MHz.

That was fine for most areas, but the railroads ran into a snag in some regions, including Philadelphia.  There the 220-MHz slots were either not available, or were priced at a prohibitive level.  The railroads asked the FCC simply to allocate the needed frequencies for free, so that they could meet the Congressionally-mandated deadline, but the FCC essentially said tough beans, go buy them like everybody else does.  And Congress did not fund the costs associated with the PTC mandate, so the rail lines have been doing it on their own dime.  So at the time of the Philadelphia crash, PTC was not working, but not because of any hardware problems.  The bureaucracy had simply not done its job yet.

PTC is not a flawless system, and it is not absolutely certain that it could have prevented the Philadelphia crash even if it had been working at the time.  Putting on the brakes for a train is not as simple as jamming your foot on the brakes of your car.  A friend of mine is a locomotive engineer on an excursion train that operates near Austin.  He has explained to me how the brakes on each car have to be applied at a certain carefully judged rate, and sometimes even in a certain order, so that the train doesn't undergo stresses that can cause severe shocks or even break couplings and separate the cars.  Even just locking the brakes so the train skids along the track can severely damage the wheels, necessitating extensive repairs.  But sometimes it's necessary in an emergency.

We will never know whether PTC could have prevented the Philadelphia train wreck.  But excessive-speed wrecks are exactly the sort of thing that PTC was designed to prevent.  While making everybody pay for frequency allocations seems to be the fairest way to do things in most cases, the FCC ought to consider making exceptions in situations involving serious safety issues.  Sometimes the old ways are better, and allowing for emergency no-fee allocations in situations where an organization is caught between an FCC rock and a congressional hard place seems like a good idea.  But it won't bring back those who are no longer with us because of what happened in Philadelphia. 

Sources:  I referred to news articles on Brandon Bostian at http://www.cbsnews.com/news/amtrak-crash-brandon-bostian-cellphone/, a list of fatalities in the wreck at http://6abc.com/news/name-released-of-8th-victim-in-deadly-amtrak-crash/719973/, and the Wikipedia articles "2015 Philadelphia train derailment," "Positive Train Control," and "For Want of a Nail."