Monday, 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, a list of fatalities in the wreck at, and the Wikipedia articles "2015 Philadelphia train derailment," "Positive Train Control," and "For Want of a Nail."

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