Why Can't Modern Technology Prevent Train Wrecks?
*By George Bibel
Professor of mechanical engineering
University of North Dakota
*
*08/22/2012 5:42 pm*
http://www.huffingtonpost.com/george-bibel/modern-tech-prevent-wrecks_b_1823148.html
Train wrecks more-or-less occur the same way they did 100 years ago,
albeit far less frequently. Trains still come off the tracks or derail;
and trains still collide. Collisions are usually caused by human error
(the operator essentially drives through a stop signal); derailments
typically occur because of equipment failure. About 30 percent of
equipment-related derailments occur because of faulty track and rail.
Human error can also cause derailments -- too fast on a curve,
incorrectly set track switch and vandalism are a few examples.
On Monday, 21 cars of an 80-car coal train derailed killing two innocent
bystanders
<http://www.foxnews.com/us/2012/08/22/investigators-looking-into-md-train-derailment/>
in Ellicott City, Md. As tragic as the news is, it's unusual for
derailing trains to kill people simply because trains spend most of
their time in the middle of nowhere and that is where they are most
likely to derail. Also trains travel slower through cities to minimize
the possibility of derailments and crossing accidents. Unfortunately, in
this case, not slow enough for the unknown circumstances associated with
the derailing coal train reportedly traveling at 25 mph.
In 2011, over 400 trains derailed on main track; down 90 percent from 35
years ago. Few things associated with potential mortality have improved
that much. Motor vehicles deaths, for example, are down about 1/3 in the
same period. While cars are certainly technologically superior and safer
than 35 years ago, we attribute most of that improvement to stricter
enforcement of DUI laws.
Rail transport has always been safer than the alternative. In the 1880s
someone determined travel by train was 60 times safer than travel by
stagecoach. In 1867, with far fewer people and vehicles, accidents with
horses killed about four pedestrians per week in New York City.
"Put all your eggs in one basket, and watch the basket." Today a typical
freight train replaces
<http://www.amtrak.com/ccurl/216/645/CriticalLink2007_5.pdf> 280 trucks.
It is far easier to monitor the safety and behavior of one train and one
train crew than 280 truckers and trucks. Self-steering trains are simply
safer (and greener) than anything traveling on rubber tires. Recognizing
this fact, federal regulators are loath to allow hazmat shipments to
change from rail (about seven times safer) to roads.
In fact laws left over from the robber baron days (John D. Rockefeller
bought up all the oil rail shipping capacity to freeze out the
competition) require railroads to ship everything requested. All other
modes of transportation (ship, barge, truck and plane) can refuse hazmat
materials as a matter of safety and excess risk. Because of potential
liability railroads would also prefer to refuse shipping hazardous
materials.
Not too long ago rail equipment safety was based on visual inspection.
Equipment was removed from service just short of failure. Today the
inspection methods are far more sophisticated and proactive; and, should
in fact take much of the credit for the 90 percent reduction in
derailments.
Today trackside sensors look for overheated bearings and wheels, out of
round wheels and dragging equipment. Machine vision is increasingly used
to monitor wheel and brake shoe wear and freight car damage. High water,
rock slides, earthquake, avalanche and high wind detectors are located
as needed. Ground penetrating radar detects drainage problems that cause
track problems; and special cars with lasers look for track shifted out
of spec.
Unfortunately just like it is impossible to prevent the 200,000 or so
potholes that grow annually in New York City, it is impossible to stop
wear and tear on railroad track and equipment.
The rail and equipment wears and grows metal fatigue cracks. Metal
fatigue, explained as simply as bending a paper clip back and forth till
it breaks, occurs in all moving machinery -- including airplanes.
Fatigue cracks can grow inside rails making them far less detectable
than potholes. (Consider the safety implications of a pothole that grows
internally and suddenly opens up underneath a passing car.) To find
internal fatigue cracks the railroad companies periodically inspect
their rails with ultrasonic sensors; similar to those used by doctors to
internally inspect humans. To get a "clean" ultrasonic reflection the
rail surface is periodically ground smooth. Eventually the rail, cross
ties and even the crushed rock holding the ties in place wears and must
be replaced. And the track shifts for a variety of reasons.
The challenge is to successfully manage the risk to an acceptable level.
Unfortunately the risk can never be reduced to zero.
/--------------------------
You can read more about train wrecks by checking out the author's 'Train
Wreck: The Forensics of Rail Disasters' here
<http://jhupbooks.press.jhu.edu/ecom/MasterServlet/GetItemDetailsHandler?iN=9781421405902&qty=1&source=2&viewMode=3&loggedIN=false&JavaScript=y>.
/
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