Thursday, March 17, 2011

A skeptical look at Unstoppable

Railroads hold an almost universal curiosity for most folks. Probably because of the fact that they're both familiar and somewhat mysterious. Most of us have been on a train of one sort or another, but almost no one knows how to work one. You might say that's the same for airplanes, yet there are half a million (or so) licensed pilots in the U.S. There aren't even 100,000 locomotive engineers. Anyone can own a share of a plane and there are lots of small aircraft fields. But trains run on tracks, and almost nobody owns their own railroad tracks (and almost none of that truly privately owned track is standard gauge).

Because railroading is such a close-knit fraternity, there is relatively little documentation out where the rest of us can read it about how you drive a train.

I have done a little bit more research than the average joe on trains because of my CalTrain commute and I'm curious. I know at least a little bit about the signaling aspects and a little bit about mechanically how a modern diesel-electric locomotive operates. So I was super excited about seeing Unstoppable. And I liked the movie quite a bit. However, there were a few moments in the movie where I couldn't completely suppress the suspension of disbelief.

1. The police were shooting at a fuel cut-off switch. Ok, if such a switch existed, why didn't the hostler who lost control of the train just hit it when he realized the train was going to get away from him? This one is arguably defendable - the guy, after all, was not depicted as being a bright guy. You could say that he didn't think of it. But wouldn't it have been easier for them to try taking a long stick and poking at that switch from the truck while they were driving along side rather than trying to jump onto the ladder?

2. Why didn't the cops shoot the fuel tank full of holes and spill the fuel? Diesel fuel doesn't catch on fire when you shoot it. The mythbusters have been over that time and time again. Certainly dealing with the diesel spill would have been far better than the possibility of having to deal with the spilled phenol (or whatever the McGuffin chemical was).

3. Why were they trying to lower an engineer from a helicopter? Why didn't they just put a second guy on the locomotive that they got in front of the train and have him hop on from there?

4. I may be wrong about this, but I always thought air brakes were fail-safe. That is, the lack of air pressure makes the brakes close. If that were true, then the hostlers would not have been able to move the train at all without having all of the brake lines connected. It would take air pressure from the locomotive to open the brakes to let the train move. Someone who knows trains more than me should chime in on this one.

5. There's just no way that the attempted derailment they set up should have failed. If a portable de-railer had any chance of not working, then they could have just put a couple of sticks of dynamite under a rail and blown it up. It's not as if a derailment wasn't going to screw up that section of track anyway.

6. The hostler wouldn't have put the generator into notch 6. The notches are like gears in a car. What they do is connect up the windings of the generator being driven by the diesel motor in various combinations of series and parallel modes. This allows the generator to either generate high voltage and low current or vice versa for feeding into the traction motors (the electric motors that drive the driven axels). Higher notches generally mean higher speeds. The hostler was moving the train at basically walking speed. He'd have not been able to do his job any better by throwing it into "high gear" any more than that would have been a good move for a car with a stick shift.

7. The movie was, indeed, based loosely on a real-life incident that took place in Ohio. The so-called "Crazy Eights" train (CSX locomotive number 8888) was being moved in the yard and the hostler jumped out of the cab to realign a switch and failed to reboard. In that incident, the airbrakes not being connected was a normal yard procedure, and the hostler set the throttle to 100% believing the engine was configured for dynamic braking (in dynamic braking, the traction motors are converted into generators, and the energy they produce is dissipated in a large bank of air-cooled resistors as waste heat), which translates to full braking power. Instead, the engine was configured normally and full power was applied. He set the independent brake for the locomotive, but it was unable to overcome the engine and the train sped up. CSX was able to stop the train using the same technique that was successful in the film (without quite so much drama, of course). They also had a locomotive ahead of the runaway that they planned to place in front of the train to slow it further, but this was not necessary.

8. Applying the brakes at the end of a powered train poses a risk of "stringlining" if the train goes around a curve. To illustrate what stringlining means, imagine a piece of string sitting on a table. Now form that string into an arc (as if it were a train going around a curve). Now put your finger down on one end of the string, and pull the other forward along the tangent line. The string will deform the curve and eventually become a straight line. Tension in a train consist caused by either tail-braking or head-thrust while going around a curve will tend to cause the cars to want to pull to the inside of the curve - basically in concordance to the centripetal force required to turn the train. I believe this, in fact, was what Frank was up to by working the brakes of the trailing locomotive the way they did while the train was on the elevated curve in the film.

9. Why did it take them so long to try that truck trick to get someone into the cab (or, as mentioned above, to hit the fuel shutoff switch from outside)?

The only other complaint I might have about the film is actually a fairly common one for movies - a lot of technical dialogue that you see taking place between experts on film is often implausible because experts talking amongst themselves assume similar levels of technical expertise, and so leave out a lot of common knowledge. You can't really do that in a film, though, because the audience won't understand, so you have experts talking to each other using the sort of language they'd use to explain stuff to outsiders who don't have that common expertise. Particularly over the radio in crisis situations. It happens all the time in all sorts of genres, from trains to submarines, to airplanes, to computers... I don't envy the challenge that such situations pose to script writers, but it always sticks out like a sore thumb to me.

2 comments:

Ragnar Lodbrok said...

:) well put

mackat4ck said...

I believe with csx 8888 they did try to shoot the cutoff switch and they also did try to derail it and both attempts didn't work. Also air brakes aren't "failsafe" as you call it, and I imagine that's because if you are going down a hill and you run out of air, you don't want your brakes to lock on.

Otherwise, some good points.