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Bad TV Technology: NCIS: LA and Trains - RonO's Ramblings

Nov. 11th, 2013 12:46 pm Bad TV Technology: NCIS: LA and Trains

The main action sequence of the episode of NCIS: Los Angles that first aired on November 5, 2013 featured a train – one engine and two cars each containing two tanks of chlorine gas.  As a moderate rail-fan with an incomplete knowledge of rail details, I think I spotted at least three major flaws – two of which might have (ahem.) derailed the plot if I’d let them.

First: The train had been hijacked by a recently fired brakeman, who was otherwise about to be promoted to engineer.  He was taking action because the railroad owners were covering up that they were routing dangerous cargo through residential areas.  His protest was to take the train and drive it to LA Union Station.

But, I’m pretty sure that the central control of the switches has as much, or more, to do with where a train ends up.  So, his plans to get this train to Union Station were pretty much shot from the moment it became known that the train wasn’t properly manned.

Second: It turned out that the hijacker had been duped by a couple of others who instead planned on setting off explosives under the tracks, derailing the train and causing the chlorine gas tanks to break open, injuring and killing a lot of people in or near a major metropolitan area.

When the hijacker learned this, he attempted to stop the train.  However, the brake line between the engine and the first car failed catastrophically, leaving him without breaks.  As I understand it, modern train brakes are still based on the old Westinghouse Brake – namely that they are held disengaged by the air pressure in the system.  A break in the brake line that caused the air to pour out (as shown in the episode) should have caused the brakes on the two cars to engage.  As long as the brakes on all of the trucks engaged at about the same time, or the brakes engaged back to front, the cars would have simply decoupled from the engine and stopped.  If the front car’s brakes engaged first, the rear car could have derailed.

Third: Once the hijacker learned that the brakes weren’t working and that he couldn’t decouple the train while moving, he “reversed the polarity” of the engine to slow the train that way.  Now, as I understand it, the primary  brake on a diesel-electric engine is to drop a big resistor across the wheel motors (and use the fans on the top of the engine to dump the resulting heat).  So this wasn’t that far off what he would have already been doing.

But, this somehow locked the wheels not only on the engine, but also both cars, resulting in them throwing sparks from the friction between the wheels and the rails (done, no doubt, by the visual effects crew).  Now, I think a dead-short on the wheel motors would cause them to lock (or come pretty darn close), which would cause sparks there.  But the wheels on the cars should have been still free (after all, their brakes didn’t work).

Finally, I suspect that locking the wheels on the engine without brakes on the cars would have just about assured that one or both of the rear cars would derail – the exact thing that they didn’t want to happen.

Now, they were right with the amount of distance a train at speed – even a fairly light train like they showed – would take to stop.  But I think this was as much to create tension when one of the main characters was trying to defuse the bomb with seconds before the train tripped it.

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Date:November 11th, 2013 09:38 pm (UTC)
Pretty much right on all counts. The person driving the train (usually called the engineer in the USA) doesn't actually control where the train goes — the dispatcher running the switches remotely does so. (At least in the LA Metro area, most or all main line switches are controlled by a dispatcher. Only industrial sidings are manually operated. It is generally possible to defeat remote switches manually, but you have to stop the train, unlock, and manually throw a power switch, which sort of defeats any plan of driving your train at speed into LAUPT.

If a dispatcher knew of a "rogue" train in the system, s/he would almost certainly have routed it into a place where it would have deliberately derailed, albeit hopefully without doing so much harm. With a hazmat load, it gets pretty dicey to do that, particularly in built-up areas. (I do worry sometimes about all those tank cars of non-odorized natural gas parked across from my house in Fernley, for instance. Not a good place for a derailment, not at all.)

Trains in the USA do indeed still use the Westinghouse air brake, and if the train breaks apart, the brakes automatically apply. In the scenario described, the train should have "gone into emergency" and ground to a halt eventually. There are ways to defeat this (turning the angle cock on the air lines so that the parts of the train are isolated from each other), but that generally requires deliberate sabotage, since the entire system is specifically designed against such accidental failures.

As described, the engineer could have been trying to first engage dynamic braking, which, as you imply, turns the engines into resistors. That won't stop the train entirely, but it will slow it down. Alternatively (and this is the only thing that could have caused the sparks), you could possibly get the engine grinding the wheels in reverse. This has been done very occasionally, such as one case when a train got out of control coming down into the LA Basin and in a last-ditch (and ultimately futile) effort to stop it before it derailed, the engineer put the train into reverse. This did slow it down, but also turned a set of million-dollar locomotives into very large, heavy paperweights as it destroyed the engines. (The train ultimately derailed anyway, just not as badly as it would have done.) And as you say, the cars behind the engine wouldn't have been sparking unless they'd already come off the rails and were scraping them from the wrong side.

Nobody in movies/TV knows anything about how trains work. It's a pity, really, because there are perfectly dramatic stories about real train accidents that could be told. Indeed, in the days before radio communications and lineside signals and interlockings, you had situations where a dispatcher could issue what was known as a "lap order" and realize that he'd just killed people -- long before they were dead! That's because it might take an hour for the collision to play out, but there was no way to get word to the crews to stop their trains before disaster struck on account of there being no open train order stations between the trains.