Wednesday, May 13, 2015


At least one person on Fox news has claimed that the recent tragic Amtrak accident, where a train was apparently going 106mph in a 50mph zone, was due to a lack of maintenance.  Let's take a look at this.

For starters, if a train was going twice the speed limit, we have to suggest "operator error" as a contributing factor, I'd hope.  That, in turn, will lead to the question of why the Acela (?) train's operators felt the need to do this--it will in turn have a lot to do with what incentives management puts before them.

But that said, here's a map of the Port Richmond area, and the curve in question is in the northernmost area of the neighborhood.  It appears to have a radius of about 1000 feet/300 meters.  The train's velocity, 106mph, is about 47m/s, and thus the centripetal acceleration (v^2/r) would be somewhere in the range of 7.5m/s^2--more than enough to knock a railroad car with center of mass at least 1.5m above the track off a standard gauge track, no matter how well maintained the tracks were.

Now the tilt of Acela--say 8 degrees--would increase the lateral force which can be endured to perhaps 6m/s^2, or a velocity of about 95mph, if it were used, but that leaves no room in play for other lateral forces.  Hence the 50mph speed limit.

So what would the maintenance issues be here?  Well, the track theoretically could have buckled and made things worse, but all in all, the major issues in play are not the track, but rather signaling and brake work--really things that don't require a lot of effort or money.

In other words, since no train in existence could navigate that curve at that speed, and since the operators run this route daily, I'd be very surprised if any honest investigation finds anything except that management set incentives to exceed speed limits and mis-allocated funds that ought to have been spent on signaling and brakes.

And since Amtrak is funded by government, I of course am not expecting an honest investigation.

One other note; if, instead of using a locomotive/carriage model, you used a doodlebug configuration where the engine, generator, and fuel were kept below the level of the passengers, this curve might have been navigable at 106mph if the overall center of mass had been reduced to 1.1m or less, plus or minus--and this is very achievable.  If passenger rail is to survive, some thinking outside the locomotive/carriage box needs to be done.

Update: Amtrak's union and others are arguing that management failed the public by failing to install "Positive Train Control" in that corridor, and they are probably correct that this system would have helped greatly.  But as one who has worked in electronics reliability....sorry, you can't ignore the engineer/operator in this equation, and his motivations!

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