Track Dynamics cause of San Marcos Derailment

[dldance]

UP spokesman said, "the investigation has narrowed the cause to the dynamics between the track and the train, which include the weight of railcars going past a curve and their positioning behind one another. ... investigation determined the train left the track just after passing an S-Curve..."

Source: Austin-American Statesman

Comment/Question:
Since 5 of the cars were empty tank cars, this sounds to me like fancy talk for a stringline derailment since they have ruled out the track or the wheels?

dd

[dldance]

More from the San Marcos Daily Record---

Railroad calls derailment 'highly unusual'
By BRAD ROLLINS - Staff Reporter
Posted: Tuesday, Mar 01, 2005 - 08:50:23 am CST

A Union Pacific Railroad official says the company is stumped by initial results of an internal investigation that found no apparent cause for a Feb. 11 freight train derailment in a San Marcos neighborhood.

An unspecified "combination of train and track dynamics" caused a box car loaded with scrap paper to lift off the rails when the train passed through an S-curve behind San Marcos City Hall, spokesman Mark Davis said. Seven cars, five of them containing sulfuric acid and xylene, overturned more than two miles further down the track.

Calling the circumstances "highly unusual," Davis said investigators found no problems in any of three areas that typically lead to train derailments: human error, tracks and mechanical systems. Davis said measurements of track and rail car width met Federal Railroad Administration and company regulations. Additionally, no defects such as cracks or gouges were found in the rails, he said.

The spokesperson said he didn't know of any other situations in which a train derailed for no apparant reason.

"That's why its taken so long to find a cause," he said. "They kept going back and checking everything and couldn't find any defects."

Spurred by the mysterious derailment, railroad engineers will use computer simulation and modeling to "try to find the relationship between track geometry and different kind of rail cars."

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Thus it appears to be more complex than a stringline derailment.

dd

[mudchicken]

ddl:

Train dynamics related incidents are fairly common and include issues created by buffing, long car/short car, unbalance with a high center of gravity (common is "S" curves ), loads/empties, uneven braking by the consist, slack actions and so on.

If that car were in any way loaded improperly (all in one end/ all to one side), you have the trigger to a big mess. They are looking for the "trigger" and have not found it yet. DHarmon should be having fun with this.

[kenneo]

Reference back some time to a disussion here on stopping a train quickly and safely in an "emergency" situation.

If that car had been off balance as Mudchicken suggests (and that was my first thought, as well), a slack run-in from what ever cause (such as an improper brake application, for example) with the unbalance to the outside of the curve or the load all being in one end of the car, would easily have popped the car off the tracks. From the thread, it then appears it was drug for two miles until something stopped the car dead in its tracks which then caused the "rest of the story".