Thursday, February 19, 2009

Yellow Line Hit by Derailment Bug

News Channel 8 is reporting yet another derailment, this time on the Yellow Line.

And we thought, for a moment, that the name of this blog was too harsh! Ha! I'm thinking of replacing the "s" with an "f."

At least the Yellow Line Twitter feed is a little more current.

I wonder if the Orange Line Metro tweeters were out shooting a cool new PSA today!

1 comment:

Anonymous said...

The power steering mechanism failed to maintain continuous and proper contact with the fixed guideway assembly.

I thought they had replaced this relatively new interlocking following the last derailment. Maybe they only replaced one half of the pocket and this happened at the other end.

It sounds as if there are a few possibilities here.

1. The trucks don't swivel enough.

If the trucks are tight they could have trouble in a curve. The Breda cars were chronic track jumpers in the yards, until Metro replaced all of its yard switches with longer, gentler ones.

The CAF 5000 series cars have a history of derailments. Perhaps they are tighter than the Breda cars.

2. The train was going too fast.

In a crossover the speed command logic will "look back" at the rear of the train to see if it has cleared the interlocking. When it has, the speeds are increased.

I don't know in which switch the truck derailed. If the train were given full speed ahead with the rear truck still in the last switch (the one on the main line) there could be a problem.

3. There was a rail or wheel defect.

A recently turned wheel can have a ridge that rides up on the rail if conditions are right. Try to imagine two corrugated surfaces rubbing against each other. The one will grab the other and not let go.

A train wheel in a curve riding up on the rail would be set up for a derailment. That is why they lubricate the rails in long curves. Lubricating the rails in a switch is highly unusual.

If the switch point did not tuck properly it could cause a wheel to split the switch. That could happen to any wheel and the more worn the wheel the more likely it would be to pick the point.

If the gauge were slightly wide or the rails were not in proper alignment the train could fall off.

It will be interesting to see where all the fingers point this time. Last time their "fix" was to spend a ton of money replacing a relatively new interlocking.

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