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CTA meets snowplow

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CTA meets snowplow
Posted by BaltACD on Friday, November 17, 2023 8:12 AM

Never too old to have a happy childhood!

              

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Posted by samfp1943 on Saturday, November 18, 2023 8:18 PM

BaltACD

  I think the reason that no one seemed to notice that thge colision was as you haver reported was that the original information was somewhat incmplete; the photo was just of the 'still' photo of the damaged car, and the injuries to /'passengers'.  

Currentlky, TRAINS Newswire has a follow on story in regards to an NTSB investigation of the collision.   Apparerntly, the 'snow plow'(?) was out and being used in a training exererise (there was an included note that 6 of the injured were on the snow plow.  and khere is a partial quote from the NEWSWIRE% article:

FTA:"...[NTSB investigator] Homendy said NTSB investigators have downloaded information from the train’s event recorder and determined the two-car train was going 26.9 mph when it struck a “Snow Fighter” snowplow near the Howard Street station in the Rogers Park neighborhood on the city’s North Side [see “Chicago L train hits maintenance equipment …,” Trains News Wire, Nov. 16, 2023]. The event recorder set the time of the collision at 10:31 a.m.

The design problem, she said, stemmed from the fact that the CTA’s braking algorithm called for the train to be able to stop in 1,780 feet, while a new system would call for 2,745 feet to stop. “The braking distance should have been longer,” she said. “… That is a design problem. Why is it different today? Over time, cars get heavier, there are more passengers; we’ll have to look at some changes that have been made to the system.” Part of the NTSB’s ongoing investigation, she said, will be determining remedies for the braking issue..."

 

 

 


 

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Posted by BaltACD on Saturday, November 18, 2023 10:47 PM

1000 foot difference in acknowledged braking distance is not acceptable.  26.9 MPH at impact would indicate, to me, that the brakes weren't applied in accordance with ANY signal indication and likely weren't applied until impact.

FTA should not accept any increase in braking distances for any reason, Homendy needs to up her game and learn when she is being given a snow job.

Never too old to have a happy childhood!

              

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Posted by Overmod on Sunday, November 19, 2023 9:47 AM

A back-of-the-envelope calculation indicates that a train at 60mph (88fps) decelerating at the maximum 'comfortable' rate of 1.5fpsps would take a little over 2200' to reach the 'accident' speed.  Presumably emergency braking would result in considerably shorter distance and time.  Note that this would involve bailing off the brake a la Decelostat to maintain the constant rate as the train lost momentum, and it does not require any correction for loaded vs. empty.

So the formulae used for the two measures of "braking distance" Ms. Homendy mentioned need to be specified, together with their assumptions, before we can make more sense out of what I, like Balt, think is somewhat seasonally-appropriate weather, metaphorically speaking.

 

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Posted by Falcon48 on Wednesday, November 22, 2023 1:57 PM

I rather suspect that, when all the dust settles on this accident, the braking rate will prove not to be an issue.  CTA trains have both dynamic and track brakes (like the PCC cars of yore).  I've been on CTA trains where the track brakes were used, and they decelerate very rapidly, much more rapidly than a standard commuter train in emergency and more like a bus where the brakes have been slammed on.

The fact that work equipment (the plow) was involved makes me wonder if the plow was designed to not trigger the signal system.  That would explain why the passenger train was apparently able to approach the plow at speed (the signal system CTA uses, if it detected the plow, should have automatically slowed and stopped the following train long before a collision became unavoidable).  The curve where this occurred is pretty blind to a southbound train due to a bridge over the tracks (which can be seen in the photos) so a motorman wouldn't have had much time (if any) to respond on his own if his first warning was the sight of the plow ahead.

I expect all will be revealed when NTSB digs into this further.  They're usually pretty good at unravelling stuff like this.

  

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Posted by JL Chicago on Wednesday, November 29, 2023 8:25 PM

According to my records CTA trains are supposed to decelerate at 3 mph/sec at full service using dynamic and 6 mph/sec at full emergency using both dynamic and track brakes.  So I'm thinking either the ATC cab signal was off/defective, or the snow plow for some reason didn't shunt the track circuit, or there was something slippery on the rails.  As you mention, putting on the track brakes means grabbing something fast if you're standing before you fall over.  It akin to slamming the brakes on a CTA bus.

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Posted by gmpullman on Wednesday, November 29, 2023 9:51 PM

Falcon48
The fact that work equipment (the plow) was involved makes me wonder if the plow was designed to not trigger the signal system.

That was one of my first suspicions. I wonder if the wheels of the plow were still crusty&rusty presuming it had just been taken from storage and brought out on the main. I recall there were similar problems with RDCs, hy-railers and many forms of M-of-W equipment. Sometimes shunts were used. 

The old Michelin rubber tired motor car used sliding wire brushes to allow the signal system to detect its presence.

 The Michelin railcar in Akron, Ohio in 1932 by Historical Railway Images, on Flickr

 

Regards, Ed

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