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Old 06-23-2009, 11:07 PM   #31
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While I agree illegals put a strain on the system, more importantly is health care for profit. Until that issue is addressed, the system will never get better.
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Old 06-24-2009, 02:34 AM   #32
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Infrastructure doesn't generate enough ongoing profit for those involved.
But it does provide ongoing employment for kin and hacks.
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Old 06-24-2009, 09:06 AM   #33
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So the investigators yesterday came out with a little more information.

They confirmed that this particular train was in automatic mode, and was being driven by the computer. They also confirmed that the emergency brakes had been applied. The button had been depressed in the driver's cabin, and the brakes themselves had the bluing that you would expect from emergency application. Also, the tracks had "skid marks" on them.

What they didn't say was how long the skid marks were, or how early the brakes had been applied.

It's frustrating that they didn't include this important information, so I tried to figure it out myself.

If you go to Google Earth and look at the accident scene, you can measure from the point of impact back in a straight line until that straight line gets obstructed by something, and then you know how far away the driver should have been able to see the stopped train. When you do this, you will see that the accident happened at a curve, under a bridge, and the visibility was actually pretty bad. The driver, if she had been paying 100% attention to the track in front of her, would have first seen the corner of the stopped train when she was about 355 meters away. At that particular location, according to the Washington Post, the train speed limit is 59 miles per hour. A train traveling at 59 miles per hour will cover 355 meters in 13.5 second. She wouldn't have seen the full train until she was about 160 meters away or 6 seconds from impact.

I don't know how long it takes to stop a train traveling at that speed. In normal operation, the trains take a while to stop, but they are trying to do it gently for the passengers' comfort.

So she had 13.5 seconds to see the stopped train, realize it was stopped, notice her own train wasn't stopping, still wasn't stopping, and slam on the emergency brake. She did all those things, but apparently not fast enough.

The head of Metro said that there is no evidence that she did anything wrong. But autopsy results, blood tests, cell phone, and texting records haven't been released yet.

The train had an unusual configuration. It had a lead car that normally isn't used as a lead car. In theory, it should have worked fine, but trains were seldom set up that way. And that lead car was overdue for brake maintenance. It's possible that the unusual configuration caused the autopilot to misread the situation and not stop.

I mentioned multiple layers of failure before. We now have: unusual train configuration, possible bad brakes, train stopped on a curve, and a "driver" who may have taken a couple seconds too long to apply the emergency brakes.
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Last edited by glatt; 06-24-2009 at 09:42 AM.
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Old 06-24-2009, 11:05 AM   #34
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Google Earth has an image with a train directly at the end of your yellow line? Impressive!
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Old 06-24-2009, 11:21 AM   #35
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I heard that a passenger had told his family, the night before, that he would hop the train to work in the morning. It's as if it were a set-up! [\levity]
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Old 06-24-2009, 11:23 AM   #36
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That's a great post glatt, thanks.
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Old 06-24-2009, 12:44 PM   #37
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Quote:
Originally Posted by Happy Monkey View Post
Google Earth has an image with a train directly at the end of your yellow line? Impressive!
Yeah, it was lucky! And it was a 6 car train, like the ones involved in this accident, so I could measure it and put place marks in Google Earth to show almost exactly where the stopped train was. And then measure back from those points to see the sight lines.

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That's a great post glatt, thanks.
Thanks!
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Old 06-24-2009, 05:44 PM   #38
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Superb analysis, Glatt.
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Old 06-24-2009, 06:02 PM   #39
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Fairly accurate, too. The brakes were apparently on for 300-400 feet, or about 120 meters.
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Old 06-24-2009, 08:42 PM   #40
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Thanks for that info HM. 300-400 feet, huh? That's a much better driver reaction time than I expected. Judging from the damage, the train must have been going very fast. In fact, many of the passengers said the train hit at full speed. So it sounds like the brakes were not very effective. I'd expect the speed to be reduced dramatically over that distance, based on my own experience on Metro. I bet only some of the cars had brakes that were working, or there were other problems with the brakes.
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Old 06-24-2009, 09:49 PM   #41
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Old 06-24-2009, 10:45 PM   #42
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That's good work, Glatt, but I'm not *entirely* convinced. Maybe the track is raised so the driver can see over the green areas beside the track. Does the driver sit on the left, right, or center of the train? Is the seat elevated? How are the pylons on the bridge aligned? What angle was the sun coming from?

There are so many possible sources of minor error that a couple of little things like this could add up to seriously affect the calculations.

That said, you figures are probably in the ballpark.

To me, two facts stand out - the investigators say the brake pedal had been pressed down, yet passengers report feeling no braking. Add that to all that stuff about old train cars with poorly maintained brakes, and I'm happy to jump to a conclusion.
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Old 06-24-2009, 11:15 PM   #43
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The driver sits on the right, IIRC, and is not elevated. The track was not elevated.

The rails show 300-400 feet of braking. I would imagine that in a seatbeltless vehicle like a subway car, the slamming of the emergency brakes would feel much like a collision, so there may be confusion. The brakes were apparently triggered by a button, not a pedal, so they are probably pretty close to all-or-nothing.
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Old 06-25-2009, 07:51 AM   #44
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For what it's worth, we have had a very wet spring, and foliage is very lush here right now. It's quite possible that the vegetation along the side of the tracks is more overgrown in real life than in the image found on Google Earth, and the sight lines may be even shorter as a result with all the weeds hanging off the chain link fence. I also don't know where the supports for the bridge are located, since they aren't visible in the Google Earth image, so I measured as if there were none. The presence of bridge supports would also make the sight lines worse than my post.

My point was that 355 meters was about the farthest away the driver could possibly see any part of the stopped train. My gut tells me that it was more like 250 meters before it became obvious.
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Old 06-25-2009, 10:10 AM   #45
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Quote:
Originally Posted by glatt View Post
So she had 13.5 seconds to see the stopped train, realize it was stopped, notice her own train wasn't stopping, still wasn't stopping, and slam on the emergency brake. She did all those things, but apparently not fast enough.
The average emergency reaction time is something like 0.25seconds, or something to that effect as I recall. See event, process, take action.

This is an online test where you test your own:

http://getyourwebsitehere.com/jswb/rttest01.html
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