With bi-directional signaling, that seems possible but highly improbable since the third train would shunt, or at least weaken the signal from behind, the "back end." Furthermore, aren't the coded signals polarized by direction; and are not the reverse signals red by a direction of travel relay?
If tests showed a train was lost, ie, did not adequately shunt the circuit from the front end, a weak stop ("restrictive" since a dispatcher could give permission to move) command should be picked up to protect the train at the station.
HarveyK400While blame has been assessed to a relay failure, the logic escapes me. The struck train had braked to a stop in compliance with a restrictive signal in the block approaching the occupied block at the station. In both cases, the occupied station block (train A) was not cleared to re-energize the relay for the approach block. The question is how did the track circuit for the approach block become energized and transmit a clear code behind the struck train?Even if the relay behind the struck train (B) failed to drop, the following train (C) would get a restrictive code or no code and begin braking in ATO mode upon entering the block before the operator had to put the train into an emergency stop. If, as reported, the struck train (B) failed to shunt the approach block track circuit, the following train (C) would get the same restrictive signal to brake as the struck train.I can only speculate that a stray clear signal leaking from the adjacent track, being stronger than no signal from the shunted circuit, was picked up by the train C on-board antennae; and, as a result of post-collision testing, energized the track circuit relay as well.
While blame has been assessed to a relay failure, the logic escapes me. The struck train had braked to a stop in compliance with a restrictive signal in the block approaching the occupied block at the station. In both cases, the occupied station block (train A) was not cleared to re-energize the relay for the approach block. The question is how did the track circuit for the approach block become energized and transmit a clear code behind the struck train?
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
This isn't about six planes losing engines and crashing; but more analogous to finding missing bolts or cracks during inspections, grounding all planes for inspections, and releasing them for service if no defect is found.
aegrotatio I was searching high and low for WMATA Metrorail control system image and this video just JUST published. Important details reveal that central control maintains a near-realtime view of all trains in the system even on dead circuits. There can be 2 or 3 trains in EACH block during normal operation. A block is 400 to 1000 feet long. In the case of a circuit anomaly, an Absolute Block is imposed, which means 1 train per 400-1000ft block. Trains enter the block through communication with the Metro control center which grants a Permissive block at which trains move at restricted speed. At no time are trains "lost" in the system as I jhave been saying before. Here is the video: http://www.wtop.com/?sid=1724694&nid=25
I was searching high and low for WMATA Metrorail control system image and this video just JUST published.
Important details reveal that central control maintains a near-realtime view of all trains in the system even on dead circuits.
There can be 2 or 3 trains in EACH block during normal operation. A block is 400 to 1000 feet long.
In the case of a circuit anomaly, an Absolute Block is imposed, which means 1 train per 400-1000ft block. Trains enter the block through communication with the Metro control center which grants a Permissive block at which trains move at restricted speed.
At no time are trains "lost" in the system as I jhave been saying before.
Here is the video:
http://www.wtop.com/?sid=1724694&nid=25
Interesting. Thanks for posting that.
You are confusing the term "block" as they are using it here, with a single, track circuit "block".
You are also confusing the train dispatching system's ability to track trains with the signal safety system that keeps them apart.
There can be only one train allowed in a track circuit block at a time. In addition, no train is allowed in the track circuit block immediately behind the train, either. That's so there is room for reactive braking should the following train exceed authority.
The "permissive block" set up to allow operation in what can be viewed as "dark" territory had no direct relation to the track circuit blocks. It's a big as it needs be to accomodate the manual operation and to protect against following trains. Think manual block or track warrants as an analogous.
The dispatching control center tracks trains for supervisory control. It is not part of the safety system (except when they give permission to move manually i.e. permissive blocks). That the control center doesn't lose track of trains means nothing to the signal safety system.
A "turned off" track circuit is the same as one that show as occupied. The problem with the crash was there was one that showed the track as clear when there was a train in it.
The simplest way to think about a track circuit is a circuit with a battery on one end and a relay on the other. The two rails are the "wires" that connect the battery to the relay. When no train is present, the circuit is complete and the relay picks up. When a train is present, the wheelsets create a short circuit and the relay drops.
That math doesn't add up.
6 anamalous signals out of 3,000 sensors that protect about 20 trains, I'm not sure the math is working for you on your statement.
blue streak 1 RWM: Hypothetical question. How would the FRA react if a calss 1 had 6 track circuits not detecting and the level of traffic carried (i know not possible)?
RWM: Hypothetical question. How would the FRA react if a calss 1 had 6 track circuits not detecting and the level of traffic carried (i know not possible)?
That's not what Metro said. They said they had 6 circuits that were defective. They didn't say they weren't detecting trains. More likely, they were shunting too easily - indicating trains where there were none. This is a very common defect. TOLs are everywhere!
It's how you look at it! Only 6 dangerous failures on a very large transit system.
If only 6 aircraft engines had fallen off (or wings had fallen off, or landing gear had failed) on there Airliners in flight within a large airline system, and the Operator claimed only one resulted in a fatal accident.
Would the press let the Operator and Manager of the offending airline get away with that statement? This would be headlines for weeks!
Don U. TCA 73-5735
blue streak 1HarveyK400 The good is that a huge gulf exists between "system-wide" failure reported by the media and the 6 failed block circuits that have been found around a system the size of Metro. RWM: Hypothetical question. How would the FRA react if a calss 1 had 6 track circuits not detecting and the level of traffic carried (i know not possible)?
HarveyK400 The good is that a huge gulf exists between "system-wide" failure reported by the media and the 6 failed block circuits that have been found around a system the size of Metro.
The good is that a huge gulf exists between "system-wide" failure reported by the media and the 6 failed block circuits that have been found around a system the size of Metro.
Probably order proceeding at restricted speed on dispatcher authority for the failed blocks; and no more than medium speed under track warrant authority for parts of the system with similar signaling.
Now, they are saying there is a problem in the system. I guess everyone is pointing fingers.
The General Manager of WMATA disputes the Washington Post's yellow journalism story today that claimed the failures are "system-wide." They found 6 examples of possible anomalies that potentially cause the intermittent failure experienced in the accident out of 3,000 track circuits.
They aren't system-wide and the Post should be ashamed of themselves..
Good news, bad news, and the lack of perspective.
The bad is that system-wide tests and statement that there was no problem a couple months ago are belied by inspectors finding anomalies in 6 track circuits on the system as of today.
If the GM is half as smart as a pet rock, he'll say, "Look, folks, I'm a political appointee/MBA. You really need to ask the technical types who are supposed to:
Asking a typical government-organization 'manager' about technical problems is like asking the check-out clerk at the local Wal-Mart about brain surgery.
Of course, the problem is that the system is in Washington DC. How deeply would Congress dig into a similar mishap at BART? (Hint: They would actually have to go beyond the beltway and out of the glare of the various media 'Washington Bureaus.')
Chuck
Now the Washington Post is reporting multiple track failures system wide. If you were the General Manager would you have wanted to admit such? Congress will have a field day. Want to bet his answers will be " I don't recall"
Awesome! Who's at fault?
Who's at fault?
An engineer (civil, mechanical or electrical) asks, "What went wrong?"
A lawyer, politician or blame-assigner asks, "Who's at fault?"
If this is, in fact, a fully automated system, the answer is, "Nobody is at fault. There was an electrical or mechanical failure." Hopefully, the engineers among the accident investigators will find out what failed and how such failures can be prevented in the future, and the lawyers, politicians and blame-assigners will stifle themselves until the final report is submitted.
If things could be made perfect, there would be no need for erasers on pencils...
Chuck (Former Air Force QC inspector)
Great question. Isn't the Metro pretty much fully automated? Hope it isn't another texting moment...
http://news.yahoo.com/s/ap/20090623/ap_on_re_us/us_dc_metro_train_derailment
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