[PRCo] MetroRail Signalling

[Phillip Clark Campbell]

Mr.Alan Schneider;

Thank you very much for this report.  Thank you to the many contributors on
this subject.  The news reports  'seem'  well done and I was able to glean
much information from them;  comments from contributors underscored these
observations and brought much clarity to this disaster.  The postings have been
most productive  --  'mostly.'

I have changed the subject line and have questions to seek a greater understanding
of the signaling system.  I found the URL for the included article:
http://www.fredericknewspost.com/sections/news/display.htm?StoryID=91910
because I wanted a closer look at the included photo:
http://www.fredericknewspost.com/photos/09/06/26/91910_large.jpg

It is already established that  'computers'  handle the signals through  'ATC;'  while I
understand the concept I am not familiar with the details.  My reference is the US&S
signals as used on PRC interurbans.  Rails were gapped and insulated;  an impedance
bond allowed ground return around the insulated rails while keeping the signal circuit
current within the block.

'Parallel'  construction is evident in the MetroRail photo but the rails are not gapped and
insulated are they.  Please note the dual set of cables between the rails in each track
that arc through a half circle before attachment to each of the rails;  this  'suggests'  an
insulated gap in the rails which, again, is not clearly evident.  There are far more cables
between the rails than the parallel US&S impedance bond.

Also noteworthy is the large gap in the 600-volt(?) 3rd-rail.  As the cabling between the rails
of each track seems identical and the 3rd-rail is gapped on both tracks I am  'assuming'  that
such a gap in the 3rd-rail exists wherever such  'signal cables'  exist.   Is this true?  Why is
it necessary to gap the power supply at signal cabling locations?  Why aren't the running
rails gapped, or are they?  I assume each truck has a 3rd-rail shoe on each side;  it then
'seems'  that current is never disconnected from the train as the gap  'seems'  shorter than
truck spacing, or is it?  The right hand track has ties that extend further than standard
'apparently'  to accommodate 3rd-rail in the gap area;  the same may be true of the other
track but the ties could be covered by the ballast.

If someone is able to give some clarity to the computer style ATC signals circuits it will
be most appreciated.  Thank you to one and all for such efforts.



 Phil
Without  a   'coast'   but  not  a   'cause.'
--  --
"If thou wouldst rule well, thou must rule for God,
and to do that, thou must be ruled by Him ...
Those who will not be governed by God...
........will be ruled by Tyrants."
William  Penn,  founder  of  Pennsylvania





________________________________
From: "alschneider2 at juno.com" <alschneider2 at juno.com>
To: etennyson at cox.net
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Sent: Sunday, June 28, 2009 10:27:36 AM
Subject: Re: METRORAIL DISASTER-DEFFERED MAINENANCE?


FrederickNewsPost.com

Source: Metro circuits were malfunctioning for five days
Originally published June 26, 2009


By Marge Neal 
 

  

 Photo by Associated Press


Workers install new fencing Wednesday in Washington, at the site where two Metro trains crashed Monday. 
  

 
 Two track circuits in the area of Monday's deadly Metro crash alternately reported the track as vacant and then occupied almost constantly from June 17, when a part of a signaling device was replaced, until the time of the crash, according to a Metro source. 
The circuits appeared to have intermittently lost track of the trains involved in the crash of two Metro trains that killed nine people, according to Metro documents obtained by The Frederick News-Post. 
The documents show what is known as "flip-flopping," with the circuit alternately reporting the track as "occupied" and then "vacant." The report for track circuit number B2-304, where the stopped train was located, starts at 4:45 p.m. and ends at 5:38 p.m., about 40 minutes after the crash. 
Throughout the time period covered by the report, the circuit shows the track either occupied or vacant as often as every couple of seconds. 
At 4:57:03 p.m., about the time of the crash, the report shows the track to be vacant until 5:37:44, when it reports the track is occupied. Less than a minute later, the report again states the track was vacant, even though train wreckage was on the track. One second after that, the track was reportedly occupied again. The circuit flip-flopped again before finally showing the track to be occupied at 5:38:40. 
On June 17, a part of the track signaling device known as a Wee-Z Bond was replaced in the area of the crash, according to a Metro source who spoke on the condition of anonymity. The Frederick News-Post agreed to the request because of the compelling nature of the information. 
The two track circuits involved in the crash -- B2-304 and B2-312 -- share the bond that was replaced. The component feeds the receiver for one and gets the signal from the transmitter for the other. 
Both circuits continued to alternately report the track as vacant and then occupied almost constantly from June 17, when the part was replaced, to the time of the crash, according to the Metro source. 
"Without seeing the schematic drawings of the (Wee-Z Bond), I cannot say it failed or contributed to this crash," Najm Meshkati, professor of civil and environmental engineering at the University of Southern California, said Thursday. "I can say the system did not get back to its normal operating mode after the replacement was made." 
The replacement part did not perform its intended purpose, Meshkati said. The part could have been defective, or it could have needed to be recalibrated or reset to work properly, he said. 
Metro, he said, needs to take a "hard look" at its systems safety practices and philosophy. 
"It is important not to blame," he said. "It's important to find the root cause of the problem and change the safety culture of the organization." 
The Frederick News-Post has also learned that Matthew L. Matyuf, superintendent of the Automatic Train Control division, was relieved of his duties after the crash. 
"I can confirm that the ATC superintendent has been temporarily assigned to a special project," Lisa Farbstein, Metro's chief spokeswoman, said Thursday. "It happened post-incident, and I do not know what the project is." 
Wednesday night, investigators from the National Transportation Safety Board conducted tests using a similar train at the crash site, according to a press release from the agency. When the train was stopped at the same location as the stopped train that was hit, the train control system lost detection of the test train. 
Investigators are continuing to examine trackside circuits and train control system data to understand how the train control system functioned on the day of the crash, according to the release. 
Recorder data have been recovered by the struck train. The striking train did not have any onboard accident data recorders, according to NTSB. 
The operator of the striking train, Jeanice McMillan, was killed in the impact. NTSB investigators found metal-to-metal compression streak marks on both rails of the track for about 125 feet ending near the point of impact, consistent with heavy braking, the release states. 
McMillan apparently pressed a "mushroom" button to activate an emergency brake. 
The operator of the struck train was interviewed Thursday morning, according to the release. He told investigators that he operated his train in manual mode during his entire shift that afternoon. He said he had stopped to wait for a train that was stopped in front of him when his train was struck. 
NTSB said investigators will continue to document evidence at the accident scene and intend to conduct sight distance tests using trains similar to those involved in the crash.