planemad
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Tcas In Trains

Sat Jan 29, 2005 7:00 am

Does a similar system like TCAS in aircraft exist in trains?

Sam D.
 
ANCFlyer
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RE: Tcas In Trains

Sat Jan 29, 2005 10:07 am

Yes . . . Alaska Railroad has something very similar . . . using GPS each train knows where the other is, and so does dispatch. Dispatch can also stop a train via remote control . . .
FOR THOSE THAT FOUGHT FOR IT, FREEDOM HAS A FLAVOR THE PROTECTED WILL NEVER KNOW OR UNDERSTAND
 
57AZ
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Automatic Train Stop Systems...

Sat Jan 29, 2005 11:39 am

However, very few railroads can justify the additional equipment and upkeep. What ANCFlyer is referring to is technically called Automatic Train Stop. ATS was required by the Interstate Commerce Commission for railroads to operate high speed trains at 80+mph. Most railroads avoided the unnecessary expense by limiting their trains to 79 mph. ATS until recently was limited to trackside activation using trip arms located at wayside signals. One drawback to this method of activation was that some of the systems could be circumvented, particularly on subway systems. In the case of the California train wreck, something like the ATS system that ANCFlyer mentioned probably wouldn't have made a difference-just my personal observation colored with a decade of field experiance.
"When a man runs on railroads over half of his lifetime he is fit for nothing else-and at times he don't know that."
 
dc10tim
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RE: Tcas In Trains

Sat Jan 29, 2005 11:52 am

Sam,

Loooooooooooooong story, so I wont bother you with it all. Basically, after the Clapham crash in '88, Automatic Train Protection (ATP) was delevoped in the UK, which was never fully implemented here, although it was in other countries. This stops trains going through red signals. This could have prevented several major accidents since but there you go....... When Labour came to power in '97, they promised TPWS (Train Protection and Warning System), which is only effective up to 75mph. This wouldn't have stopped most of the accidents that have happened (Ladbrooke Grove etc.) so basically a waste of money.

Tim.
Obviously missing something....
 
57AZ
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Railroad Operations

Sat Jan 29, 2005 2:20 pm

Also, consider the fact that a red signal does not always mean stop. Many railroads have signals that utilize a red signal aspect that means either proceed at restricted speed or stop and proceed. These signals display a red light with a number plate mounted below the lamp. Also, under certain circumstances a dispatcher or interlocking operator may authorize a train to pass a signal displaying a stop indication. Railroad signaling and operations are a lot more complex than the average layperson realizes.
"When a man runs on railroads over half of his lifetime he is fit for nothing else-and at times he don't know that."
 
dc10tim
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RE: Tcas In Trains

Sat Jan 29, 2005 8:02 pm

57AZ,

We must use a different system over here. Everything has to stop at a red signal. Basically there are four main signal displays, green, two yellows, yellow and red. Proceeding at a restricted speed as you mentioned would be shown by a single yellow light. Two yellows indicate it is ok to pass, but the next signal is set at yellow, indicating a speed restriction ahead.

TPWS, as I described above, only comes into effect when a train passes a red signal. This means a train can speed pass a signal set on red at 75mph before the braking comes into effect. Imagine how long it will take to stop a 3-4 thousand ton freighter at that speed. It's basically a cheapo option. ATP on the other hand is far more complex. It governs the speed of the train in ordinary operation and will slow the train down before any red or yellow signals.

Tim.
Obviously missing something....
 
TGV
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RE: Tcas In Trains

Sat Jan 29, 2005 9:53 pm

In France we use the system described by 57AZ on main lines (except high speed line where there is a cab-signalling system with continuous monitoring of the speed).
So double red is stop and wait, single red stop and proceed (run at sigh), yellow, the next signal has a stop indication, green is normal speed.
Plus a lot of other indications (blinking green, blinking yellow, blinking red, two yellow on horizontal or vertical lines, these two blinking, white, purple… as mentioned Railways signalling is complex).

An ATP system has been implemented sin the middle of the eighties in France.
Basically it is a computer on board the train that reads beacons located on the track, and which can send variable information depending on the status of the following signals, and fixed information regarding the track gradient until the signal.
The computer then calculates the breaking curve that should be respected by the driver to safely stop at the signal, taking into account the braking characteristics of its train. If the driver stays below the curve, nothing happens. If not the systems takes over and triggers an automatic braking.

Similar ATP systems exist in most of European countries (unfortunately for UK these systems appeared when the conservative governments had decided not to invest in the railways).

While ATP systems are efficient to avoid passing signals at danger, this will not help in case of any obstacle on the track (being on a level crossing), if signals are opened.
Tests have been made for obstacle detection on level crossings, but the reliability was not deemed satisfactory. Furthermore this implied to have a longer closing time for the level crossing (because the detection should be made when the train is at a sufficient distance from the level crossing to stop).

A European common signaling system has been developed, and is now in its first phase of implementation in various countries. It is based on interoperable beacons and on-board systems, with normalized MMI (man Machine Interface) on board the trains. And it goes with a common communications system for railways, GSM-R, derived from the general GSM system.
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57AZ
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RE: Tcas In Trains

Sun Jan 30, 2005 5:07 am

As TGV pointed out, there are limitations to what signalling systems can protect. Basically, they cannot protect trains from obstacles or damage to the track structure if the signal circuit is unbroken. One example is the Bayou Canot accident involving the Sunset Limited. Even though the barge knocked the bridge out of alignment, it did not break the rails which would have caused the Automatic Block Signal to change from a green "proceed" indication to a red "stop" indication.

There are a couple of situations where signal systems can be designed to take other factors into affect before allowing a train to pass. The most common is the slide detector, used in mountaineous areas where there is a danger of rockslides. This consists of an electric fence erected along the right of way, which is connected to the Automatic Block Signal system. If the fence should be damaged during a slide, the broken circuit will cause the signal to display the most restrictive indication-either a "restricting" or "stop" indication, depending on the signal. Signal systems can also be used to stop trains from crossing bridges over large bodies of water if the wind speed detected is higher than the maximum safe wind speed allowed. The Florida East Coast Railway used such a system on their bridges on the Key West Extension as some of these bridges were over a mile in length. If the wind speed on any section of a bridge exceeded 40 mph, the block signal at the end of the train would prevent the train from going on to the bridge.

There are significant differences in the US and British signal systems. UK systems are route signalling whereas the US uses speed signalling. Also, signal indications differ from railroad to railroad. On the Norfolk Southern, there were four different signal aspects that are used for "restricting," depending on what part of the railroad you are on due to the mergers. On the Southern Railway divisions, a restricting signal could either be an amber aspect on a low (dwarf) signal, a red over amber indication on a mast/bridge signal or a red indication on a mast/bridge signal with a number plate below the signal head. Even with automatic protection, if the crossing involved were just beyond the end of the signal block, it would not prevent a collision between a train and an obstruction.
"When a man runs on railroads over half of his lifetime he is fit for nothing else-and at times he don't know that."
 
trident3
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RE: Tcas In Trains

Sun Jan 30, 2005 7:24 am

"This wouldn't have stopped most of the accidents that have happened (Ladbrooke Grove etc.) so basically a waste of money."
Surely it would have prevented Ladbrooke Grove, which was caused by a commuter train going through a red light. It would not have prevented Potters Bar or Hatfield which were both caused bytrack defects.
"We are the warrior race-Tough men in the toughest sport." Brian Noble, Head Coach, Great Britain Rugby League.
 
dc10tim
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RE: Tcas In Trains

Sun Jan 30, 2005 10:19 am

Hello Trident3,

As has been said earlier, it's a bit complicated. Ladbrooke Grove was probably a bad example. Southall would have been a better example, where a freight train was crossing the 'fast' lines ahead of an oncoming train. The thing with TPWS, as I understand it, is that at crawling pace it is ineffective too, as it assumes the driver has control. The HST that ploughed into it was traveling at over 100mph, so it would have been useless there too. The irony is that after the Clapham crash the Great Western line out of Paddington was the only line to which ATP was fitted, as a pilot scheme. It had been inactivated in the loco that was hauling the train on that day however, so it could have been avoided altogether. This is because the track circuits would have been 'activated' when the Thames train passed onto the main line and the system recognise that the section was already occupied.

Tim.
Obviously missing something....

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