Tower 18 Routesetting

Incidentally, in real life, how likely are the trains to stick to the timetables? For example, if they happened to arrive on the loop two minutes early, would they just hang around at the first station, or would they keep dwell time down to a minimum? I'm inclined to expect the latter, in which case perhaps timetables should use the "set down only" option or similar to enforce this? I don't know.

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Incidentally, in real life, how likely are the trains to stick to the timetables? For example, if they happened to arrive on the loop two minutes early, would they just hang around at the first station, or would they keep dwell time down to a minimum? I'm inclined to expect the latter, in which case perhaps timetables should use the "set down only" option or similar to enforce this? I don't know.

I would imagine the latter - to clear the loop. Once out of the loop the intervals are much greater of course. I know that, like London Underground, CTA dispatchers can hold trains verbally (or by signals) to even out the interval. There was an incident report I found while researching the area of somebody impersonating CTA officials by using a two-way radio to issue "instructions". On that report they mentioned holding trains back for regulation purposes, amongst other things.

It was mentioned before but today is the first I've had a chance to look at it. Yes, it was a bug relating to approaching from Clinton. What seems to happen in real life when there is a train at Clark/Lake is that the following train will get slowed approaching "LP2 153" (the board immediately between the manual scissors and the 3-way junction) but will then accelerate and approach "LP2 151" at a low speed. Again, I don't know for sure, but I suspect it's some kind of control that broadly equates to "overlap track clear or berth occupied occupied for time". Whether there really are overlaps is questionable.

The CTA is an odd duck that makes full use of cab signals with automatic train control, but also retains wayside automatic signals in the loop area and still relies somewhat on mechanical automatic train stop.

BTW, I am having trouble locating the LP2 153 automatic in relation to the LP2 151 automatic. Green Line trains approaching Tower 18 from Clinton do not pass any autos before LP2 153. Also, I am not sure the NX panels would be set up to line routes between a controlled signals (prefixed with X) and an automatic signal (one of the LPs).

There are a couple of colour light signals not related to pointwork which aren't shown in the sim. I'm not sure what their purpose is.

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BTW, I am having trouble locating the LP2 153 automatic in relation to the LP2 151 automatic. Green Line trains approaching Tower 18 from Clinton do not pass any autos before LP2 153. Also, I am not sure the NX panels would be set up to line routes between a controlled signals (prefixed with X) and an automatic signal (one of the LPs).

"LP2 153" should actually be "LP2 154" (thanks to the hidef videos released while I was developing this) and can be seen here.

Where would you route to on an NX panel if not an exit "signal" or notional exit point?

Cheers.

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There are a couple of colour light signals not related to pointwork which aren't shown in the sim. I'm not sure what their purpose is.

Those are automatic block signals that are seen at various points around the loop and in the downtown subways. I suspect they exist as a method to enable higher levels of traffic density where cab signals require too much space. Consider the LP1 151 automatic. There is only one train length between it and Tower 18's home signal. Under pure cabs a train approaching from behind would likely be stopped partway down the platform at Clark/Lake due to signal overlap in case the cab code takes longer to register.

If you remember this incident, each of the stub tracks at O'hare have been filled with lines with automatic signals on timers with trip stops.

The only LP signal Pink and Green lines pass near Tower 18 is LP2 151 at 24:57.

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Where would you route to on an NX panel if not an exit "signal" or notional exit point?

You would run it to signal governing opposing movements into the interlocking.

North American interlockings have well defined limits compared to UK interlockings, which are rather losey goosey.

BTW I have a number of Tower 18 interlocking photos here. Just scroll down to files beginning with CTA_TOWER-18.

Not really: I don't recall the location of them all without watching again, and there are only something like 2-4 for the entire loop area. I do recall one anti-clockwise/LP1/outer leaving Randolph/Wabash immediately before the curve. There is still a yellow LP1 plate (133 I think). My first thought was visibility around the curve but then there are cab signals so why would that be needed. Spacing isn't an issue there - you want to space signals closer (or blocks shorter) closer to the pinch points - in this case Tower 18 for example.

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The only LP signal Pink and Green lines pass near Tower 18 is LP2 151 at 24:57.

Did you see the video I posted?

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Where would you route to on an NX panel if not an exit "signal" or notional exit point?

You would run it to signal governing opposing movements into the interlocking.

Okay, that makes sense. There are a small number of cases like that in the UK - well, more so on NX panels rather than NX VDUs, though there are some.

You have to understand the difference between a North American interlocking and a UK interlocking. Of course a UK interlocking has very strictly defined limits and these are marked on scheme drawings and signaller panels. But drivers in the UK have no need to know where an interlocking boundary is as there are no rules specific to such for drivers. Engineers in the US/CA do have specific rules governing interlockings, hence the need to make it easy to know when you're entering an interlocking and exiting same.

On the same basis, UK interlockings cover a wide or complex area (rarely both!); the most common NA interlocking is probably that of three signals, a switch, an "OS" track, and three approach "tracks" (which are more likely combinations of several approach tracks).

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BTW I have a number of Tower 18 interlocking photos here. Just scroll down to files beginning with CTA_TOWER-18.

Thanks - was hoping for close ups of the panel but the video linked to in the manual is about as close as I've seen.

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The only LP signal Pink and Green lines pass near Tower 18 is LP2 151 at 24:57.

Did you see the video I posted?

I do not believe that UK interlockings require signals at every entry-exit point, something that most NA interlockings do.

but recently railroads have been chopping them up in smaller logical chunks to reduce the re-testing burden if changes need to be made.

Using the Pink line southbound this is the sequence of signals/block markers you pass:
X116 (protecting the diamonds)
[cross the diamonds]
LP2 154 (back-to-back with X108)
Scissors crossover
LP2 151
Start of Clark/Lake platform
LP2 150
End of Clark/Lake platform

Correct - because there is no notion for a UK driver to be in a particular interlocking. You can pass through an interlocking without passing a single signal, and conversely can pass a score of signals in the same interlocking. It all depends.

But, again, it's not like we're comparing apples and apples here. The US doesn't have many stations that would not fit into a single SSI - New York Penn, Grand Central, Newark NJ, Chicago Union (to a degree - it's logically quite a simple layout despite looking large), and Los Angeles UPT are the only ones that come to mind. Hoboken and Jamaica possibly.

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Correct - because there is no notion for a UK driver to be in a particular interlocking. You can pass through an interlocking without passing a single signal, and conversely can pass a score of signals in the same interlocking. It all depends.

That is such a strange system to have developed. Probably something to do with your reliance on manual block. Under old North American manual block rules you would sometimes have ABS block stations with crossovers and semi-automatic signals in the "correct" direction of travel only. Trains running reverse would stop before fouling the crossovers.

That is such a strange system to have developed. Probably something to do with your reliance on manual block. Under old North American manual block rules you would sometimes have ABS block stations with crossovers and semi-automatic signals in the "correct" direction of travel only. Trains running reverse would stop before fouling the crossovers.

Oh, I see. It's not one with a wayside signal attached to it.

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Correct - because there is no notion for a UK driver to be in a particular interlocking. You can pass through an interlocking without passing a single signal, and conversely can pass a score of signals in the same interlocking. It all depends.

That is such a strange system to have developed. Probably something to do with your reliance on manual block. Under old North American manual block rules you would sometimes have ABS block stations with crossovers and semi-automatic signals in the "correct" direction of travel only. Trains running reverse would stop before fouling the crossovers.

All of our interlockings can be sold or transfered to different railroads. Also I have never known a situation where the vital logic wasn't in the field adjacent to the track. True area interlocking is almost unheard of.

Well no, precious few of them do!

It's certainly not strange to us, and also nothing to do with manual block - in fact, manual block would be closer to the US definition of an interlocking. Mind you... define "manual block" as there is a possibility you're talking about something else.

They used to be (remote relay rooms) but with electronic interlockings there is no need. Indeed, surely it would be better to have the interlocking close at hand in case it needs a bit of TLC instead of driving 50 miles or more? Another difference: the link between signallers and their signals, tracks, and points is safety critical (vital) in the UK; in the US many such controls and indications are sent over the airwaves, and AIUI indications cannot be relied upon.

(A couple of months ago I used a hand held scanner to "listen" to the over-the-air transmissions while on a train between Seattle and Chicago. While it couldn't see far in front, there was usually enough signal to determine when we would pass another train. Fun and legal)

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It's certainly not strange to us, and also nothing to do with manual block - in fact, manual block would be closer to the US definition of an interlocking. Mind you... define "manual block" as there is a possibility you're talking about something else.

Admission of train to a block via a manually operated signal with procedural control for train spacing.

I've been trying to drill down to why the signaling in the US and many other places was so divergent.

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They used to be (remote relay rooms) but with electronic interlockings there is no need. Indeed, surely it would be better to have the interlocking close at hand in case it needs a bit of TLC instead of driving 50 miles or more? Another difference: the link between signallers and their signals, tracks, and points is safety critical (vital) in the UK; in the US many such controls and indications are sent over the airwaves, and AIUI indications cannot be relied upon.

Have fun when the Russians or Chinese get into your tubes and start crashing trains.

Information security aside, just maintaining vital communications links (and debugging it) is a major pain, especially if you need them to be reliable.

I think there are also regulatory requirements that prevent the sort of remote logic you folks seem to be going nuts for.

For example any change to any part of the SSI software would require EVERY part of the entire SSI territory to be re-tested and certified as well.

All that aside just not being tied to a single large central logic center means that interlockings can be transferred and upgraded as atomic units and no single event can wipe out the entire system.

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(A couple of months ago I used a hand held scanner to "listen" to the over-the-air transmissions while on a train between Seattle and Chicago. While it couldn't see far in front, there was usually enough signal to determine when we would pass another train. Fun and legal)

I don't get the concern about open channel communications in the UK. Here having the train crew be able to hear everything is going on leads to better situational awareness. Many accidents have been prevented thanks to one crew hearing something odd on the radio.

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It's certainly not strange to us, and also nothing to do with manual block - in fact, manual block would be closer to the US definition of an interlocking. Mind you... define "manual block" as there is a possibility you're talking about something else.

Admission of train to a block via a manually operated signal with procedural control for train spacing.

Ok, when the word "manual" is used it implies old fashioned lever frame boxes. In that case, I'm not sure what your comment means as the US and UK both have forms of automatic signals and manual/controlled signals.

Of course there is one disadvantage to having large complicated interlockings like we do:

http://www.raib.gov.uk/cms_resources/101223-SI2010-MiltonKeynes.pdf

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It's certainly not strange to us, and also nothing to do with manual block - in fact, manual block would be closer to the US definition of an interlocking. Mind you... define "manual block" as there is a possibility you're talking about something else.

Admission of train to a block via a manually operated signal with procedural control for train spacing.

Ok, when the word "manual" is used it implies old fashioned lever frame boxes. In that case, I'm not sure what your comment means as the US and UK both have forms of automatic signals and manual/controlled signals.

I think the keyword there is "procedural", ie absolute block (where correct procedure ensures safety, at least traditionally) as opposed to track circuit block (where actual train detection ensures safety). I might be wrong though.

Ok, when the word "manual" is used it implies old fashioned lever frame boxes. In that case, I'm not sure what your comment means as the US and UK both have forms of automatic signals and manual/controlled signals.

FIFY Railways around the world evolved at different rates with different rules and different requirements. Each suits its own purpose.

You've clearly been watching too many movies. :doh The links to the trackside are extremely simple and no part of the interlocking, control equipment, or trackside is connected to the Internet. Or Bluetooth. Or NFC. I doubt one could even write a virus to fit inside an SSI's memory, it is that small.

And this is exactly why it is so simple. The more complicated you make something, the more effort it takes to debug it, and the more that can go wrong.

The "nuts" to which you refer is what we call "safety". Yes, it is a requirement that the signallers see exactly what is going on. For the US, it's different and is not vital. It's different, that's all.

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For example any change to any part of the SSI software would require EVERY part of the entire SSI territory to be re-tested and certified as well.

Not true.

All that aside just not being tied to a single large central logic center means that interlockings can be transferred and upgraded as atomic units and no single event can wipe out the entire system.

Transferred to where though? No two interlockings are alike. The hardware can be transferred elsewhere, just as equipment from different manufacturers is supposed to work together.

Upgrade? This isn't Windows with the latest fancy gizmos!

As for wiping out the entire system, I fail to see any benefit in remotely locating the interlockings.

A couple of years ago I was in a Norfolk Southern dispatch center and they were talking about the ability to transfer control to another dispatch center - but it was pointless because nobody in the other centers was trained on this center's areas. Too expensive to maintain competency elsewhere. And another example, several years ago, a lightening strike in Jacksonville, Florida, caused severe delays to commuters 1,000 miles away in sunny Chicago. Remote (trackside) interlockings in both cases, but as much use as a chocolate teapot if there's nobody to control them.

Again, it's a requirement that signallers know exactly who they're talking to, at an absolute location: safety. That way accidents are avoided by only the desired recipient receiving what could be safety critical communication.