Merging T Junction

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Merging T Junction

Postby Zanthra » Tue Nov 28, 2017 11:45 am

I am not in general a big fan of the standard T junction for dual track train systems, it always seemed cramped and complicated, so I decided to develop an alternative. In this design the side tracks are merged together into a bidirectional single rail, before merging onto the closer of the through rails. It then allows the train to shuffle down onto the other rail if it is on the wrong side of the tracks. Due to the short time the train spends in the intersection, a minimal number of signals are necessary for good performance, but some optional signals can be used to improve things further. This is probably not something new, but I have not seen it before, and some others might be interested in it.

From the advice below and testing with chain signals i fixed the signaling issue on trains leaving to head westward, and also removed the Y split from bidirectional single rail to a dual rail system to the north, as I am using this mostly to serve turnaround stations off the main rail line (each station has staging spaces for all the trains it serves, so trains can never back up to block the rails).

T-Intersection Update3.jpg
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Last edited by Zanthra on Fri Dec 08, 2017 5:13 am, edited 5 times in total.
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Re: Merging T Junction

Postby Lav » Tue Nov 28, 2017 12:05 pm

The only important difference I see is when a train is coming from east turning to the north, with another train coming from the north and turning in either direction. Regular junction would let them pass through independently, whereas in your setup one of the trains will have to wait.

On the other hand you're saving on rails, signals and a tiny bit of space.

It's not a worthy bargain IMHO. But then maybe you're extremely short on stone... :-D
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Re: Merging T Junction

Postby mrvn » Tue Nov 28, 2017 1:40 pm

The full signal between the two main tracks allow a train to enter the T-junction even when it can not leave it because the bottom track is full.
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Re: Merging T Junction

Postby Zanthra » Tue Nov 28, 2017 7:04 pm

Mostly I like it from an aesthetics perspective. The direct cross of the normal T-Junction I feel is not particularly pleasing. Another thing is I can have a bidirectional single rail offshoots off the main trunk lines connected with this as well by simply not splitting the side tracks after the T-Junction.

mrvn wrote:The full signal between the two main tracks allow a train to enter the T-junction even when it can not leave it because the bottom track is full.


Even if a train from the right stops on the bottom track, it won't block the opposite track since it's separated by the standard and chain signals on the shift lines. No need to worry about clearing the intersection on the bottom rail since they both have to take turns on the next block to the left anyways, at least this way a train can clear the shift so a train behind it can turn north. The rightmost signal on the bottom track could be a standard signal as well now that I think about it.

If you are referring to a train entering the main line from the side track, chain signals force a train to reserve an entire trains length past the next standard signal before they can pass, so the upper track will be cleared if a train from the side track enters the T Junction. Any train longer than a single locomotive will have to reserve both of the standard signals (the one on the shift line and the one on the exit) before it can enter the T-Junction to turn to the west.

Nevermind the previous, I was mistaken about chain signals in this regard; they only reserve enough to slightly cross the next standard signal, not clear it. You are correct, a chain signal is needed on the leftmost shift track to prevent a train from potentially blocking the opposing lane. I need to rethink a lot of the train stuff I have built, since I always assumed that any train passing a chain signal would always clear the block the chain signal covers. Thanks.
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Re: Merging T Junction

Postby mrvn » Tue Nov 28, 2017 11:40 pm

Zanthra wrote:Mostly I like it from an aesthetics perspective. The direct cross of the normal T-Junction I feel is not particularly pleasing. Another thing is I can have a bidirectional single rail offshoots off the main trunk lines connected with this as well by simply not splitting the side tracks after the T-Junction.

mrvn wrote:The full signal between the two main tracks allow a train to enter the T-junction even when it can not leave it because the bottom track is full.


Even if a train from the right stops on the bottom track, it won't block the opposite track since it's separated by the standard and chain signals on the shift lines. No need to worry about clearing the intersection on the bottom rail since they both have to take turns on the next block to the left anyways, at least this way a train can clear the shift so a train behind it can turn north. The rightmost signal on the bottom track could be a standard signal as well now that I think about it.

If you are referring to a train entering the main line from the side track, chain signals force a train to reserve an entire trains length past the next standard signal before they can pass, so the upper track will be cleared if a train from the side track enters the T Junction. Any train longer than a single locomotive will have to reserve both of the standard signals (the one on the shift line and the one on the exit) before it can enter the T-Junction to turn to the west.

Nevermind the previous, I was mistaken about chain signals in this regard; they only reserve enough to slightly cross the next standard signal, not clear it. You are correct, a chain signal is needed on the leftmost shift track to prevent a train from potentially blocking the opposing lane. I need to rethink a lot of the train stuff I have built, since I always assumed that any train passing a chain signal would always clear the block the chain signal covers. Thanks.


And the problem is a train coming from the north blocking the upper W-E track.
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Re: Merging T Junction

Postby Zanthra » Wed Dec 06, 2017 9:05 pm

I updated the image above to have the proper chain signal placement. I also removed the Y split to dual tracks to the north, as that can be used as a matter of course from bidiretional single rails, and I find I am not using that much and mostly sending the single rail to turnaround stations off the main line.
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Re: Merging T Junction

Postby mrvn » Thu Dec 07, 2017 12:28 pm

On the south most track you have 4 normal signals. You should only have a normal signal if a full train fits after that signal. Otherwise a chain signal before that will possibly not work right. So assuming short trains it should be chain - normal - chain - normal. This would also mean the trains on the main track no longer take precedence over the bidirectional track.

And for the bidirectional track there should be a full signal before the crossing. A train coming from the north will have to reserve all the chain signals along the bidirectional track, including those crossing the main tracks. If your outpost/train station is some distance from the main tracks then that could leave them blocked for quite a while without reason.

If you add a full signal at the end of the bidirectional track then a train can leave the station and cover the bidirectional track before it has to reserve the t-junction.
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Re: Merging T Junction

Postby Zanthra » Thu Dec 07, 2017 7:18 pm

mrvn wrote:On the south most track you have 4 normal signals. You should only have a normal signal if a full train fits after that signal. Otherwise a chain signal before that will possibly not work right. So assuming short trains it should be chain - normal - chain - normal. This would also mean the trains on the main track no longer take precedence over the bidirectional track.

And for the bidirectional track there should be a full signal before the crossing. A train coming from the north will have to reserve all the chain signals along the bidirectional track, including those crossing the main tracks. If your outpost/train station is some distance from the main tracks then that could leave them blocked for quite a while without reason.

If you add a full signal at the end of the bidirectional track then a train can leave the station and cover the bidirectional track before it has to reserve the t-junction.


Thanks for looking over these and providing advice I appreciate it. I changed the bottom rail signals to Chain - Normal - Chain - Normal, although Chain - Normal - Normal - Normal should work fine too. I also added the normal signal leading to the T-Intersection. It took me a while to realize that won't cause any problems. For long bidirectional rails occasional passing lines are generally recommended to avoid contention as well. As for train length, I use 1-2 trains that just fit in stations built like this since they are just so easy to build keeping with the rule that every train station must have a place to park every train that it serves (an extra signal on the turnaround would let it park a fourth train too).
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