Why would you ever want to use a one-way path signal?

[jez]

I'm not understanding something when it comes to path signals.

pathSignal.png (87.83 KiB) Viewed 2459 times

I'm sure this has been explained somewhere but I was unable to really understand this in all the stuff I read. Why do you ever need to use a one-way path signal? The explanation I've read is that "a path signal can be entered from behind whereas a one-way path signal can't". However, the path finder preferences heading for path signals that face the train, so why is this an issue? The path finder will never let a train move if it could crash. Nevertheless, I tried to (artificially) create a scenario where a train might go in an undesirable direction without a one-way path signal (see screenshot) and even then, I couldn't actually cause it to do so.

Train 4 is waiting at the station and has a free path to go where it wants to go. It can reach the track going northeast if it crosses the regular path signal facing away from it, and it must do this because I've stopped the other train on the track. But it doesn't. It still stays at the station saying "waiting for free path", so it refuses to cross the back of a path signal that is NOT one-way. If I flip the direction of the path signal, the train starts going on the indicated path.

So, firstly, why is the train not entering the back of this path signal given that it's not one-way, and secondly, why would you ever need to use a one-way path signal?

[skc]

The path-finder penality for going through the back of a path signal is quite high, so that's why the train is waiting to cross to the right-hand (and blocked) track, before swinging to the left and heading to the top-right of your image.

As for regular vs. one-way path signals: you COULD place signals at between the end of the platforms and the cross-overs, you would have to use regular path signals.
One setting, relating to trains reversing a signals if they've waited a long time, which I think defaults to "don't reverse", will have different results for regular path signals vs. one-way path signals.

[jez]

OK but it still doesn't explain why, in practice, you'd ever need to use one-way path signals. I mean, in what scenario would you need to use them?

[Redirect Left]

OK but it still doesn't explain why, in practice, you'd ever need to use one-way path signals. I mean, in what scenario would you need to use them?

I personally use them in situations like this, where i'd like a station to be both a terminus, but also a thru depending on route, but I'd also like to control the flow, and only allow X paths access to a specific platform. So in this setup, trains coming upwards cannot use the last platform. This ensures a nice flow of traffic and makes sure one direction doesn't get entirely stalled by a rush from the other direction, there's always one platform guaranteed in use for the other side. It also allows for on-the-fly changing of restrictions, given the track is pre-laid and i can just tweak as necessary if i greatly increase or decrease flow of traffic going thru, or terminating from one side.

[Eddi]

the backward penalty usually takes care of most things, but in some cases you need to force the "no entry" to prevent deadlocks and stuff

[Transportman]

OK but it still doesn't explain why, in practice, you'd ever need to use one-way path signals. I mean, in what scenario would you need to use them?

It is useful to prevent trains from going a direction they should not go even if they become lost or if your network is missing a piece of track somewhere. A lost train will still respect the fact that it should not drive through the back of a one-way path signal so it will not go somewhere it would get stuck or block large parts of the network, but for trains not lost the penalties of driving through the back of two way signals is large enough to prevent it in most cases (only for stretches with a small number of signals the penalty might not be sufficient). So they are basically the safe option that works in 99% of the cases for beginners, for the remaining 1% there are other signals.

[sheenanelson]

OK but it still doesn't explain why, in practice, you'd ever need to use one-way path signals. I mean, in what scenario would you need to use them?

It is useful to prevent trains from going a direction they should not go even if they become lost or if your network is missing a piece of track somewhere. A lost train will still respect the fact that it should not drive through the back of a one-way path signal so it will not go somewhere it would get stuck or block large parts of the network, but for trains not lost the penalties of driving through the back of two way signals is large enough to prevent it in most cases (only for stretches with a small number of signals the penalty might not be sufficient). So they are basically the safe option that works in 99% of the cases for beginners, for the remaining 1% there are other signals.

hello,
so for cases where the penalty is not sufficient, what are we supposed to do?

[numbat]

Train 4 is waiting at the station and has a free path to go where it wants to go. It can reach the track going northeast if it crosses the regular path signal facing away from it, and it must do this because I've stopped the other train on the track. But it doesn't. It still stays at the station saying "waiting for free path", so it refuses to cross the back of a path signal that is NOT one-way. If I flip the direction of the path signal, the train starts going on the indicated path.

I can't quite see the signals on the entrance lines, but I believe Train 4 is not moving because the block immediately outside the station (that contains the cross over) is currently occupied by your stopped train. regardless of what type of signal you have facing away from it, the implied signal at the exit of the station is stopping it.

Unless I'm mistaken, without a one-way signal, train 4 has two exit routes, one being the green path you highlighted, the other by taking the crossover to the line to the south of that green path (assuming the other train isn't there). If you wanted to force it to always use the green path, then you can put a one-way signal on the other line.

Cheers,
Chris.

[Transportman]

OK but it still doesn't explain why, in practice, you'd ever need to use one-way path signals. I mean, in what scenario would you need to use them?

It is useful to prevent trains from going a direction they should not go even if they become lost or if your network is missing a piece of track somewhere. A lost train will still respect the fact that it should not drive through the back of a one-way path signal so it will not go somewhere it would get stuck or block large parts of the network, but for trains not lost the penalties of driving through the back of two way signals is large enough to prevent it in most cases (only for stretches with a small number of signals the penalty might not be sufficient). So they are basically the safe option that works in 99% of the cases for beginners, for the remaining 1% there are other signals.

hello,
so for cases where the penalty is not sufficient, what are we supposed to do?

Force the direction with a one way signal or add more signals to increase the penalty, depending on requirements. Most often, it will be a one way signal as longer stretches of track really should be just one way to prevent long waits and possibly gridlocks.

[Emperor Jake]

95% of signals should be one way path signals. Two way path signals are only needed at bidirectional station platforms, as well as certain middle track or single track configurations.

[Eddi]

why always talk in these absolutes? might as well be: 5% of signals need to be one way, 5% need to be two way, and the other 90% can be either, doesn't matter.

[Emperor Jake]

It's an approximate guideline, it'll vary considerably depending on your network configuration and station density etc

[mak]

Personally I only use path signal (both way) unless I need a train to not go the wrong way and possibly cause a blockage.
i.e. double track(s) one in one out