Talk:Advanced signalling examples

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Why have pre-signals to be two-way?

"Pre-signal exits are signals leading away from the pre-signal block, and should normally be two-way signals, so as to give the train a choice. If they were one-way signals, the trains would all attempt to go to what they consider the "best" choice, even if there are other green signals they could go to as well. Therefore, an exit will in almost all cases have to be a two-way signal."

Sacha: I do not understand this statement. I had a station with two tracks where I used pre-signals. As long as the exit signals were on way (into the station), the trains did no choose a free track, rather they would always go for the same one. The lightening seemed to work well, but the trains were always ignoring the green light at the free track and would rather wait in front of the red light at the occupied track. I do not understand the logic behind this.

dgym: Sacha, this is a "feature" of normal signals, there are two differences between one way and two way signals. The first is obvious - trains may not go the wrong way through a one way signal. The second difference is completely non obvious but critical: when a train is presented with a fork in the tracks it determines which path would be best (shortest) for it to get to its destination, if its prefered path is governed by a one way signal then it will always choose it, and wait for the signal to change green if required. If however the prefered path is governed by a two way signal which is red, it will not choose that path (even if the alternative doesn't lead to its destination). This means that it is important to use two way signals when you want the train to choose between a number of routes that you know are viable (such as multiple platform entries), and to use one way signals when you want the train to correctly choose a route that it knows is viable (such as a fork in the tracks terminating in two very different stations). This happens regardless of any pre-signal or post-signal settings.

New graphics?

It seems that the current version of OpenTTD doesn't sport the same semaphore graphics that are presented in the pictures. What about an update?

Combo signals

Unlike pre-signals, combo signals with no exit signals always show red.

Looks like this is not true. It will be simply green (v0.4.8).

Ok, it was true for ttdpatch, but is not true any more for OpenTTD. I remove it.


I am going to merge this into Signals. I don't approve of having a separate "Advanced" article (it isn't that advanced anyway), instead favouring a nice detailed page that's ordered in such a way you can read as much or as little as you need. The tutorial takes care of the basics anyway. Anyhow, any objections, say so. Mintra 14:30, 19 October 2007 (CEST)

"Optimal pre-signaled station" exit?

Probably a silly question, I am attempting to replicate the example given here, how do I signal the exit side of such a station?

  • Just use regular one-way signals, no special setups are needed for the exit --Timitry 15:00, 3 March 2009 (UTC)
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