Please pardon me for digressing again, this time on pre-signal and standard signal, for I have related observations to share.
First of all, the
wiki says that "stations act as 'de-facto' signal points". This is not true in general, as only stations registered on a passing train's schedule behave like a signal point. This concept has already been illustrated by Frank in
this thread. The related pitfall can be made clear with an example. Assuming the following set-up with trains running from left to right :
++++++++S++++++++X++++++++++++Y++++++++++++++++Z++++++++S++++++++>>
Originally you have a line with a few trains passing through this track section, stopping at all stations
X,
Y and
Z. Later, you have a new line that reuses the same track portion but its trains don't stop at any of the stations
X,
Y and
Z. The result is, the new line's trains will wait at the 1st
S for a relatively
long time if the track between the 1st
S and the 2nd
S is not clear of any train; and once the track is clear and they can start moving, they will reserve a
lengthy track portion from where they are up to the 2nd
S.
However, that is not the complete picture either. I would like to point out further that, actually
all stops on a passing train's schedule will behave like a signal point -- whether the stop is a station or just a way point.
As an illustration for pre-signal, let's assume the following set-up :
++++++++P++++++++W+++++++S++++++++S++++++++>>
2 trains are running consecutively from left to right, one closely following the other.
W here means a way point on the
2nd train's schedule.
P is a pre-signal and
S is a standard signal. When the 1st train drives past
P, the 2nd train stops and waits at
P; but since
W behaves like a signal point, the 2nd train will start to move once the 1st train has driven past the
first S.
Similarly, as an illustration for standard signal, let's assume the following set-up :
++++++++S++++++++W+++++++S++++++++S++++++++>>
Again, 2 trains are running consecutively from left to right, one closely following the other. This time, the 2nd train which has been blocked at the 1st
S will start moving once the 1st train has driven past
W.
IMHO, it is really quite ridiculous that way points also behave like a signal point and affects the behaviour of real signals. Besides, if stations are intended to be de facto signal points, they should be consistently so under all cirumstances, except of course in the case of long block signal.
As you can see, the behaviour of all 4 signals depends on the passing train's schedule, and all of them will potentially exhibit irregular or inconsistent behaviour as trains with different schedules pass through them. The down side is, one has to be clear how the schedule of
each line or train interacts with
each signal along the track to decide if things work out as intended; otherwise, pitfalls can easily be overlooked. If you are not careful enough, you can accidentally let a train wait for an unnecessarily long time or reserve an unnecessarily long portion of track, potentially increasing the likelihood of deadlocks.
Again, I would say that it will be better if all signals' behaviour is dependent only on track layout and respective signal placement. Anyway, all we can do now is to watch out for the pitfalls and be careful in using the signals.
@emaxectranspoorte : If a railway system is complex, it is quite likely that there will be a few trains with different schedules running on the same track section. In that case, the inconsistent behaviour of the signals will more likely than not make your system difficult to manage.
Another small observation :
If you place a choose signal or pre-signal
after a standard signal and have a train X running between the 2 signals, when another train Y arrives at the standard signal, the standard signal cannot block this second train from proceeding as it usually does. This is the same as with long block signal mentioned before.
+++++++Y+S++++++X+++++++C/P++++++++++++>>
