JFS wrote:Hello John,
...
Hope that helps,
Hello Howard, I
think that helps!
If I've correctly followed the principles involved, it appears that:
1. where multiple signals read up to a signal forming part of a rotation locking scheme then each and every such signal must participate in that scheme; and
2. every movement that has the effect of removing the obstruction the rotation lock is intended to protect must likewise be controlled by a signal that will release the rotation lock, regardless of whether such movement is via the route controlled by the signal that first applied the lock or via some entirely different route.
Just to take the Hawes Junction layout as an example, what I think you are saying is that:
1. in addition to any rotation locks applied by down running line signals that read up to the Down Advanced Starting signal there needs to be a shunt signal reading over the crossover from up line(s) to down line (in this case from the Back or Branch Platform Line at HJ) and that this must share the rotational lock applied to the down running line signals; and
2. The route over the crossover from down line to up must, conversely, be signalled so as to release the rotation lock applied by any of the signals referred to in (1).
It gets more complicated than that, because at Hawes Junction there was also a trailing connection in the down line immediately in rear of the Down Advanced Starting signal that led into the engine sidings to the west of the running lines (including that famous stockaded turntable). It seems that any movement through that connection in either direction also needs to be controlled by signals participating in the rotation locking scheme on the same basis. This would mean that the ground signal that controls the movement from down line to engine sidings must release the rotation lock (because the movement authorised is one that removes the obstruction to the rotation lock is intended to protect) even though such movement is likely to be over a different route to that controlled by the signal(s) that caused the lock to be applied in the first place.
Similarly, if an engine is to move onto the down line from the engine sidings then, say, wrong road along the down line and over the crossover leading to the up side, exit from the engine roads must be controlled by a shunt signal which also participates in the rotation locking scheme.
I don't doubt that in principle rotation locking can be applied in this way, but it does appear that as soon as you have multiple connections to a running line over which rotation locking (and its releases) must be enforced then the complexity of the locking is considerably increased.
Have I got the hang of it?