(19-07-2010, 10:56 PM)interesting_signal Wrote: Another issue I'm unsure of is the shunting/reversing of passenger trains. Should my signal 1004 be a main signal (for the purpose of shunting/reversing passenger trains) or is a PL acceptable? Then would 1003 LOS need to be a fixed red too?
To modern standards any signal that authorises a right-away running aspect for a train should be a main signal; in the past the railway economised by only providing a GPL (or exceptionally an elevated PL) as the exit signal from goods sidings if there was not a large number of train movements (e.g. typically under a dozen per week).
Your question particularly asked re provision of routes for the moving of passenger trains around the layout. Where a main running move exists to route the train in the right direction, then this suffices and no specific shunting route is provided; i.e. there is no need nowadays to provide a PL aspect on a platform starter to inform the driver that they are required to travel only sufficient distance to clear a set of points and get behind a GPL in order to be routed back towards the station into a different platform. The driver is expected to know the move they are going to make and not continue as far as the main route actually gives authority; this is a change from earlier times when there was far less possibility of verbal communication between driver and signaller and hence specific signals were provided so that there was no possible ambiguity re the intended move.
If however there is a need for such a movement to be made where there is no such running move already provided, then the route is provided as a shunt route and therefore display a PL aspect. In many cases therefore, such routes are provided along a running line in the opposite direction for which it is signalled and therefore will be limited by a LOS. Do remember that wherever there is a LOS there will be a move up to it and that this constitutes an opposing move conflicting with the normal running moves along that line; hence any such signal must be a controlled signal rather than an Automatic.
Your specific query related to signal 1004- to be honest I can't see that number but assume that it must be the one at the other end of the Up Platform at station D to 128. A GPL is exactly what you should have here and similarly 1003 is also correct as a LOS. Providing as main signals would just be more expensive and potentially give more potential miseading problems to confuse drivers on the Down Main. Hence you got this correct.
PJW