The rulebook states you must not depart a train in passenger service from the authority of a shunt signal (note a Permissive aspect on main signal is not considered a shunt signal) without published permission or if the Signaller instructs the driver to do so.
This is because a shunt signal does not prove the line is clear to the next signal and overlap, nor does it require the points to be fitted with FPLs. A shunt route may have a shorter overlap than normal or no overlap at all. A main aspect route must be clear through to the overlap and all points locked before it will show proceed, and a permissive aspect will prove the points are locked, and that only the expected section(s) of route are occupied before displaying proceed (I think, not a signalling engineer!).
It's more complex. I'll split the subject up, as that makes it easier to explain.
Starting with the simpler(-ish) parts:
If the facing points are power operated and have a FPL, it doesn't matter which aspect / signal / route is used, the FPL will be used. So that will apply for main aspects and for shunt signals.
However, if the route is not the same as that available from a main signal aspect, in other words it diverges from a main signal aspect route, the facing points in this route may not have been fitted with a FPL. As there was no requirement in the past for points only used for freight/goods, empty stock or light engine trains / moves to have FPLs fitted.
Of course, the railway (BR in fact, before privatisation) moved the goalposts and decided that all new power operated points would have FPLs fitted as standard regardless. And if the machine was renewed, the new machine would be provided with a FPL. In addition, in some areas, on some lines, FPLs were fitted to existing point machines. Hence some lines/points used for freight/goods, empty stock or light engine trains are FPL fitted.
Note that often ground frame mechanical operated points or mechanical points operated from signal boxes were not upgraded, as this was more work and because more equipment was required, far more expensive.
Anyway, as a result, its now extremely difficult without access to railway information to know if facing points on a line that is not normally used for passenger trains are FPL fitted.
Okay, now signals and routes.
There are broadly three signal types:
- Main aspect (red/yellow/double yellow, green)
- Position Light (PL, calling on) signal associated with a main aspect signal head (two white lights at a 45% angle)
- Elevated GPL
- Ground Position Light (GPL)
Yes, that's a list of four, but the only difference between the last two is the type of head, the signal controls are the same.
The last three are all shunt signals. Normally, in service passenger trains are not signalled using any shunt signals. There are limited exceptions. For example, a Position Light aspect signal associated with a main aspect signal may be used when a DMU or EMU has to enter an already occupied platform line because that unit is planned to join (couple up) with a unit already in the platform. Note, if its not planned, then other steps are required before this move can be done.
For shunt signals including PL (associated with a main aspect) and GPL, a proceed aspect has a different meaning to a main aspect. When it's showing "off" (proceed) it's telling the driver that the train may pass the signal, but that the section of line may not be clear ahead, therefore the driver is to proceed at a suitable speed to stop short of a possible train ahead.
There is normally no requirement to prove that the next signal is lit.
Because the signal can show proceed with a train in section ahead of it, normally not all of the track circuits (or axle counter sections) are required to be proved clear. In some cases, the line may not have continuous track circuiting.
Points in the route will be set and proved just like with a main aspect. But points ahead of the next signal (regardless of type) may not be set or if set, proved. Indeed, normally overlaps are not provided.
Normal direct locking by the track circuit(s) or axle counter section(s) do apply, to electrically lock the route over the points when a train is on that track circuit(s) or axle counter section(s).
In addition, the route will only go to the next signal regardless of type. So if there is GPL before you get to a main signal, the route will only go to that GPL and no further.
Now compare to a main aspect, for example a signal showing a yellow aspect.
The requirements before the signal can clear are:
- There must be no opposing or conflicting routes already set
- The next signal must be proved to be lit
- All track circuits and axle counter sections between this signal and the next signal must be proved to be clear. Plus the overlap track circuit(s) or axle counter section(s) must be proved to be clear. A normal overlap is 200 yards (183 metres), but in some cases, this can be reduced to 50 yards.
- All points in the route and in the overlap must be set correctly and detected in the correct position (the overlap requirement may be relaxed in some cases).
- Any GPLs between this signal and the next signal must be showing proceed.
As you can see, there are significant differences.
Yes, quite a lot of charters do need to get points clipped, usually for goods loops/lines. There was one particularly fiddly operation with a charter running several trips onto a goods line that needed points to a Yard clipping, but in between the trips a freight needed to enter or exit the yard (forget which). I felt quite sorry for the MOM who didn't have particularly long to unclip, get the freight through, and reclip it back up.
MOMs have much more work when manually operating and clipping failed power operated points at busy, major junctions.... Points may need to be moved before each train move over the junction!
The relief can be seen on their faces when a S&T faulting team arrives and fixes the problem
