Some specific signals

SA38R (the repeater leaving Severn Beach): always seems to be yellow, even if the home signal SA38 shows green. Is this prototypical? (The repeater/distant signal distinction always seemed a little odd to me.) Similarly, is there a reason most of the signals on the Avonmouth line don't seem to show green?

UB106A (first signal on the up Badminton line past Westerleigh Junction): shows red if the points at Westerleigh are set for the up Charfield line; why?

538 (reversing shunt signal on the up Filton line at Lawrence Hill GF): wrong-line running seems to be permitted from here to signal 540 at Dr. Day's Junction; why here but not in general?

" said:

SA38R (the repeater leaving Severn Beach): always seems to be yellow, even if the home signal SA38 shows green. Is this prototypical? (The repeater/distant signal distinction always seemed a little odd to me.) Similarly, is there a reason most of the signals on the Avonmouth line don't seem to show green?

Distant signals fixed at caution (as SA38R appears to be) aren't all that uncommon - they're usually provided where there's no great benefit to providing a working distant, generally where the linespeed's low. In this case, all I can think is that SA38 signal generally won't be cleared until the train occupies the berth track circuit (otherwise how do you know it's left Severn Beach?) to avoid tying up the junction beyond, by which time it will already have passed the distant anyway.

There's not really a distinction between distant and repeater (I believe they're all formally referred to as distant signals nowadays?) - the main thing is that neither is capable of displaying a red aspect!

SA38R, i can offer no better explination to what Late Turn has said. haven't managed to get out to severn beach via train so i haven't had a look at whether the repeater has once aspect, or 2 or even is its not a signal board at all but rather a fixed stopping board.

I'll start from the begining and hopefully tie what everyone has said together
DT2. the simple answer is no. emergency buttons aren't for protecting a crossing. they are simply for emergency use only.
However if your saying that DT2 should have one, then surely DT5 (Avoncliff), UT3 (between youngs and fishers crossings), uc114 and dc113 (signals either side of charfield hall farm crossing), um 129 (near yatton), and um148 and um147 (between bridgewater and highbridge) should all have emergency indicators as these are all auto signals that could protect crossings? That one could of been thought through a bit better before asking it.

DT2. the simple answer is no. emergency buttons aren't for protecting a crossing. they are simply for emergency use only.
However if your saying that DT2 should have one, then surely DT5 (Avoncliff), UT3 (between youngs and fishers crossings), uc114 and dc113 (signals either side of charfield hall farm crossing), um 129 (near yatton), and um148 and um147 (between bridgewater and highbridge) should all have emergency indicators as these are all auto signals that could protect crossings? That one could of been thought through a bit better before asking it.

Another issue to consider here is that generally speaking, emergency replacement switches on 1960s Western Region interlockings cannot be relied upon. I cannot remember 100% why but I think it has something to do with there not being a direct indication back to the box or something similar. Firefly or Geoff will no doubt know the total reason. As this is the case, the use of these signals to protect a crossing would not be allowed anyway, and in reality the Signalmen would just use the previous controlled signal.

Modern SSI interlockings have replacement facilities which can be relied upon, and as such are often used to protect crossings.

What's the right way in general to manage level crossings, then?