semi-autos and shunt signals

Generally the route can be selected in advance by the signalman and will only clear when the preceding train has cleared the section concerned.

The signal should not clear again unless the lever is first returned to the normal position and again reversed or some sort of automatic working has been selected for the signal (e.g. King Lever reversed.



for the most part, that is correct. There are still a few places where shunt signals can be cleared onto occupied roads, for coupling purposes etc, but even here it will only generally ignore some of the track circuits in the route (the ones where the stationary train may be expected to stand e.g. in a platform)


The track circuit does indeed return the shunt to danger and the signal lever will need to be normalised before the signal can clear again.

The route indicator is displayed automatically

There will be only one lever. The approproate signal is automatically selected based on the route set

Harsig beat me to it, I spied your message but had to answer some important email first. When I returned to DD lo and behold you had an answer!

However, I can add a couple of points I think which may be of use to you.

These days a signal operator is clearing routes rather than signals even though the route may consist of a single signal! Route selection is a non-safety function.
The SO will push a button to clear a route and when/if the route clears s/he will see an HKE i.e. the button is illuminated yellow.
Lever frames may be manual or auto release depending upon age. Normally the only significance is that an SO may be unaware of some types of signal failure on an auto release site whereas on a manual release site s/he will usually have to operate a release button before being able to clear a route again.
When a route has been cleared the safety signalling ensures that the trainstop comes to the fully on position after the passage of each and every train taking that route. At the same time safety signalling circuit contacts will 'knock down' the route selection on the non-safety signalling circuitry to automatically cancel the selection. This ensures that a route is not automatically reselected although in some circumstances i.e King lever operation it is desirable to ensure by appropriate circuitry that route reselection is allowed.
Where track circuits are 'ignored' in shunt signal selections because they are known to be occupied it is normal to ensure that such tracks have been occupied exclusively, i.e. whatever is on them is at rest, usually by the operation of a time relay.
In the case of theatre signs it is the setting of points in the route that enables multiple routes to be controlled from a single lever and set the correct route number. Similarly it is also possible to control running and shunt signals on the same post from a single lever. Northfields westbound signals for instance are a good example of the practice.

Referring back to the automatic release feature of a frame, if say a delta track relay (used to detect a train clear of the switches of a set of points or otherwise detect the position of the front of a train) failed then the lever would not return to the normal position in the frame, being caught on the backlock even though the train had cleared the backlock track circuits. The auto release would engage and restore the lever to normal after 2 minutes. The SO would probably only notice this if the train headway on the route was close to 2 minutes or less and might report 'signal slow to clear' but would otherwise would never see a problem. On a manual release site s/he would simply be unable to clear the route without taking a manual release first.

Of course routes are not always selected by the SO but sometimes by the Programme Machine!

Two good points there that I forgot to mention, I must be getting rusty now I'm into my third year of retirement!

Interestingly despite what they tell you in signal school you can find SRs on V style frames too! ISTR 7s in Acton west has an SR.