I would suggest single horn tone at whistle boards. Should be two-tone to give a clear indication of a train and not a lorry.
IMHO, in all circumstances when a full horn application is needed, train drivers should use both tones. It's much more distinctive. I've lost count of the number of times that I've discussed with my team (I was an S&T team leader) "is that a train approaching or is a truck on the nearby road?" ...
While on about train horns, if a group of infrastructure staff are clearly already aware of your train, when pulling away from a signal, we don't need to be deafened by a full application of the horn. A very quick hoot is all that is needed. The horns are rather loud when you are only a handful of metres away...
The Rule I'd question is in the Track Circuit Block Regulations; what the signaller must do if there is a Track Circuit failure.
The Rule (and I paraphrase, as I don't have the Regulations to hand) is that the signaller should NOT set the route, but should key all sets of points in the route (and others as required by the Route Tables), then authorise the train to pass the entry signal at danger.
The purpose of the rule is two-fold:
a) if the track circuit failure is intermittent, it prevents the entry signal unexpectedly clearing and reverting to danger ahead of the train
b) if the faulty track circuit is before any points in the route, then those points will remain locked even after the passage of the train, so preventing any other moves over that junction until the track circuit clears again.
Both very valid reasons. But...
I investigated an incident a few years ago, where the faulty track circuit was the last in the route - i.e. after any points or conflicting moves. The junction was a conventional double-line junction - trains from A could turn left to B, or turn right to C. The faulty track circuit was after the junction, on the line towards C. The signaller had keyed the points for a train to travel from A towards C, and authorised it to pass the signal at danger. A second train then approached from B. Even though the first train had not yet reached the junction, the signaller keyed all the points centre, then set the route for the train to travel from B to A - causing some of the points ahead of the first train to swing. The first train then "ran through" the trailing points and damaged them.
If the signaller had set the route for the first train, then the route-locking over the points would have been maintained, and setting route for the second train would have been impossible. Although such route-setting is contravening the above rule, it would have (in this instance) saved the signaller from making a costly and potentially more dangerous mistake.
There are other circumstances where in my view, it's better to use the route. For example if there is only one set of points in the route and they are already directly locked by the track circuit fault (so can't the moved on power anyway), if no trains are booked to use the points in the opposite direction, why not call the route?
Also, if the relevant track circuit failed during the passage of the train, the route locking will not cancel for that part of the route anyway (not until the track circuit is working normally again). So for the next train, you may as well call the route again.
There are rather a lot of annoying instructions (not usually in the rule book) that apply to S&T. The amount of paperwork or the electronic equivalent has gone nuts since the carve up of BR occurred. Most of which doesn't improve safety of performance.
My favourite though is the instruction that we are supposed to prove that a signal disconnection is effective.
Fine if you are taking out of service an operational signal or item of signalling equipment, as it's easy to comply.
But the fun begins when you get asked to disconnect (restrict to red / danger) a signal that is already stuck at red by a failure. The signaller can't clear it, so we can't test that our disconnection is effective. Hence we can't tell the signaller that the signal is restricted to red... Hence the signaller cannot rely on it staying red... This is especially important for automatic signals that are not provided with either an emergency replacement switch on the signallers panel or a signal post replacement switch.
