A related question.
On my cycle wanderings I regularly use the Stoke Canon Level Crossing. The crossing is CCTV▸ -equipped and has split full width barriers.
On a number of occasions the barriers have been closed for up to 8 minutes - yes, I have timed it - for the passing of 3 services.
This is not, I think, what you would call an intensively worked section of line. Is this entirely down to the local signalling configuration (long track sections) or decisions made by the signallers (who I believe are based at the Exeter Box)?
If you have Train 1 on the Down Main, Train 2 on the Up Main, and Train 3 on the Down:
Barriers dropped, say two minutes before Train 1 arrives at the crossing, so the driver gets greens on the approach. The first signal that could give a yellow could be 1,800m or so in rear of the crossing, and you don't want the driver to see that as yellow as the train approaches, you want the driver to see a green. At a line speed of 80mph, say, you really do need to start those barriers dropping two minutes before the train gets there. There will probably be an annunciator in the signalbox, to give awareness that the train is approaching, at a certain distance in rear of the crossing - a track circuit or a treadle
Say it's 2 minutes 20 seconds before Train 1 has cleared the crossing. By which time, Train 2 could be within three minutes of arrival. You wont lift the barriers to drop them again in less than a minute. So they stay down.
Train 2 clears the crossing 5 minutes 40 seconds after the barriers were dropped. And now Train 3 is about, following maybe four minutes behind Train 1 on the Down, and not much more than three minutes from the crossing. Again, you don't want to lift the barriers. Train 3 arrives at the crossing 8 minutes or more after the barriers were first dropped
This is a general explanation, not specific to Stoke Canon Crossing. It works for two-aspect signals. But it does give you an idea of why you'd have to wait there for a while, sometimes. With three aspect signals, when you wouldn't want to show the driver a double yellow even further in rear of the crossing, the barriers may need to be dropped earlier. Just admire the Saxby and Farmer built signalbox. A listed building, I believe, and disused for around 40 years now