That's not what the national standard for driving requires, is it?
I believe it is, yes. Having just checked, multiple sources cite numbers around that range; often 5-8 seconds. This one for example:
https://www.driving101.co.uk/hub/beginners/mirrors-effective-use/ Obviously, the required frequency will vary, as you say, but it's often more than is practical for a cyclist doing a full 'shoulder check' movement.
EDIT:
Highway Code rule 161 says (first of three points):
'use your mirrors frequently so that you always know what is behind and to each side of you'
I suggest that 'frequently' is very much in the 5-8 second area, though I certainly agree that it'll be way fewer seconds in a busy town than it would be in the Fens / other long straight roads with no junctions.
Now I'm wondering how you look rearward if you think it's easier at remarkably low speed.
I rotate my head to point in a backward direction and look down the road. I'm calling that a 'shoulder check' as a shorthand for 'look backwards in a manner sufficient to establish comprehensive situational awareness of traffic and events behind me which may be actionable', which is a teeny bit verbose. Earlier you said:
If you're going too fast to look back safely, you're probably going faster than is safe.
It's from the above that I inferred that you considered it easier to look backwards when going more slowly.
Is it always worth knowing? Most drivers around here where we have to share the roads are cool, so beep-beep-beep would be mostly an irrelevant worry any time I wouldn't otherwise look. The few drivers who are a problem that you might be able to react to... well, you tend to hear them coming a long way off, as they're all revs, rage and thundering tyres. And what can you do anyway? It's been pretty obvious most times I've had to hit the hedge.
Well I think it is, yes. I entirely agree that, often, a problematic vehicle approaching will be audible. That's not always true though, notably in a strong headwind, where the nature of sound transmission means that you may not hear something approaching from behind. I invariably, on knowing that there is a vehicle behind me from whatever source (mirror, radar, engine or wheel noise reflections in something, etc.) want to know whether it's going around me or about to fail to do so since the diver is not paying attention. If I know this, I can then potentially do something about the impending problem. If I don't, I can't, and I don't much like that option. So, yes, I always want to know. If you don't, that's fine too of course.
How often I look behind tends to be based on how many seconds of road behind me were clear when I last looked, and I don't find it difficult to hear approaching large vehicles in most wind conditions because I don't deafen myself with headphones or straps that catch the wind over my ears. Rain thumping on my hood does make it more difficult but even then, it's do-able, as the rain is a far higher pitch than the tyres. I suspect rain would make it more difficult to hear the beeper than it does the cars.
Me too. In addition to large vehicles, I also like to hear small, quiet vehicles though, since I'd also rather not be hit by them, though I suppose a small car is preferable to a large lorry if a collision is compulsory for some reason. Even though I'm not deafened by headphones or straps, etc., and have apparently working hearing, I am 100% certain that I sometimes do not hear things approaching. For those instances, mirror and radar are useful to me. Obviously they aren't to you, but plenty of people do find that helpful and I'm one of them.
