> > Strictly, I think knowing what's behind you isn't so much
> > a safety issue, as a "whether you can e.g. take the
> > middle of the road because there isn't any traffic coming
> > up behind you", issue.
>
> I consider knowing at (almost) all times what’s behind me
> very much a safety issue. It does make a difference in how
> close to the edge of the road I ride, for instance, though
> whether a car back prompts me to move towards or away from
> the centre of the road depends on the width of the road, the
> traffic, the conditions, and the behavior of the driver. If
> I see that someone’s back there on a twisting, rolling
> stretch where passing is difficult, I know to wave him
> around when it’s safe for him to pass, something that I can
> often see before he can. I feel much safer with him in
> front of me than back there getting more impatient by the
> second.
I do basically agree with this although I contradicted it.
We'd be basically safe on a bicycle trundling along in the
gutter at the road side, but not absolutely so, since the
road surface there isn't so carefully maintained or mended
after works: there's a roadside "cycle lane" near my home
that is more like an obstacle course.
My own experience of cycling on Scottish roads is that almost
all drivers are courteous and considerate, but they do get
impatient quite quickly - not to the point of deliberately
breaching the "Highway Code", although it isn't wise to push
your luck, but after even a slight hold-up they will go
for the earliest apparent opportunity to pass you, and that
can get a bit too exciting. On the other hand, I usually
signal "not safe to pass" by getting firmly in their way,
which also lets me go faster, up the middle of the road.
The flipside that I currently practise is to stop sometimes,
to let all the traffic behind me pass, before entering a stretch
of road where this is liable to happen. There aren't formal
hand signals either way, but you can improvise.
Your safety basically depends on what the car behind does, more than
on what you do, so in a way it doesn't matter if you can see behind
or not. But, the more information you have about other road users,
the better - and particularly when using and approaching junctions.