Following up to Adrian Tupper

but it will save lives without slowing journeys or
making driving a pain in the butt, I would have thought)

They may make money. It's not unusual for the limit to be 20mph outside
schools and I think this is frequently ignored.

they are all 30 round here, not that that's the point. The
cameras I pass on one regular daily run are thusly
several on 50 dual (was 70 until recently,so you can picture the
layout)
one on steep downhill 30 (no particular hazards)
none outside schools, shopping centres or junctions where low
speed would be good.
I'm inclined to conclude they are placed where most people speed,
rather than protecting hazards to pedestrians. The downhill 30
seems designed to catch out relatively "innocent" people who fail
to brake enough for the downhill.

I might as well have a rant about the one on the A303 while I'm
at it Picture up hill two lanes, down hill one lane (crawler lane
type layout) . At end of stretch of uphill 2 lane a blind brow.
If there's one spot in the whole country where high speed is
safer, its there. Overtake and get back in well before the brow
in case a lunatic is in wrong lane or there's some other hazard
over the hill. so what do they do? Put a speed camera on the safe
bit so people end up still overtaking when they get near the
brow. no doubt they noted accidents at that spot so concluded a
camera would cure the problem. A nice piece of concrete island
would cure it much better. the camera just has the effect of
stooping overtaking and moving overtakes somewhere less suitable.
--
Mike Reid
Walk-eat-photos UK "http://www.fellwalk.co.uk" -- you can email us@ this site
Walk-eat-photos Spain "http://www.fell-walker.co.uk" -- dontuse@ all, it's a spamtrap