In reply to FactorXXX:
On arterial roads of the type you describe (sorry, MK brain, I'm used to those roads being mostly NSL or at least 40 rather than 30) average speed cameras are ideal for what you describe.
Remember the point of speed cameras is to prevent people speeding, not as an income source. The best speed cameras are the ones that bring in £0 and reduce accidents/the severity of accidents because people aren't speeding (but were before it was installed). If people still speed but get caught, you've brought in a bit of money but haven't had a material effect on road safety, which in the end is the whole point of the exercise.
Sure, you could argue that random checks make people fear being caught so they won't speed as much, but in reality unless you're blind you can see* a camera van, and people learn where the fixed cameras are even if they aren't yellow (there are or were a load of camouflaged ones around the Hadfield area and they aren't hard to spot).
* My usual argument is that if you're one of those drivers who thinks they are attentive enough to speed, if you get caught that proves you weren't, as the speed camera you didn't see could have been a small child running out wearing dark colours instead.
Post edited at 23:52