So surely what we need to be doing is encouraging people to maintain a sensible speed at all times, rather than taking the half-a***d approach of only protecting certain areas.
There are horrific car accidents - many of which are likely to have speeding as a cause - in many places, not just schools, so I personally consider the blanket deterrent provided by lots of hidden cameras at unknown locations to be worth more than the localised protection provided by visible cameras.
That said, I don't see any reason why there couldn't be both. Visible cameras at blackspots to provide deterrent; hidden cameras at undisclosed locations for the purpose of actual enforcement of the limits. Personally, I would be in favour of putting a hidden camera a short distance ahead of a "dummy" visible one, so that people who slow down for the camera are still caught, but still providing the localised protection benefit.
Define "too slow"?
There is really no need to make motorways any faster. Many cars are significantly less fuel efficient travelling at motorway speeds as it is; we don't want to make that any worse.
Then you have to consider the safety implications, as well as the increase in noise and pollution levels around motorways, which will be horrible for everyone living nearby (I'm not sure exactly how far you could hear a busy 80mph motorway from, but I imagine it's a mile or more, given that I live about a mile from 50mph dual carriageway and can clearly hear it at all times during the day)
However, I'd like to see a review as well, in particular bringing 30mph limits in built-up areas down to 20 or 10, and possibly raising 30 limits on wider roads with less pedestrian traffic to 40.
You're probably right, but I don't think people should not be fined for speeding just because it was safe in that specific circumstance. There needs to be the blanket understanding that speeding is unacceptable in all circumstances, because yes, one day it might be entirely safe, but the next day it could cause life-threatening injury to a pedestrian or someone in another car.