We've had a Watchman camera on test for ages now on the A24 - covering a junction where a number of people have been killed or seriously injured. Since it's installation - and bear in mind that this is a test site with "camera on test" signs around it - there has been one serious incident (sadly involving a S210 320). The problem has always been that the locals know how risky the section of road can be, and drive accordingly. Others view the lights on the dual carriageway as a grand prix start and ignore the 60. Whereas in the past it was very difficult to guage how fast people were coming towards you (at the junction you're just under a slight brow in the road and visibility is not very good - can make for an interesting exit down the little slip road too!), now you know that the vast majority of people will be at or below 60 when you cross (you can drive straight across to turn north (waiting in the central gap)).
Within the last month a new test site has emerged - for those who know the A24 this is between the Hop Oast and the the southern Southwater roundabouts, southbound. This is an average speed camera trial. Of note is that you can easily spot the second of the pair of cameras, bit it took a while to spot the first set as they are very close to a bridge (on the southern side on the southbound carriageway).
Again I can understand why they have chosen this stretch - nice and open with good sightlines means even I have used this to be "naughty" when no-one else is around. Not known as an accident blackspot, but I have seen seen some really stupid driving / speeds from cars and bikes over the years.