Speed cameras

There was a brilliant idea (well brilliant for a local authority, anyway) involving speed cameras. The particular camera is located on Gravel Hill, Bexleyheath. You know the one as you come away from the High Street and the usual congestion of multiple traffic lights into a relatively good stretch of road down the steepish incline of Gravel Hill. Even on a push-bike your speed would naturally edge over the 30mph limit. The camera appears to have been placed with these facts in mind and an obvious revenue producer.
Anyone a few months ago (maybe longer) a solar powered (I think) speed indicator was installed about 100 yards or so before the camera. Now that, I thought was a brilliant idea. Why is this not adopted elsewhere?
Today I realised why. Proceeding down Gravel Hill last night I noticed that the speed indicator is no longer working! Lack of sun-power? In June?
Again it just indicates that the only reason for its installation appears to be to provide employment for a few council workmen and sales for the equioment manufacturer.
What a shame!