[SV650rules]

A lot of the camera van haunts have a grey electrical box at side of road and some cables buried in the road, these continuously monitor traffic speed and log the data. The Police (or camera partnership) can access this data and if there have been enough vehicles speeding they will put a van there for a day. I am sure some of the flashing speed signs we see in 30 and 40 limits also collect data for speed of traffic passing through them.

It may seem random where the speed vans park up, but spots are carefully chosen to catch greatest number of speeders.

Speeding up to try to prevent someone overtaking is on of the more nasty things drivers do, they can be doing 40 but when they see you are trying to pass (or approaching a straighter stretch of road) they will speed up, and probably slow down again if you drop back behind them.