Square white box's every so often on road, what are they for?

Question

On only some A roads without any speed limit you see these white boxes every so often. What is there purpose?

Answer 1

Aaron s has got it dead right. They are mainly used by surveyors, but, where you see two sets on the same carriageway within a short distance, usually 1/4 mile apart, they are then also used by plod to gauge speed as this is a measured 1/4 mile as set out in the road traffic act/vosa guidlines for speed checks carried out from a static point.

Answer 2

think the police can check your speed by them they time you from one to the other as they are all ways it twos

Answer 3

they are used by traffic surveying vehicles to gauge journey times on major routes they trigger sensors on the underside of surveying vehicles, they can be painted white squares,circles, dots, or pelicans like at the crossings.

the police can also use these  to gauge speed