UK Dopers - what are those things on motorway bridges?

General Questions
#1

Recently (I don’t know if they are new or if I have just been unobservant in the past) I have noticed odd devices attached to bridges over motorways.

They look almost like the “old style” CCTV camera housings, but appear to be hollow - the shape is almost like a rectangular cowbell, or maybe those loudspeakers you get at outdoor fairs, for want of a better description, and they are angled down slightly towards the road. Sometimes there is one above each lane.

I don’t think they are cameras - as I say they appear to be hollow, rather than having a lens in the end. Are they some kind of radar thing maybe? Are they something that’s likely to catch me for speeding? (If I were that way inclined)

#2

I’ve always presumed they’re CCTV, the ones used by the police for traffic management and stuff. Around here, they’re high on a post at the side of the road, one housing pointing each way, with an aerial on top. I’d presume the housing projects well over the lens to protect it from the weather - possible because there’s no need for a wide field of vision.

#3

They are traffic monitors; I’m not sure how they work, but they are part of the ROMANSE traffic monitoring network.

I don’t think they are designed to gather detailed info about individual cars, but rather just density and speed of traffic.

#4

They are usualy found on top of traffic light posts. They simply count the number of cars that pass through the intersection, to optimize traffic light timing.

They have a red LED on top of them. During the night, you can see the LED blinking each time a car passes.

#5

I doubt the ones in Suffolk are :wink:

#6

There are similar projects nationwide - I think they all link up because you can get in-car systems that receive data from them (as distinct from GPS navigation units)