Who controls variable speed limits on motorways?

I am a law-abiding elderly lady, except for when I can see no reason for a restriction. I use the M42 a lot and am frequently frustrated by the seemingly unnecessary speed controls. Yesterday morning was an example. I drove up from London and picked up the northbound M42 at the M40 junction at around 11.00am. The road was virtually empty. In fact, there was nothing using the outside lane at all. No adverse weather conditions. Yet the 60mph limit was showing all the time. Who is responsible for activating these signs?

Asked on 20 April 2013 by PF, via email

Answered by Honest John
The Highways Agency. Some of the signs are automated according to traffic levels felt through pads in the roadway, and some are manually controlled. Even though they are annoying to the point where most drivers ignore them, they can prevent traffic 'bunching' and coming to a stop. That's why you can't see the reason for them, because traffic simply continues to flow.
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