The Highways Agency says the cameras will cut accidents
A £12m scheme to install variable speed cameras on the M20 in Kent is being rolled out.
They will be placed in overhead gantries in Maidstone after public consultation revealed 56% of people were in favour of the move.
They activate when a driver breaks the speed limit displayed on digital signs.
The Highways Agency said they would cut congestion and accidents, but the Association of British Drivers said they were unnecessary and wasted money.
Spokesman Nigel Humphries said the cameras, between junctions four and seven, were "all about bullying and regulating drivers for the sake of it".
"We think there's not much that can be achieved positively by these schemes that can't be done by warning signs, matrix signs and advisory speed limits," he said.