Motorists using a stretch of the M6 will have to go to 50mph between junctions 10a at Wolverhampton and 12 at Cannock – and then down to 40mph up to junction 13 near Stafford.
The Highway Agency have confirmed that new average speed cameras on the seven and a half mile stretch went live earlier this month.
The work, costing £121 million, is intended to open up the hard shoulder to traffic and impose variable speed limits at busy times.
A spokesperson from the Alliance of British Drivers said: ‘Average speed cameras are usually set at 50mph. That’s also the speed at which drivers are normally asked to travel along a section of motorway with roadworks in order to protect the workers.
‘Changing the speed limit to 40mph for small stretch appears on the surface to be a cynical attempt to catch unsuspecting drivers who are used to adhering to 50mph limits when work takes place on a motorway.’
The new speed limit comes after more than 6,400 drivers were caught breaking a 50mph speed limit in four months on the M54 in Staffordshire.
The speed limit could be in place for up to 18 months.