Traffic rules have been changed to cut speed limits on part of a main route into Lynn to the level that cameras have been enforcing on drivers for nearly a year.
Average speed cameras have been enforcing a 60 mile per hour limit along the A17 between the Pullover roundabout and the Lincolnshire border since January.
But new signs, showing the same limit, have now been installed at junctions where the road is technically classed as a dual carriageway.
However, despite an apparent loophole in the restrictions now being closed, police say they have not faced a legal challenge to any penalty imposed through the use of the cameras since they went live.
In a statement, Norfolk County Council said this week: “When the road was created, part of it was deemed legally to be dual carriageway so the speed limit was set at 70mph.
“However, this section also had a number of junctions along it so at points where, for safety reasons, we would advise people to slow down, technically they could speed up.
“Following discussions locally about safety along this stretch of road, we have now changed the traffic regulation order so that it remains at 60mph throughout and erected signs to make people aware this is the case.”
Meanwhile, police have confirmed that a second set of average speed cameras is to be installed in West Norfolk over the coming months.
A proposal to install the equipment on the A149 around Dersingham has now been approved.
Officials say they expect the cameras to be in place by the spring, though no date has been set for when they will go live.
The area is one of several stretches in West Norfolk where campaigners have called for additional safety measures following fatal collisions in recent years.
Other high-profile sites which have been the subject of such calls include the A47 around Middleton, East Winch and West Bilney and the B1145 between Lynn and Gayton.