A blunder has meant that speed cameras installed on a motorway cannot be used because one has been put in the wrong place, the Highways Agency admitted.
Work is under way to widen the M27 between Fareham and Portsmouth
The Specs cameras measure the average speed of traffic on the M27 between Fareham and Portsmouth in Hampshire.
They are set to control a 50mph limit during nine months of road works.
But a week after the cameras were put up, the Highways Agency said they cannot be used eastbound because one camera had been put in the wrong place.
The agency said a camera to monitor traffic coming on to the motorway at junction 11 has been positioned too far back from the junction.
Roger Jones, Highways Agency spokesman, said: "The eastbound carriageway is being currently monitored by the police until we have the additional camera in place.
"We weren't picking up the traffic coming from junction 11 for Fareham and Gosport.
"Another camera has been ordered and we are expecting it to arrive fairly soon. Then it has to be tested before it is operational.
"We are asking drivers to mind the 50mph speed limit and keep to that speed limit."
He said the cameras on the westbound carriageway were in operation.
The Specs cameras, nicknamed "yellow vultures" because of their position overlooking the road and their colour, use automatic number plate recognition technology to track a vehicle between two points and work out its average speed.