More than 100 motorists a week are being caught speeding on a busy road on the outskirts of Taunton, but many did not realise they were breaking the limit.
Magistrates have raised the issue with police and highways experts after 5,336 motorists were filmed speeding by mobile police camera between May 1, 2011, and April 30, 2012.
A new stretch of dual carriageway and a lack of repeat 30 mile per hour signs are at the heart of the problem.
The A358 between Henlade and the M5 roundabout includes a new short stretch of dual carriageway. Although 30 mile per hour signs have existed on the Taunton side of the roundabout west of the stretch, and on the approach to Henlade east of the stretch for some years, some motorists see the new road layout and assume a higher limit is in force.
Legislation does not allow for repeat 30 mile per hour limit signs to be installed.
Councillor David Fothergill has called for the speed limit from the roundabout to Henlade to be increased to 40mph, which would allow more signs and painted warnings. Consultations are under way.
Harvey Siggs, Cabinet member for highways, said: “We need to listen, involve the police and challenge speeders. We already have signs, chevrons and lights along this stretch – if this is not enough, we will be fighting on behalf of motorists in lobbying the Department for Transport for change.”