Road safety bosses say they are stunned after a speed camera caught out more than 5,500 motorists in five weeks.
The camera, on the M6 near Carlisle, was installed to protect workers carrying out repairs and is expected to net £168,000 from fines issued so far.
A Cumbria Safety Cameras spokesman said he could not understand why so many drivers are ignoring the 50mph limit, which is clearly signposted.
Pressure group Safe Speed called the figures “disgusting”.
The camera was installed between junctions 43 and 44 of the M6 on 29 January and will stay while bridge repairs are carried out.