One hundred and seventy drivers are to have their convictions for speeding overturned after a mistake was found.
The motorists were convicted for breaking a 40mph speed limit
The motorists were convicted for breaking a 40mph speed limit in Cornwall on the A30 at Whiddon Down between January 2006 and January 2007.
But the police and the drivers were summonsed using an incorrect form.
Drivers will be compensated, have their fines refunded and any points administered taken off their licences.
The mistake was found by police and the Crown Prosecution Service (CPS), who identified that the drivers were summonsed using an incorrect Temporary Speed Restriction Order.
Following a meeting between the Devon and Cornwall Safety Camera Partnership project staff, police, the CPS and HM Court Service, the force is writing to each of the drivers identified as incorrectly summonsed.
Ch Insp Steve Torr of the force's Criminal Justice Department said: "An internal investigation has been commenced to establish how the processes have been incorrectly applied.
"We are working with all agencies involved with the Safety Camera Partnership to ensure the continued accuracy of the administrative processes, and to ensure effective detection and prosecution is carried out."
However, the force said that the use of temporary speed restrictions on the A30 roadworks were essential to ensure the safety of road users and workers on the site.
Ch Insp Steve Torr added: "The fact remains that each of these drivers was exceeding the speed limit".
A number of other offenders were properly dealt with by way of fixed penalty ticket, police said.