Cameras which monitor the speed of cars travelling through a tunnel on the main route between Plymouth and Cornwall could be used to prosecute speeders.
Up to 50,000 vehicles a day use the tunnel
The digital cameras were installed in the Saltash Tunnel on the A38 in 2004.
No-one has been prosecuted so far because strict government guidelines banned such camera use on roads which were not accident blackspots.
But the guidelines have been changed. The Highways Agency said it would publicise any changes in camera use.
Unlike traditional speed cameras, which rely on film, the tunnel is equipped with the digital SPECS system.
It was installed for evaluation purposes and can operate 24 hours a day.
However, drivers' groups said its use would just be for revenue-raising, not improving safety.
Up to 50,000 vehicles a day use the tunnel, which has a 30mph speed limit.
A Highways Agency evaluation study in 2005 found that 25% of all motorists passing the cameras - some 12,500 drivers - were speeding.
A £60 fixed penalty for each could generate a potential £750,000 a day in revenue.
John Hatton from the Association of British Drivers said: "It makes you ask the question as to why they're going to turn these cameras on.
"What's it going to achieve instead of just perhaps making lots of money every day?
"It is not actually changing the safety of the tunnel at all."
The Highways Agency said any decision about the cameras' use would be taken in collaboration with the police and the area's safety camera partnership.