Vandals caused about £20,000 worth of damage by torching a speed camera.
A burning tyre was placed on top of the device in Chatsworth Road, Chesterfield, and the blaze also spread to a car parked nearby.
It is the second attack on a camera in the town in two months. About £8,000 worth of damage was caused to a device in Derby Road in a similar fire.
Police are scrutinising CCTV footage to try to trace the culprits behind the latest attack.
It happened in the early hours of Sunday.
Insp Matt Pickard, from Derbyshire Safety Camera Partnership, said: "On this occasion property has been damaged but it is only a matter of time before someone is injured or worse through this irresponsible behaviour.
"If this happens the culprits will not just be facing charges for criminal damage."
The films from both of the cameras were unscathed in the attacks, according to the safety partnership.