Drivers in Derby are being warned to take extra care after investigators tracked a large scale motor insurance fraud to the city.
It is thought criminals cause accidents in order to make a claim.
Insurance companies believe one technique fraudsters use is to brake sharply, causing the car behind to run into them.
Its thought they often pick out elderly or female drivers as they believe they are more likely to accept responsibility for the resulting crash.
Investigators say gangs then often provide false witnesses before claiming for damage and injuries which have not occurred.
They have warned the practice has begun occurring in Derby.
David Dawson, an accident investigator for Ravenstone UK, said: "They will create an accident, or they may even make up an accident that never happened.
"They will then submit a claim for compensation for personal injury, hire of replacement cars and repairs to vehicles not damaged or with damage exaggerated.
"Some of these claims can run into tens of thousands of pounds."
He added that while cases are still uncommon - motorists should never admit liability for an accident but pass the case straight to their insurers.