Four out of five drivers involved in hit-and-run accidents in Lincolnshire are escaping prosecution.
Figures from Lincolnshire Police show there were 40 accidents where a vehicle hit someone and failed to stop between October 2010 and July this year.
But only seven drivers were charged.
Police say the fail to stop accidents will include some where the driver is completely unaware there has been a collision – and there is more the public can do to help officers track down drivers.
A Lincolnshire Police spokesman said: “Incidents where motorists fail to stop at the scene of a collision leaving a pedestrian or other motorist seriously injured are, thankfully, very rare.
“The vast majority of accidents will involve a minor injury caused by a passing wing mirror, for example, and the driver may be unaware of what has happened.
“Without the registration of the offending vehicle, or good CCTV coverage of the area where the incident occurred, it can be difficult to trace the vehicle involved.
“If the vehicle can be traced, there must be sufficient evidence to secure a successful prosecution.
“Our advice to anyone involved in a collision with a driver who fails to stop at the scene is to report the incident to police straight away and to try and provide as much information about the vehicle as possible.
“If any nearby people were witnesses to the incident, ask if they will remain at the scene until police arrive or leave their details so police can be contacted later.”
Lincolnshire Road Safety Partnership spokesman John Siddle also said some drivers may not be aware there has been an accident, but others will have reasons not to stop, such as drink or failure to have insurance or a driving licence.
He said: “There’s a whole heap of reasons as to why people would make off, but certainly if they have had a collision and they have injured somebody, the only right thing to do is to stop and render assistance to that person.
“As a driver, we must always remember that we have to stop to exchange details.”
In order to help police, victims – where possible – and witnesses should note down as many details as they can about the vehicle, including its registration, make and model.
“If you get time to take a picture of it with a mobile phone, even better,” he said.
Mr Siddle said police are adept at tracking down cars where there is forensic evidence as paint is “very specific”.