Having heavily tinted windscreens is a major cause of accidents and is the same as "wearing sunglasses at night", according to a new safety campaign.
Car windscreens must let in at least 70% of light
Dorset Police say there has been an increase in collisions involving cars with excessively tinted windows - and motorcycle riders with tinted visors.
Sergeant Steve Quill said: "These windows and visors do appear to contribute to many of the accidents".
Regulations state windscreens must let in 75% of light and side windows 70%.
Sgt Quill added: "It also seems to be a worrying trend among motorists and motorcyclists to alter the tint of the windows on their vehicles or use tinted visors.
"It is the responsibility of the driver to make sure that their tinted windows comply with the law. That responsibility extends to motorcycle riders and their helmet visors.
"Excessive tinting of windows has a similar effect to wearing sunglasses at night so they can seriously reduce a driver's visibility making it harder to spot potential hazards such as pedestrians, cyclists and other vehicles."
Dorset Police will be targeting cars with tinted windows to check they comply with regulations.
"Windows Workshops" are also being provided for drivers and motorcyclists to find out whether their windows or visors are legal or not.