Roadside saliva tests as part of a nationwide plan to crack down on drug use at the wheel have been started by the French Police on Monday at the Rivera.
Interior Minister Michele Alliot-Marie was in the Mediterranean town of Antibes for the launch of the operation, which will see some 50,000 drug screening kits handed out across France.
Quicker to use than urine or blood tests, the experimental tests -- similar to ones currently used in southern Australian -- are hoped to help save hundreds of lives, French officials say.
If the result is negative, a red line appears on the stick within a few minutes. If positive, the stick stays white.
Any positive result has to be followed up with a blood test since certain medicines can be mistaken for drugs -- with drivers facing a maximum fine of 4,500 euros (6,700 dollars), two years in jail and the loss of their licence.
Of the first 10 tests carried out in Antibes, three tested positive for cannabis.
One of the drivers insisted he had smoked marijuana three days earlier, appearing to contradict claims that the tests cannot detect cannabis use past a few hours.
A French study in 2005 suggested that smoking cannabis doubled the risk of fatal accident, and multiplied it by 15 when mixed with alcohol. It blamed cannabis for 230 road deaths per year.