Devon and Cornwall Police are beginning a campaign targeting motorists who drive after taking drugs.
Drug drivers face the same penalties as drink drivers
Recent statistics show the number of fatal crashes involving drug taking is on the increase.
The force has almost completed training all their traffic officers in detecting drug use.
A series of roadside coordination tests will be used. They will include raising a fingertip to the nose and walking in a straight line.
The dilation of eye pupils will also be measured.
People found to be driving while under the influence of drugs are charged under the same legislation as drink drivers and are liable to the same penalties.