A new kit for detecting cannabis has been approved for use in police stations across the UK.
A positive saliva test with the new device means officers will no longer have to call a doctor before asking for a blood sample if they suspect a driver of being on drugs.
The testing kit is able to detect THC, the active ingredient in cannabis, while equipment capable of accurately identifying other substances is still under development.
A total of 644 accidents were caused by drug-drivers using both illegal and medicinal substances, including 49 deaths, according to the most recent figures from the Department for Transport, from 2011.
The number of 17 to 24-year-olds who drive after taking drugs increased from five per cent to nine per cent in the 12 months to May, according to a survey by the RAC.
Policing and criminal justice minister Damian Green said: "Those who take drugs and go out on the roads are a menace to pedestrians, other motorists and themselves."
Motorists can already be punished for driving while impaired by drugs, but the new testing equipment will make it easier for the police to prove a case.
Offenders will face up to six months in jail and a fine of up to £5,000 as well as an automatic driving ban of at least 12 months