The Government has revealed more details about new road safety measures. 

From December, police in Wellington will do random roadside saliva tests - screening for cannabis, methamphetamine, MDMA, and cocaine. 

Drivers coming back positive will need to do a second test that checks for 25 substances. 

Transport Minister Chris Bishop says the swab could detect drug use several hours beforehand. 

"I think it picks up recent usage, so a week or so ago - no. But if you smoked up the night before and you're out on the road in the morning, then it will pick it up."

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