Officers from Cleveland and Durham police have joined forces for a summer crackdown on people driving under the influence of drink or drugs.
During the month-long campaign motorists will be stopped and tested at random.
Anyone found committing a traffic offence or involved in a collision will also have to take a breath test.
Those suspected of being under the influence of drugs will be subjected to a blood test.
Insp Mick Little, from the Cleveland and Durham Specialist Operations Unit, said: "We work all year round to try to get the message across, but the summer months present different problems, with the focus being on afternoon drinking.
"We can probably all see the attraction of enjoying a drink in a beer garden or at a barbecue on a sunny afternoon.
"All I'm asking is that you leave the car at home and get a taxi or walk."