Police are "heartened" after more than 600 motorists passed breath tests during an operation to crack down on drink-driving this week.
The tests were carried out as part of an ongoing safety campaign across the Durham force area.
Voluntary breath tests were taken by 602 drivers in a three-hour period to search for alcohol or drugs in their system.
Police were pleased when all the tests came back negative.
Not only is this a relief for the force but it will be a warning to drivers who could see theircar insurance costs soar if they are caught over the limit.
The tests were carried out in the morning, aiming to catch out people still over the limit from the night before.
Uniformed officers positioned at lay-bys around the county pulled over motorists at random and invited them to take a breath test.
Acting Chief Inspector Ken Cook, of the force's strategic road policing department, said: "This was a concerted effort by our staff to ensure that motorists are abiding by the legislation.
"The overall aim is to reduce the number of casualties on our roads and I am heartened by the fact that every single one of the tests carried out was negative.
"I hope this is a sign that our strong message with regards to the potential consequences of drink-or drug-driving is being heard by our motoring public."
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