BETTER driving campaigners have urged motorists not to drink and drive at all, when the new laws come into force.
The Scottish Government has said one pint of standard strength beer, one small measure of spirits, or a small glass of wine would probably be under the new limit.
However, its message is do not have a single drink and then get behind the wheel.
Tim Shallcross, head of technical policy for the Institute of Advanced Motorists, agrees.
“Working out whether you are over the limit is fraught with danger,” he said.
“It varies so much from person to person and is not even just a question of age, sex or weight. People’s metabolism differs. Some eat likes horses and don’t put on a pound, others just have to walk past a chocolate shop and they gain three inches. It’s the same with alcohol.”
The other question people inevitably ask is whether they can drive after drinking the night before.
On average, it takes an hour of sleep to lose a single unit of alcohol. So if someone stops drinking at 11pm, after four pints, they may be safe to drive at 7am the following day.
But again, these calculations are dangerous. Mr Shallcross said: “Give yourself a safety margin, an extra two hours.
“The last unit can be quite stubborn and getting rid of it can take three or four hours.”