THE message is outwardly puzzling.

Justice Secretary Kenny MacAskill says the best advice regarding drinking and driving is that drivers should take no alcohol, none at all. Yet the Scottish Parliament will vote today to confirm the minister's plan for a new limit of 50mg alcohol per 100ml of blood.

This measure, coming into force on December 5, brings us into line with many other countries in Europe, yet seems illogical.

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When Mr MacAskill himself confirms drivers at the new limit will still be three times more likely to die in a road accident, surely a zero-tolerance approach would be more sensible?

However, although some countries, such as Hungary and the Czech Republic, bar drivers from having any alcohol in their bloodstream at all, that is technically problematic.

Alcoholic mouthwashes, for instance, or liqueur chocolates, could put otherwise law-abiding citizens on the wrong side of the law.

With a very low limit, people could still fail tests the morning after having a drink. So even in countries that effectively prohibit any drinking by drivers, the limit is not zero. Sweden for example, allows drivers up to 20mg per 100ml, and still many of those caught are tested in the morning, victims of their drinking on the night before.

One problem is that different people process alcohol differently according to their metabolisms. Meanwhile, at very low levels of blood alcohol it is technically difficult to be sure of the cause. This makes it almost impossible to fairly impose a zero-limit. Yet warning drivers to drink nothing remains the best advice.

That is why, paradoxically, Mr MacAskill is right to say that alcohol at any level impairs driving while passing a law that merely tightens the allowable level.

The caveat is that it would be understandable if this causes some confusion. The new rules will have drivers attempting to work out what they can drink, in how big a glass, and whether they should do so at all.

Many people are still unaware of the imminent change, and many of those who are aware find or will find it puzzling. So a crucial addition is a policy of effective communication to get those messages across.

That is why a new campaign - encompassing TV and radio adverts, digital and social media campaigns and a range of events around the country in key locations such as supermarkets - is very much welcome.

Critics of the change argue tightening the rules is unnecessary, and penalises the sensible driver who would otherwise feel safe to take a single drink when out with friends, or over dinner. Further restrictions only serve to inconvenience many, to avert the risk posed by what is now a small minority of drivers.

But friends and relatives who have lost a loved one to drink-driving cannot understand why it is permitted at all.

The truth is that the new rule is sensible and balanced, but with the change in the law imminent, greater effort to explain it and how it will affect drivers is essential.