That innocuous phrase: "Just one more" might seem harmless in the convivial atmosphere of the pub, but for drivers, going over the limit can and does have devastating consequences, week in, week out.

In 2009, 30 people died and 920 people were injured due to drink-driving incidents in Scotland. Sometimes the casualty was the driver; sometimes it was a passenger, another driver or a pedestrian who just happened to be in the wrong place at the wrong time.

What can be done, should be done, to reduce this depressingly predictable death toll. The Scottish Government and its cross-party supporters therefore deserve a pat on the back for pressing ahead with plans to reduce the drink driving limit from 80mg of alcohol per 100ml of blood, to 50mg.

The measure, which will bring Scotland into line with other European countries including Germany, France and Spain, should ultimately save lives.

Bringing in the new limit, however, poses certain difficulties which must be overcome if it is to command maximum public support.

In many cases where a driver is slightly over the new limit, for instance, there will be little outward sign for watching police cars that the driver's ability is impaired, unlike with more inebriated motorists. The obvious answer? Random breath tests, but that would bring with it an extra policing costs that could hardly be justified at a time when police budgets are facing severe cuts.

Also, blood alcohol limits are notoriously hard to translate into safe drinking limits from one individual to the next. While it should in theory be legal to drink a small glass of wine or a pint of beer and remain within the new legal limit, wines and beers vary in strength and there are also disparities between men and women, and those of different height and weight, when it comes to how the body processes alcohol. What's more, different individuals will judge what constitutes a small glass of wine differently from others. Will the driver who misjudges the safe amount, and finds herself slightly over the new limit but well below the old one, be subjected to the full force of the law, a 12-month ban and possibly a fine or prison sentence? Any weakening of the penalties because the legal limit has been lowered, could send out a confusing, counter-productive message.

There will, of course, also be different legal alcohol limits on either side of the Border, but that is a simple fact of devolution and not a reason not to proceed. Clear signage around the Border should obviate any problems.

These issues must be ironed out, but overall, this is a welcome change for the better. "Don't drink and drive" must continue to be the message of police road safety campaigns as that, in the end, is the safest message of all.