Most drivers who are found to have exceeded alcohol limits do so because they have miscalculated the amount of alcohol they were consuming, says research.
So don't have any.
So much depends on factors such as age, weight, gender and metabolism that there is no rule of thumb in terms of working out how many drinks you can legally have before driving home.
Police in Britain, like our own, believe that the only infallible rule is not to drive at all if you want a drink and not to drink at all if you want to drive. It's easy really.
However, there are those who will risk it anyway and there will again be those alcohol-impaired drivers during our Christmas holiday binge who will achieve their 15 minutes of fame - in court, in hospital or on the slab.
Many will have lost their licences and jobs after being judged as over the alcohol limit at a checkpoint, but they will be the lucky ones.
That will be better than killing someone else or themselves as a means of bringing their Christmas celebrations to an obscenely abrupt end.
Late December will never again have the joy normally associated with it when that fatality happens.
It will be remembered for damp streets, flashing lights, crackling radios, hot metal ticking as it cools, fluorescent vests, moaning blanket-covered victims and some making no sound at all and ambulances being driven slowly and silently.
No point in rushing now.
It can all start when a hostelry spills its patrons on to the streets to make their way home or on to a party, and the kind act of an offered ride to friends, a girlfriend, a mate's sister, with typically two up front and two in the back.
It's often no act of kindness in the end, as the celebration of a birth 2000 years ago is turned irreversibly into an unwanted reminder of lives taken and ruined before their time, thanks to cocky drivers who took their chances with more drinks than they should have had.
From scenes I have witnessed over the years, the driver could well live - but won't if he or she wasn't belted in. Seatbelts are the first thing you forget with a drop on board.
His scalp will be embedded in the windscreen's headrail, his viscera will have added an organic skein to the crumpled metal of the bonnet lid, which shared in the task of decelerating the car as it stubbed itself out like a cigar against a bridge parapet.
That's all that will be left near the car, for the rest of the body will be under a blanket. Later, his mother will identify him after the thoughtful mortuary people have framed the recognisable parts of his face with clean fabric.
She will not know then that he is literally not all there, but she will know he had been drinking, that he was driving, that he is now a statistic and that he will be remembered by others not as a loving and loveable son, but as a sad case of someone who took a chance and took his life and ruined the lives of others.
If they were fortunate enough to have belted themselves in, the other occupants may well have lived, although often during the next few years they will wish they had died along with the driver.
It doesn't require much speed to distort a car's passenger cell when it hits an immovable object.
Even if the car was travelling below suburban speed limits, it can be twisted and misshapen to the point of being unrecognisable, wrapped around the concrete abutment.
In the rear, the girlfriend probably struck the front passenger on the back of the head, with her own head, which in itself was not too damaging, but the wine bottle clutched tightly in her arms imploded to press long shards of glass into her throat and face a fraction of a second after impact. One knee pierced the passenger's door until it separated on the very intrusion bar that was designed to protect her.
The sister retained her sight, at least. Relaxed in sleep at the time of impact, her head lolled uncontrollably into the rear quarterlight sub-pillar, and the base of the skull fractured neatly on the hard, painted metal. She wouldn't wake from her sleep until Easter, and would have to learn to talk all over again, and learn, too, that the five-month-old foetus had become detached and was too small to survive.
Soon after having his own skull cracked by the rear passenger's impact upon it, the mate up front lost consciousness, which was fortuitous, because in the previous few milliseconds, painful signals were coursing to his brain from the effects of the engine and gearbox, which had suddenly appeared in the space already occupied by his lower half.
The elbow that had been resting on the window frame, would be found along with the rest of his forearm almost untouched on the grass.
The driver's funeral will cost more than $20,000. Quite a few would turn up; the authorities will remember him only in their road toll statistics.
There will be no such statistical immortality for the survivors, each of whom will cost the state about the same amount as that funeral every week during their time in hospital. They will be regarded as fortunate to have survived, and they will never really count towards the road toll figures, because deaths seem to register more than injuries, however bad they are. But hospital staff will remember all of them, especially those drunks who vomit and spit at them, as so many do, every year.
One blinded, never to work again, another barely able to communicate but at least able to move around, unlike the wheelchair-bound mate, who can propel only one wheel and will never be without a headache for the rest of his life, with tubes and plastic bags to take away the waste products of the few body functions which remain.
A year on and our survivors need never have lived at all, for all we will remember of them. Our driver, of course, will still be a moveable statistic, as the umpteenth road death in a year during which the toll rose again, as it often does.
So, if you are having a drink this Christmas, don't take the car - get a taxi. There will be plenty around.
But of course, people will drink and drive, and some might lose only their licences and jobs if nabbed by the police - but they could lose their lives and take others with them if they are not.
Merry Christmas, everyone.
I hope you remember it for all the right reasons.
Dave Moore is a motoring expert who talks all things car-related every Tuesday on Morning Talk.