Drink-driving proposals inconsistent with the scientific evidence


Sir, – Current drink-driving legislation stipulates that drivers found with blood alcohol concentrations (BAC) of 51 to 80 mg of alcohol per 100 ml of blood (mg%) receive three penalty points and a €200 fine. Minister for Transport Shane Ross proposes to replace this penalty with a three-month ban on driving. It is claimed that the new legislation is justified by scientific evidence but we believe that some of this evidence is not as sound as generally assumed and that, in all the circumstances pertaining to this issue, Mr Ross’s proposal is unnecessarily severe.

The Road Safety Authority (RSA) website (rsa.ie) boldly asserts that “Any alcohol impairs driving and increases the risk of a collision. This is not an opinion, it is a scientific fact”. Mr Ross and the previous minister for transport have endorsed this assertion. However, this assertion is not true because alcohol is naturally formed by the microflora or microbiome of the human gastrointestinal tract. The typical BAC resulting from this unavoidable source is about 5 mg% but in unusual cases, referred to as “auto brewery syndrome”, can be as high as 115 mg% or more. It is therefore disingenuous to claim that “Any alcohol impairs driving”. “Any alcohol” implies zero (0 mg%) alcohol in the blood of a person who has not had a drink of alcohol but this is scientifically inaccurate. Rather the pertinent question is at what lower BAC level does driving impairment set in?

The RSA website cites a dated American 1988 literature review to support the claim that there is no threshold level of BAC below which driving is not impaired. However, a recent well-designed study by S Charlton and N Starkey, of the University of Waikato, New Zealand, in 2013 compared the effects of driver BACs of 50 mg% and 80 mg% with a placebo (a mock alcoholic drink containing no alcohol) on the standard of driving. Whereas a BAC of 80 mg% significantly impaired driving quality, a BAC of 50 mg% did not significantly impair quality of driving when compared to the placebo. So, the threshold Irish level of 50 mg% to 80 mg% BAC at which the new proposed legal penalties would apply seems to be somewhat out of step with the best available evidence. It is also noteworthy that the BAC legal limit is 80 mg% in the United States and in England and Wales.

The RSA website also states that alcohol is a contributory factor in 38 per cent of fatal road accidents, ie significant BACs are recorded in drivers/pedestrians in 38 per cent of these accidents. This correlation is popularly interpreted to mean that 38 per cent of road accident fatalities are caused by alcohol. However, the fraction of total fatal accidents caused by alcohol may well be a lot lower than 38 per cent because other confounding factors may impair driving – drowsiness, emotional upset, prescription drugs, road standard, speeding, tailgating, bad weather, etc – some of which may be present in addition to blood alcohol. In order to isolate the direct effect of BAC on road fatalities, road accident statistics would have to be fully controlled for these confounding variables, but these confounders are not taken into account in the RSA statistics. The RSA and the Minister need to appreciate that correlation is just that; it does not mean causation.

A further argument against adopting the proposed new penalties resides in the fact that regular drinkers develop both functional and metabolic tolerance to alcohol, whereas the proposed legislation applies the “one size fits all” standard to the penalties. And finally we feel that legal challenge to the proposed legislation in its current form would be likely on the basis that it is inconsistent with the scientific evidence.

We accept that Mr Ross is acting with the best of intentions, if not on the best evidence. It is fully accepted that drink-driving is a matter for serious concern and we have no wish to argue that it is acceptable for anybody to drive having ingested small amounts of alcohol. But it must also be appreciated that losing one’s driving licence, even for three months, can be an enormous burden. Under the Minister’s proposals this would happen at a BAC of 51mg%, even though driving ability was not impaired at all. We feel it would be more appropriate to retain the present penalty for a first offence of a BAC level of 50 mg% to 80 mg% and to apply the three-month driving ban only in the event of a second offence. This would accommodate the equivocal evidence that driving is significantly impaired at the lowest BAC levels in the 50mg% to 80mg% range, but would sound a clear warning that flirting with drinking and driving will not be tolerated. – Yours, etc,

Prof (Emeritus)



Biochemical Toxicology


School of Biochemistry

and Cell Biology,

University College Cork;

Prof (Emeritus)


School of Biochemistry

and Cell Biology,

University College Cork.