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NIHR Signal A lower drink-drive limit in Scotland is not linked to reduced road traffic accidents as expected

Published on 10 September 2019

doi: 10.3310/signal-000815

Lowering the drink-drive blood alcohol limit in Scotland was not followed by reduced road traffic accidents, perhaps because of a lack of enforcement. While there was a 0.7% reduction in alcohol bought in pubs and restaurants after the new legislation (on-trade sales), there was no significant change in sales of alcohol from shops or supermarkets (off-trade), where most purchases are made.

Drink-drive accidents account for around 13% of all road deaths in Britain. In an attempt to improve this situation, Scotland reduced the legal limit from 80mg of alcohol per 100ml of blood to 50mg per 100ml of blood in 2014. This NIHR-funded study compared official figures on accidents and alcohol consumption for two years before, and two years after the change.

The findings suggest that changes to the legal limit alone may not be sufficient to reduce drink driving. Changes may need to be supported by more intensive efforts to raise awareness of the limits and enforce them, and strategies to target those not complying.

  •   Public Health, Trauma, Substance misuse
A lower drink-drive limit in Scotland is not linked to reduced road traffic accidents as expected

Why was this study needed?

Despite a 75% reduction in deaths and serious injuries related to drink-driving across Great Britain between 1980 and 2010, drink-drive accidents still accounted for 13% of all road deaths in 2012.

As well as the human toll, in Scotland alone this costs around £80 million a year.

In Europe, 50mg of alcohol per 100ml of blood is the most common drink-drive limit. Lowering the drink-drive limit to this level from 80mg of alcohol per 100ml of blood has been linked to fewer alcohol-related road traffic accidents and deaths in France, Australia and Austria.

Scotland lowered its limit to 50mg per 100ml in December 2014, while the limit in England and Wales stayed at 80mg per 100ml.

This study is the first to measure the impact the law change had on road traffic accidents and alcohol consumption in Scotland.

What did this study do?

This natural experiment looked at whether lowering the legal drink-drive limit in Scotland led to fewer road traffic accidents or reduced alcohol consumption.

Scottish data was compared for the two years before and the two years after the law changed. It was also compared with data from England and Wales for the same period (2013 to 2016), where the drink-drive law was unchanged.

The number of road traffic accidents came from official police statistics (STATS19). Rates of accidents were calculated two ways: as accidents per 1,000 vehicles on the road and accidents per 100,000 members of the population.

The study analysed total accidents, rather than those specifically linked to alcohol, meaning that any reductions in alcohol-related accidents could be masked by rises in accidents from other causes.

What did it find?

  • Lowering the drink-drive limit in Scotland did not reduce the rate of road traffic accidents in the two years after the law changed, compared with the two years before (rate per 100,000 population; relative risk (RR) 0.98, 95% confidence interval [CI] 0.93 to 1.03).
  • Lowering the limit also had no effect on the rate of accidents in Scotland compared with England and Wales over the same period (RR 1.03, 95% CI 0.98 to 1.09).
  • When taking into account the volume of traffic flow, the Scottish rate of road traffic accidents was actually 7% higher, relative to England and Wales, after the law changed (RR 1.07, 95% CI 1.02 to 1.13). This was the opposite of what was expected.
  • Lowering the drink-drive limit in Scotland was associated with a 0.7% decrease in sales per person of alcohol from pubs, restaurants and other ‘on-trade’ premises (-0.7%, 95% CI -0.8% to -0.5%).
  • There was no significant decrease in alcohol sales per person from shops, supermarkets and other ‘off-trade’ sales (-0.3%, 95% CI -1.7% to +1.1%). Off-trade sales account for over two-thirds of all alcohol consumed in Scotland.

What does current guidance say on this issue?

The UK Government has strict maximum alcohol limits for drivers (measured from blood, breath or urine), and penalties may include fines, driving bans or imprisonment.

The number of drinks the legal limit equals differs for each person at a given time. The way alcohol affects an individual depends on:

  • their weight, age, sex and metabolism (the rate their body uses energy)
  • the type and amount of alcohol they are drinking
  • what they have eaten recently
  • their stress levels at the time.

What are the implications?

The results suggest that lowering the legal drink-drive limit may not in itself reduce road traffic accidents.

The researchers believe that poor enforcement of the new law, such as insufficient ongoing publicity after the initial campaign in 2014, and not enough random breath testing, is the most likely explanation. The authors also note likely low public awareness given lack of sustained media campaigns after changes were introduced.

The fact that drink driving has already become less acceptable, and there have been large improvements in road safety, may also have contributed.

Further reduction in the UK’s alcohol-related road traffic accidents may require a different strategy.

Citation and Funding

Lewsey J, Haghpanahan H, Mackay D et al. Impact of legislation to reduce the drink-drive limit on road traffic accidents and alcohol consumption in Scotland: a natural experiment study. Public Health Res. 2019;7(12).

This project was funded by the NIHR Public Health Research Programme (project number 14/186/58).

Bibliography

Department for Transport. Reported road casualties in Great Britain: estimates for accidents involving illegal alcohol levels: 2016 (provisional). London: Department for Transport; 2018.

Sykes W, Groom C, Kelly J and Hopkin J. A qualitative study of drinking and driving: report of findings. London: Department for Transport, 2010.

UK Government. The drink drive limit. London: UK Government; accessed August 28, 2019.

West R, Elander J and French D. Mild social deviance, Type-A behaviour pattern and decision-making style as predictors of self-reported driving style and traffic accident risk. Br J Psychol. 1993;84(2):207-19.

Expert commentary

In 1967, Barbara Castle championed synergistic initiatives including breathalyser tests, coroners reporting blood alcohol, compulsory seatbelts and motorway speed limits. By 1969, her Ministry of Transport reported a ‘marked fall in road accidents’. Drink driving casualties continued to decline as social attitudes and behaviour improved.

Scottish legislation failed to reduce road traffic accidents further, for which this report blames ‘a lack of enforcement’.

The 1967 population driving after drinking was more diverse than today’s law-breakers. ‘Social deviance’ predicts traffic accident risk (West et al., 1993) and incidents disproportionately involve heavy drinking ‘outlaws’ (Sykes et al., 2010). That ‘outlaw’ population probably ignored the 2014 legislation.

Professor Woody Caan, Editor of the Journal of Public Mental Health; Royal Society for Public Health Professorial Fellow

The commentator is a member of the Alcohol and Health Alliance