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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.

Share your views on the research.

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.

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.

Impact of legislation to reduce the drink-drive limit on road traffic accidents and alcohol consumption in Scotland: a natural experiment study

Published on 26 June 2019

Lewsey J, Haghpanahan H, Mackay D, McIntosh E, Pell J & Jones A.

Public Health Research Volume 7 Issue 12 , 2019

Background It is widely recognised that drink driving is a leading cause of road traffic accidents (RTAs). There is evidence that changing the drink-drive limit from a blood alcohol concentration of 0.08 to 0.05 g/dl is effective in reducing RTAs. Scotland changed the blood alcohol concentration limit to 0.05 g/dl on 5 December 2014. Aims To assess whether or not the numbers and rates of RTAs and per capita alcohol consumption in Scotland were reduced because of the 2014 drink-drive legislation. To assess whether or not the 2014 change in legislation provided good value for money. Design A natural experimental, quantitative study. The control group was England and Wales, that is, the other countries in Great Britain, where the drink-drive legislation remained unchanged. Setting Great Britain. Participants The entire population of Scotland, England and Wales for the period of January 2013–December 2016. Intervention The change to drink-drive legislation in Scotland. Outcome measures The counts and rates of RTAs; and per capita alcohol consumption. Methods For the numbers and rates of RTAs (both traffic flow and population denominators were used), and separately for the intervention and control trial groups, negative binomial regression models were fitted to panel data sets to test for a change in outcome level after the new 2014 legislation was in place. To obtain a ‘difference-in-differences’ (DiD)-type measure of effect, an interaction term between the intervention group indicator and the binary covariate for indicating pre and post change in legislation (‘pseudo’-change for the control group) was assessed. For off- and on-trade per capita alcohol sales, and separately for the intervention and control trial group, seasonal autoregressive integrated moving average error models were fitted to the relevant time series. Results The change to drink-drive legislation was associated with a 2% relative decrease in RTAs in Scotland [relative risk (RR) 0.98, 95% CI 0.91 to 1.04; p = 0.53]. However, the pseudo-change in legislation was associated with a 5% decrease in RTAs in England and Wales (RR 0.95, 95% CI 0.90 to 1.00; p = 0.05). For RTA rates, with traffic flow as the denominator, the DiD-type estimate indicated a 7% increase in rates for Scotland relative to England and Wales (unadjusted RR 1.07, 95% CI 0.98 to 1.17; p = 0.1). The change to drink-drive legislation was associated with a 0.3% relative decrease in per capita off-trade sales (–0.3%, 95% CI –1.7% to 1.1%; p = 0.71) and a 0.7% decrease in per capita on-trade sales (–0.7%, 95% CI –0.8% to –0.5%; p < 0.001). Conclusion The change to drink-drive legislation in Scotland in December 2014 did not have the expected effect of reducing RTAs in the country, and nor did it change alcohol drinking levels in Scotland. This main finding for RTAs was unexpected and the research has shown that a lack of enforcement is the most likely reason for legislation failure. Future work Investigations into how the public interpret and act on changes in drink-drive legislation would be welcome, as would research into whether or not previous change in drink-drive legislation effects on RTAs in other jurisdictions are associated with the level of enforcement that took place. Funding This project was funded by the National Institute for Health Research (NIHR) Public Health Research programme and will be published in full in Public Health Research; Vol. 7, No. 12. See the NIHR Journals Library website for further project information.

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