Title: Evaluation of legislation to reduce the drink drive limit in Scotland: a natural experiment
Funder: Chief Scientist Office, Scotland

Abstract: Background: It is well recognised that drink driving is a leading cause of road traffic accidents (RTAs). The British Road Safety Act introduced a legal blood alcohol concentration (BAC) limit of 0.08 g/dL in 1967 which is still in place today, with the exception of Scotland where the BAC limit was reduced to 0.05 g/dL on 5th December 2014. Aim: The overall aim of this research is to evaluate the change in drink driving legislation in Scotland. Research questions: 1) Has the change in drink driving legislation in Scotland been effective (reduction in RTAs)?; 2) Has the change in drink driving legislation in Scotland led to a reduction of inequalities associated with socio-economic deprivation?; 3) Has the change in drink driving legislation in Scotland led to a reduction in population alcohol consumption?; 4) Has the change in drink driving legislation in Scotland provided good value for money (been cost-effective)? Research design: we will employ a natural experimental design and analytical approaches to measure the causal effect of the change in BAC legislation in Scotland. Our control group will be England and Wales, the other countries in GB that still have a 0.08 g/dL BAC law. The data for the intervention and control groups used to measure effectiveness comes from the same data source and covers the same study period (four years in duration, two years pre- and post-legislation change - 5th December 2012 to 5th December 2016). We will follow MRC guidelines on best practice for conducting natural experiments Outcomes: The primary outcome measure for the effectiveness study is weekly rates of all RTAs. The secondary outcome measure of effectiveness is alcohol consumption per capita. For the economic evaluation, outcomes are weekly rate of RTAs (for a cost-effectiveness analysis); years of life lost and quality adjusted life years (for a cost-utility analysis); and contingent valuation values related to prevented fatalities as well as human injuries (for a cost benefit analysis). Impact: The scientific quality of the studies in the existing evidence base evaluating a change of BAC legislation from 0.08 g/dL to 0.05 g/dL is poor. Our study will directly address the methodological shortcomings of previous research and enrich the evidence base. It will be the first study to evaluate whether socio-economic deprivation influences the magnitude of the intervention effect, and the first to evaluate whether a reduction in BAC limit (for a whole country) has led to a reduction in that country’s population drinking.

Lay abstract: It is well recognised that drink driving is a leading cause of road traffic accidents. The British Road Safety Act introduced a legal blood alcohol concentration (BAC) limit of 0.08 g/dL in 1967 which is still in place today, with the exception of Scotland where the BAC limit was reduced to 0.05 g/dL on 5th December 2014. The fact that a change in drink driving policy has happened in Scotland but not in other parts of Great Britain provides a perfect opportunity to conduct a ‘natural experiment’ to assess whether the change was effective. Did it result in health gains for Scotland as a whole? Did it help reduce differences in health outcomes between the least and most deprived groups in society? If health gains were seen, did the amount of change seen offer good value for money? We will compare rates of road traffic accidents between Scotland and England and Wales (these two countries combined will be our comparison group), and both before and after the change in legislation occurred. By measuring socio-economic deprivation, we will also assess whether the change in legislation has had the desired effect (reducing road traffic accidents) for some groups in society but not others. We will also see if the change in legislation has had any impact on how much alcohol Scotland is drinking as a whole. To assess whether the change in legislation has provided good value for money, we will compare any change in levels of road traffic accidents to associated costs. These costs include the costs of the public-awareness advertising campaign highlighting the change in drink driving law, costs associated with changing the legislation in the Scottish Parliament, as well as costs associated with road traffic accidents (e.g. hospitalisations, coroner costs). Our study will enhance the current knowledge around whether changing drink driving policy leads to improvements in public health.

Research activity codes: 3.1 PRIMARY PREVENTION INTERVENTIONS TO MODIFY BEHAVIOURS OR PROMOTE WELL-BEING
Health categories: CANCER AND NEOPLASMS;CARDIOVASCULAR;INJURIES AND ACCIDENTS;ORAL AND GASTROINTESTINAL;STROKE