Principal investigator: Bruno Benevit
Original title: None for the Road? Stricter Drink Driving Laws and Road Accidents
Authors: Marco Francesconi and Jonathan James
Location of the Intervention: Scotland
Sample Size: 32.508 local authorities per month
Sector: Public Sector Economics
Primary Variable of Interest: Traffic accident rate on roads
Type of Intervention: Legislation on alcohol consumption
Methodology: DID, RDD, Synthetic Control
Summary
Alcohol consumption is a major risk factor for traffic accidents. To safeguard citizens' lives, many policymakers establish restrictions on alcohol consumption by drivers, aiming to reduce this behavior. To assess the effectiveness of this type of measure, this article used administrative data from Scotland to verify the impact of reducing the blood alcohol concentration limits accepted by the country's legislation on the incidence of drunk driving and the rate of road traffic accidents. The estimates revealed that the reform did not have a significant impact on these two aspects, a result mainly explained by the lack of affordable alternative transportation and weak law enforcement. No significant externalities were identified in areas such as alcohol consumption or criminal activities beyond drunk driving.
- Policy Problem
Driving under the influence of alcohol is a major risk factor for traffic accidents, contributing to one of the biggest global public health problems. According to the authors, more than 160.000 road collisions were reported in 2018 (FRANCESCONI; JAMES, 2021). Over the last three decades, traffic accidents have consistently been the second or third leading cause of death for Britons aged 5 to 34. Medical studies indicate that lowering blood alcohol concentration limits (Blood Alcohol Concentration– BAC) can significantly reduce the risks of accidents associated with drunkenness.
Limiting BAC has become a frequently used policy by public managers around the world to mitigate the incidence of traffic collisions. According to the World Health Organization (WHO), adopting the 0,05 BAC limit represents a criterion of good governmental practice for this problem, being adopted by 45 countries and covering approximately 2,3 billion people. In 2001, the European Commission recommended the adoption of the 0,05 BAC limit. However, despite the UK government commission recommending a reduction of the limit from 0,08 to 0,05 BAC, its members England, Wales and Northern Ireland were the only European countries with the recommended limit.
In this context, Scotland implemented a reform to reduce the legal limit for BAC (Drink Drive Limit – (DDL) in 2014, accepting the reduction suggested by the WHO and differentiating itself from the rest of the United Kingdom by keeping the BAC limit unchanged. At the same time, the penalties for drivers caught driving above the limit remained unchanged in both Scotland and the rest of the United Kingdom. Thus, measuring the impacts of this measure is fundamental to understanding the effectiveness of this public policy.
- Policy Implementation Context
The reduction in the BAC limit in Scotland was motivated by concerns about the high mortality rates related to excessive alcohol consumption. Before the 2014 DDL reform, the 0,08 BAC limit had been in place for over 45 years and was considered inadequate to address the high rates of disease and mortality in the country, such as cirrhosis and liver disease. Life expectancy in Scotland was among the lowest in OECD countries, which increased the pressure for change. The new law reduced the limit to 0,05 BAC, aligning Scotland with other European countries.
The authors also highlight that alcohol consumption patterns and traffic accident rates in Scotland are similar to those of countries such as the USA, Canada, Singapore, and Mexico, as well as England and Wales, where the legal blood alcohol limit for driving is 0,08 BAC.
Alongside the reform, its dissemination was widely promoted through advertising campaigns on television, radio, and digital media, especially in border regions with England, where the 0,08 BAC limit was still in effect. Additionally, the variability in alcohol metabolism among individuals made precise assessment of BAC levels difficult, which could create uncertainty for both drivers and authorities in enforcing the new rule.
Regarding the local repercussions of the DDL, the impacts on the alcohol industry have generated concerns within the alcohol sector, which has been responsible for 4% of the country's GDP since 2000. The measure could negatively impact alcohol consumption in bars and restaurants, affecting the local economy, which was still recovering from the global financial crisis amidst ongoing fiscal adjustments in the United Kingdom.
- Evaluation Details
To assess the impact of the 2014 DDL reform in Scotland, several datasets were used. The primary one was the Road Accident Database (RAD), which includes information on over 1,2 million recorded accidents from January 2009 to December 2016. Each record contains details about the accident, such as the age and sex of those involved, the exact time and location of the accident, and the severity, which can be fatal, serious, or minor. In addition, the RAD includes data on alcohol involvement, collected from breathalyzer tests conducted at the scene of the accident. While it does not provide the exact alcohol level, it indicates whether the test was negative, positive, or if the driver refused to take it.
The sample considered in the study encompasses 378 local authorities (LAs) in Great Britain, with 347 in England and Wales and 31 in Scotland. The results analyzed include total accident rates, accident rates by severity level, and accident rates related to alcohol consumption, calculated as the number of accidents per category in a specific local authority divided by the number of registered vehicles in the same area. The observations considered were measured at the LA-year level, comprising 32.508 observations.
The data showed that Scotland had lower accident rates than the rest of Great Britain, especially for minor accidents. The introduction of the reform did not show a noticeable slowdown in collision rates in Scotland, suggesting that the stricter limit may not have had a significant impact.
- Method
The study analyzed the impact of the DDL reform on the incidence of accidents and offenses related to driving under the influence of alcohol. To this end, three main methods were used to assess its impact. The first was the Difference-in-Differences (DID) method, which compares the road accident rate before and after the reform between Scotland and other regions of Great Britain. This method adjusts for specific trends in each group and allows observation of changes in accident rates, including those related to alcohol consumption, over time.
The second method adopted is Spatial Discontinuous Regression (RDD), which focuses on regions near the border between Scotland and England. This method assesses unobserved regional differences and adjusts the results according to proximity to the border between the two regions, allowing the capture of unobservable cultural and behavioral similarities.
Finally, the Synthetic Control method was employed to construct a synthetic counterfactual of Scotland, replicating the characteristics of road accidents in Scotland before the reform using data from untreated regions. Among these characteristics, age group, day of the week, sex, time of day, regional population density, and the number of vehicles involved in accidents were considered. The method combines data to approximate pre-reform conditions and improves the accuracy of the estimate of the reform effects by comparing the evolution of accidents before and after the intervention.
As outcome variables, the study assessed accidents according to injuries (fatal, serious injury, minor injury, and all injury types) and breathalyzer test results (positive, refused, and positive or refused). The study also adjusted the data for seasonality effects and controlled for variables such as weather conditions, road congestion, socioeconomic status, and alcohol availability.
- Main results
The results obtained using the DID method indicated a 1,3 percentage point reduction in the total accident rate after the implementation of the 0,05 BAC law in Scotland, corresponding to a decrease of approximately 5% compared to the average accident rate. However, this reduction became insignificant when specific controls and fixed effects were included. Furthermore, no significant effects were observed on serious, fatal, or minor accidents. The analysis also revealed a statistically significant increase in accidents involving refusals to take a breathalyzer test, with no change in accidents resulting in positive tests. This increase may be related to the lack of change in alcohol consumption behavior among drivers who were aware of the new limit.
The results obtained using the RDD method indicated that the reform of the 0,05 BAC law in Scotland did not have a significant impact on overall accident rates, as well as on serious and minor accident rates. The effect was observed only in fatal accidents and in accidents with at least one driver who tested positive for alcohol or refused to take the test, but this only occurred when considering distances greater than the border (up to 200 km). Unlike the results of the DID method, the distinction between accidents with test refusals and those with positive tests did not alter the null effect conclusion for both types of accidents. These findings corroborated the results identified by the DID method, showing that alcohol restriction did not cause significant changes in road accident rates.
The results obtained using the synthetic control method showed no significant impact of the 0,05 BAC law reform in Scotland on traffic accident rates. The analysis, which examined different times of day, days of the week, ages and genders of drivers, as well as types of accidents and characteristics of urban and rural areas, revealed that the law did not alter accident rates under any of these conditions. The data indicated that there was no difference in accident rates during the day or at night, nor on weekends. Furthermore, the law did not affect accidents involving young drivers, men, or in areas with a high concentration of licensed alcohol establishments. Overall, the results confirmed that the reduction in the BAC limit did not bring about significant changes in road accident rates.
According to the authors, the lack of effect of the stricter alcohol limit policy can be explained by two main mechanisms. First, there was no improvement in the availability or reduction in the cost of alternative transportation, such as taxis and buses, after the reform. Second, law enforcement was also unaffected, evidenced by the consistent number of police officers, breathalyzer tests, and arrests for drunk driving. Furthermore, the reform failed to reduce alcohol consumption among drivers, nor did it alter related behaviors, such as cell phone use while driving or compliance with other traffic regulations. Finally, the results suggest that the reform did not generate significant behavioral changes among drivers.
- Lessons in Public Policy
In this article, the authors investigated how traffic accidents and alcohol testing were impacted by the DDL Reform implemented in Scotland in 2014, which reduced the permitted BAC limit for drivers in the country. The results showed that the reform did not have a significant effect on the overall accident rate, as well as on serious, fatal, and minor accidents. Although a reduction in the total accident rate was observed in some analyses, this reduction became insignificant when further adjustments were made. Furthermore, the analysis revealed an increase in accidents involving drivers who refused to take the alcohol test, but no impact was found on accidents with positive tests.
These results indicated that the reduction of the BAC limit in Scotland did not cause substantial changes in traffic accident rates, even when considering different times of day, days of the week, and driver characteristics. For policymakers, this indicates that the reform may not have achieved the desired effect in terms of road safety. The analysis reinforced the need for a more detailed evaluation of alcohol control policies and other measures that could effectively reduce traffic accidents.
References
FRANCESCONI, M.; JAMES, J. None for the Road? Stricter Drink Driving Laws and Road Accidents. Journal of Health Economics, 2021.
