Road traffic injuries are a well-known public health concern with more than 1.19 million fatalities each year. They are the leading cause of fatalities among 5- to 29-year olds and are the 12th leading cause of death among all age groups, resulting in more than 50 million people being injured or disabled (1). Two-thirds of these fatalities occur in individuals of working age (18–59 years), leading to significant health, social, and economic consequences that reverberate throughout society. More than half of all road traffic deaths occur among vulnerable road users, including pedestrians, cyclists, and motorcyclists (1).

Multiple strategies have been developed since the late 1970s, mainly at the national level. However, less attention has been paid to implementing urban-specific road safety strategies (2). Nonetheless, most of the population lives in cities, both in low-middle and high-income countries. In cities, due to traffic congestion and lower speed limits, the number of fatalities is typically low, but there is a high number of traffic crashes involving many non-severe injuries, frequently affecting vulnerable users such as pedestrians, cyclists, two-wheeled motorists, and other personal mobility vehicles such as scooters (3).

From a health standpoint, road safety has usually been addressed from the perspective of health, treatment at emergency departments, or hospital admissions, especially at sub-national levels (4). There are fewer experiences of public health organizations involved in road safety at small area levels, probably because the actions primarily depend on other sectors such as police or mobility departments.

Barcelona is a Mediterranean city with 1.6 million inhabitants, covering 101.35 km², and a density of 15,992 people per km². The city attracts more than 12 million tourists annually. Every working day, there are more than 6.10 million commuting trips in the metropolitan area, of which 72.3% are internal to the city (4.42 million), and the remaining are connections. On weekdays, 74.6% of the trips starting or ending in Barcelona and carried out by city residents are made using sustainable modes of transportation: 46.4% on foot, by bicycle, or personal mobility devices, and 28.2% by public transport. With more than 270,000 two-wheeled motor vehicles registered, the modal share of private vehicles is 25.4%, with motorized two-wheeled vehicles accounting for 7%. Specifically, walking and metro journeys account for a high percentage, together representing 55.5% of the total flow.

In the early 1990s, the Agència de Salut Pública de Barcelona created a road traffic information system, working in close collaboration with the police and the mobility department. This system allowed monitoring of road traffic injuries and the evaluation of road safety interventions to inform policies and decision-makers. Documenting the experiences of road safety in cities for more than two decades is important to help inform the global dialog on road safety. This paper aims to discuss how road safety has been addressed for more than 20 years in Barcelona city by a public health organization, with special emphasis on evaluating the effectiveness of 10 road safety interventions, highlighting key success factors, and addressing the challenges encountered in the process.

Throughout the implementation of road safety policies in Barcelona, we assessed the effectiveness of several legislative and infrastructure interventions in terms of their impact on the number of collisions and injuries (Figure 2). The legislative policies evaluated include a helmet law (11), the penalty points system, and a motorcycle driver’s license (12). The infrastructure interventions assessed included speed radars (13, 14), 30 km/h speed limit zones, safe routes to school (15), advanced stop lines for motorcycles (16), and red-light cameras. We also estimated the cost–benefit ratio of speed radars (17). Table 2 summarizes the objectives, study designs, and main results of these evaluations conducted by the Agència de Salut Pública in Barcelona.

In this section, we discuss the overall impact of the interventions discussed above on road traffic injuries from January 2008, when most interventions had been implemented, until December 2023. The analysis was conducted by gender, injury severity, and mode of transport. We conducted a pre-post evaluation using a temporal series based on the Police Register of traffic crashes from the local police of Barcelona. The outcome variable was the number of injured individuals, analyzed using generalized linear models with a robust Poisson distribution. We adjusted for possible confounders, such as linear trend, seasonal patterns, and regression to the mean, using sine and cosine functions. The effects of the financial crisis since 2010 and the pandemic since March 2020 were also included. No adjustment was made for mobility exposure, as the interventions aimed to modify mobility itself. The aim was to assess magnitude trends rather than the risk of injury. For more detailed methods, see the Supplementary material.

This study highlights the imperative of analyzing traffic injuries through an intersectoral approach, particularly from a public health perspective, given their significant scale. Evaluating the health impact of interventions is essential, as it enables the informed shaping of policies that extend beyond the health sector and profoundly affect the wider population. The article presents compelling evidence of the effectiveness of road safety interventions within urban settings, recognizing the distinct characteristics of space, roads, and transportation modes compared to interurban areas, which is a context with limited existing evidence.

Moreover, this study emphasizes the ongoing need to assess the health impact of policies under varying circumstances. Even interventions with established effectiveness may not consistently yield positive outcomes. As exemplified in this study, the influence of speed cameras on the beltway differed from their impact on arterial roads and intersections (e.g., red-light radars), illustrating the nuanced effects of interventions in diverse urban settings. This evaluation approach is essential for refining strategies and tailoring interventions to optimize their effectiveness in specific urban environments.

Nearly all the evaluations discussed in this paper were published in peer-reviewed journals, providing robust evidence of the effectiveness of these interventions. These findings align with other published experiences and suggest that similar strategies could be successfully implemented in other cities. However, the transferability of these interventions requires careful consideration of local contexts, as factors such as population characteristics, commuting patterns, and urban infrastructure can significantly influence outcomes (19). Therefore, while these interventions offer a valuable framework for road safety improvements, new implementations should always be evaluated to ensure they achieve the desired impact in different settings.

The estimated prevented injuries due to road safety policies in Barcelona over more than two decades is substantial, particularly severe injuries. Although being a rough estimation it aims to quantify effect of road safety policies to support further implementation. Some of the reduction since 2008 can also be attributed to the financial crisis, which appears to have affected car users more than motorcyclists. In addition to the financial crisis, policies to reduce car use, such as increased parking costs and traffic calming measures, may have led more people to switch from cars to motorcycles. Furthermore, some moped users might have transitioned to motorcycle use after he change in driver license law (12).

As conditions evolve over time, it is challenging to isolate and assess the effectiveness of each individual intervention over an extended period. Despite this limitation, the use of generalized linear models with a robust Poisson distribution provides a robust statistical framework for analyzing injury trends. This approach accounts for key confounders such as linear trends, seasonality, the financial crisis, and the COVID-19 pandemic, enhancing the reliability of the findings. Additionally, the analysis spans a broad period (2002–2023) and examines trends by severity, gender, and mode of transport, offering a comprehensive and nuanced understanding of road safety outcomes. However, as the study relies on observational data, it cannot establish direct causality, and unaccounted-for confounding factors may still influence the results. Several factors were important for success. Firstly, an essential factor was the recognition by public health professionals of road safety as a critical issue in health outcomes monitoring. Secondly, the early establishment of a comprehensive information system that integrated data from health and police sources proved instrumental in characterizing incidents, prioritizing road safety measures, and facilitating evaluation. Thirdly, effective collaboration and coordination among public health, police, and mobility professionals were achieved through a formalized agreement. Intersectoral collaboration for road safety in Barcelona involved regular coordination through joint committees, data sharing, and integrated action plans of mobility and road safety. The public health agency provided insights on injury trends, determinants, evaluation, monitoring and follow-up of action plans. In police role, there was enforced traffic laws and analysis of incident reports, and the mobility department focused on infrastructure improvements, and developing plans. Together, they allocate resources, engage the community for input (Mobility Pact) projects to test and refine strategies, such advanced zones for motorcycle. Continuous communication and monitoring ensure alignment, enabling to collectively reduce traffic-related injuries and fatalities while improving urban mobility.

Finally, civic engagement—evident in participation in the Mobility Pact, and more recently, the advocacy efforts of civil society groups—highlighted concerns about health impacts, particularly in road safety and air quality, thereby advancing road safety policies.

Several challenges mainly focused in developing a surveillance system and evaluating interventions merit attention. First, despite being well-documented for decades, significant gender-based inequalities in mobility patterns (20), modes of transportation, and consequently, the nature, frequency, and severity of injuries (21, 22), must be acknowledged. It is imperative to consistently incorporate a gender perspective into surveillance systems, data analysis, and the design and evaluation of interventions (23).

Second, another methodologically significant challenge in assessing road safety concerns the calculation of rates, which requires a denominator representing exposure to mobility (21, 22). While the resident population serves as a common denominator for numerous health issues, including country-wide analyzes of road safety, this approach is less practical at the city level due to the dynamic nature of population movement. To address this issue, precise denominators are essential, enabling risk analysis at smaller geographic levels and the inclusion of factors such as age groups, gender, mode of transport, and type of collision. This is important when implementing policies to reduce car usage, especially in a globalized society where, beyond daily commutes, individuals engage in extensive travel for tourism. Cities therefore experience substantial fluctuations in daily travel patterns, emphasizing the need for exposure denominators that reflect population movement.

Third, there is a pressing need to make progress in the interoperability of diverse data sources, likely linked through some form of common identifier. This would enable the severity and type of injuries to be studied, drawing from health sources, in conjunction with the circumstances of collisions, as reported by police sources. Harnessing the strengths of each source would provide a more comprehensive understanding of the impact of road incidents.

Fourth, it is essential to integrate the perspective of socioeconomic inequalities into road safety analysis (24). To achieve this, individual information on social class, educational level, place of residence, and the location of collisions is required. However, such information is often lacking in existing data sources due to data protection concerns. Moreover, collisions frequently occur outside individuals’ residential area due to their mobility (22). Addressing these challenges is vital for a comprehensive understanding of the impact of socioeconomic inequalities on road traffic injuries. It is highly recommended that this individual data becomes available for public health officers and researchers.

Fifth, while health records effectively document diagnoses and procedures—primarily due to their link with economic outcomes—details such as the external cause of the injury (e.g., frontal collision, pedestrian hit), mode of transport (e.g., bicycle, motorcycle), and position in the vehicle (e.g., driver, passenger) are often inadequately recorded. Although the ICD-10-CM provides a framework for detailed encoding, the absence of specific reporting or the use of non-specific codes poses a significant challenge. Comprehensive data on these factors is crucial for studying the nature and severity of injuries related to the vehicle involved and the circumstances of the collision, which would facilitate the design of preventive measures.

Sixth, intersectoral collaboration can be hampered by various political agendas. Road safety, framed within the “health in all policies” approach, requires a collaborative strategy that highlights the co-benefits for health, extending beyond the health sector to encompass multiple sectors. However, engaging these sectors has often proven challenging. In certain instances, policymakers have supported measures detrimental to health, often relying on overly narrow economic arguments that prioritize short-term gains for specific sectors over long-term societal benefits. Furthermore, some policymakers may misunderstand “Health in All Policies” as an expectation that health decision-makers resolve issues beyond their domain. Perceptions can be shifted by introducing the concept of “Health For All Policies” and emphasizing co-benefits, offering win-win solutions for all sectors (25). In Barcelona, for instance, health arguments have been effective in advocating for policies facing resistance, such as car restrictions within the city. Recognizing and integrating cross-sectoral action is imperative for advancing toward Sustainable Development Goals. Finally, evaluating all road safety policies and interventions, as with any health-related issue, is imperative. Determining their impact on health and health inequalities is crucial, as their effectiveness may vary among different territories and population groups. It is important to emphasize that the reported and evaluated interventions are the result of long-term planning and the gradual evolution of mobility in the city. These interventions were not all planned simultaneously but developed over time in response to emerging needs. Furthermore, the evaluations focused on interventions for which sufficient data were available, including adequate sample sizes, geographic distribution, follow-up data, and, when possible, comparable areas for controlling confounders. At the same time, they show the evolution of mobility policies in the city that gives priority to pedestrians, active mobility and reduces car use. The commitment to evaluation upholds the principles of transparency and accountability. Assessing the effectiveness of road safety interventions requires planning assessments alongside interventions, including comparison groups, and collecting exposure and outcome measures both before and after implementation. Additionally, it is vital to document interventions thoroughly, including details about the location and dates of implementation.

To strengthen the evidence base for policy-making, it is necessary conducting a more comprehensive cost–benefit analysis of road safety interventions in the future. Such an analysis would provide valuable insights into the economic and societal impacts of these measures, helping to identify the most cost-effective strategies for reducing road traffic injuries. By considering both direct costs, such as implementation and maintenance, and indirect benefits, including health outcomes and productivity gains, policymakers can make more informed decisions about allocating resources to maximize public health and safety outcomes.

In conclusion, the surveillance and evaluation of road safety interventions at the city level are pivotal for optimizing resources, tailoring strategies to local conditions, and continuously enhancing urban safety. This comprehensive 25-year assessment of road safety interventions in Barcelona reveals the complexity of implementing and appraising diverse strategies. The findings reveal a spectrum of effectiveness among interventions, with some demonstrating remarkable success and others falling short. This holistic evaluation approach, encompassing legislation, infrastructure, and economic considerations, provides indispensable insights for ongoing improvements and future road safety initiatives. These findings offer valuable insights to other cities but it needs to be approached with careful adaptation and additional evaluation.

A public health perspective serves as a guiding principle, ensuring a thorough understanding of the impacts of interventions on individuals, communities, and populations. Aligned with preventive and equity-focused principles, this approach contributes to the formulation of evidence-based strategies that promote and safeguard health and well-being. The estimation of prevented road traffic injuries in Barcelona serves as a testament to the effectiveness of the interventions implemented at the local level, providing a robust foundation for continual policy evaluation and refinement. These findings significantly contribute to the broader field of road safety and public health, offering invaluable insights for evidence-based strategies in injury prevention and advocacy for sustainable transportation modes at the city level.