3.2 Dependent variables
We analyzed the convergence of RSA, CRL and DRL. Information to establish the year in which each country implemented each policy was systematically gathered and coded according to a standardized scheme from the WHO reports on road safety (World Health Organization, 2004, 2010, 2013, 2019), national traffic laws, peer-reviewed journals, governmental and international organization reports, and personal communication via email with road safety country representatives. The WHO reports identify whether each country has an RSA and CRL. The WHO applies a specific methodology to collect reliable information per country. Since 2010, it biannually sends a questionnaire that must be completed by five representatives of each country, and for this information to be made public, these national representatives must agree on their responses as well as provide official documents, such as traffic laws or any other legal instrument, stating that the information is accurate. Then from each available source, we extracted, and when necessary translated, the dates when the RSAs were created, and the norms which regulated CRL and DRL use in traffic laws. In reference to the RSAs, we identified in the WHO reports the specific names of each agency and proceeded to locate their institutional websites and other reports to find the years in which these organizations were created. Regarding CRL, we looked at the seat-belts’ sub-section, and for DRL, we focused on the use of lights’ sub-section We also located definitions of the concepts “beginning of sunlight” or “end of sunlight” to determine when the use of lights was mandatory. Similarly, we proceeded to identify when these laws were for the first time enacted after evidence of policy adoption was confirmed. In Table S.5 (supplementary material) we present the years of enactment for each policy for 181 independent countries. Coverage for RSAs was 97%, for CRL 98%, and for DRL 83%. We treated policy convergence as an event that occurred, and absence of convergence when the policy had not been adopted. The dependent variables were thus: i) ‘Time to adopt a RSA’; ii) ‘Time to adopt CRL’; and iii) ‘Time to adopt DRL’.
3.3 Independent variables
a. Types of convergence
Global convergence. We explore whether global convergence has been reached, by using the shape parameter ρ of the Weibull function of the survival analysis models as we describe below. In reporting the results, following Kogut and Macpherson (Kogut and Macpherson, 2011), we also call this shape parameter “time,” as its sign provides information on whether baseline adoption increases or slows during the observed period. A declining hazard rate can represent statistical bias arising from unobserved heterogeneity, meaning that conditions to accept the global convergence thesis are not met (Kogut and Macpherson, 2011). For the thesis of convergence to be supported, the parameter ρ should increase significantly.
We also use two international treaties to observe factors that can be associated with global policy convergence: the “Geneva Convention on Road Traffic”, and the AAUTPV. International treaties, understood as variables that represent global forces, have been used to predict the convergence of policies, particularly in the realm of human rights (Cole, 2012). The Geneva Convention on Road Traffic was designed to promote the development of traffic safety by establishing certain uniform rules. Information of which countries signed the convention and the date of the signature is provided by the United Nations (United Nations, 1995). This variable was dichotomous in which ‘0’ corresponds to the period before the signature, and represents not having signed the convention, and ‘1’ the period after having signed the convention, representing whether a country has agreed to adhere to road safety policy recommendations. The AAUTPV was promoted to establish rules of reciprocity between signing countries. This agreement set the conditions to discuss the uniform provisions concerning CRL as well as DRL. Information of which countries signed the agreement and at what date is provided by the United Nations (67). Like the Geneva Convention, this variable was dichotomous in which ‘0’ corresponds to the period before the signature and represents not having signed the agreement, and ‘1’ the period after having signed the agreement, representing whether a country has been more inclined to adopt CRL and DRL.
Regional convergence. To determine whether a regional convergence has occured, we use the ρ of the Weibull function of the survival analysis when restricting the analysis for Europe and LAC, respectively. For Europe, we also consider the Creation of the European Transport Safety Council. This variable was set to be dichotomous, with ‘0’, corresponding to the period before 1993, representing the absence of this institution, and ‘1’, the period of 1993 onwards, representing the time period following the launch of this institution. Results for Africa, Asia and the Pacific, and Western Asia are available in supplementary material (Table S.6).
Unintended convergence. To assess unintended convergence outcomes, we assess three variables. Population. Population has been obtained from the WB (World Bank, 2020). We logged this variable to correct for its skewed distribution. Political violence. This variable is defined by the systematic and sustained use of lethal violence by organized groups that result in at least 500 directly related deaths over the course of the episode. Each episode is designated to span a certain number of years and judged to have been of a certain, general “magnitude of societal-systemic impact”. An eleven-point scale, 0-10 gathered from the Center for Systemic Peace was used (Marshall, 2021). Average yearly total number of hours of bright sunshine. According to the World Meteorological Organization (WMO), bright sunshine duration during a given period is defined as the sum of the sub-period for which the direct solar irradiance exceeds 120 Wm−2. Data were gathered from the WMO ((Organization (WMO) and World Meteorological Organization (WMO), 2018).
b. Mechanisms of convergence
Variables representing mechanisms of convergence were introduced to examine if policies were or not adopted. These were divided into three: imitation/learning, coercion, and competition.
Imitation/learning. World Health Organization road safety global campaign. In 2004, this UN body launched a global campaign to promote the implementation of road safety measures to reduce the toll of traffic fatality and injury rates across the world (World Health Organization, 2010, 2013). From 2004 until the present, this organization has written a series of reports and carried out several world and regional forums to endorse a series of road safety best practices. This variable was dichotomous with ‘0’ corresponding to the period before 2004, and representing the absence of the global campaign, and ‘1’ representing the period of 2004 onwards, following the launching and dissemination of the global campaign.
Imitation/learning. Existence of road safety NGOs. The presence of a road safety NGO in each country represents whether a country has this type of institution. Information was obtained from the Global Alliance for NGOs for Road Safety (Global Alliance for NGOs for road safety, 2020). This variable was dichotomous, with ‘0’ corresponding to countries without membership to the Global Alliance for NGOs for Road Safety, and ‘1’ representing countries with membership.
Coercion. Type of importer-exporter vehicle country. Three categories were used to classify a country within the vehicle global trade market: i) ‘Vehicle-importer country’, was a country which did not export any type of vehicle; ii) ‘Vehicle-importer-exporter country’, was a country in which its vehicle importation trade value was higher than its exportation trade value; and iii) ‘Vehicle-exporter country’ was a country where the vehicle exportation trade value was higher than its importation trade value. Information was gathered from the United Nations Commodity Trade Statistics Database (United Nations, 2020). To determine the category of each country we added up its total amount of vehicle exports trade value and compared it to its total amount of imports vehicle trade value. This was applied for the period in which data for the country was available.
Competition. Type of importer-exporter vehicle country. We use the same categories and data to assess the coercion mechanism, but with an inverse result, namely that Vehicle-exporter countries are more likely to adopt DRL and accept RSA.
3.5 Statistical Method
To obtain valid estimates to test the convergence thesis and the mechanisms of global diffusion, we employ survival analysis. This method allows explaining events occurring to countries over a specified period (Brandon Tuma, 1984; STRANG, 1991; Jenkins, 2005; Cleves et al., 2008). Survival analysis has been used for various types of events ranging from decolonization (Strang, 1994) to policy adoption (True and Mintrom, 2001; Murillo and Martínez-Gallardo, 2007; Wotipka and Ramirez, 2008; Zeveleva and Nazif-Munoz, 2021). We use the Weibull hazard function since its ρ value can be used to interpret whether policy adoption significantly increases during the observed period, and thus leads to policy convergence.
It is important to notice that since outcomes could be a result of modeling countries as if they had been equally exposed to the same time risk, we defined the onset of risk depending on when the country had acquired national independence. However, if the country had obtained independence before the year in which the first policy was enacted, its exposure to road safety policy adoption started in the year in which the policy was enacted for the first time. Information about countries’ independence was obtained from the CIA’s World Factbook (Central IntelligenceAgency, 2011). Under this modeling, Norway, Belgium, Denmark and Finland were not part of the analysis of the diffusion of RSA, CRL and DRL, since they were the pioneers of each policy respectively.
Furthermore, since unobserved heterogeneity could also arise from road safety information that countries share due to their regional closeness, implying that unobserved processes could bias the results of the parameters (Cleves et al., 2008), we adjust the precision of the estimates for their adoption time rates in reference to 22 regional clusters based on the United Nations geoscheme (please see in Supplementary material Table S.8 the regional cluster list with the countries). In other words, each regional cluster is assigned a random effect—whose distribution does not depend on the observed variables— to model the potential impact of road safety information exchange among countries within each cluster.