The principle of legality constitutes one of the basic principles of the government’s rule of law, and as a result, it has been recognized as one of the most essential guarantees of human rights. The goals of sustainable development have a strong link with the principle of legality, and achievements in accomplishing a goal can frequently contribute to the accomplishment of other goals in addition. The United Arab Emirates’ constitutional framework, regulations, and rules, along with the goals for sustainable development (SDGs), were profoundly affected by the principle of legality. The method in which international standards and laws have been integrated into the UAE’s national legal framework provides definitive proof of this effect. The research concluded that all published and unofficial legal regulations have to be respected in order for public authorities to use within the limits of the principle of legality. These involve adhering to the standards of positive legitimacy and the fundamental regulations the community agrees on.

South Korea has experienced rapid economic development since the 1960s. However, pronounced regional disparities have concurrently emerged. Amid the escalating regional inequalities and persistent demographic challenges characterized by low fertility rates, regional decline has become a pressing issue. Therefore, the feasibility of expanding transportation networks as a countermeasure to regional decline has been proposed. This study utilizes the synthetic control method and spatial difference-in-differences methodologies to assess the impact of the 2017 opening of Seoul–Yangyang Expressway on economic development and population inflow within Hongcheon-gun, Inje-gun, and Yangyang-gun. The purpose of this study is to evaluate the effectiveness of highway development as a policy instrument to mitigate regional decline. Findings from the synthetic control method analysis suggest a positive impact of the opening of the expressway on Hongcheon-gun’s Gross Regional Domestic Product (GRDP) in 2018, as well as Yangyang-gun’s net migration rates from 2017 to 2019. Conversely, the spatial difference-in-differences analysis, designed to identify spillover effects, reveals negative impacts of the highway on the GRDP and net migration rates of adjacent regions. Consequently, although targeted transportation infrastructure development in key non Seoul Metropolitan cities may contribute to ameliorating regional imbalances, results indicate that such measures alone are unlikely to suffice in attracting population to small- and medium-sized cities outside the Seoul Metropolitan Area.