National and regional potential accessibility convergence by decay and decades in Germany, France, Spain, Poland and Romania in the years of 1960-2020

The paper seeks to adapt methods of national and regional beta and sigma convergence from socio-economic sciences to a spatial framework. The process of reducing disparities in accessibility levels is commonly linked with the concept of territorial cohesion. We dynamically explore this concept by integrating economic terminology and applying it within a spatial context. This is accomplished through the utilization of beta and sigma accessibility convergence indices at both national and regional levels. We further extend the potential accessibility-based territorial cohesion index by using absolute and relative approaches. Accessibility indices are calculated for Germany, France, Spain, Poland, and Romania, covering six decades and various decay parameters (half-lives) from 1960 to 2020. Our analysis uncovers significant variations among the countries in terms of the pace, phases, direction, and underlying causes of both national (inter-country) and regional convergence processes. The approach presented serves as a model for dynamic, comparative analyses of accessibility changes across countries, examining both national convergence in potential accessibility and regional convergence in its diversity over the long term. It also provides a robust foundation for further research into phenomena such as club accessibility convergence, the impacts of cohesion policy, and the interplay between European spatial and transport policies and national strategies of major EU countries in shaping accessibility dynamics and regional development.