Accessibility and Network Structure in the German Commuting

A great deal of attention has recently been paid to the analysis of the structure and evolution of (complex) networks, starting from pioneering contributions in the physical and social sciences – and more recently in the regional and transportation sciences – mainly concerning the relevance of highly connected nodes (hubs). The presence of hubs identifies a network as Scale-Free (SF), because of its intrinsic characteristic of exhibiting power-law distributions in its connectivity structure, and thus highly heterogeneous patterns. The focus of this paper is to explore the homogeneous vs. heterogeneous characteristics of the German commuting network, by focusing on the role of accessibility. The concept of accessibility has a long tradition in the transport economics literature, starting with the fundamental works by Hansen in the 1950’s and later on by Weibull in the 1980’s. These authors defined accessibility as the potential of opportunities for spatial interaction. Accessibility conceived in this manner should also capture spatial structure effects and thus the network configuration properties, such as connectivity. This conventional accessibility function – in the light of the related economic activities – is be used as a suitable instrument to identify the major German hub/attraction nodes. As the functional form in this potential accessibility, the power-decay function will be considered – in addition to the negative exponential function – in order to explore the spatial configuration patterns, i.e. whether people perceive commuting cost in log-like way. The connectivity network analysis will then be developed as a benchmark to testing the results emerging from the spatial-economic analysis. In our application we consider home-to-work commuters traveling between 439 German districts, for the year 2002. The final results seem to highlight the tendency, in Germany, towards a multi-nodality network, where accessibility can play a fundamental role