Accessibility and Impedance Forms: Empirical Applications to the German Commuting Network

Accessibility plays a fundamental role in the transport network. In fact, accessibility may be used for investigating the (un)even distribution of economic activities, or the (dis)equilibrium in the development of different regional performances. In particular, accessibility analysis can be considered as a first exploratory step in the understanding of people's needs and behaviour, especially in the framework of transport network structures. From the methodological viewpoint, accessibility has a long tradition, starting in the 1950's with the pioneering work by Hansen, who defined accessibility as the potential of opportunity for interaction. Such a definition can also be considered as an integrated framework of all subsequent definitions. The aim of this paper is to explore accessibility in the German commuting network, by focusing attention on the relevance of the impedance form associated with it. The conventional (potential) accessibility function - in the light of the related economic activities - is used as a suitable instrument to identify the major German hub/attraction nodes. In this formulation, different types of decay functions are used as impedance forms. In our applications we consider home-to-work commuters travelling between 439 German districts, for both 2003 and 2007. We carry out a comparative analysis of the accessibility values in these years, by outlining the different emerging hierarchies, resulting from the use of different impedance forms. In addition, we explore which type of accessibility indicator best matches the connectivity network. The final aim is to identify - by means of different accessibility functions - homogeneous vs. heterogeneous characteristics of the German commuting network.