Access graph: a novel graph representation of public transport networks for accessibility analysis

Abstract

We study shortest-path-based accessibility by building a so-called access graph where two nodes share an edge if one is reachable from the other within a given time budget. This is achieved by obtaining generalised travel times between all pairs of nodes and directly connecting the pairs where the generalised travel time condition is satisfied. We then observe the time evolution of the access graph, increasing the time budget from zero to the maximum travel time in the network. Average degree and degree distributions of the newly proposed access graphs for 51 metro networks are analysed and two global measures are proposed as network-level indicators of accessibility. For all metro networks in our empirical analysis, a logistic-like growth of average degree with time budget is observed. We see a large potential of the introduced graph representation for in-depth studies of accessibility.