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Multiplex networks in metropolitan areas: generic features and local effects

Emanuele Strano, Saray Shai, Simon Dobson, Marc Barthelemy. ‎J. R. Soc. Interface  12: 20150651 (2015)
[Journal] [arXiv e-print] [PDF] [slides] [cover image]

Most large cities are spanned by more than one transportation system. These different modes of transport have usually been studied separately: it is however important to understand the impact on urban systems of the coupling between them and we report in this paper an empirical analysis of the coupling between the street network and the subway for the two large metropolitan areas of London and New York. We observe a similar behavior for network quantities related to quickest paths suggesting the existence of generic mechanisms operating beyond the local peculiarities of the specific cities studied. An analysis of the betweenness centrality distribution shows that the introduction of underground networks operate as a decentralizing force creating congestions in places located at the end of underground lines. Also, we find that increasing the speed of subways is not always beneficial and may lead to unwanted uneven spatial distributions of accessibility. In fact, for London – but not for New York – there is an optimal subway speed in terms of global congestion. These results show that it is crucial to consider the full, multimodal, multi-layer network aspects of transportation systems in order to understand the behavior of cities and to avoid possible negative side-effects of urban planning decisions.