Fractal model and multiscale accessibility indicators to see polycentrism differently

Résumé En

Polycentric organization is a common reality in many urban areas. The transport network is then designed to encourage exchanges between the secondary and main hubs, with a view to facilitating the functioning of the labour market and supporting economic activity. In this model of polycentric hierarchical organization, morning rush hour commuting is the main criterion for sizing transport infrastructure.Faced with the need to reduce greenhouse gas emissions, public actors are promoting alternative models, such as the transit oriented development. Although highlighting the soft modes and public transport, this perspective does not fundamentally question the priorities of the previous period: the challenge is always to promote access to the centres and the vision of the transport network remains highly hierarchical. Moreover, the difficulties of implementing this doctrine and its inability to moderate automobile dependency lead us to question its effectiveness.Faced with this observation, we apply the concept of Fractal Oriented Development (Frankhauser et al., 2017), multi-scale by nature, which differentiates the analysis support, fractal, from the measures of accessibility carried by this support, evolving according to the scales. This makes it possible to re-establish importance at the local level, and to differentiate rank in the hierarchy of city sizes and functions, by adapting to the practices of the inhabitants and local development trajectories. Some simulations will be drawn from the Ile-de-France Region case. Results of this modelisation will be discussed in light of recent analyses of the use of accessibility in urban policies (Fol and Gallez, 2017).