How periurban morphology impacts public transport cost in low Density areas?: An analysis of 100 French metropolitan areas

International audienceMobility in low density and periurban areas is a major issue for an urban sustainable development. In fact these motilities refer to many actual questions: accessibility, car dependence, social exclusion, land consumption, transport oriented development (TOD)… If some works try to include periurban morphology in the analysis of mobility in low density areas, none or only a few have linked morphology and cost of public transports in almost 100 metropolitan areas.This research proposes to analyse how periurban morphology can impact public transport cost in periurban areas. Combining GIS (geographical information system), spatial analysis and statistics (regressions, khi²…), this work provides results based on the analysis of 100 French “aires urbaines” (metropolitan areas). Our work aims to stimulate ideas regarding urbanism, mobility and public transports in these territories. It has three main steps:-A morphological typology of French periurban areas. This typology is based on built areas’ form, with methods developed in early quantitative geography and in recent works (Hagget, 1973; Beguin, 1979; Guerois, 2003, Emangard, 2008).-A comparison of public transport cost between areas, using a theoretical public transport networks linking all periurban people to the agglomeration core, and an estimation of morphology impact on these costs. The use of theoretical networks, with identical rules of conception, allows comparison between cities.-A reflection on network optimisation (three optimised theoretical networks are tested: trunk/feeder connection, bike riding to station, public transport only in main roads) and an analysis of impact of periurban morphology on these optimised networks.The results of this work are quite numerous. First, we have quantified the periurban population living in each morphological type: 17% in dispersed houses, 34% in linear settlement and 49% in compact settlement. We have also observed regional organisations: there is more dispersion in South West of France, more linear settlements in North coast and Alps Valley, more compact organisations in North East. Secondly, if most of politicians only focus on density, our work highlights the role of morphology on public transport cost, especially the impact of dispersion. Third, comparing different theoretical network organisations, we highlight that combining hierarchical public transports network with bike approach to station is the best way to obtain a high demographical coverage with a moderate cost