Urban congestion and households' vulnerability within the Bordeaux Metropolitan Area

This paper is part of a research project entitled STRATEGIE (interactionS TRAnsport and TErritories in GIrondE : Modelling and Monetize), supported by three local authorities in France [Région Aquitaine, Bordeaux Métropole and Département of Gironde (2015-2019)]. The research project focus on interactions between land use and transport in the Bordeaux metropolitan area with a particular attention paid to the social and economic aspects of sustainable mobility in suburban areas. Traditional approaches of urban durability are often too focalized on the environmental footprint of urban growth, thus neglecting other stakes of social sustainability of housing and transport linked to urban forms. However, the interaction of mobility constraints with location choices and access to housing is essential to understand contemporaneous patterns of spatial inequalities. The growth in house prices in French urban areas during the last decade (an increase of about 100% between 1998 and 2008) has considerably impacted housing accessibility for a large spectrum of households. As a consequence, a growing part of medium and Low income families have been led to move away from city centers to find a place to live and particularly to achieve ownership in suburban or exurban areas, thus reinforcing the connexion between owner-occupied housing tenure and car-based suburbanization. This phenomenon of urban relegation has important negative effects on the mobility of these households: lengthening of travel times and distances and consequently increasing travel costs combined with growing automobile dependency (Dupuy, 2011). As a consequence suburban congestion may have a disproportionate impact on medium and low income households located in exurban areas. The combination of exurban relocation of low income households with increased suburban congestion and oil vulnerability creates a risk of increased vulnerability of exurban low income households, defined as the combined increased of social isolation and poverty due to housing and transport increasing costs and irreversibility of location and mobility choices. This research aims to contribute to a better understanding of the combined impact of increasing land and house prices and suburban congestion on the vulnerability of exurban households within the metropolitan area of Bordeaux. The urban area of Bordeaux is nowadays one of the more attractive French urban areas, with a population growth rate of 8% between 2009 and 2014. The population growth is nevertheless more and more concentrated in the suburban and exurban areas, with mean annual growth rates ranging from less than 1% in the central city to more than 3% in more recently urbanized municipalities. These areas disproportionately concentrate families (rather than single person households) with more than 2.5 persons by household and medium and low income households. Beyond 15km from the city center, the median income is significantly lower than in more central areas and is continually decreasing with distance until 50km. Congestion appears to be very important in the urban area, with an overall loss of time estimated at 60% of theoretical travel time in 2013, and an increase of 3% between 2009 and 2013. Moreover, the main congestion peaks occur along the peripheral ring of the urban area, thus impacting mainly households living beyond 15km from the city center and having centripetal journeys to work. It seems thus essential to develop a spatial approach of the impact of urban congestion on households' mobility and location choices. For that, our approach consists of the following three main steps: (i) construction of spatial indicators of urban congestion (ii) assessment of congestion impacts on households' vulnerability and (iii) analysis of the impact of congestion on mobility practices, location choices and housing markets