Undoing the lock-in of suburban sprawl: Towards an integrated modelling of materials and emissions in buildings and vehicles

Suburban sprawl emerged during the 20th century alongside the widespread ownership of cars. This type of low-density housing generates enduring car dependency due to the long lifetimes of buildings. A more sustainable mobility system would require a deep transformation to densify urban forms and thus foster proximity of homes, work, and services. Here we explore the evolution of long-lived residential building stocks and the potential for breaking of this lock-in by selective demolishing of detached houses to densify urban forms. We assess impacts on land use, material demand and stocks, and greenhouse gas emissions. We use a novel dynamic, Material Flow Analysis (MFA) model applied to a Swedish case study that accounts for the co-relations of building stock and car fleets through residential density. The model includes different municipality types and we explore three different speeds for the change in urban form. An accelerated densification requires more bulk materials in construction but fewer scarcer materials in cars. However, the up-front emissions of accelerated densification construction are only compensated by mobility savings in the long-term, by 2100. Emissions trends for the three scenarios are far from the urgent decarbonisation necessary. However, the denser final built environments may have social benefits and can free up significant land.