Gravity-based accessibility measures for integrated transport-land use planning (GraBAM)

In transportation planning a paradigm shift is occurring: from mobility-oriented analysis (which evaluates transport system performance based on quantity and quality of physical travel) to accessibility-based analysis (which considers a broader range of impacts and options) (Litman, 2010). The instrument described in this paper, is an example of this shift which gives to accessibility measures a central role in transport and urban planning. Such accessibility instruments have been developed both for scientific and planning motivations. In the academic field the important role of transport infrastructures for spatial development is well recognized: areas with better access to the locations of input materials and markets will be more productive, more competitive and hence more attractive than remote and isolated areas (Linneker, 1997). However, the impact of transport infrastructures on spatial development has been difficult to be verified empirically; in fact, modelling analysis, such as those based on accessibility measures, is necessary to investigate these impacts and to analyse the effects of transport infrastructure and service improvements on the spatial distribution patterns. In other words, the scientific question the accessibility instrument here presented, wants to answer is “what are the impacts on the land use induced by changes in the transportation system?” The scientific question has direct implications for planning, related to the distributive issues of transport interventions: the goal of the accessibility instrument is to assess and to value the benefits of changes in either the land-use or the transportation systems, as a performance indicator of integrated land-use and transport planning. In other words, the question the instrument wants to address is “who reaps the accessibility benefits from investments in the transport system and where are these located?