Using accessibility indicators and GIS to assess spatial spillovers of transport infrastructure investment

Abstract

This paper proposes a methodology to measure spatial spillovers of transport infrastructure investment and to monetize them by distributing the costs of the infrastructures envisaged according to the regional distribution of the potential accessibility benefits. We use a transport master plan (the Spanish "Plan Estratégico de Infraestructuras y Transporte" 2005-2020, PEIT) as a case study for applying our methodology. In order to calculate and map regional spillovers, economic potential values are computed using network routines in a Geographic Information System (GIS) by comparing two scenarios: firstly, the scenario PEIT 2020; and secondly the scenario which includes the improvements envisaged for the year 2020 in all the regions except the region whose spillover effects are being analyzed. The differences between these two scenarios represent the potential spatial spillover effects of this region on the rest of the regions. This procedure is repeated for each of the Spanish regions in order to calculate a matrix of inter-regional spillovers in economic potential units. In a second step, this matrix is monetized by distributing the costs of the investment in infrastructures envisaged in the region according to the regional distribution of the economic potential benefits. This inter-regional matrix of investments flows characterizes the "inner", "export", and "import" values of each of the regional road investments. Subtracting from the direct investment the exports to other regions and adding the imports from other regions, an estimation of the real investment of the plan in each region taking into account all the spillover effects is obtained. This value can be compared with the direct investment in the region, analyzing whether one region has more or less direct investment than real. The proposed methodology makes it transparent which regions benefit more from national transport investment irrespective of where the investment occurs. The spillover matrix can be a valid instrument, especially in federal states or in the case of transnational projects, in the field of regional economics because it offers very useful information for both planners and policy makers.