Measuring the spatial connectivity of urban public transport : a GIS application of the ICON indicator.

A well-designed urban public transport policy provides significant benefits: reduces congestion and costs, and decreases the number of accidents and environment impacts. Accessibility indicators are used by planners to assess the spatial effects of their proposals and to identify those areas requiring actions to ensure minimum conditions of service. They are also used in decision making on the implementation of new infrastructure projects or improvement of the existing ones. The paper first reviews the ICON indicator, which evaluates the connectivity of a location to the transport networks as a function of the minimum time required to reach the connection nodes of each network and the utility provided in these nodes. In the interurban ICON these networks include roads, railways, ports and airports. ICON is being used in planning and in project appraisal in interurban contexts to quantify in an understandable way the relationship between transport infrastructure and services endowment and variables that are spatially defined. But it has been seldom used in the urban environment context because its particularities introduce important methodological difficulties. The paper presents the adaptation of the ICON indicator to the public transport endowment of urban areas. It includes (a) the definition of a suitable URBan Indicator of CONnectivity (URBICON) providing a quantified spatial measure of connectivity to the transport networks and (b) an analysis of the possible uses of URBICON in regional, urban and transport planning and in project appraisal, through its integration with other spatial information (population, economic activity) and GIS tools. An application to the case of the city of Barcelona is presented, considering the public transport endowment in the year 2004. The URBICON provides an easy way to detect the areas that were poorly covered by the public transport system in 2004. Some of them are already covered by new or improved infrastructures and services and others should be served by 2014. This possibly shows that the zones detected by the URBICON correspond to those where planners have somehow decided to improve public transport services. URBICON thus appears as a powerful quantitative indicator to support urban planning.