Measuring transit accessibility: A dispersion factor to recognise the spatial distribution of accessible opportunities

Abstract

This study advances the methodology of transit accessibility, particularly the cumulative opportunities by including the spatial distribution of accessible opportunities to assess the performance of transit systems and networks in meeting diverse travel needs. In cities where both population and employment are growing in suburban areas, a process of dispersion occurs distributing employment and other activities to centres outside the city centre. This growth causes significant change and diversification in people's travel patterns and needs. As the role of public transport systems becomes increasingly complex, transit accessibility models must address urban sprawl and the change of urban form from monocentric to polycentric. This study characterises the spatial distribution by the degree of clustering (or dispersion) of accessible opportunities, which is then included in the transit accessibility measure. This new accessibility component could be a meaningful indicator for transit agencies and planners to assess the performance of multi-destination transit networks. The transit accessibility measure incorporates a new transit connectivity index to consider that attractiveness of opportunities deteriorates with decreasing route directness and service frequency and increasing travel time. The proposed measure is applied to the transit network in Brisbane, Australia. The results of the accessibility analysis are compared with and without the dispersion factor to demonstrate its effectiveness.