Optimizing Public Transit Quality and System Access: The Multiple-Route, Maximal Covering/Shortest-Path Problem

Walking Accessibility to Public Transport: An Analysis Based on Microdata and GIS

In this paper we analyse the role of walking accessibility to transit facilities. Microdata and GIS tools have been used to calculate distances walked by different population groups in accessing Metro stations. Distances walked by the population were used to determine the threshold distances of the station service areas and calculate the population covered by the Metro network. With respect to Metro ridership, different distance-decay functions were adjusted and the sensitivity of the population groups to the distance was measured. Two indicators were proposed, based on the distance-decay functions, to measure access quality and potential demand. The Madrid Metro network was used as the study area. Results show that young people and adults, men, immigrants, and public transit captives are willing to walk longer distances and are less sensitive to the effect of distance. When walking distances have been used in order to fix the limit of catchment areas, the amount of the population covered is lower than when a standard threshold (0.5 miles) is used, but overestimations affect each age group in a different way. The access quality indicator shows that the population group in the worst situation is children and that stations in the centre of the network have higher access quality values. However, the synthetic accessibility indicator shows that potential demand is lower for the most central and most peripheral stations than for the stations located in the intermediate areas. It has been proved that both indicators are sensitive to changes in the spatial distribution of population groups within the catchment areas. These results demonstrate some of the advantages of the proposed methodology and argue in favour of its use in public transport planning.

Distance-Measure Impacts on the Calculation of Transport Service Areas Using GIS

Access coverage is important in public transit planning, as this is the means by which service is provided to riders. In fact the proximity of demand (population and employment) to stops or stations on the network to a great extent explains its greater or lesser usage by potential users. Coverage of service areas can be delineated by GIS through the creation of buffers around transit facilities based on Euclidean (straight-line) distance. A second method is based on calculations of distances along a street network (network distance). The choice of the distance calculation method affects significantly the final results in terms of population covered. This paper assesses the overestimation of the straight-line-distance method, which is the most widely used in coverage analysis, by comparing it with that of network distances. It investigates systematically the factors influencing this overestimation, such as the density of stops or stations, the coverage distance thresholds and the characteristics of the area analysed (street-network design, barriers, and population distribution in the neighbourhood of the bus stop or station). Finally, it concludes that the network-distance method provides systematically better estimates of transit ridership than the Euclidean distance method.