Measuring transit system accessibility using a modified two-step floating catchment technique

Previous research has drawn attention to the importance of measuring accessibility to public transit services for transport planning and decision-making purposes and to the use of GIS to produce accessibility maps. Existing measures have been criticised for their lack of sophistication and reliance on simple operations such as Euclidean buffering. This paper introduces an accessibility measure based upon enhanced 'floating catchment' techniques, which have to date not been applied to measure access to public transport opportunities. We demonstrate that, after essential modifications to reflect the characteristics of transit service provision, this approach captures many detailed aspects of accessibility including proximity, the balance between service supply and demand, cumulative opportunity, and temporal availability. We illustrate its application using a case study based in South Wales, integrating publicly available digital transport timetables and information on bus stop locations with geospatial analysis tools to provide a realistic appraisal of bus transit accessibility. Such measures could clearly form the basis of future studies of social exclusion and access to public transport opportunities. We conclude by drawing attention to the potential for including more intelligent demand-side and supply-side modelling inputs and by reiterating the policy importance of developing more accurate evaluations of the current and future state of the public transport network.