The composite index provides an overview of public transport accessibility, combining the results of the closeness centrality, degree centrality, contour catchment, nodal betweenness, nodal resilience and nodal connectivity indicators in a comprehensive visualisation. To calculate it, between 0 and 12 points for each component index are allocated except for the resilience index, which leads to deductions for nodal averages with negative values. Thus the highest possible composite score for an activity node is 60. The results are further moderated by an international benchmarking coefficient that includes network coverage, global betweenness, average network resilience and a factor for the degree of contiguity of the urbanised area (in partial compensation for the adverse accessibility effects from public transport networks extending across scattered settlements).
The composite index remains cursory, however, because this calculation procedure invariably leads to subjective assumptions regarding how different component indicators are converted and weighted, and how the benchmarking coefficient is constructed. We therefore do not conceive of the composite index as a precise numerical instrument of inter-city comparison and for the same reason, refrain from presenting it as a network diagram with individual nodal values like the component indicators. Rather, we produce a scale map with nodal catchment areas shaded in traffic light colours according to performance brackets, and use it primarily as a visualisation tool to draw generalised conclusions and to engage with stakeholders in debates about public transport accessibility.
Composite Accessibility Index
where:
Si = Composite accessibility index for node i
cs = Network benchmarking coefficient
Ci = Closeness centrality index for node i
Di = Degree centrality index for node i
Qi(30)= 30-minute contour catchment for node i
actm = Number of residents and jobs in the metropolitan area
Bi = Betweenness index for node i
Vi = If Vi>1: Connectivity index for node i
Ri = If Ri<0: Average resilience index for segments converging in node i, weighted by departures per hour
The composite index remains cursory, however, because this calculation procedure invariably leads to subjective assumptions regarding how different component indicators are converted and weighted, and how the benchmarking coefficient is constructed. We therefore do not conceive of the composite index as a precise numerical instrument of inter-city comparison and for the same reason, refrain from presenting it as a network diagram with individual nodal values like the component indicators. Rather, we produce a scale map with nodal catchment areas shaded in traffic light colours according to performance brackets, and use it primarily as a visualisation tool to draw generalised conclusions and to engage with stakeholders in debates about public transport accessibility.
Composite Accessibility Index
where:
Si = Composite accessibility index for node i
cs = Network benchmarking coefficient
Ci = Closeness centrality index for node i
Di = Degree centrality index for node i
Qi(30)= 30-minute contour catchment for node i
actm = Number of residents and jobs in the metropolitan area
Bi = Betweenness index for node i
Vi = If Vi>1: Connectivity index for node i
Ri = If Ri<0: Average resilience index for segments converging in node i, weighted by departures per hour
