Transit modal complementarity: measuring the access provided by transfers

This research investigates the interactions among transit (public transport) modes by inferring complementarity from a comparison of access provided by various transit modal combinations over a period of 160 years. A unique historical dataset of transit networks and services including buses, trains, and trams, generated for the Greater Sydney region for a period spanning from 1855 to 2015 was used. Access to population was measured for each year by 11 different modal cases formed by combinations of the three transit modes at a spatially disaggregated level as well as the regional level. The changes in access provided by the different modal cases were compared temporally and spatially to infer complementarity among the modes. Throughout the study period, trains, buses, and trams (when available) were found to be highly sub-additive at the regional level. Spatial comparison of complementarity was also demonstrated for Sydney’s Central Business District as an example. Such an investigation of access by modal combinations is a useful planning tool to ensure equitable supply and to investigate transfer benefits and penalties.