Benefits from a new transit line: Exploring the impact of rare users and spatially heterogeneous variations in intensity of use

What are the city-wide benefits of introducing a new transit mode? Justification of a new transit mode is often based on claims of transformational change regarding mode share, ridership, or passenger-kilometers travelled (PKT). Detractors argue that these dramatic benefits are not experienced uniformly across populations or places. This paper quantifies the extent and intensity of the change in travel behaviour caused by the addition of a new mode and builds on measures of increased ridership and PKT to explore who is travelling on the new mode and in what ways. Recent advances in smartcard data analysis provide detailed insights into transit ridership but are often temporally limited, restricting the ability to analyse long-term behavioural trends. While research on transit ridership patterns exists, few studies compare users of the old and new modes in terms of spatial distribution and intensity of use. This study relies on a long baseline of data to estimate the home locations of travellers and their intensity of use. Our findings challenge assumptions about infrequent users and reveal that rare users significantly influence ridership patterns. Increased reach of ridership is substantiated based on the appearance of new cards 48 % higher than usual after the light rail introduction. However, only about 4 % of new card IDs make trips at a rate equivalent to a daily commute. The results show strong spatial patterns, with 50 % of frequent light rail riders having inferred home locations at the new stations and 63 % of daily riders not using the bus to access the light rail. This approach suggests that (1) rare users, though they ride less often, have a notable impact on ridership trends; (2) transit-access distances are shorter than conventional assumptions of approximately half-a-mile; and (3) ridership benefits show strong spatial patterns.