Causal impacts of demand responsive transit on public transit demand: A spatial assessment framework

Demand-responsive transit (DRT) offers a flexible travel option complementary to the existing fixed-route transit (FRT), improving accessibility and mobility. However, how the adoption of DRT reshapes the new public transit (PT) system, consisting of DRT and FRT, has not yet been sufficiently explored. This study proposes a spatial assessment framework based on causal impact inference to evaluate the impact of DRT on the PT system and performs empirical analysis for DRT service areas in rural areas of Korea. Our framework identifies the spatial area where significant changes in the PT system occur and quantifies the changes in terms of DRT and FRT, respectively. Then, the effects of sociodemographic and built environment factors on changes in the PT system are investigated using regression models. The bias of spatial analysis resulting from the choice of spatial units, known as the modifiable areal unit problem, is identified and addressed by the community-level residential clustering method. The results indicate that approximately half of the residents in the service area experienced a significant increase in PT usage of around 30 %. The service area with a lower population density, a lower proportion of elderly residents, a lower business population, a lower existing bus trip rate, and a higher bus stop density is more likely to benefit from DRT in increasing PT usage. These findings provide valuable insights into devising strategies to introduce new DRT services and evaluate existing ones.