Assessing the impacts of metro loop lines on transit accessibility and equity

Metro loop lines improve travel efficiency by connecting radial lines and improving the transport environment, but their impacts on accessibility and equity remain underexplored. This study examines these impacts by comparing changes in transit accessibility before and after the opening of metro loop lines in Guangzhou. Transit accessibility to destinations is measured using travel data from the Amap API and a gravity-based accessibility model. On this basis, transport equity is assessed by the Gini coefficient, the Palma ratio, and the bivariate local indicator of spatial autocorrelation (BiLISA). The analysis is conducted under five travel time thresholds to consider the boundary effect of the Modifiable Temporal Unit Problem (MTUP). Results show that loop lines improve accessibility, especially in peripheral regions, benefiting vulnerable groups and reducing social-spatial inequities. Accessibility gains exhibit sensitivity to travel time threshold selection, peaking between 45 and 75 min. Overall, the loop line is shown to be an equitable transit investment from the perspective of accessibility-based distributive justice.