Do different datasets tell the same story about urban mobility - A comparative study of public transit and taxi usage

Understanding human movements and their interactions with the built environment has long been a research interest in transport geography. In recent years, two important types of urban mobility datasets - smart card transactions and taxi GPS trajectories - have been used extensively but often separately to quantify travel patterns as well as urban spatial structures. Despite the fruitful research outcomes, the relationships between different types of transport flows in the same geographic area remain poorly understood. In this research, we propose an analytical framework to compare urban mobility patterns extracted from these two data sources. Using Singapore as a case study, this research introduces a three-fold comparative analysis to understand: (1) the spatial distributions of public transit and taxi usages and their relative balance; (2) the distance decay of travel distance, and (3) the spatial interaction communities extracted from the two transport modes. The research findings reveal that the spatial distributions of travel demand extracted from the two transport modes exhibit high correlations. However, more in-depth analysis (based on rank-size distribution and log odds ratio) reveals a higher degree of spatial heterogeneity in public transit usage. The travel distance of trips from public transit decays faster than that of taxi trips, highlighting the importance of taxis in facilitating long-distance travels. Both types of trips decay much faster when travel distance is beyond 20 km, which corresponds to the average distance from the urban periphery to the center. The spatial interaction communities derived from public transit are different on weekdays and weekends, while those of taxis show similar patterns. Both transport modes yield communities that reveal the city's polycentric structure, but their differences indicate that each of the transport modes plays a specific role in connecting certain places in the city. The study demonstrates the importance of comparative data analytics to urban and transportation research.