Key Characteristics of Multimodal Public Transport Across the Entire Commuting Process: Quantitative Evidence from Shanghai

Determining the critical factors influencing commuters’ choice of public transport is essential for increasing its commuting mode share. This study examines multimodal public transport (metro and bus) across the entire commuting process by utilizing survey data on commuting behavior and Internet-extracted data. The concept of travel time ratio, defined as the ratio of public transport travel time to car travel time for the same origin–destination (OD), is introduced to perform a quantitative analysis. A classification and regression tree (CART) model is then applied to identify and rank the key characteristics affecting public transport selection for commuting, and a marginal utility analysis quantifies their impact on commuting behavior. The results show that the travel time ratio is the most critical variable influencing commuters’ choice of public transport. Under the same commuting task, the average travel time of public transport is 25% longer than that of cars. This figure can reach nearly 70% for buses and 10% for the metro, which is the main reason for the low efficiency of public transport. Service characteristics optimization has a more substantial impact on increasing the commuting mode share for metro services than for buses. For every 0.1 decrease in the travel time ratio, the average commuting mode share for the metro and buses increased by 3.7% and 2.4%, respectively. To attract more commuters to public transport, it is necessary to maintain the travel time ratio within the range of 1–1.5. For bus services, in addition to improving commuting efficiency, it is essential to optimize convenience characteristics, such as transfer times, walking distance, and service frequency. This includes ensuring no transfers and maintaining a walking distance of less than 880 m. If the walking distance exceeds this threshold, the travel time ratio should be reduced below 1.1. Commuters without a private car demonstrate a higher tolerance for bus services, with a travel time ratio threshold of 1.8, provided that the overall service frequency is within 7 min. When fully served by the metro, if its service distance is within 6 km, the travel time should be comparable to that of cars to remain competitive. This study provides a quantitative basis for increasing the commuting mode share of public transport and improving its service quality.