From Feeder-Trip Counts to Occupied Feeder Vehicle-Kilometers: Evaluating Directional Feeder Activity and Occupied-Phase CO2 for Low-Carbon Sustainability Assessment at Peripheral Metro Stations

Metro feeder activity is commonly summarized by trip counts, although equal counts can correspond to different occupied distances and emissions. Using occupied taxi-trip records from 19 days in June 2023 at six purposively selected peripheral stations on Lanzhou Metro Line 1, this study links directional feeder activity, occupied distance, occupied feeder vehicle-kilometers traveled (VKT), and occupied-phase CO2. Egress dominates in the evening peak and off-peak under the three entrance-buffer specifications, whereas morning balance is buffer-sensitive; Access is more spatially concentrated than Egress. Under the 150 m reference specification, 200,493 feeder trips average 5.451 km and generate 1,092,957 km of occupied VKT. Count-proportional allocation produces station-level VKT errors from −26.7% to +22.3%; five of the six station rankings change under VKT, and top-10 count and attributed-VKT grids overlap by 6.67 of 10. At the same occupied VKT, the all-battery-electric scenario yields 82.10 t of occupied-phase CO2, 37.6% below the proxy-fleet base of 131.57 t; contextual non-occupied-VKT assumptions raise the estimate to 177.80–197.35 t. Counts and occupied VKT capture different operational dimensions. Low-carbon sustainability assessment should combine service frequency, occupied distance, and vehicle technology to support station-area carbon monitoring.