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[5OlXCzC1-15] Rising car dependence at Hiroshima University: A three-year empirical analysis of commuting behaviour, transit-service changes, and CO2 emissions (2023-2025)

Sonoko Watanabe, Makoto Chikaraishi, Shinji Kaneko (Hiroshima University)

キーワード：

commuting; CO2 emissions; modal shift; transit-service withdrawal; carbon neutrality; Smart Campus

In 2021, Hiroshima University released its Smart Campus 5.0 declaration, committing to carbon neutrality by 2030 for direct operations and 2040 for indirect emissions including commuting. Using three years (2023-2025) of administrative commuter-allowance data covering approximately 1,600 faculty and staff annually, this paper examines whether commuting behaviour is moving toward this goal. The empirical pattern is the opposite. The private-car share rose from 62.0% in 2023 to 68.9% in 2025 (+6.9 percentage points), while the combined share of bicycle, motorcycle and walking nearly halved from 11.8% to 6.7%. Public-transit shares remained flat near 25%. Translated into emissions using Ministry of Land, Infrastructure, Transport and Tourism mode-specific factors, per-commuter annual CO2 rose from 663 to 752 kg (+13.4%). Decomposing the per-capita increase shows that essentially all of it stems from the modal shift; emission factors and commute distances changed by less than one percent. Beyond the cohort trend, we identify a specific accelerating event: the April-2024 termination of the Green Phoenix express bus between the CBD of Hiroshima and the Higashi-Hiroshima campus. Of the 52 affected commuters tracked, nine (17%) switched to private cars within a year, contributing an estimated additional 5.5 tonnes of CO2 per year. Spatial analysis further shows that commuters residing outside the residential inducement zones commute by car 14 percentage points more than zone residents and emit 29% more CO2 per person. The headline message is that commuting behaviour at Hiroshima University is moving counter to the institution's declared carbon-neutrality goal, with both incremental modal shift and discrete service withdrawals contributing. Reversing the trend will require targeted policy interventions on both location and transport dimensions.