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[5OlXCzC1-16] Toward carbon-neutral commuting at Hiroshima University: A joint residence-mode policy simulation

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

キーワード：

residence-mode joint choice; mixed logit; self-selection; location optimization plan; transit-pass subsidy; carbon neutrality; Smart Campus

To meet the 2040 carbon-neutral commuting goal of Hiroshima University's 2021 Smart Campus declaration, this paper evaluates which policy levers can redirect commuting behavior toward the target and quantifies their costs and effects. We build a bivariate mixed-logit model of joint residence and commuting-mode choice estimated on 4,256 person-year observations from the Hiroshima metropolitan area. The model identifies two latent attitudinal dimensions: a strong pro-car attitude that jointly shapes suburban residential choice and car commuting, and a weaker pro-transit attitude that pulls households toward transit-accessible neighborhoods but, conditional on residence, does not translate into actual transit use — pinning down the residence-mode self-selection. We simulate ten policy scenarios for the 2025 cohort (N = 1,391): broad and geographically-targeted inducement-zone subsidies (residential and urban-function), three transit-pass subsidies, and four combinations. The simulation reveals that broad inducement subsidies applied uniformly across the 199-town zone — which spans both Higashi-Hiroshima and Hiroshima City — increase per-commuter CO2, paying to worsen the carbon outcome because the broad zone redistributes car-oriented entrants toward longer commutes. Targeted subsidies restricted to the 36 inducement-zone towns inside Higashi-Hiroshima reverse the sign: both the residential subsidy and the urban-function subsidy achieve substantial reductions in CO2. A fully-targeted combined scenario (urban-function plus spatially-restricted PT-pass subsidy) delivers −70 kg/commuter/year (−11.9%) and a 7.6-pp public-transit share gain at ¥12.5 M/month — the lowest cost among dual-objective packages. The direct implication is that residential inducement subsidies should not encourage residence far from the principal workplace, even within a designated inducement zone; otherwise they undermine the carbon-neutrality goal they should support.