Decarbonizing transport in low-density territories is constrained not only by price signals but also by coordination frictions between transport modes. This study examines the relative roles of economic incentives and multimodal coordination in shaping mobility equilibria, CO₂ emissions, and welfare outcomes in the Nord Franche-Comté region of France. We develop a multimodal equilibrium framework incorporating private cars, regular carpooling, and public transport while accounting for coordination costs in multimodal travel chains. Alternative policy regimes combine conventional carpooling, carbon-related incentives, fuel taxation, and Mu-CAR, an intelligent Mobility-as-a-Service infrastructure designed to reduce intermodal transaction costs. Pricing instruments alone generate limited changes in modal shares and emissions, whereas Mu-CAR induces a structural shift from solo driving towards carpooling and public transport. Mu-CAR achieves an annual CO₂ abatement of 2,429.96 tCO₂, compared with 222.62 tCO₂ under regular carpooling, representing more than a tenfold increase in emissions abatement. The Mu-CAR + CR + FT scenario reaches 2,619.30 tCO₂/year while maintaining a net welfare gain, although additional pricing instruments yield diminishing environmental benefits and reduce welfare gains. Sensitivity analysis further show that Mu-CAR’s relative environmental and economic performance is strongly conditioned by travel distance, with environmental and economic advantages occurring over different distance ranges. These findings indicate that transport decarbonization depends fundamentally on the coordination architecture of mobility systems, with pricing instruments playing a complementary role. Conceptually, the study extends the Avoid–Shift–Improve framework by identifying coordination as an enabling mechanism for shifting travellers towards lower-carbon and integrated mobility.
