This paper offers new insights into crafting effective emission policies by examining demand for household vehicle fleets. I find evidence that fleet-level adjustment in fuel economy preferences is closely linked to the usage potential of electric vehicles. I estimate a role-dependent model of fleet choice, which allows for trip optimization and captures complementarity preference for vehicle attributes based on travel demands. The shift toward high-fuel-efficiency driving tends to dominate complementary preference for high-range electric vehicles and large utility vehicles, and failure to account for within-fleet substitution underestimates the effectiveness of emission policies.
