Abstract Modal shift, or the transition from one mode of transportation to another, is increasingly recognized as a key demand-side strategy for rapidly reducing CO 2 emissions without necessitating major transformations in transportation systems or further technological advances. However, the current contribution of modal shift to CO 2 reduction remains limited, particularly in regions with a strong car dependency. This study investigates changes in commuting and school transportation modal shifts across 1,700 municipalities in Japan using data from the 2000, 2010, and 2020 National Censuses. The analysis identified critical thresholds in car usage rates (∼30%) and population densities (∼4,000 persons/km 2 ) where municipalities tended to diverge into either car-dependent or transit-oriented urban forms. These findings highlight accelerating polarization providing a framework for designing targeted interventions to support the transition to transit-oriented and low-carbon urban development. Car-centric municipalities require measures such as vehicle electrification to mitigate emissions, whereas municipalities near these thresholds present unique opportunities for targeted interventions that promote public transit and active mobility. This study underscores the importance of tailoring mobility strategies to local urban contexts and offers insights applicable to similar urban dynamics globally.
Hidaka et al. (Fri,) studied this question.