A quantitative spatial model for evaluating transport-induced spatial reorganization

Interregional transport improvements, such as highway and high-speed rail expansions, can significantly affect the spatial distribution of economic activity by enhancing agglomeration economies. Quantitative spatial models (QSMs) are a key tool for evaluating these effects; however, recent theoretical studies have identified a fundamental limitation: widely used QSMs invariably predict that transport cost reductions result in population dispersion rather than agglomeration in metropolitan areas. This prediction contradicts empirical evidence, suggesting that existing models cannot adequately represent transport policies' complex spatial impacts. To address this issue, this study extends a QSM to better incorporate the mechanisms driving economic agglomeration. We incorporate recent theoretical advancements to develop a more generalized QSM that addresses restrictive assumptions that otherwise systematically predict dispersion. We apply our extended model to Japan's highway network improvements, demonstrating that it successfully reflects economic agglomeration trends in major metropolitan areas. Furthermore, we estimate the spatial impacts of emerging autonomous vehicle technologies and truck platooning, finding that these innovations could help form a larger megalopolis centered on Tokyo, Osaka, and Nagoya.