From connectivity to complexity: The influence of high-speed rail on urban knowledge complexity

Knowledge complexity is a key determinant of regional competitiveness, yet the mechanisms and micro-level carriers through which transportation infrastructure shapes it remains insufficiently understood. This study examines the impact of high-speed rail (HSR) on knowledge complexity using patent and socio-economic data from 268 Chinese cities over 2005–2020, applying a multi-period difference-in-differences approach. Results show that HSR significantly enhances urban knowledge complexity, and the findings remain robust after addressing endogeneity concerns. Mechanism analysis reveals that HSR promotes complexity primarily through diversified agglomeration and network externalities, while specialized agglomeration has no significant effect. Moreover, HSR reshapes the relationship between agglomeration and network effects by substituting localized specialization with networked knowledge flows and enhancing the innovative potential of diversification through cross-regional complementarities. At the micro level, HSR triggers knowledge combination through two channels: a sharing mechanism that emphasizes collaborative interactions and collective knowledge externalities, and a matching mechanism that facilitates the strategic acquisition and recombination of external knowledge via technology transfers. By integrating agglomeration and network externality frameworks, this study provides empirical evidence on how HSR shapes urban knowledge complexity. The findings offer China-specific policy implications and transferable insights for regions pursuing innovation-driven growth through improved connectivity.