Under the background of China’s urban agglomerations: how does high-speed rail foster city-to-agglomeration knowledge flow

With the development of China’s high-speed rail (HSR), knowledge flow between regions has become a channel for innovation. Contextualised within China’s urban agglomeration policy, we focus on city-to-agglomeration knowledge flow and use a staggered difference-in-differences (DID) model to explore the effect of HSR connectivity on knowledge flow. HSR connectivity does not significantly promote the inter-city knowledge flow but significantly fosters knowledge flow directed towards urban agglomerations. We highlight that the agglomeration effect is reflected in the intensive short-distance knowledge flow and specialisation within agglomerations. This effect enhances the attraction of agglomerations to external long-distance knowledge flow. We further show that the positive effect of HSR frequency on city-to-agglomeration knowledge flow becomes stronger as the HSR network matures. Theoretically, this study contributes to demonstrating that the effect of transport infrastructure on knowledge flow is fundamentally moderated by the spatial structural context of destination regions. Our findings highlight the role of urban agglomerations in shaping the cross-boundary knowledge-flow effects of HSR and inform how policy should evolve with the maturity of the HSR network.