Urban agglomeration policy and coordinated road infrastructure development

Fostering seamless mobility across administrative borders by coordinating road networks is a key objective of transportation infrastructure development. China's Urban Agglomeration Policy (UAP) is an important practice in this realm, yet empirical evidence on its effects remains limited. This study addresses this gap by utilizing station-level traffic flow data to create a new traffic flow disparities indicator and employing a staggered Difference-in-Differences strategy for the period 2010 to 2017. The findings reveal that the UAP significantly reduced traffic flow disparities between adjacent cities, with improved coordinated road infrastructure development serving as the driving mechanism. The UAP narrowed disparities in road length (quantity) between interprovincial adjacent cities, promoted the coordinated development of road quantity and technical standards (quality) among intraprovincial adjacent cities, and enhanced cross-border road infrastructure connectivity, enabling less-developed cities to catch up with their more developed counterparts. The effects are more pronounced in areas with initially larger disparities, particularly among interprovincial adjacent cities compared to intraprovincial ones, and on highways compared to ordinary national roads. These findings underscore the importance of strategic transportation infrastructure planning in promoting coordinated road infrastructure development and mitigating regional traffic flow disparities.