Administrative division adjustments, road infrastructure integration, and traffic flow equalization: Evidence from city–county mergers in China

The drivers and consequences of intra-city transportation infrastructure integration are critical but often overlooked in the literature. This study examines whether the policy experiment of city–county mergers (CCMs, che xian she qu) in China fosters infrastructure integration and evaluates its impact on traffic flow equalization and balanced economic development within cities. The CCM policy divides a prefectural city into three types of intra-city division: reformed counties (former counties transformed into new districts), original districts, and unreformed counties. Using a staggered difference-in-differences approach and road traffic-flow data between 2005 and 2017, the analysis finds that the CCM policy promotes traffic flow equalization and balanced economic development between reformed counties and original districts but simultaneously increases disparities between reformed and unreformed counties. Mechanism analysis reveals that the policy reduces differences in road density and technical standards between reformed counties and original districts and boosting traffic flow in cross-border areas. However, these mechanisms do not apply to reformed versus unreformed counties. The opposing effects ultimately exacerbate intra-city traffic and economic disparities among all districts and counties, reinforcing the core–periphery structures of cities and leaving unreformed counties in the “agglomeration shadow.”