Regional transportation integration is a key aspect in promoting regional integration and high-quality economic development, as it can improve inter-regional connectivity, decrease transportation costs, and facilitate the flow of labor, capital, technology, and data. However, regional transportation integration is also difficult to quantitatively evaluate, causing difficulties in comprehensively understanding the specific transportation–economic relationships for different regions that are planned for integration. This article studied 41 cities in the Yangtze River Delta, which is known as the largest regional integration project in China. Two sets of index systems were created to quantitatively evaluate regional transportation integration and high-quality economic development. Coupling coordination degree analysis was then performed to investigate the relationship between the two systems. It was found that areas with a high degree of coupling coordination are located in the Z-shaped belt with the Shanghai–Nanjing–Hefei and Shanghai–Hangzhou–Ningbo urban agglomerations. Furthermore, specific developmental gaps between regional transportation integration and high-quality economic development were identified and mapped, showing areas with transportation development falling behind economic development and vice versa. Based on these findings, a number of policy suggestions are provided from the perspective of province and regional development. It is recommended to continue to invest in transportation development and integration in the well-coordinated Z-shaped region and areas with transportation development falling behind economic development, while it is not recommended to use transportation investment to solve economic problems for those under-developed regions that already have relatively advanced transportation than economic development.

This paper investigates the impact of high-speed railways (HSR) on urban innovation levels by improving intercity accessibility. We employ prefecture city-level data within three megacity regions in China from 2009 to 2018. Using the number of invention patents granted as a proxy for the innovation level of a city, we find that HSR facilities significantly improve urban innovation levels through better regional intercity accessibility and that there is a diminishing effect as commuting time increases. The impact mechanisms of innovation improvement can be explained by an ever-increasing potential of interaction activities among talents and technology investment opportunities among cities. We contribute to the literature by highlighting the spatial attenuation impact of HSR on urban innovation levels as well as the underlying mechanisms. Particularly, talent interaction exerts a larger effect on urban innovation levels than technology investment opportunities. Moreover, we unravel the heterogeneous effects that more innovative cities and cities with double first-class universities gain more from the improved intercity accessibility brought by HSR. This research has policy implications that promoting HSR facilities improves innovation levels of cities with different resources.