How can HSR promote inter-city collaborative innovation across regional borders?

Many studies have shown that high-speed rail (HSR) can reshape the spatial pattern of economic geography. However, there needs to be more logical argumentation and rigorous empirical design on the paths and mechanisms involved. This paper considers the impact of the border effect on HSR links and innovation clusters from the perspective of inter-regional collaborative innovation. It provides a logical and compact theoretical framework for HSR to reshape the pattern of the economic geography of innovation and then give a data-based empirical test. Using a benchmark sample of 285 cities in China from 2001 to 2020, the paper empirically examines the impact of HSR links on collaborative innovation and its mechanism in different border samples. The results show that HSR can break through various types of regional borders, shorten the tangible and intangible distances between regions, and increase cross-regional collaborative innovation through three primary mechanisms: market integration, matching human capital, and activating innovation activities. The paper also inspires how to improve collaborative innovation in regions with economic, cultural, policy, and administrative borders in addition to traditional geographical borders and verifies the negative superposition effect of regional borders to provide adequate references for policymakers.