## 7 Conclusions  
This study selected the Yangtze River Delta urban agglomeration as the research area and combined it with the current situation of the transportation development of the Yangtze River Delta urban agglomeration to construct the urban agglomeration transportation integration index system and evaluate the development status of the Yangtze River Delta urban agglomeration transportation integration. From the perspective of transportation integration, the study examined the influence mechanism of transportation infrastructure on industrial agglomeration. The transportation integration index of Yangtze River Delta urban agglomeration in 2019 and 2020 was 0.3937 and 0.3906, respectively, 4.62% and 3.8% higher than that in 2011. Owing to the impact of COVID-19, both passenger and cargo transportation in the Yangtze River Delta urban agglomeration in 2020 were affected to a certain extent. However, overall, the transportation integration index of the Yangtze River Delta urban agglomeration from 2011 to 2020 showed a clear upward trend. The transportation integration index value of Yangtze River Delta urban agglomeration in 2020 ranked the top five cities as Shanghai, Hangzhou, Hefei, Suzhou, and Nanjing. This indicates that the transportation network of urban agglomerations in Yangtze River Delta mainly takes \"Shanghai-Nanjing-Hangzhou\" as the core, and Suzhou and Hefei as the secondary core in the periphery, presenting a spatial pattern of a multi-center structure. The cities with Ti values in the Yangtze River Delta in 2020 were Huangshan, Huaibei, Yancheng, Suqian, and Zhoushan. These cities are located at the edge of Shanghai, Hangzhou, Nanjing, Hefei, and other metropolitan areas, and their transportation integration level is low. These areas urgently need to speed up the construction of relevant transportation infrastructure so as to promote the integrated development of transportation of higher quality in the Yangtze River Delta urban agglomeration. At present, the levels of local transportation integration in the Yangtze River Delta's urban agglomerations significantly contribute to the local industrial agglomeration. Owing to COVID-19, the positive impact of local transportation integration on local industrial agglomeration has diminished. When the spatial effect is considered, the improved industrial agglomeration in neighboring areas has a negative spillover effect on the local industrial agglomeration. At present, transportation integration in other regions positively affects industrial agglomeration in the Yangtze River Delta, but the effect is not significant. Transportation integration in urban agglomerations mainly affects regional industrial agglomeration through the \"cost effect\". The marginal contribution of this paper is as follows: First, taking urban agglomeration's transportation infrastructure as a starting point, the evaluation index of urban agglomeration's transportation integration is constructed, which is included in the analysis of the impact of urban agglomeration's industrial agglomeration as an important exogenous variable, and the explanatory framework of its related theories is improved. Second, the heterogeneity of cities is fully considered, and the heterogeneity of the impact of transport integration on industrial agglomeration is empirically studied, which expands the research field of transport economics and enriches the connotation of external economic benefits of transport infrastructure to a certain extent. Finally, the variable measuring labor cost is introduced to study the impact of labor cost changes caused by transportation integration in urban agglomeration on industrial agglomeration, and we empirically reveal the impact mechanism of transportation integration in urban agglomeration on industrial agglomeration.