Last weekend, China opened a massive cross-sea tunnel and bridge system, the Shenzhen-Zhongshan Link, in Guangdong Province. This engineering feat spanning 24 kilometers (15 miles) features two bridges, two artificial islands, and even a long underwater tunnel. The Pearl River estuary, where the Pearl River flows into the South China Sea, is one of the world’s most densely populated areas. It includes Hong Kong, Macau, and nine major cities in Guangdong Province. Overall, a staggering 86 million people live there. However, the region has long faced challenges in transportation due to its wide …