China has officially opened its longest underwater highway tunnel to traffic, marking a significant milestone in the country's infrastructure development.

After nearly four years of construction, the Taihu Tunnel, China’s longest underwater highway, is now ready to accommodate vehicles.

Stretching 10.79 kilometers (6.65 miles), the Taihu Tunnel runs beneath Lake Taihu in eastern China’s Jiangsu Province, located roughly 50 kilometers east of Shanghai.

To construct the two-way tunnel, which features six lanes and a width of 17.45 meters, over 2 million cubic meters of concrete were used, according to Xinhua, China’s state news agency.

The tunnel’s ceiling is illuminated with vibrant LED lights, designed to reduce driver fatigue and enhance safety during travel.

Part of the 43.9-kilometer Changzhou-Wuxi Expressway, the tunnel opened to the public on December 30, 2021. It offers an alternative route for travelers between Shanghai and Nanjing, the capital of Jiangsu province.

The tunnel connects the expressways of Suzhou, Wuxi, and Changzhou, easing traffic congestion in the cities surrounding Lake Taihu while boosting economic growth in the Yangtze River Delta region.

How does the Taihu Tunnel compare to other global projects? The world’s longest underwater highway tunnel is Norway’s 14.3-kilometer Ryfast Tunnel, linking Stavanger with the municipality of Strand.

The Tokyo Bay Aqua-Line’s underwater tunnel, which forms part of a highway beneath Tokyo Bay, stretches for 9.6 kilometers.

When it comes to underwater tunnels, the Channel Tunnel holds the record as the longest, with its submerged section running for 37.9 kilometers, connecting England and France by rail.