Asked by: Rob Haynes, London
Line 3 of the Guangzhou Metro in China has a main branch line that is 60.4km (37.5 miles) long. If you discount urban metro lines, the title currently goes to the Seikan Tunnel in Japan, which connects the islands of Hokkaido and Honshu. This is 53.85km (33.5 miles) long and is also the deepest rail tunnel in the world, running 100m below the seabed. This record will be beaten next year when the 57.1km (35.5 mile) Gotthard Base Tunnel through the Swiss Alps opens. And both will be eclipsed by the 123km (76.4 mile) tunnel planned to cross the Bohai Strait in China by 2023.