Tokyo Bay Aqua-Line
The 29th longest tunnel in the world
The Tokyo Bay Aqua-Line (Tōkyō-wan Akua-rain), also known as the Trans-Tokyo Bay Expressway, is an expressway that is mainly made up of a bridge–tunnel combination across Tokyo Bay in Japan. It connects the city of Kawasaki in Kanagawa Prefecture with the city of Kisarazu in Chiba Prefecture, and forms part of National Route 409. With an overall length of 23.7 km, it includes a 4.4 km bridge and 9.6 km tunnel underneath the bay—the fourth-longest underwater tunnel in the world.
Tunnel data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).