The portion of the Tokyo expressway built over Nihonbashi bridge, a historic landmark in Chuo Ward, has long been criticized as a blight on the urban landscape and there have been calls to move the section underground. Moves to address this situation have gained momentum as the transport ministry and three other parties decided last month to pick a candidate underground route around next spring. The aging expressway — built in time for the 1964 Summer Olympic Games — is ripe for renovation anyway, and major redevelopment projects already planned for the area add to the momentum. The problem is that moving the expressway underground is going to cost hundreds of billions of yen more than renovating the existing overhead structure. The project should be carefully weighed from various angles, including the benefits against the massive expense.

The current stone-built Nihonbashi bridge with two arches was completed in 1911. It survived the Great Kanto Earthquake of 1923 and the massive U.S. air raid of March 1945. It was designated as an important national cultural asset in 1999. After the original wooden structure was constructed by the Tokugawa shogunate in 1603, the bridge served as the starting point of five major roads during the Edo Period — the Tokaido, Nakasendo, Nikko Kaido, Oshu Kaido and Koshu Kaido. The current bridge — the 20th in history built on the site — still serves as the starting point of seven national highways.

Tokyo's cityscape, including the area along the Nihonbashi River, changed greatly in the early 1960s as construction of the metropolitan expressway network took place at a feverish pace so it could be unveiled ahead of the Olympics. Since it was feared that buying up land for expressway construction would take too much time, many sections were built over rivers and canals dating back to the Edo Period. Because of this design, parts of the network remind us of where the outer moat of Edo Castle lay.