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.

The section running above Nihonbashi bridge was completed in 1963. It is part of the 2.9-km section between the Takebashi and Edobashi junctions of the Tokyo Metropolitan Expressway Ring Route.

Attempts have been made in the past to move the section over Nihonbashi underground. In 2006, Prime Minister Junichiro Koizumi had a private advisory panel issue a proposal for the construction of an underground tunnel. The project fell by the wayside when talks on how to divide the construction cost among the government and other parties ended in deadlock. In a 2012 proposal on renovating the metropolitan expressway network, a panel of the Land, Infrastructure, Transport and Tourism Ministry said overhead sections, including the segment above the Nihonbashi River, produce a “sense of oppression” and ruin the cityscape. It called for replacing the overhead sections of the ring route with underground tunnels.

The plan to bring the Nihonbashi section underground took a step forward in July when infrastructure and transport minister Keiichi Ishii and Tokyo Gov. Yuriko Koike separately announced that they will start studying the idea in earnest. This paved the way for a meeting Nov. 1 attended by representatives of the ministry, the metropolitan government, the Chuo Ward office and Tokyo Metropolitan Expressway Co. They agreed to decide around next spring which part of the Takebashi-Edobashi section should go underground and make a draft route.

The biggest hurdle will be the cost — estimated to run as high as ¥500 billion. The expressway operator said it is ready to shoulder around ¥140 billion to renovate the aging section — built more than half a century ago — which will be needed anyhow if the section is left as an overhead structure. The remaining expenses are to be split among the national government, the metropolitan government and Chuo Ward. But talks on how to divide the cost will not be easy. It is envisaged that the underground construction project will start after the 2020 Games and last 10 to 20 years.

The tunnel route needs to be carefully weighed since various underground infrastructure such as subway lines, power cables, telecommunications lines, gas pipes and water and sewage mains run through the area. The construction cost could be bloated even further if technical problems emerge in building the tunnels.

Advocates feel strongly that reclaiming the sky over the historic landmark will improve the urban landscape in Nihonbashi, which would in turn benefit tourism in the neighborhood. Those anticipated benefits — and what it would bring to the area’s future — will still need to be weighed against the massive additional cost.

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