The following article is available. The start of construction seems to be after the end of the 2020 Olympic Games.
If realized, the landscape near Nihonbashi will be considerably improved.
＞Elevated capital of Nihonbashi, Tokyo, underground construction of special zones, Ministry of Land, Infrastructure, Transport and Tourism
2016/01/05 Nihon Keizai Shimbun morning edition 5 pages 684 characters
There is a plan to move the Metropolitan Expressway, which runs directly above Nihonbashi, Tokyo, underground. The Ministry of Land, Infrastructure, Transport and Tourism and the Tokyo Metropolitan Government are positioned as projects under the National Strategic Special Zone, and in March we will begin procedures for city planning in conjunction with redevelopment around the area. The project cost is expected to be around 500 billion yen, and the financial resources will be adjusted with the aim of starting construction after the closing of the Tokyo Olympics in 2020.
Underground is a 2.9-kilometer section between Takebashi and Edobashi Junctions (JCT) on the Toshin Beltway, the capital city. Currently, it is likely that a viaduct that passes over the Nihonbashi River will be transferred underground, such as a redevelopment site on the south side of the river. Discussions are already underway at public and private liaison meetings.
