Yanba Ōhashi Bridge, Extradosed bridge in Naganohara, Japan

Yanba Ōhashi is an extradosed bridge over the Agatsuma River, now the Yanba Agatsuma Lake, in Naganohara, Gunma Prefecture. It is 494 m long and 73.5 m high, with a two-lane roadway 6.0 m wide (13.5 m including both sidewalks). Construction began in 2008 and the bridge opened on 1 October 2014 at 15:00, carrying Prefectural Road 377 from Kawarabhata to Ōto.

A first Yanba Bridge, completed in 1933 as part of the Nakanojō-Ueda prefectural road, once carried National Route 145 over the Agatsuma River here. The present bridge was planned as a replacement road for the Yanba Dam: construction began in 2008 under the provisional name Lake Surface Bridge No. 1, and it opened on 1 October 2014 at 15:00. In 2009, with its piers still scaffolded, it became a symbol in the debate over the dam's construction.

The bridge's name comes from the Yanba area it spans, and its Japanese name 八ッ場大橋 is written with the small ッ. It is one of three replacement bridges built for the dam, alongside Fudō Ōhashi (Lake Surface Bridge No. 2) on Prefectural Road 375 and Maruiwa Ōhashi (No. 3) on National Route 145.

The bridge carries Prefectural Road 377 (Kawarahata-Oto line) over the Agatsuma River, not Route 375; Route 375 crosses the reservoir on the Fudō Ōhashi nearby. It has two lanes plus sidewalks on both sides, so walking across is possible. The deck sits 73.5 m above the water, and the 494 m span is exposed to wind and fast-changing mountain weather.

During the 2009 debate over whether to halt the Yanba Dam, the half-built bridge, its piers still wrapped in scaffolding, appeared in news reports as a symbol of the project's uncertainty. Gunma Prefecture kept the work going, and the national government separated the bridge from the dam itself in March 2010.