Okaya Viaduct

The Okaya Viaduct is a concrete structure that crosses the Nagano Expressway and connects the northern part of Okaya city with surrounding areas. The bridge was built using an innovative five-span continuous frame box girder design to handle traffic efficiently.

Construction of the viaduct started in 1983 and was completed in 1986, after which it opened to traffic. The project represented a significant step in the region's infrastructure development and demonstrated Japanese engineering expertise.

The viaduct received the Tanaka Prize from the Japan Society of Civil Engineers, marking its contribution to Japanese engineering advancement.

The viaduct is visible from the Nagano Expressway and offers drivers a good view of the structure while passing through. Visitors can best observe the bridge from viewing points or nearby roads.

At the time of its completion, the viaduct held the record for the longest span of its type in Japan and was surpassed worldwide by only one other bridge. This technical achievement made it a notable example of engineering prowess from that era.