| Carries: | 4 lanes of Seto-Chūō Expressway (upper) 2 rail lines (lower) |
| Crosses: | Seto Inland Sea |
| Locale: | Honshū and Shikoku |
| Maint: | Honshu–Shikoku Bridge Authority |
| Design: | Double-decked bridge system |
| Length: | 13.1km (08.1miles) |
The [1] is a series of double deck bridges connecting Okayama and Kagawa prefectures in Japan across a series of five small islands in the Seto Inland Sea. Built over the period 1978–88, it is one of the three routes of the Honshū–Shikoku Bridge Project connecting Honshū and Shikoku islands and the only one to carry rail traffic. The total length is 13.1km (08.1miles), and the longest span, the Minami Bisan-Seto Bridge, is 1100abbr=onNaNabbr=on.
Crossing the bridge takes about 20 minutes by car or train. The ferry crossing before the bridge was built took about an hour.
The bridges carry two lanes of highway traffic in each direction (Seto-Chūō Expressway) on the upper deck and one railway track in each direction (Seto-Ōhashi Line) on the lower deck. The lower deck was designed to accommodate an additional set of Shinkansen tracks for a proposed extension of the Shinkansen to Shikoku.[2]
When in 1889 the first railway in Shikoku was completed between Marugame and Kotohira, a member of the Prefectural Parliament,, stated in his speech at the opening ceremony: "The four provinces of Shikoku are like so many remote islands. If united by roads, they will be much better off, enjoying the benefits of increased transportation and easier communication with each other."
While it took a century for this vision of a bridge across the Seto Inland Sea to become reality, another of Ōkubo's ideas, mentioned in a drinking song he composed, was accomplished twenty years sooner:
I'll tell you, dear, don't laugh at me,
a hundred years from now, I'll be seeing you
flying to and from the moon in a space ship.
Its port, let me tell you, dear,
will be that mountaintop over there!https://www.city.mitoyo.lg.jp/kakuka/kyouikuiinkai/shogai/1/1920.html
The bridge idea lay dormant for about sixty years. In 1955, after 171 people died when a ferry wrecked in dense fog off the coast of Takamatsu, a safer crossing was deemed necessary. By 1959, meetings were held to promote building the bridge. Scientists began investigations shortly after, and in 1970, the Honshu-Shikoku Bridge Construction Authority was inaugurated. However, work was postponed for five years by the "oil shock" of 1973; once the Environment Assessment Report was published in 1978, construction got underway. The ferry disaster also led to the creation of the Akashi Kaikyō Bridge.
The project took ten years to complete at a cost of US$7 billion; 3.646e6m3 of concrete and 705,000 tons of steel were used in construction. Although nets, ropes and other safety measures were employed, the lives of 13 workers were lost during the 10 years of construction. The bridge opened to road and rail traffic on April 10, 1988.
Six of the eleven bridges are separately named, unlike some other long bridge complexes such as the San Francisco–Oakland Bay Bridge. The other five bridges are viaducts. The six named bridges from north to south are listed below.
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