| Great Seto Bridge (瀬戸大橋 Seto Ōhashi) |
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Great Seto Bridge from Honshū (left) via the islands of Hitsuishijima and Yoshima to Shikoku |
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| Carries | 4 lanes of roadway (upper) 2 rail lines (lower) |
| Crosses | Seto Inland Sea |
| Locale | Honshū and Shikoku |
| Maintained by | Honshū-Shikoku Bridge Authority |
| Design | double-decked bridge system |
| Total length | 13.1 km (8.1 mi) |
| Opened | 1988 |
| Toll | 4,850 yen |
The Great Seto Bridge (瀬戸大橋 Seto Ōhashi), or Seto-Ohashi Bridge, 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. At 13.1 kilometers (8.1 mi), it ranks as the world's longest two-tiered bridge system.
Crossing the bridge takes about 20 minutes by car or train. The ferry crossing before the bridge was built took about an hour. The non-discounted toll from Kojima, Kurashiki (Okayama Prefecture on the Honshu side) to Sakaide (Kagawa Prefecture on the Shikoku side) is ¥3,500, and vice-versa.
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 Shinkansen rail line in each direction.
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When in 1889 the first railway in Shikoku - between Marugame and Kotohira - was completed, a member of the Prefectural Parliament, Jinnojo Ōkubo (大久保諶之丞 Ōkubo Jinnojo, 1849–1891), 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:
The bridge idea lay dormant for about sixty years. In 1955, after 171 lives were lost 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 project took ten years to complete at a cost of US$7 billion; 3.646 million cubic meters (128.8 million cubic feet) 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 are as follows.