The Akashi Kaikyo Bridge is, with a length of almost four kilometers, the world's longest suspension bridge. Opened in 1998, it spans the Akashi Strait (Akashi Kaikyo) between Kobe and Awaji Island and is part of the Kobe-Awaji-Naruto Expressway, one of three expressways which connect Honshu with Shikoku.
The Bridge Exhibition Center at the foot of the Kobe side of the bridge provides well-presented information about the planning and construction of the bridge and about other suspension bridges around the world, although the detailed explanations are available in Japanese only.
The bridge has three spans. The central span is 1,991 m, and the two other sections are each 960 m. The bridge is 3,911 m long overall. The two towers were originally 1,990 m apart, but the Great Hanshin earthquake on January 17, 1995, moved the towers so much (only the towers had been erected at the time) that the span had to be increased by 1 m.
The bridge was designed with a two hinged stiffening girder system, allowing the structure to withstand winds of 286 kilometres per hour (178 mph), earthquakes measuring up to magnitude 8.5, and harsh sea currents. The bridge also contains tuned mass dampers that are designed to operate at the resonance frequency of the bridge to dampen forces. The two main supporting towers rise 282.8 m above sea level, and the bridge can expand because of heat by up to 2 m over the course of a day. Each anchorage required 350,000 tonnes (340,000 long tons; 390,000 short tons) of concrete. The steel cables have 300,000 kilometres of wire: each cable is 112 centimetres in diameter and contains 36,830 strands of wire.
The Akashi-Kaikyo bridge has a total of 1,737 illumination lights: 1,084 for the main cables, 116 for the main towers, 405 for the girders and 132 for the anchorages. On the main cables three high light discharged tubes are mounted in the colors red, green and blue. The RGB model and computer technology make for a variety of combinations. 28 patterns are used for occasions as national or regional holidays, memorial days or festivities.
The Maiko Marine Promenade consists of observatory hallways under the bridge's platform, about 50 meters above the water. Accessed by elevator from the base of the bridge (Kobe side), the hallways offer interesting views of the bridge's interior, the Akashi Strait and Osaka Bay.
Bridge enthusiasts should also consider participating in the "Bridge World" guided tour, which includes a visit to the very top of one of the bridge's 300-meter-tall towers. The tour is in Japanese only, held twice a day on Thursdays, Fridays, Saturdays and Sundays, takes 2.5 hours, involves a lot of walking, costs 3000 yen per person and requires advance reservations