Crossing Akashi Strait (ja. 明石海峡, Akashi-Kaikyō), this connection links Hyōgo Prefecture on Honshū with Tokushima Prefecture on Shikoku, using Awaji Island for most of its length. The route connects to the Sanyō Expressway at its northern terminus, allowing traffic to connect to Himeji, Kobe, and other major cities on Honshū.
This connection uses two suspension bridges. The more well-known of the two is the Akashi-Kaikyo Bridge, the world's longest suspension bridge, which connects Kobe to Awaji Island. The other bridge is the Ohnaruto Bridge, connecting Awaji to the city of Naruto across the Naruto whirlpool.
Although the connection was initially designed to accommodate railway service as well as road traffic, economic considerations turned it into a road connection only.
Also known as the Great Seto Bridge, this line connects Okayama Prefecture to Kagawa Prefecture. A series of six major bridges and five viaducts are used. The six bridges are: the Shimotsui-Seto Bridge, Hitsuishijima Bridge, Iwakurojima Bridge, Yoshima Bridge, Kita Bisan-Seto Bridge, and Minami Bisan-Seto Bridge.
The Seto-Chūō bridges are also used by JR trains (Seto-Ōhashi Line), and are designed to accommodate high-speed Shinkansen service in the future, although there are no current plans to extend the Shinkansen to Shikoku.
Commonly known as the Shimanami Kaidō (しまなみ海道), this connection links Hiroshima Prefecture to Ehime Prefecture. The link consists of nine bridges: the Shin-Onomichi Bridge, Innoshima Bridge, Ikuchi Bridge, Tatara Bridge, Ohmishima Bridge, Hakata-Ohshima Bridge, First Kurushima-Kaikyo Bridge, Second Kurushima-Kaikyo Bridge, and Third Kurushima-Kaikyo Bridge. It is the only route which can be crossed on bicycle or foot.