Honshi–Bisan Line

The line's defining feature is the Great Seto Bridge, a chain of bridges spanning the islands of the Seto Inland Sea. The railway is carried on the lower deck of a combined rail–road structure, running beneath the Seto-Chūō Expressway that occupies the upper deck. Only six stations lie on the route — Chayamachi, Uematsu, Kimi, Kaminochō and Kojima in Okayama Prefecture, then Utazu on the Shikoku side — with the long bridge crossing falling between Kojima and Utazu. The company boundary sits at Kojima, 12.9 km from Chayamachi: the 12.9 km to Kojima belong to JR West and the 18.1 km on to Utazu to JR Shikoku.

Building a rail connection across the Seto Inland Sea was a long-held ambition, but the project became entangled in the financial crisis of the Japanese National Railways (JNR) in the early 1980s. As the government moved to rein in JNR's mounting debts, the railway portion of the Seto Bridge came under scrutiny. On 21 July 1983 it was reported that the JNR Reconstruction Supervisory Committee had proposed to the prime minister halting construction of the Kojima–Sakaide railway works, on the grounds that the projected debt burden was out of all proportion to the modest passenger revenue the line could be expected to earn. Political pressure from Shikoku interests kept the suspension out of the committee's subsequent emergency recommendations, and the project went ahead.

The line opened in two stages in 1988. On 20 March the 13 km section between Chayamachi and Kojima opened on a provisional basis, timed to carry visitors to the Seto Great Bridge Expo '88 ('Seto-Ōhashi Haku '88'). Then on 10 April the 18 km Kojima–Utazu section opened together with a connecting cut-off line to Sakaide, coinciding with the inauguration of the Great Seto Bridge road-and-rail system. This completed the through route and provided the first rail connection between Honshu and Shikoku; until then passengers had travelled via the Uno Line and the Uko train ferry to Takamatsu. The opening also facilitated electrification of the Yosan Line between Takamatsu and Matsuyama on Shikoku.

Operating fast trains across a high, exposed sea bridge brought its own challenges. From 22 July 1989 the maximum speed of limited-express diesel railcars on the bridge was cut from 95 km/h to 65 km/h. The restriction was eased on 21 November 1991, when the newer 2000 series diesel railcars were permitted to return to 95 km/h on the bridge. Because the line had been built as a costly new sea crossing, a surcharge fare was applied to the Kojima–Utazu section from 10 January 1996, an extra charge that has remained a feature of fares over the bridge.

The enormous cost of the crossing left a long financial tail. The debt of the Seto-Ōhashi rail division, amounting to some 490 billion yen, was finally repaid in 2001. In the following years the line was brought into the modern fare-and-ticketing fold: the Chayamachi–Kojima section was added to the ICOCA smart-card area on 1 September 2007, and the Kojima–Utazu section together with the Sakaide cut-off followed on 1 March 2014. JR West also gave its part of the line a route identity, assigning the colour blue and the route symbol “M.”

Today the Honshi-Bisan Line remains the backbone of rail travel between Honshu and Shikoku, carrying the frequent Marine Liner rapid service between Okayama and Takamatsu as well as limited expresses running through onto the Yosan and Dosan lines, alongside JR Freight traffic. One-man operation was introduced on local trains over the Chayamachi–Kojima section from 15 March 2025. For most travellers the line is simply the rail half of the Seto-Ōhashi crossing — a short but strategically vital corridor whose six stations and single great bridge knit the national network across the Inland Sea.

• 198321 July: it is reported that the JNR Reconstruction Supervisory Committee has proposed halting construction of the Kojima–Sakaide railway works, citing a projected debt burden far exceeding likely passenger revenue; Shikoku political pressure keeps the suspension out of the committee's emergency recommendations.
• 198820 March: the 13 km Chayamachi–Kojima section opens on a provisional basis, timed to carry visitors to the Seto Great Bridge Expo '88.
• 198810 April: the 18 km Kojima–Utazu section and a connecting cut-off line to Sakaide open with the inauguration of the Great Seto Bridge system, completing the first rail link between Honshu and Shikoku (previously served by the Uno Line and the Uko train ferry) and facilitating electrification of the Yosan Line between Takamatsu and Matsuyama.
• 198922 July: the maximum speed of limited-express diesel railcars on the Seto bridge is reduced from 95 km/h to 65 km/h.
• 199121 November: the newer 2000 series diesel railcars are allowed to return to 95 km/h on the bridge.
• 199610 January: a surcharge fare is introduced on the Kojima–Utazu section.
• 2001The debt of the Seto-Ōhashi rail division, some 490 billion yen, is fully repaid.
• 20071 September: the Chayamachi–Kojima section is added to the ICOCA smart-card area.
• 20141 March: the Kojima–Utazu section and the Sakaide cut-off line are added to the ICOCA smart-card area.
• 202515 March: one-man operation begins on local trains over the Chayamachi–Kojima section.