Izu Kyūkō Line

The idea of a railway down the eastern Izu coast long predated the Izukyū company. Plans originally called for the Japanese National Railways (JNR) to build a spur from Atami, on the Tōkaidō Main Line, towards Shimoda, but in the 1930s funding was constrained by the tight fiscal policy pursued under Prime Minister Osachi Hamaguchi during the Great Depression, compounded by a number of technical difficulties. Only the northern end was built at first, as the Itō Line: the initial 8.7-kilometre section from Atami to Ajiro opened on 30 March 1935, and the 8.3-kilometre extension from Ajiro to Itō followed on 15 December 1938, both electrified at 1,500 V DC from the outset. Further construction southward was delayed and then cancelled with the outbreak of the Second World War.

Work south of Itō resumed only in the post-war era, when the private-sector Tokyu Corporation acquired the rights to complete the line to Shimoda and established the Izukyū Corporation to build and operate this section. The whole line from Itō to Izukyū-Shimoda opened on 10 December 1961. Construction had been hard and dangerous: because the route passes through long-established hot-spring country, spring water seeped into the ground as the tunnels were bored, repeatedly causing cave-ins, and a number of construction workers were killed in the accidents.

From its opening the line was conceived as an extension of the national network rather than an isolated branch. Most of its superior trains ran — and still run — through from Itō onto JR's Itō Line and the Tōkaidō Main Line beyond, and many daytime local trains continued through to Atami. Because the JNR Itō Line sets of the day carried a first-class car (later the Green car), and because the villa districts along the coast promised affluent demand, Izukyū from the start owned not only second-class (later ordinary) cars but first-class cars too, coupling them into its own local trains; in time it ran a special "Royal Box" car as well, though its own trains no longer carry Green or Royal Box accommodation today. Its early fleet leaned on its parent: Izukyū borrowed Tōkyū 3000 series cars from 1961 to 1964, and brought in new Tōkyū 7000 and 7200 series cars for the summer peaks of the 1960s.

The line's relationship with the JR network has shaped its services ever since. Through local-train running between Izukyū-Shimoda and Atami was once mutual with JNR and then JR East, but since 1 December 2002 it has been one-way, with Izukyū trains running onto the Itō Line rather than the reverse. The line's regular passenger service today consists of just two types — limited expresses and local trains — supplemented by extra expresses and temporary rapid services during the busy tourist seasons. The JR East limited expresses that work through to Izukyū-Shimoda from Tokyo include the Odoriko and the luxury Saphir Odoriko.

Modernisation has continued in the twenty-first century. Suica IC cards were introduced across the whole line on 13 March 2010, after which PASMO and other cards interoperable with Suica also became usable. Staffing has been steadily reduced: Izu-Hokkawa and Inazusa became all-day unstaffed stations on 1 April 2012, with further stations unstaffed in 2015 and 2021, and Izukyū ended its sale of JR East Suica cards on 25 October 2021. From 2017 the line also began replacing its older ATS-Si signalling — compatible with JR East's ATS-SN — with ATS-P.

Beyond its scheduled trains, the Izu Kyūkō Line is closely tied to Izu's tourist trade. On 21 July 2017 the cruise-style sightseeing train THE ROYAL EXPRESS, formed from Izukyū's 2100 series "Resort 21" stock, began running between Yokohama on the Tōkaidō Main Line and Izukyū-Shimoda. Unusually for a private railway, the line also hosts Imperial and other royal-use trains, because the Suzaki Imperial Villa lies near Shimoda; the first such Imperial train of the Reiwa era ran in 2019. Together the scenic coastal run, the through limited expresses and these special trains have made the line one of the best-known tourist railways of the Izu Peninsula.

• 193530 March: the initial 8.7 km section of the Itō Line, from Atami to Ajiro, opens, electrified at 1,500 V DC.
• 193815 December: the Itō Line is extended 8.3 km from Ajiro to Itō, also electrified at 1,500 V DC; further work south is delayed and then cancelled by World War II.
• 196110 December: the Tokyu Corporation-founded Izukyū Corporation opens the whole Izu Kyūkō Line from Itō to Izukyū-Shimoda; cave-ins from hot-spring water during tunnelling had killed a number of construction workers.
• 1961From opening, Izukyū borrows Tōkyū 3000 series cars (used until 1964) and, for the line's superior services, runs through onto JR's Itō Line and the Tōkaidō Main Line.
• 20021 December: mutual through-running of local trains with JR East ends; thereafter local services run one-way, from the Izu Kyūkō Line onto the Itō Line only.
• 201013 March: the Suica IC card is introduced across the whole line, after which PASMO and other Suica-compatible cards also become usable.
• 20121 April: Izu-Hokkawa and Inazusa become all-day unstaffed stations, with ticket windows closed and machines removed.
• 201721 July: the cruise-style sightseeing train THE ROYAL EXPRESS, formed from Izukyū 2100 series 'Resort 21' stock, begins running between Yokohama and Izukyū-Shimoda.
• 2017Replacement of the line's ATS-Si signalling (compatible with JR East's ATS-SN) with ATS-P begins, proceeding section by section.
• 2019The first Imperial ('Omeshi') train of the Reiwa era runs onto the line, which — unusually for a private railway — hosts such trains because of the Suzaki Imperial Villa near Shimoda.
• 202125 October: Izukyū ends its sale of (unregistered) JR East Suica cards; further stations along the line are also made unstaffed during the year.