Itō Line

The line originated as part of a much larger scheme. Under Appended Table No. 61 of the amended Railway Construction Act, the government planned a railway running "from Atami in Shizuoka Prefecture via Shimoda and Matsuzaki to Ōhito," and the original intention was a double-track line linking Atami with the town of Shimoda. The fiscal-austerity policy pursued under Prime Minister Osachi Hamaguchi during the Great Depression forced the plan to be cut back, so that only the Atami–Itō section was built, and only as a single track.

Construction was difficult. The eastern shore of the Izu Peninsula is a steep coast where the mountains press right down to the sea, and the route had to be driven through faulted, soft strata that demanded numerous tunnels and bridges. When hot springs gushed out during the boring of the Usami tunnel and other workings, the engineering experience gained was fed back into the contemporary construction of the Shimizu and Tanna tunnels. The first 8.7-kilometre section, from Atami to Ajiro, opened on 30 March 1935, bringing Kinomiya, Izu-Taga and Ajiro stations into service.

The Ajiro–Itō extension, 8.2 kilometres long, opened on 15 December 1938, completing the line through to Itō and opening Usami and Itō stations; both sections were electrified at 1,500 V DC from the outset. As a tourist route the line attracted attention immediately, and through trains from Tokyo Station began running soon after the line was completed. Further extension southward was first delayed and then abandoned with the outbreak of the Second World War.

The Itō Line holds a notable technical distinction: it was the first section of the Japanese National Railways (JNR) network to be equipped with centralised traffic control (CTC). A CTC trial began on the Kinomiya–Itō section on 11 May 1958, and full CTC operation started on 20 May 1958. Through this period the line steadily took on its modern role as a feeder to the wider network and a corridor for Izu tourism.

The southern through route was realised in 1961. The private-sector Tokyu Corporation acquired the rights to complete the line on to Shimoda and set up the Izukyū Corporation to build and run that section; when the Izu Kyūkō Line opened on 10 December 1961, through services between the two lines began. In 1968 the line gained its only stretch of double track: on 9 September that year the parallel Tōkaidō Main Line tracks between Atami and Kinomiya were shifted onto a new alignment, and the old double-track pair was turned over to the exclusive use of the Itō Line, completing the 1.2-kilometre double-track section. Although the whole line had been graded for eventual doubling, no further duplication followed.

Freight operations over the line were abolished on 1 February 1984. With the breakup and privatisation of JNR on 1 April 1987, the Itō Line passed to JR East, while JR Freight became the line's Class II operator, reviving freight service in the limited form of rolling-stock delivery movements to the Izukyū line. Jurisdiction over the line moved to JR East's Yokohama Branch on 1 October 1996, and the signalling was upgraded from ATS-SN to ATS-P in late November 2004. From 8 March 2015 every station except Atami and Itō became unstaffed, operated through a remote station-control system. Today the line is part of the Tokyo metropolitan suburban fare zone and the Suica area, carries Odoriko and Saphir Odoriko limited expresses through onto the Izukyū Line, and through some commuter trains runs onward via the Tōkaidō and Ueno–Tokyo Lines.

• 193530 March: the first section, Atami–Ajiro (8.7 km), opens; Kinomiya, Izu-Taga and Ajiro stations open.
• 193815 December: the Ajiro–Itō extension (8.2 km) opens, completing the line through to Itō; Usami and Itō stations open. Both sections were electrified at 1,500 V DC from opening.
• 195811 May: a centralised traffic control (CTC) trial begins on the Kinomiya–Itō section — the first CTC installation on the JNR network; full CTC operation starts on 20 May.
• 196110 December: the Izu Kyūkō (Izukyū) Line opens south of Itō and through services between the Itō Line and the Izukyū Line begin.
• 19689 September: the Tōkaidō Main Line tracks between Atami and Kinomiya are shifted to a new alignment, and the old double track becomes exclusive to the Itō Line, completing its 1.2 km double-track section.
• 19841 February: all freight operations over the line are abolished.
• 198525 February: the aged CTC equipment is replaced and put into use.
• 19871 April: with the breakup and privatisation of JNR, the line passes to JR East; JR Freight becomes its Class II operator, reviving freight service only for rolling-stock delivery to the Izukyū line.
• 19961 October: jurisdiction over the whole line transfers to JR East's Yokohama Branch.
• 2004Late November: the train protection system is upgraded from ATS-SN to ATS-P.
• 201319 August: year-round semi-automatic (push-button) door operation begins for first trains at Atami and Itō stations.
• 20158 March: every station except Atami and Itō becomes unstaffed, operated via a remote station-control system.