Hakone Tozan Line

The line's origins lie in a horse-tramway era predecessor. The Odawara Horse-drawn Railway opened a line from Kōzu Station via Odawara to Hakone-Yumoto on 1 October 1888; its operator was renamed the Odawara Electric Railway in 1896 and the route was electrified in 1900, running as a 600-volt-DC tramway. Plans to push a mountain railway deeper into Hakone were repeatedly studied from 1896 onward but only took firm shape in 1910, when the Odawara Electric Railway resolved to extend from Yumoto up to Gōra. A construction licence was granted on 1 March 1911, on the explicit condition that the work spoil the natural scenery as little as possible.

Settling the alignment proved difficult. An early plan for a rack (Abt-system) railway with grades as steep as 125 per mille was abandoned after the company's chief engineer, Mitsugi Handa, was sent to Europe in 1912 to study Switzerland's Bernina Railway, which had long 70-per-mille adhesion grades. Concluding that an adhesion railway could not climb 125 per mille, the engineers redesigned the line as an 80-per-mille adhesion railway with three switchbacks, modelled closely on the Bernina line. The revised plan, unprecedented in Japan for its gradient, was approved by the Railway Bureau in 1913; the Bernina connection later led Hakone Tozan and the Rätische Bahn to conclude a sister-railway agreement in 1979.

Construction was protracted and costly. The outbreak of the First World War in 1914 cut off planned imports of materials and rolling stock, so American-built cars were purchased instead, and a 1916 survey showed that tunnelling between Miyanoshita and Ninotaira would harm the hot-spring veins, forcing a longer alignment hugging the hillsides and the addition of Kowakidani Station. The Hayakawa Bridge, reusing a truss span cascaded from the Tōkaidō Main Line's Tenryū River bridge, took nearly two years to erect and was the hardest single work. After more than seven years, all work was finished on 24 May 1919, and on 1 June 1919 the mountain railway opened for electric service between Hakone-Yumoto and Gōra.

On 1 September 1923 the Great Kantō Earthquake devastated the line: most of the track collapsed or was buried, nearly half the structures were partly destroyed, and almost every bridge but the Hayakawa Bridge — which survived with only minor damage — was wrecked. All seven mountain cars derailed or were buried, though none burned. Restoration work ran from January 1924, and the line was reopened section by section through to 28 December 1924. In January 1928 the Odawara Electric Railway was merged into Nippon Denryoku (Japan Electric Power), then spun off again in August 1928 as the Hakone Tozan Railway Co., Ltd.

The next decades extended the line down the mountain and linked it to the wider network. On 1 October 1935 the railway began through operation between Odawara and Gōra, after improving the right-of-way from Kazamatsuri and developing a special coupler with the Railway Ministry to allow safe two-car running on the 30-metre-radius curves and 80-per-mille grades; this cut the Odawara–Gōra journey to about 50 minutes. The company joined the Odakyu Group on 1 June 1948. On 1 August 1950 Odakyu Electric Railway trains began running through from Shinjuku to Hakone-Yumoto: because Odakyu used 1,067 mm narrow gauge while the mountain line used 1,435 mm standard gauge, the Odawara–Hakone-Yumoto section was laid with dual (three-rail) gauge and its voltage raised from 600 to 1,500 V DC.

Rising tourist traffic — the line carried over ten million passengers in 1991 — drove a programme to run three-car mountain trains, which required platform extensions (the works at Tōnosawa, boxed in by tunnels, were largely dug by hand) and an uprating of the mountain section from 600 to 750 V DC; three-car service began on 14 July 1993. Because the standard-gauge mountain cars carried fewer passengers than Odakyu's longer trains, the dual-gauge operation was steadily wound back: from the 18 March 2006 timetable revision all Odawara–Hakone-Yumoto trains became Odakyu cars, most three-rail track was removed, and only the short Iriuda–Hakone-Yumoto stretch was kept dual-gauged so mountain trains could still reach Iriuda Depot.

In recent years the line has weathered both disaster and corporate change. On 13 October 2019 Typhoon Hagibis caused severe damage — mudslides and washed-out structures concentrated between Ōhiradai and Kowakidani — and closed the Hakone-Yumoto–Gōra mountain section for months; test runs resumed on 9 July 2020 and full service was restored on 23 July 2020, about nine months after the closure. On 1 April 2024, as part of a reorganisation of the Odakyu Hakone Group, the operating company was renamed from Hakone Tozan Railway Co., Ltd. to Odakyu Hakone Co., Ltd., ending the Hakone Tozan Railway name in use since 1928, though the line keeps its popular nickname, the 'Hakone Tozan train'.

• 18881 October: the Odawara Horse-drawn Railway opens a line from Kōzu via Odawara to Hakone-Yumoto, the line's tramway-era predecessor.
• 1900The predecessor tramway (renamed Odawara Electric Railway in 1896) is electrified, running as a 600 V DC line.
• 19111 March: a licence is granted to build the mountain railway from Yumoto up to Gōra, on condition that it spoil the natural scenery as little as possible.
• 19191 June: the mountain railway opens for electric service (600 V DC) between Hakone-Yumoto and Gōra, after all construction was completed on 24 May.
• 19231 September: the Great Kantō Earthquake devastates the line; most track and nearly every bridge except the Hayakawa Bridge are wrecked, and all seven mountain cars are derailed or buried.
• 1924Restoration proceeds from January; the line is reopened section by section, with the final Ōhiradai–Miyanoshita stretch restored on 28 December.
• 1928The Odawara Electric Railway is merged into Nippon Denryoku (Japan Electric Power) in January, then spun off in August as the Hakone Tozan Railway Co., Ltd.
• 19351 October: through operation begins between Odawara and Gōra; the lower tram section to Hakone-Itabashi is retained, and Odawara–Gōra journey time falls to about 50 minutes.
• 19481 June: the Hakone Tozan Railway becomes part of the Odakyu Group.
• 19501 August: Odakyu Electric Railway begins through trains from Shinjuku to Hakone-Yumoto; the Odawara–Hakone-Yumoto section is made dual gauge and uprated from 600 to 1,500 V DC.
• 197215 March: Ninotaira Station is renamed Chōkoku-no-Mori, serving the Hakone Open-Air Museum.
• 199314 July: three-car mountain trains begin running after the Hakone-Yumoto–Gōra section is uprated from 600 to 750 V DC and platforms are extended.
• 200618 March: all Odawara–Hakone-Yumoto trains become Odakyu cars; most dual-gauge track is removed, leaving only Iriuda–Hakone-Yumoto three-railed for depot access.
• 200815 March: a new Odakyu Romancecar through service to Kita-Senju begins, and door-cut operation at Kazamatsuri ends after station improvements.
• 201913 October: Typhoon Hagibis severely damages the line; the Hakone-Yumoto–Gōra mountain section is closed for months.
• 202023 July: full service is restored across the line, about nine months after the Typhoon Hagibis closure (test runs had resumed on 9 July).
• 20241 April: the operating company is renamed from Hakone Tozan Railway Co., Ltd. to Odakyu Hakone Co., Ltd., ending the Hakone Tozan Railway corporate name in use since 1928.