Beginning with the Kōbu Railway
The Kōbu Railway opened between Shinjuku and Tachikawa on 11 April 1889 and extended to Hachiōji on 11 August. These staged openings established the eastern predecessor of the Chūō Main Line, more than twenty years before completion of the inland trunk route across Honshu.
Hachiōji was a center for raw silk and silk textiles. The railway connected that market with transport toward Tokyo. Initially, Kōbu contracted operations to the Nippon Railway, with trains able to run via Shinjuku and Shinagawa to Shimbashi. A long bridge over the Tama River west of Tachikawa delayed the Hachiōji section. Kōbu began operating independently in 1891, building its own operating organization.
Choosing a route through the mountains
A short railway west of Tokyo left the Yamanashi basin’s external transport difficulties unresolved. Private Kōshin and Yamanashi railway proposals faced engineering and financial obstacles. Local proponents formed a railway-promotion alliance in 1891 to seek state investment. The Railway Construction Act of 1892 included the Chūō route.
Options toward Tokyo included routes via Hachiōji or Gotemba. The army considered rack railways slow and limited in capacity and feared vulnerability to attack from the sea if the route joined the coastal Tōkaidō. It favored the Hachiōji route without rack operation. Parliament selected the alignment in 1894, but war delayed construction. Railway authorities advanced from both Hachiōji and Nagoya, extending the national undertaking beyond Kōbu’s original operations.
People and machinery at mountain worksites
Eastern construction beginning in 1896 confronted mountains at Kobotoke, Sasago and elsewhere. Tunnels, bridges and ordinary earthworks required different arrangements. Heavy water inflow impeded Kobotoke tunnelling and required pumping; fissures and ground pressure prompted changes to supports and portal works. Valley access routes bringing machinery and materials to portals were essential to sustained excavation.
The approximately 4.66-kilometer Sasago Tunnel required excavation, spoil removal, ventilation and masonry to proceed together. Hydroelectric power from the Sasago River supplied lighting and small electric locomotives. The construction report also records steam equipment for ventilation and rock drilling. Rails, machinery, bricks and stone had to be transferred from existing railheads into mountain sites. Workers maintained transport, drainage and supports alongside excavation.
Early operation on steep routes
Hachiōji and Kōfu were connected in June 1903. Steep terrain led to switchback layouts at Hatsukari, Sasago, Katsunuma and other stations, placing stopping and working areas on flatter ground beside the gradients. Five daily return services initially took approximately four hours between the cities. Steam locomotives hauled heavy trains uphill, while smoke in long tunnels added to crews’ difficulties.
The railway redirected freight from Yamanashi. Much had previously passed through Kajikazawa to Fuji River shipping and then the Tōkaidō. Bulk goods moved toward rail after the Chūō route developed, and Ōtsuki became a gateway connecting the northern foot of Mount Fuji with the main line. Some horse-drawn railways lost parallel sections; others became feeders. Regional transport reorganized around stations.
Electric city services and the joining of two ends
Kōbu also extended into Tokyo, reaching Iidamachi in 1895. The Iidamachi–Nakano section adopted 600-volt DC electric services in 1904; the line reached Ochanomizu by year’s end. Multiple cars could be controlled together, suited to closely spaced urban stations and frequent stops, while steam trains continued serving mountain routes. Kōbu was nationalized in October 1906.
Passenger and freight services began between Miyanokoshi and Kiso-Fukushima in May 1911. Closing this Kiso Valley gap joined the eastern and western sections, completing the inland trunk route to Nagoya. A private railway had first linked the Tokyo and Hachiōji markets; state mountain construction then incorporated it into a longer network.
References: [3]
Continuing improvements after completion
City connections and mountain traction continued changing. Tokyo Station opened in 1914, followed by an elevated connection carrying the Chūō Line into it in March 1919. Electrification between Hachiōji and Kōfu was completed in 1931: passenger trains adopted electric locomotives in April and freight trains in July.
Installing overhead power equipment required lowering trackbeds in some older tunnels and building substations. New locomotives, power supplies and civil works together eased constraints from steep gradients and long tunnels. The Chūō Main Line combined a private local railway, national mountain works, urban electric services and trunk-route improvement, accumulating capacity through continued construction and operating changes.
References: [3]