The Seikan Tunnel (, or , ) is a dual-gauge railway tunnel in Japan, with a segment running beneath the seabed of the Tsugaru Strait, which separates Aomori Prefecture on Honshu, Japan's main island, from the northern island of Hokkaido. The tunnel's track level lies approximately below the seabed and below sea level. Following several decades of planning and construction, the tunnel opened on 13 March 1988.
The Seikan Tunnel forms part of the standard-gauge Hokkaido Shinkansen as well as the narrow-gauge Kaikyō Line operated by the Hokkaido Railway Company (JR Hokkaido). Its name, "Seikan," is derived from the on'yomi readings of the first characters of , the nearest major city in Honshu, and , the nearest major city in Hokkaido.
By total length, the Seikan Tunnel is the world’s longest undersea tunnel, surpassing even the Channel Tunnel (although the latter has a longer undersea section at vs for the Seikan Tunnel). It is also the second deepest transport tunnel below sea level and was the deepest until Norway's Ryfylke Tunnel opened in 2019. It is the second longest main-line railway tunnel following Switzerland’s Gotthard Base Tunnel, which began operations in 2016.
History
thumb|left|Location of the [[Tsugaru Strait in Japan]]
thumb|1988 Seikan Tunnel 500 yen coin
The idea to connect the islands of Honshu and Hokkaido by a fixed link was proposed by the Imperial Japanese Army in the late 1920s for strategic reasons and was part of the army's idea of linking the Japanese main islands with Japanese-held Korea and the Sakhalin Islands, the latter then being divided with Japan and the Soviet Union. induced by the loss of overseas territory at the end of World War II and the need to accommodate returnees. In 1954, five ferries, including the Tōya Maru, sank in the Tsugaru Strait during a typhoon, killing 1,430 passengers.
On 22 March 1964, the Japan Railway Construction Public Corporation was established, and excavation work began that year. Construction had begun during the heyday of the Seikan ferry route, but the ferry became mostly supplanted by air travel. On the freight side, due to the deterioration of labour-management relations at JNR at the time, including frequent strikes and legal compliance struggles, freight rail transportation stagnated and lost market share to ferries and coastal shipping.
By mid-1982, the tunnel had only to complete. On 27 January 1983, Japanese Prime Minister Yasuhiro Nakasone pressed a switch that set off a blast that completed the pilot tunnel. by detonating a dynamite charge on the last few meters of the earth. having cost a total of ¥1.1 trillion (US$7 billion) to construct (almost 12 times the original budget, much of which was due to inflation over the years). Construction of the tunnel itself was projected to cost ¥538.4 billion, but actually cost ¥745.5 billion, and construction of the line running through the tunnel was projected to cost ¥689 billion, but ended up costing ¥900 billion. To commemorate the opening, a commemorative 500 yen coin depicting the tunnel was issued by the Japan Mint in 1988.
Once the tunnel was completed, it became used by all railway transport between Honshu and Hokkaido, was also discontinued. However, 90% of passenger transport is still by plane due to travel time and cost. For example, to travel between Tokyo Station and Shin-Sapporo Station by train takes eight hours, with transfer from Shinkansen to narrow-gauge express train at Shin-Hakodate-Hokuto Station. By air, the journey is 1 hour and 45 minutes, or 3 hours and 30 minutes including airport access times. Deregulation and competition in Japanese domestic air travel has brought down prices for the Tokyo-Sapporo route, making rail travel more expensive in comparison. a later and more luxurious Cassiopeia overnight train service was often fully booked. Both were discontinued following the commencement of Hokkaido Shinkansen services in March 2016, with freight trains being the only regular service utilizing the narrow-gauge line since then.
Because the tunnel is shared with freight trains, Shinkansen services cannot operate at their full design speed within it. While trains run at up to south of Morioka and outside the tunnel, speeds are limited to inside the tunnel. During major holiday periods, freight traffic is suspended, allowing Shinkansen trains to operate through the tunnel at up to , reducing travel times.
Before the opening of the tunnel, research was conducted into a "Train on Train" where a narrow-gauge freight train would piggyback on top of a faster standard-gauge train. However, research ended in 2015 without being placed into use.
As of March 2019, Shinkansen services connected Tokyo Station and Shin-Hakodate-Hokuto Station in 3 hours and 58 minutes, with the final extension to Sapporo Station proposed to open in 2038 and expected to reduce the Tokyo–Sapporo rail journey to approximately five hours.
Surveying, construction and geology
<!-- ##### TRAFFIC DATA #### -->
{| class="wikitable" style="margin:5px 5px 0 10px; float:right;"
|+Tsugaru Strait traffic data
|-
! Year !! Passengers<br />(persons/yr) !! Freight (t/yr) !! Mode
|-
| 1955 || 2,020,000 || 3,700,000 || Seikan Ferry || 17,000,000 || 1971 Forecast
|-
| 1999 || ~1,700,000 || — || Seikan Tunnel
|-
| colspan=4|
|}
left|thumb|Typical tunnel cross section. (1) Main tunnel, (2) service tunnel, (3) pilot tunnel, (4) connecting gallery
left|thumb|Profile diagram of the undersea tunnel section
Surveying started in 1946 and construction began in 1971. By August 1982, less than 700 metres of the tunnel remained to be excavated. First contact between the two sides was in 1983. The Tsugaru Strait has eastern and western necks, both approximately across. Initial surveys undertaken in 1946 indicated that the eastern neck was up to deep with volcanic geology. The western neck had a maximum depth of and geology consisting mostly of sedimentary rocks of the Neogene period. The western neck was selected, with its conditions considered favourable for tunnelling.
The geology of the undersea portion of the tunnel consists of volcanic rock, pyroclastic rock, and sedimentary rock of the Neogene period. The area is folded into a nearly vertical syncline, which means that the youngest rock is in the centre of the strait and encountered last. Divided roughly into thirds, the Honshu side consists of volcanic rocks (notably andesite and basalt); the Hokkaido side consists of sedimentary rocks (notably Tertiary period tuff and mudstone); and the centre portion consists of Kuromatsunai strata (Tertiary period sand-like mudstone). Igneous intrusions and faults caused crushing of the rock and complicated the tunnelling procedures.
Two stations used to be within the tunnel—Tappi-Kaitei Station and Yoshioka-Kaitei Station. They were the first railway stations in the world built under the sea. Both closed with the construction of the Hokkaido Shinkansen, but continue to serve as emergency escape points. In the event of a fire or other disaster, the stations provide the equivalent safety of a much shorter tunnel. The effectiveness of the escape shafts at the emergency stations is enhanced by having exhaust fans to extract smoke, television cameras to help route passengers to safety, thermal (infrared) fire alarm systems, and water spray nozzles.
<gallery widths="200px" heights="160px">
File:Seikan_Tunnel_entrance_-_dual-gauge_track.jpg|Entrance to the tunnel from Honshu side; note the dual-gauge tracks
File:Seikan-tunnel-yoshioka.jpg|Former Yoshioka-Kaitei Station platform
</gallery>
Maintenance
A 2002 report by Michitsugu Ikuma described, for the undersea section, that "the tunnel structure appears to remain in a good condition." The amount of inflow has decreased with time, although it "increases right after a large earthquake".
See also
- Seikan Tunnel Tappi Shakō Line
- Train on Train, an experimental concept for conveying freight at higher speeds through the tunnel
- JR Freight Class EH800, AC freight locomotives used to haul trains through the Seikan Tunnel
- Sakhalin–Hokkaido Tunnel
- Bohai Strait tunnel
References
External links
- The Seikan Tunnel, Aomori Prefecture Government, version of 3 May 2006 at the Internet Archive
- BUILDING BIG: Databank: Seikan Tunnel