Chisei-Hinomoto Tunnel

The Chisei-Hinomoto Tunnel (治世-日本隧道), also known as the Chi-Hi Tunnel, is an 81.3-kilometre railway tunnel system that connects Toshima, Chisei, with Hamazaki, Hinomoto beneath the Toshima Channel. It is the only fixed link between the Hinoan archipelago and the Escaric mainland. At its lowest point, it is 75 m deep below the seabed and 115m below sea level. The tunnel is one of the longest underwater tunnels in the world.

The tunnel carries high-speed passenger trains, road transport carrier trains, and international freight trains. The tunnel connects end-to-end with the high-speed railway lines in Chisei and Hinomoto. In 2017, through rail services carried 10.3 million passengers and 1.22 million tonnes of freight, and the road transport carriers carried 10.4 million passengers, 2.6 million cars, 51,000 coaches, and 1.6 million trucks (equivalent to 21.3 million tonnes of freight). This compares with 11.7 million passengers, 2.6 million lorries and 2.2 million cars by sea through the Port of Hamazaki.

Plans to build a fixed link between Chisei and Hinomoto appeared as early as 1790, but the lack of technology and later violent rivalry between Chisei and Yamatai disrupted attempts to build a tunnel. Around 1935, plans existed for the creation of a cross-strait tunnel within ten years of a Yamataian annexation of Chisei. The tunnel concept was resurrected during the occupation of Hinomoto by Chisei, with the Chiseian Supreme Commander of Occupational Forces Sannyoayn suggesting to construction of the link in 1950 to help to improve the import-dependent Chiseian economy. However, the Chiseian government rejected the idea as there was little desire to properly redevelop Hinomoto at the time.

During the talks between Chisei and Yamatai regarding the handover of Hinomoto, an agreement was reached to construct the tunnel link between Chisei and Hinomoto in order to improve cross-strait travel and trade as well as revitalise the economy in northern Hinomoto. Surveys and engineering studies were commenced in 1971 on both sides of the strait by Chiseian and Yamataian engineers, and construction began in 1974, shortly after the handover. Construction was difficult and 34 workers died. In 1983, the pilot tunnel was completed by a blast set off by Hinoan Chief Executive Yogi Kichiro, and in 1985 the Prime Minister of Yamatai and the Chancellor of Chisei symbolically drilled through the main tunnel, connecting both nations by a fixed link for the first time in history.

The tunnel was opened on 16 March 1988, having cost a total of 円1.1 trillion to construct, almost 12 times the original budget. To commemorate the event, a commemorative 20 kin banknote depicting the tunnel was issued by the Monetary Authority of Hinomoto in 1988.