Shimizu Tunnel Breakthrough Day

What Is Shimizu Tunnel Breakthrough Day?

Every December 29th is "Shimizu Tunnel Breakthrough Day" (清水トンネル貫通記念日, Shimizu Tonneru Kantsū Kinenbi) in Japan. On December 29, 1929, the Shimizu Tunnel (清水トンネル) — a 9,702-meter railway tunnel under the Mikuni Mountain Range connecting Gunma and Niigata prefectures on what is now the Jōetsu Line (上越線) — was successfully "broken through" (貫通, kantsū), meaning the pilot tunnels dug from both ends met in the middle. The tunnel, which opened for service on September 1, 1931, was at the time the longest railway tunnel in Japan and a major engineering achievement.

Engineering the Shimizu Tunnel

Construction began in 1922 from the Gunma side and in 1923 from the Niigata side. The hard rock beneath Mt. Tanigawa made it less treacherous than some other tunnels of the era, but the work still took about nine years and cost the lives of 48 workers. Loop lines were built on both sides to gain altitude and keep the main tunnel as short as possible. The tunnel provided a critical connection between the Japan Sea coast (Niigata Prefecture) and the Pacific coast (Gunma Prefecture), enabling year-round transport over a mountain route that had previously been dependent on mountain passes closed by heavy snow in winter.

Railway Tunnels in Japan's Development

Japan's mountainous topography — approximately 70% of the country is covered by mountains — has made tunnel construction essential to railway network development. From the early Meiji-era railway tunnels through the Seikan Tunnel (see March 13th) to the Shinkansen tunnels that pass beneath the Japan Alps and the Hokuriku mountains, Japanese tunnel engineering has been pushed to world-leading standards by the country's geographic demands. Japan is consistently among the world leaders in tunnel construction technology and is a major exporter of tunneling expertise.

Snow Country Connection

Nobel laureate Kawabata Yasunari's celebrated novel "Snow Country" (雪国, Yukiguni, 1937) famously begins: "The train came out of the long tunnel into the snow country" — a sentence widely understood to describe the Shimizu Tunnel. The tunnel's role as a gateway between the Pacific coast and the Japan Sea's heavy snowfall region made it a symbol of the passage between two different worlds of Japanese climate and culture.

Fun Facts

• New Shimizu Tunnel: A parallel New Shimizu Tunnel (新清水トンネル, about 13.5 km, opened in 1967) was built to double-track the line. The new tunnel carries downbound (Niigata-bound) trains, while the original 1931 tunnel carries upbound (Tokyo-bound) trains. Doai Station's downbound platform lies deep inside the new tunnel, reached by a total of 486 steps — earning it the nickname "Japan's number one mole station."
• Kawabata's Nobel: Yasunari Kawabata's "Snow Country" was among the works cited by the Nobel Committee when he became the first Japanese writer to receive the Nobel Prize in Literature in 1968 — making the tunnel obliquely referenced in his opening line a small part of literary history.