SAPPORO -- The idea of a tunnel for auto traffic between Japan's main island of Honshu with Hokkaido to the north has gained new momentum after years of being considered a wasteful long shot.
The 31-km undersea tunnel would cost 720 billion yen ($6.97 billion) and serve as a complement to the existing, rail-only Seikan Tunnel, according to a proposal submitted last month to Transport Minister Kazuyoshi Akaba.
The massive undertaking would test the engineering ability of the country that produced the Seikan Tunnel, one of the world's longest and deepest tunnels. It would face the same budget constraints and labor shortages that have hampered other big Japanese infrastructure projects in recent years.
But proponents say the project makes economic sense as a means of cutting transport costs and boosting the movement of people and goods.
"This is a well-conceived proposal," said Yoshiharu Ishii, a visiting professor at the Hokkaido University Public Policy School.
Hokkaido is the only one of Japan's big islands that is not linked to Honshu by a bridge. Cars and trucks cannot drive through the Seikan Tunnel, which is only for bullet and freight trains.
The idea of a second tunnel under the Tsugaru Strait emerged in the middle of the last decade. It evolved into a plan for a two-deck construction, with the top level for self-driving vehicles and the bottom level for freight trains. Vehicles not equipped for autonomous driving would ride on flatbed trucks.
Last month's proposal by the Japan Project-Industry Council estimates the economic benefits of a second tunnel at 87.8 billion yen a year. Agricultural shipments from Hokkaido, one of Japan's biggest farming regions, would rise by 600,000 tons, generating 34 billion yen of economic value. The tourism from increased travel would yield 53.8 billion yen, according to the proposal.
Hokkaido's capital, Sapporo, is about 1,150 km from Tokyo -- about the same as the distance between Tokyo and the southwestern Japanese city of Fukuoka. Yet truck shipments cost 34% more on the northerly route, at 210,500 yen per 10 tons, according to a study by the Hokkaido Economic Federation.
The proposed tunnel would take about 15 years to build, from initial surveys to completion. The Japan Project-Industry Council -- whose members include the nation's leading contractors and steelmakers -- estimates the construction costs could be recovered in 32 years, assuming an 1.16% interest rate on borrowing for the project.
Proposed tolls are 18,000 yen, or about $175, for large vehicles and 9,000 yen for cars. Assuming daily traffic of 3,600 trucks and 1,650 cars, the tunnel project would be economically viable, according to the proposal.
The Seikan Tunnel opened in 1988 and took 27 years to build. Plans for the rail passage under the Tsugaru Strait, famed in song for its harsh winters, gained an impetus from the 1954 Toya Maru ferry disaster. The ferry sunk while crossing the strait in a typhoon in the sea accident in Japanese history.
The tunnel construction overcame numerous challenges, including for major floods, according to the Japan Railway Construction, Transport and Technology Agency.
Tunnel boring technology has come a long way since then. By tweaking the grade, depth and other factors, the proposal makes the second tunnel shorter than the current one's 53.85 km.
A second tunnel for freight would relieve a bottleneck for the Hokkaido Shinkansen, the bullet train service linking Tokyo and the northern island. The high-speed trains must now slow down during the crossing, which they share with Japan Freight Railway.
The Seikan Tunnel also needs upgrades against the 20 tons of water that leak in every minute, construction industry players say. "If there were a bypass available, the construction could be done with less of an impact on transport," said Satoru Kurita, vice chairman of the Hokkaido Construction Industry Association.
The so-called Tsugaru Strait Tunnel Project proposal's 720 billion yen price tag does not include tunnel exits or links to existing highways and rail lines. Construction of those elements brings the total cost over 1 trillion yen.
The scale and difficulty of the tunnel project tunnel would rival that of the ongoing construction of a magnetic levitation railroad between Tokyo and Nagoya. That effort has been stalled by a dispute with a local government over the effect on aquifers.
Whether the tunnel plan is able to convince a reluctant government in Tokyo will depend in part on the stance of the Japan Rail companies, which have shown little enthusiasm for the idea.