Yes, it’s been studied before, but one only has to look at Norway’s and Iceland’s deep-sea tunnels to realize the technology could work in Puget Sound.

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Imagine crossing from Seattle to Bainbridge Island in less than 10 minutes for a toll of less than $10. Twin two-lane tunnels would cost commuters less and allow 6,000 vehicle trips per hour for 24 hours a day. It would reduce crossing times from hours to minutes. The six ferries serving central Puget Sound to Bainbridge, Bremerton and Kingston can carry only 1,100 vehicle trips per hour.

Although a Seattle to Bainbridge trip for a vehicle and driver costs only $11.80, the true cost is closer to $30, because fares cover only 42 percent of state ferry costs, if you include capital expenses. The Washington State Department of Transportation’s biennial budget projects a $506 million dollar loss for the ferry system.

A tunnel that entered at Smith Cove, near the Magnolia bridges, and emerged directly west on Bainbridge Island’s State Highway 305 would be six miles long. It would descend more than 700 feet below Puget Sound. Scandinavian contractors have proved subsea tunnels can be economically built for $37 million per two-lane mile. Twin two-lane tunnels to Bainbridge, at $50 million per mile, would cost $600 million. A replacement of ferries by a tunnel often doubles crossings in a few years. Projecting only a 25 percent increase would give 15 million annual crossings, at $10 per person it would produce $150 million in toll revenue. In addition, a tunnel could help solve waterfront traffic congestion at the Alaskan Way ferry terminal by relocating traffic away from the central business district.

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A tunnel would allow the reassignment of six ferries, with a replacement value of $950 million, eliminating annual capital costs of $200 million for years. This alone would offset the costs. These six ferries account for 50 percent of all crossings. Their replacement by a tunnel could reduce annual operating expense by $100 million.

Last summer I drove around Iceland’s scenic ring road. Just north of Reykjavick I entered the subsea Hvalfjorour Tunnel. Opened in 1998, this two-lane tunnel is 3.5 miles long and 541 feet deep, and has a $9.48 toll. It cost $130 million in today’s dollars, about $37 million per mile.

Not a single Icelandic krona was spent to build this tunnel. The tunnel owner is Spolur, a private company granted a 20-year concession to finance, design, build, operate and collect tolls. Iceland will acquire the tunnel next year free of charge. Lead lender was John Hancock Mutual Life Insurance.

Norway completed the Eiksund Tunnel in 2008. This subsea tunnel is the world’s deepest (942 feet) and almost five miles long. It cost $100 million, penciling out at $20 million per mile. Norway has also started construction of Rogfast tunnels — three in all — that will total 17 miles and reach 1,280 feet below sea level. They are budgeted to cost only $26 million per two-lane mile.

WSDOT has paid for two Cross-Sound Transportation Studies. In 1966, an engineering firm recommended a Fauntleroy-Vashon-Southworth bridge. A 1992 consultant study costing $1.3 million pointed out that Puget Sound is too wide and too deep for an underground tunnel, but suggested far-fetched floating tunnels to Vashon and Southworth. Since 1992, tunneling technology has made huge advances, making a cross-Sound tunnel a possibility.

Subsea tunnels are not new. In 1885, Victorian engineer Sir John Hawkshaw used 76 million bricks to build a four-mile subsea railroad tunnel connecting Wales and southern England.

A visit to Seattle’s sister cities of Reykjavik and Bergen may give our elected officials a timely insight into how our Scandinavian cousins finance and build their tunnels so efficiently.