Chances are, you've driven through a fair number of tunnels, some short, some long, some spanning underwater, and some cutting through formidable topographic features such as mountains that would require a lengthy detour to get from point A to point B.
These claustrophobia-inducing examples of public infrastructure—all staggering feats of engineering—were built for various reasons. While most were constructed to shave time off established land routes or built as alternatives to ferries or bridges, some of these underwater corridors provide the only way in or out of isolated locations.
Here are 10 of the world's most singular underground and underwater tunnels.
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Anton Anderson Memorial Tunnel
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Long, dark, and narrow, a roughly 10-minute jaunt through the Anton Anderson Memorial Tunnel in Whittier, Alaska—better known as the Whittier Tunnel—is a great day trip from Anchorage.
At 2.5 miles long, this single-lane roadway slicing through an Alaskan mountain is the longest combined rail/highway tunnel in North America. The tunnel serves as the only overland link between Whittier, Alaska's, roughly 200 residents—who all live under one roof—and the rest of civilization.
Traffic, which flows in only one direction at a time, is regulated according to summer and winter schedules published by the Alaska Department of Transportation and Public Facilities. Scheduled and unscheduled trains, which travel along tracks integrated into the concrete roadway, can prompt delays.
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Detroit-Windsor Tunnel
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Completed in 1930 as the first and only nation-linking underground vehicle corridor, the Detroit-Windsor Tunnel was built for $23 million. It is the third oldest underwater vehicle tunnel in the United States or Canada. It stands behind only New York/New Jersey's Hudson River-crossing Holland Tunnel (completed in 1927) and the Posey Tube (completed in 1928), which connects Alameda and Oakland, California.
The four-lane Detroit-Windsor Tunnel, which connects Detroit and Ontario, Canada, is also one of the busiest border crossings between the U.S. and Canada. Crossing under the Detroit River 75 feet below the surface at a length that's just under a mile, the tunnel has a ventilation system capable of pumping 1.5 million cubic feet of fresh air into the 85-year-old subaqueous roadway tube each minute.
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Eisenhower-Johnson Memorial Tunnel
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The highest vehicular tunnel in the United States with an average elevation of 11,112 feet, the Eisenhower-Johnson Memorial Tunnel—or, simply, the Eisenhower Tunnel—travels through the Continental Divide.
Carrying Interstate 70 along a four-lane passage about 50 miles west of Denver, the tunnel spans just under 1.7 miles from portal to portal, carrying over 30,000 vehicles daily. Open 24/7, the tunnel is a shortcut that allows motorists to circumvent the overland route along a particularly windy stretch of U.S. Route 6 through Loveland Pass.
While convenient, Rocky Mountain scenery-seekers often opt not to take the tunnel, which knocks a little over 9 miles off their journey compared to the much more scenic overland route.
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Lærdal Tunnel
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Spanning 15 miles across, the Lærdal Tunnel in Norway is one of the longest in the world. Relatively new—it opened in 2000 as a means of eliminating the ferry rides and frequently closed mountain passes associated with traveling from Oslo to Bergen along the E16 Highway—it takes about 20 minutes to travel from one end to the other.
The two-lane mountain tunnel features a trio of caves, which also serve as rest areas. Spaced roughly 3 miles apart, these areas allow drivers to take a quick break or turn around and head back the other way. Lærdal is also the first vehicular tunnel in the world to boast its very own air treatment plant.
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Mont Blanc Tunnel
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Heavily trafficked, the 7.2-mile-long Mont Blanc Tunnel was a time-saving route when completed in 1965 and was for over a decade the longest in the world. Whisking nearly 2 million vehicles a year between the bustling ski resorts of Chamonix, France, and Courmayeur, Italy, the tunnel is co-managed by both of these countries.
The concept for the tunnel dates back to 1908 when French engineer Arnold Monod created the design, which was presented to members of the French and Italian parliaments. Due to various changes in the political climate in each country, as well as World War I and World War II, the two countries did not sign an agreement to build the tunnel until 1959.
Efforts to complete the project were hampered by floods and even avalanches, but on July 16, 1965, presidents Charles de Gaulle andGiuseppe Saragat of Italy officially dedicated and opened the tunnel.
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Mount Baker Tunnel
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Seattle's art deco-tinged Mount Baker Tunnel is actually three separate tunnels: two twin-bore tunnels completed in 1940 and a third tunnel, a double-decked structure with a pedestrian/bicycle pathway completed in 1991. Together, they carry Interstate 90 beneath the hilly southeast Seattle neighborhood of Mount Baker.
The art deco-style tunnel was placed on the National Register of Historic Places in 1982. It is also the "world's largest diameter soft earth tunnel," according to the Library of Congress, which adds that the structure is a great example of modernistic architecture and is remarkable "for the material it was driven through (clay)."
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SMART Tunnel
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Completed in 2007, Malaysia's SMART Tunnel was designed and built to divert stormwater away from the oft-flooded center of Kuala Lumpur.
SMART Tunnel—which stands for "Stormwater Management and Road Tunnel"—is the longest tunnel in Malaysia and the world's longest multipurpose tunnel, but it doesn't handle both traffic along Expressway 38 and floodwater simultaneously. When needed, floodwater is diverted into a longer separate bypass tunnel underneath the 2.5-mile double-deck roadway tunnel. In this scenario, traffic can continue as normal.
During heavy, prolonged rains when the threat of extreme flooding is high, the roadway is closed to vehicles, and automated flood control gates are opened so that water can be diverted through both tunnels.
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Tokyo Bay Aqua-Line
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The Tokyo Bay Aqua-Line is a nearly 9-mile-long bridge-tunnel combination that cuts the commute time between the bustling Japanese prefectures of Kanagawa and Chiba from over 90 minutes to 15.
Completed in 1997 following over three decades of planning and construction, it also eliminates the need to travel through traffic-choked Tokyo itself. The nearly 6-mile-long tunnel section is the fourth-longest underwater tunnel in the world and the world's largest underwater road tunnel.
The complex is best known for "Umihotaru" (sea firefly), an artificial island-cum-tourist attraction that connects the tunnel with the bridge and includes restaurants, shops, and an observation deck.
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Yerba Buena Island Tunnel
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More than 200,000 motorists drive through the Yerba Buena Island Tunnel in San Francisco every day. The single-bore tunnel has carried traffic along a double-deck roadway since 1936. The tunnel is connected by a causeway to Treasure Island and Yerba Buena, a small residential neighborhood.
The tunnel, which is actually part of the San Francisco-Oakland Bay Bridge, is the "largest-diameter bore tunnel in the world," according to the California Department of Transportation. It is also one of the world's most complex tunnels because it incorporates a variety of architectural forms, allowing it to carry two levels of traffic between the two cities, the DOT notes.
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Zion-Mount Carmel Tunnel
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Spanning 1.1 miles through the middle of a sandstone mountain, the two-lane Zion-Mount Carmel Tunnel, located in Zion National Park in Utah, is the longest vehicular tunnel in the National Park System.
Completed in 1930, the tunnel features a series of galleries—giant windows carved out of the side of the mountain—that provide natural light and fresh air. Larger vehicles are now required to secure a $15 "tunnel permit" that grants drivers of these vehicles permission to pass through the structure.
When a permit-holding large vehicle or a parade of large vehicles going in the same direction needs to access the tunnel, park rangers temporarily close it to two-way traffic so that drivers can travel safely through the roadway.
