Background: This mountain pass in the Italian Alps starts an elevation of 3116 feet and ascends to just under 9050 feet, or 1.7 miles above sea level. The pass was first constructed in 1820.How It’s Unique: The Stelvio Pass has a dizzying 48 hairpin turns and an average grade of 7.4 percent. “To go down that slope, you either basically cut down the mountain to remove that slope, or you have to go back and forth and zigzag a lot,” Mahmassani says. The road, which hosts one of the more gruelling stages of the Giro d’Italia bicycle race, has a 7.4 percent grade–“huge” by American standards, Mahmassani says. Six percent grades are about the maximum for U.S. highways, he says, and require escape lanes and safety signage. “You go down or up this road, you’re going to get seasick,” he says.
3. Hunan, China
Background: This spectacular tunnel is one of the few ways to travel to the remote Guoliang village in China’s Hunan Province.How It’s Unique: Chiseled by hand in the 1970s, the Guoliang Tunnel is a road that Mahmassani calls “a sculpture more than a means of transportation.” The tunnel passes through a treacherous section of the Taihang Mountains and is lined with makeshift windows that provide scenic but terrifying views. With a clearance of only 15 feet, a width of 12 feet and a precipice around every other bend, navigating this short tunnel is a guaranteed thrill.
Background: Iceland’s Highway 1 was completed in 1974 and is roughly 830 miles long.How It’s Unique: Highway 1 is better known as the Ring Road, because it forms a giant loop that circles the whole of Iceland. Much of the road has only one lane heading in each direction as it dices through fjords, cuts across the country’s sub-Arctic desert and curves along the Atlantic coastline. The Ring Road is especially tourist-friendly, hitting most of the major Icelandic landmarks, though drivers should be prepared for unpaved stretches and antiquated bridges.
5. Rauma, Norway
Background: This mountain pass in southwest Norway opened in 1936 after eight years of construction. Trollstigen aptly translates from Norwegian to English as “Troll Ladder.”How It’s Unique: Eleven hairpin turns take drivers 2800 feet above sea level with an average grade of 9 percent. This scenic road is accented by the Stigfossen waterfall, which runs down the side of the mountain and is crossed by a small bridge on the way toward the road’s apex. Sections of the pass were cut directly into the face of the mountain during the 1930s. The pass tends to open in late May and sometimes closes through June because of the region’s harsh winters.
6. Dallas, Texas
Background: This five-level marvel of engineering can be found on the outskirts of Dallas, where Interstate 635 connects with U.S. 75. Construction crews, despite the project’s enormous scope, were able to complete the labyrinth of lanes in December 2005, a full year ahead of schedule.How It’s Unique: As Mahmassani points out, building wider roads is just not feasible in most cities. The solution for Dallas? Go vertical. Certain points of the High Five are as tall as a 12-story building, and about 500,000 commuters pass through it daily. The project required 37 permanent bridges and six temporary bridges to be built. Additionally, 300,000 square feet of retaining wall and 74,000 square feet of drainage pipe run along the interchange. In 2006, the American Public Works Association selected the interchange as one of its “Public Works Projects of the Year.”