What's the longest highway in the US?
U.S. Route 20
U.S. Highway 20 (US20) is an east–west United States highway that stretches from the Pacific Northwest all the way to New England. The "0" in its route number indicates that US20 is a coast-to-coast route. Spanning 3,365 miles (5,415km), it is the longest road in the United States,[1] and particularly from Newport, Oregon to Boston, Massachusetts, the route is roughly parallel to that of the newer Interstate 90 (I-90), which is in turn the longest Interstate Highway in the U.S. There is a discontinuity in the official designation of US20 through Yellowstone National Park, with unnumbered roads used to traverse the park.
Appalachia
The effort to connect Appalachia with the outside world has required numerous civil engineering feats. Millions of tons of rock were removed to build road segments such as Interstate 40 through the Pigeon River Gorge at the Tennessee-North Carolina state line and U.S. Route 23 in Letcher County, Kentucky. Large tunnels were built through mountain slopes at Cumberland Gap to speed up travel along U.S. Route 25E. The New River Gorge Bridge in West Virginia, completed in 1977, was the longest and is now the fourth-longest single-arch bridge in the world. The Blue Ridge Parkway's Linn Cove Viaduct, the construction of which required the assembly of 153 pre-cast segments up the slopes of Grandfather Mountain, has been designated a historic civil engineering landmark.