Interstate 81 runs 855 miles from Dandridge, Tennessee to Wellesley Island, New York at the Canadian border, hugging the Great Appalachian Valley between the Blue Ridge and the Allegheny Front. Unofficially known as "the trucker's interstate," I-81 carries one of the highest commercial vehicle percentages of any US interstate — over 30% trucks in some segments, compared to roughly 10-15% on most others.
The route is the principal long-haul alternative to I-95 for north-south traffic between the Southeast and the Northeast / Canadian border. Trucks bound from Atlanta, the Carolinas, or Tennessee toward New York, New England, or eastern Canada typically use I-81 to avoid Washington DC, Baltimore, and the Northeast Corridor. The result is heavy truck volumes through narrow valley segments with limited shoulders and few alternates.
Geographically I-81 follows the Great Valley of the Appalachians — a long, narrow corridor between mountain ridges with relatively gentle grades but frequent winter weather, persistent crosswinds, and extensive truck-vs-truck congestion. The Shenandoah Valley segment in Virginia is particularly affected, and the Pennsylvania Mountains around Scranton are notorious for snow squalls.
- Crosses six states: TN, VA, WV, MD, PA, NY
- Carries the highest commercial vehicle percentage (30%+) of any major interstate
- Follows the Great Appalachian Valley for most of its length
- Crosses I-40, I-77, I-64, I-66, I-70, I-78, I-80, I-83, I-84, I-90
- Northern terminus at the Thousand Islands Bridge into Ontario
- Concurrent with no other interstate for any meaningful distance
- Toll-free for its entire 855-mile length (one of the longest toll-free interstates in the East)