|Length:||854.89 mi (1,375.81 km)|
|South end:||I-40 in Dandridge, TN|
|North end:||Highway 137 to Highway 401 on Thousand Islands Bridge at Wellesley Island, NY/Hill Island, ON|
|States:||Tennessee, Virginia, West Virginia, Maryland, Pennsylvania, New York|
Interstate 81 (I-81) is a north–south (physically northeast–southwest) Interstate Highway in the eastern part of the United States. Its southern terminus is at I-40 in Dandridge, Tennessee; its northern terminus is on Wellesley Island at the Canadian border, where the Thousand Islands Bridge connects it to Highway 401, the main Ontario freeway connecting Detroit via Toronto to Montreal. The major metropolitan areas that I-81 connects to include Harrisburg in Pennsylvania and Syracuse in New York.
I-81 is the longest odd-numbered (and therefore the longest north–south) Interstate Highway whose number does not end with a 5, and the third-longest Interstate highway whose number does not end with a 0 or 5 after I-94 and I-64. Interstate 81 largely traces the paths created down the length of the Appalachian Mountains by migrating animals, American Indians, and early settlers. It also follows a major corridor for troop movements during the Civil War. These trails and roadways gradually evolved into U.S. Route 11. Interstate 81 parallels much of the older Route 11. Being mostly rural, it is heavily used as a trucking corridor, often as a bypass of the busier Interstate 95 to the east.
The Interstate 81 Corridor Coalition, a six-state coalition, was organized to handle issues along Interstate 81, such as truck traffic and air pollution. The commission meets annually. 
I-81 begins in Tennessee at I-40 in Dandridge, a route that connects to Knoxville to the west and Asheville to the east. I-81 meets Interstate 26 and U.S. Route 23 which go to Kingsport and Johnson City. At mile marker 75, I-81 leaves Tennessee and enters Virginia.
I-81 in Virginia is largely a rural route with brief concurrencies with I-77 and I-64. The route parallels the Appalachian Mountains for much of its route through Tennessee and Virginia, serving such cities as the twin cities of Bristol, Tennessee, and Bristol, Virginia, Roanoke, Christiansburg, Lexington, Staunton, Harrisonburg, Wytheville, and Winchester. In Harrisonburg, I-81 cuts through James Madison University. It parallels its older counterpart, U.S. Route 11, for its entire length in Virginia.
I-81 briefly enters the Eastern Panhandle of West Virginia for about 26 miles (42 km), serving the city of Martinsburg. The entire routing is in Berkeley County and serves the Eastern WV Regional Airport. The West Virginia segment was completed in 1966 and there have been no realignments since. West Virginia is currently widening I-81 to six lanes from Martinsburg north to exit 23 (US 11) connecting West Virginia and Maryland.
I-81 runs from Dandridge, Tennessee to Fishers Landing, New York. In Maryland, the Interstate highway runs 12.08 miles (19.44 km) from the West Virginia state line at the Potomac River in Williamsport north to the Pennsylvania state line near Maugansville. I-81 is the primary north–south Interstate highway in Washington County, connecting Hagerstown with Chambersburg and Harrisburg to the north and Martinsburg, Winchester, and Roanoke to the south. It is the shortest mainline Interstate in Maryland and contains the shortest portion of I-81 of all six states through which the Interstate highway passes. The Interstate was dedicated as Maryland Veterans Memorial Highway in 1987. I-81 passes through the state of Maryland at one of its narrowest points, the "Hub City" of Hagerstown where it intersects with a large number of other routes, most notably I-70. The Hagerstown Regional Airport is served by this Interstate Highway.
I-81 forms a major north–south corridor through the state of Pennsylvania, serving the boroughs of Chambersburg and Carlisle, where it meets the Pennsylvania Turnpike (I-76) but does not directly interchange with it (motorists must use US 11 to connect). Around the state capital of Harrisburg, the route forms the northeastern section of Pennsylvania's Capital Beltway. The route then travels northeast toward the Wyoming Valley, where it serves the cities of Wilkes-Barre and Scranton, then heads north through the Endless Mountains region toward the state line.
I-81 runs from Interstate 40 at Dandridge, Tennessee, to the Thousand Islands International Bridge at Wellesley Island in New York, beyond which a short stub links it to Ontario Highway 401. In the U.S. state of New York, I-81 extends 183.62 miles (295.51 km) from the Pennsylvania state line southeast of Binghamton to the Canadian border at Wellesley Island northwest of Alexandria Bay. The freeway runs north–south through Central New York, serving the cities of Binghamton, Syracuse, and Watertown. It passes through the Thousand Islands in its final miles and crosses two bridges, both part of the series of bridges known as the Thousand Islands Bridge. South of Watertown, I-81 closely parallels U.S. Route 11 (US 11), the main north–south highway in Central New York prior to the construction of I-81. At Watertown, US 11 turns northeastward to head across New York's North Country while I-81 continues on a generally northward track to the Canadian border. From there, the road continues into the province of Ontario as Highway 137, a short route leading north to the nearby Highway 401.
I-81 roughly parallels the Great Indian Warpath, an old Indian trail which connected New York to the Carolina Piedmont via Virginia and West Virginia. A series of roads linking Virginia to Maryland through Martinsburg were present on maps as early as 1873. New York was originally served by NY 2, a road built in 1924; NY 2 was replaced by U.S. Route 11 in 1927. A highway that largely followed the path of US 11 was built, and became known as the Penn-Can Highway. On August 14, 1957 the highway was redesigned as I-81. In New York, the first segments of I-81 were begun in 1954. In Maryland, the Interstate was begun with the Hagerstown Bypass in the mid 1950s. After several bouts of expansion, the freeway was completed from US 40 (now MD 144) to the Pennsylvania state line in 1958, and marked as I-81 in 1959. Bidding on contracts in West Virginia opened in July 1958. In Virginia, the first Interstate hearing was held in February 1957. At the end of 1957, construction began on a one-mile (1.6 km) stretch near Buchanan, Virginia. A four-mile (6.4 km) section of the Interstate opened in 1959. A stretch in Harrisonburg was opened as well. By late 1963, 85 miles (137 km) in Virginia were open.
The first statewide segment to be completed was that of West Virginia, which was finished in 1966. The section opened on October 19, 1966. In southern Maryland, various parts of I-81 were built in the early 1960s, and the remainder of the highway south to the Potomac River was under construction by 1965, and opened in 1966. Since then, I-81 in Maryland has remained largely unchanged. In Tennessee, by 1965, 336 of the 997 miles (546 of the 1,616 km) of Interstate highways were completed. Construction was expected to be finished in 1969, but a large portion of the work would not be completed until 1974, and most of the road was open by December 1974. The final major segment of the Interstate in the North built was a 17-mile (27 km) section in New York, opened in October 1968. That same year, work in Pennsylvania was completed. The road would not be completely built in Tennessee until August 1975. Construction on parts in Virginia would drag on it was finished on in July 1987. The segment in New York cost $270 million to build.
- I‑581 in Roanoke
- I‑77 in Wytheville; they stay joined for about 10 miles (16 km).
- I‑64 in Lexington; they stay joined through Staunton.
- US 33 in Harrisonburg
- I‑66 in Middletown
- I‑76 / US 11 in Middlesex Township (near Carlisle)
- PA 581 in Enola
- US 22 / US 322 in Harrisburg. I-81/US 322 stays joined throughout Harrisburg.
- I‑83 / US 322 in Harrisburg
- I‑78 near Jonestown
- I‑80 near Hazleton
- I‑476 in Dupont (near Pittston)
- I‑84 / I‑380 / US 6 in Dunmore (near Scranton)
- I‑476 / US 6 / US 11 in Clarks Summit
- New York
- Future I‑86 in Binghamton
- I‑88 in Binghamton
- I‑690 in downtown Syracuse
- I‑90 in North Syracuse
- Highway 137 to Highway 401; freeway ends at Canada–US border (Thousand Islands Bridge)
Interstate 81 has six related, auxiliary Interstate highways that that connect the main freeway to downtowns and other cities. I-381 runs 1.5 miles (2.4 km), connecting Bristol, Virginia to I-81. I-581 is a 6.35 mile long spur that connects Roanoke, Virginia to I-81. It is proposed to be overtaken by Interstate 73. PA 581 connects Harrisburg, Pennsylvania to Interstate 81. It runs 7.36 miles (11.84 km). I-481 serves as an eastern bypass of Syracuse, New York. I-781 extends for 4.9 miles (7.9 km), that connects Fort Drum, New York, to the Interstate. NY 281 is a north–south state highway in central New York in the United States that extends for 16.56 miles (26.65 km) across Cortland and Onondaga counties, roughly paralleling I-81, and connecting at both ends.
I-181 was a 23.85-mile (38.38 km) offshoot of I-81, linking to Kingsport, Tennessee. It was decommissioned in August 2005 when I-26 took over I-181's entire length. I-281 was replaced in January 1970 by I-481. I-81E was replaced by the current I-380.
- Adderly, Kevin (January 27, 2016). "Table 1: Main Routes of the Dwight D. Eisenhower National System of Interstate and Defense Highways as of December 31, 2015". Route Log and Finder List. Federal Highway Administration. Retrieved September 21, 2016.
- Perrier, Dianne (2010). Interstate 81: The Great Warriors Trace. Gainesville: University Press of Florida. ISBN 9780813034812. OCLC 502304332.[page needed]
- "Corridor Coalition". I-81coalition.org. Retrieved January 29, 2018.
- "I-81 Safety Conference". Harrisburg, PA: WHP-TV. Retrieved October 4, 2014.[permanent dead link]
- I-81 Corridor group[dead link]
- Natzke, Stefan; Neathery, Mike & Adderly, Kevin (June 20, 2012). "What is the National Highway System?". National Highway System. Washington, DC: Federal Highway Administration. Retrieved July 1, 2012.
- Highway Information Services Division (December 31, 2013). Highway Location Reference. Maryland State Highway Administration. Retrieved February 3, 2018.
- Washington County (PDF) pp. 13–19
- "Previous Interstate Facts of the Day". Eisenhower Interstate Highway System Home Page. See June 8, 2010. Retrieved February 3, 2018.
- Google (April 16, 2012). "Overview Map of I-81 in New York" (Map). Google Maps. Google. Retrieved February 3, 2018.
- Rice, Otis K.; Brown, Stephen W. (1993). West Virginia: A History. Lexington: University Press of Kentucky. p. 10. ISBN 978-0-8131-1854-3. Retrieved February 2, 2018.
- White, M. Wood (1873). "Counties of Morgan, Berkeley, Jefferson" (Map). White's Topographical, County & District Atlas of West Virginia. 1:310,000. M.W. White. p. 22. OCLC 62726043. Retrieved February 2, 2018 – via David Rumsey Map Collection.
- "New York's Main Highways Designated by Numbers". The New York Times. December 21, 1924. p. XX9.
- "Penn-Can Road Vital to Broome, Majority at Hearing Says" (PDF). The Binghamton Press. January 9, 1957. p. 3. Retrieved February 3, 2018 – via Fulton County Historical Society.
- American Association of State Highway Officials (August 14, 1957). Official Route Numbering for the National System of Interstate and Defense Highways (Map). Scale not given. Washington, DC: American Association of State Highway Officials – via Wikimedia Commons.
- "Interstate 81: The History". New York State Department of Transportation. [full citation needed]
- Bonnell, Robert O.; Bennett, Edgar T.; McMullen, John J. (December 15, 1958). Report of the State Roads Commission of Maryland (1957–1958 ed.). Baltimore: Maryland State Roads Commission. p. 82.
- Maryland State Roads Commission (1958). Maryland: Official Highway Map (Map). Baltimore: Maryland State Roads Commission.[full citation needed]
- Maryland State Roads Commission (1959). Maryland: Official Highway Map (Map). Baltimore: Maryland State Roads Commission.[full citation needed]
- "Bids Opened on Parts of Interstate 81". Charleston Daily Mail. July 29, 1958.[page needed]
- "I-81 History". Virginia Department of Transportation. Retrieved January 29, 2018.
- "Interstate Hwy 81 Opens Soon". Morgantown Dominion News. October 6, 1966.[page needed]
- Federal Highway Administration (2012). "NBI Structure Number: 100000210078011". National Bridge Inventory. Federal Highway Administration.
- "Where Do We Stand On The Interstate?". Kingsport Times-News. May 2, 1965.[page needed]
- "East Tennessee's Christmas Present". Kingsport Times. December 10, 1974.[page needed]
- "Final Links of Interstate 81 to Be Opened with Friday Rites". Syracuse Post Standard. October 14, 1968.[page needed]
- "Interstate Highway Construction". Somerset Daily News. October 22, 1968.[page needed]
- "Interstate 81 Four-Lane Opens". Kingsport News. August 28, 1975.[page needed]
- Virginia Department of Transportation. "Virginia Interstate Exits". Virginia Department of Transportation. Retrieved February 3, 2018.
- Virginia Department of Transportation (2013). "2012 Virginia Department of Transportation Daily Traffic Volume Estimates Including Vehicle Classification Estimates" (PDF). Virginia Department of Transportation.
- State of New York Department of Transportation (January 1, 1970). Official Description of Touring Routes in New York State (PDF) (Map). Albany: New York State Department of Transportation. Retrieved February 3, 2018.[full citation needed]
- "Fort Drum connector road officially open". Syracuse, NY: YNN Central New York. December 6, 2012. Retrieved February 2, 2018.
- Highway Data Services Bureau. "2014 Traffic Volume Report for New York State" (PDF). Albany: New York State Department of Transportation. Retrieved February 2, 2018.
- Allen, Calvin (July 16, 2003). "The Political History of I-26". Mountain Xpress. Asheville, NC. Retrieved February 2, 2018.
- American Association of State Highway Officials (June 27, 1958). Official Route Numbering for the National System of Interstate and Defense Highways as Adopted by the American Association of State Highway Officials (Map). Scale not given. Washington, DC: American Association of State Highway Officials. Retrieved February 7, 2018 – via Wikimedia Commons.
Route map: Google
|Wikimedia Commons has media related to Interstate 81.|
- Geographic data related to Interstate 81 at OpenStreetMap
- Thousand Islands Bridge System, showing the bridges and connections at the northern terminus
- Economic Development History of Interstate 81 in Virginia, a Federal Highway Administration report.