U.S. Route 23 (US 23) is a part of the United States Numbered Highway System that travels from Jacksonville, Florida, to Mackinaw City, Michigan.

US 23 in Tennessee is part of Corridor B of the Appalachian Development Highway System (ADHS) and serves as a major thoroughfare in the Tri-Cities region of the state.

The freeway was first authorized by the Appalachian Regional Development Act of 1965, and the stretch between Johnson City and the Virginia state line was constructed in segments between 1968 and 1986.

In addition to US 23, this freeway was designated as State Route 137 (SR 137) and later Interstate 181 (I-181) and was commonly referred to as "Appalachian Highway" in its early years.

In 1988, the American Association of State Highway and Transportation Officials (AASHTO) approved an extension of I-26 from Asheville, North Carolina, to I-81 in Tennessee.

The freeway immediately begins a steep descent, and trucks are advised to slow to between 45 and 20 miles per hour (72 and 32 km/h), depending on their weight.

Turning toward the northeast, the roadway continues to descend, with the grade gradually decreasing, and has a northbound scenic overlook a few miles beyond.

Continuing its descent, the highway crosses additional valleys and drops below 2,000 feet (610 m) before beginning a concurrency with US 19W at an interchange in the Temple Hill community.

The freeway zigzags over the next few miles, before shifting mostly into a northwest-to-southeast alignment, crossing into Washington County, and entering the Ridge-and-Valley Appalachians.

The roadway crosses a long viaduct over a railroad and several surface streets before reaching an interchange with US 321 and SR 67, which both connect to Elizabethton.

The highway then proceeds through residential neighborhoods in the northern part of Johnson City and turns more northeastwardly, before reaching a three-loop partial cloverleaf interchange with US 11E (North Roan Street), where US 19W splits off.

Leaving Johnson City, the highway crosses additional ridges and proceeds through a mix of farmland and residential neighborhoods before reaching an interchange with SR 75 (Bobby Hicks Drive/Suncrest Drive) in the Gray community.

A short distance beyond is a cloverleaf interchange with I-81 near the Fordtown community, which serves Bristol (the third Tri-City) to the northeast and Knoxville to the southwest.

The highway then ascends several hundred feet over the northern end of Bays Mountain, utilizing a northbound truck climbing lane and bypassing Kingsport to the west.

[15] These settlers founded the Watauga Association in 1772—a frontier pact generally regarded as the first constitutional government west of the Appalachian Mountains.

A proposal to construct a "wide road" between Johnson City and Asheville, North Carolina, reportedly existed as early as 1919.

[22] The portion of the route between the North Carolina state line at Spivey Gap and Johnson City became part of the Appalachian Scenic Highway auto trail in the mid-1920s.

The contract to pave the then-unnumbered eight-mile (13 km) stretch between the North Carolina state line and SR 36 near Ernestville was awarded on August 10, 1919, and completed on May 14, 1920.

A project to grade and drain the 6.3-mile (10.1 km) section of SR 36 in Unicoi County between the North Carolina state line and Ernestville was let on December 11, 1925, and completed on September 10, 1927.

A contract to pave the 10-mile (16 km) section between the Sullivan–Washington county line and Johnson City was awarded on June 27, 1930, and work was completed on December 22 of that year.

[31] Final construction activities were completed seven days later,[30] and the highway was dedicated by then-Governor Henry Horton in a large ceremony near the Sullivan–Washington county line on July 17, 1931.

[50] The section between Plymouth Road south of US 321/SR 67 in southern Johnson City and SR 91 was announced to have been awarded in two contracts on February 5, 1975.

[33] In 1986, the extension through the Bald Mountains was included as one of six new freeway projects dubbed "Bicentennial Parkways" in the Better Roads Program, passed by the Tennessee General Assembly.

[87][88] Between January 1986 and October 1987, an at-grade intersection with SR 81/SR 107 in Erwin was replaced with an interchange in a project that also consisted of widening the latter route.

[104][105] On September 27, 2024, flooding from the aftermath of Hurricane Helene resulted in the partial destruction of the Nolichucky River bridges, and closure of the route between the North Carolina state line and SR 81/SR 107.

[108][109] On October 30, the remainder of the route was reopened after a temporary fill was constructed in the footprint of the collapsed southbound Nolichucky River bridge section.

[110][111] The controlled-access highway that ran between Johnson City and Kingsport was initially established as State Route 137 (SR 137), with this designation extended as new sections were completed.

[117] On August 5, 2003, after completion of a nine-mile (14 km) adjacent section of controlled-access highway in North Carolina, I-26 was extended west into Tennessee, replacing I-181 from Johnson City to I-81.

[120] The Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users, signed into law on August 10, 2005, authorized the remainder of I-181 to be redesignated as part of I-26.

In order to avoid confusing motorists, crews installed small signs listing the old exit numbers at each interchange, which were left in place for the next 18 to 24 months.