US 23, in concurrency with I-26, enters Unicoi County at Sam's Gap and travels north along Stamp Ridge. Immediately after crossing the state line is a truck information station, signed "Truck Inspection," which requires all trucks to go through before continuing. The following is a 6% grade descent, accompanied with two runaway truck ramps, into the South Indian Creek valley. Between mile markers 47-48 is a scenic overlook turnoff, followed by the I-26 Erwin/Unicoi County Welcome Center, located on Clear Branch Road exit. At Temple Hill, US 19W, traveling from Burnsville, joins in concurrency. After crossing the Nolichucky River, US 23 travels along the eastern foot of Buffalo Mountain as it goes through the towns of Erwin and Unicoi. Entering first in Carter County, US 23 enters Johnson City at the Okolona Road exit. Crossing soon afterwards into Washington County, US 23 connects with US 321/SR 67, which goes to Elizabethton. At the Roan Street exit, US 19W splits off and joins US 11E, continuing towards Bluff City. Passing through Indian Ridge, US 23 leaves Johnson City proper, continuing northwesterly into Sullivan County. After crossing the county and also entering Kingsport city limits, US 23 connects with I-81, in a cloverleaf interchange. At mile marker five is the I-26 Kingsport/Sullivan County Welcome Center, which is accessible from both directions. Staying west of downtown Kingsport, US 23 cuts through Bays Mountain and then crosses the south fork of the Holston River. At the US 11W exit is the western terminus of I-26. With hidden concurrency with SR 137, US 23 continues north into Virginia, at Long Ridge, continuing towards Gate City.
Interstate 26
Interstate 26 travels concurrently with US 23 from the North Carolina state line to US 11W interchange in Kingsport. Established in August 2003, it replaced I-181 south of I-81 and displaced SR 36 and SR 81. In March, 2007, I-26 was extended north of I-81 to its current western terminus at US 11W, decommissioning I-181 completely, as all signs and exit numbers were changed-over to I-26's designation.
State Route 137 is a hidden concurrency that overlaps US 23 between the US 11W interchange and the Virginia state line, all within Kingsport. Established in 1970 as a four-lane divided freeway, it traversed between SR 354, in Johnson City and SR 93, in Kingsport. SR 137 then expanded in phases: In 1973, extended south to US 11E/US 19W; in 1976, extended south to SR 91; in 1978, extended south to US 321; by 1980, extended north to US 11W; and in 1985, extended north to the Virginia state line and south to Erwin. In December, 1985, I-181 was established, truncating SR 137 to its current routing today.
History
US 23 was established in 1930 with a complete concurrency with SR 36, from the North Carolina state line to the Virginia state line; going through Erwin, Unicoi, Johnson City and Kingsport. In 1952, US 23 was rerouted southwest of Ernestville, along SR 81 through Flag Pond and Sam's Gap into North Carolina; its old alignment remained part of US 19W/SR 36. In 1970, The first segment of a four-lane freeway, designated SR 137, was opened between Johnson City and Kingsport. Over the following decade, SR 137 continued being extended at both ends until in 1982, when AASHTO approved US 23 relocation onto the freeway, leaving behind its old alignment to SR 36 north of Johnson City to near the Virginia state line. In December 1985, I-181 was established, truncated SR 137 north of US 11W, while SR 36 replaced as new concurrency south of US 11E; all signs and exit numbers were based on US 23 designation. In 1988, AASHTO approved an extension of I-26 from North Carolina to I-81, on contingent upon the completion and certification of interstate standards in North Carolina, which happened in August 2003. Following the new designation, both SR 36 and SR 81 was removed of their concurrencies with US 23. In March 2007, the remaining spur of I-181, from I-81 to US 11W, was switched to I-26.
Interstate 181
Interstate 181 was established in December 1985 as an interstate designation of US 23, which was already built to interstate standards in the 1970s. I-181 traversed from US 321/SR 67, in Johnson City, to US 11W/SR 1, in Kingsport, totaling. US 23 continued on both directions as interstate grade to the Virginia line, to the north, and south to Erwin; by 1992, US 23 was upgraded to interstate grade south to Sam's Gap, at the North Carolina state line. All exit numbers were based on US 23 mileage. On August 5, 2003, after completion of a section completed in North Carolina, I-26 was extended west into Tennessee, replacing I-181 from Johnson City to I-81; north of I-81, I-181 continued into Kingsport. The American Association of State Highway and Transportation Officials initially ruled against an extension of I-26 along the remainder of I-181 to Kingsport, since that would give a main route Interstate Highway a so-called "stub end," not connecting to any other Interstate highway, to an international border, or to a seacoast. The numerical extension was in 2005 enacted by the effect of the , signed into law on August 10, 2005. In March 2007, I-181 was officially decommissioned, as all signs and exit numbers were changed-over to I-26's designation.
Exit list
Old exit numbers were based on US 23 distances; new exit numbers are based on I-26 milemarkers.
