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. In the U.S. state of Tennessee, the highway travels in the northeastern part of the state from the North Carolina state line at Sam's Gap in the Bald Mountains, north to the Virginia state line in Kingsport. With a predominant concurrency with Interstate 26 (I-26), US 23 is a divided four-lane freeway that follows Corridor B of the Appalachian Development Highway System (ADHS) and serves as a major thoroughfare in the Tri-Cities. Although I-26 is technically an east–west route, the highway predominantly travels in a north–south alignment in Tennessee. The route reaches a maximum elevation of at the North Carolina state line, which is the highest elevation on the Interstate Highway System east of the Mississippi River.
The freeway was first authorized by the Appalachian Regional Development Act of 1965, which created the ADHS, 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 remainder of the freeway was completed in 1995, and the stretch between the North Carolina state line and I-81 was redesignated as I-26 in 2003. After an initial denial, I-26 was extended north to Kingsport in 2007, replacing the remainder of I-181.
Route description
The freeway begins at the Virginia state line at a partial interchange with SR 36 (the old route of US 23) and SR 346, where the route continues into Virginia as a four-lane divided highway. Here, a pair of one-lane ramps carry US 23 and unsigned SR 137 across both routes; SR 346 is not directly accessible from the freeway, and the southbound lanes are indirectly accessible from SR 23 via an entrance ramp from SR 346. Here, the freeway curves to the southwest, and then to the southeast a short distance later, zigzagging over the next few miles through a predominantly residential area on the outskirts of Kingsport. The freeway then reaches a partial cloverleaf interchange with US 11W, where I-26 begins, and transitions into a more direct north–south alignment. The Interstate immediately crosses the Holston River, which is split into two channels here by a wide island called Long Island, on a long pair of viaducts. It then begins a steep ascent over the north end of Bays Mountain, where the eastbound lanes utilize a truck climbing lane. Passing through a deep artificial cut at the top of the mountain, the route then begins a descent, where the westbound lanes also contain a truck lane. A short distance later, the Interstate reaches a partial cloverleaf interchange with SR 93 (John B. Dennis Bypass), which continues to the north as a controlled-access bypass of Kingsport.