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The Appalachian Development Highway System (ADHS) is a series of highway corridors in the Appalachia region of the eastern United States. The routes are designed as local and regional routes for improving economic development in the historically isolated region. It was established as part of the Appalachian Regional Development Act of 1965, and has been repeatedly supplemented by various federal and state legislative and regulatory actions. The system consists of a mixture of state, U.S., and Interstate routes. The routes are formally designated as "corridors" and assigned a letter. Signage of these corridors varies from place to place, but where signed are often done so with a distinctive blue-colored sign.

A 2019 study found that the construction of the ADHS led to economic net gains of $54 billion (approximately 0.4 percent of national income) and boosted incomes in the Appalachian region by reducing the costs of trade.

History

In 1964, the President's Appalachian Regional Commission (PARC) reported to Congress that economic growth in Appalachia would not be possible until the region's isolation had been overcome. Because the cost of building highways through Appalachia's mountainous terrain was high, the region's local residents had never been served by adequate roads. The existing network of narrow, winding, two-lane roads, snaking through narrow stream valleys or over mountaintops, was slow to drive, unsafe, and in many places worn out. The nation's Interstate Highway System, though extensive through the region, was designed to serve cross-country traffic rather than local residents.

The PARC report and the Appalachian governors placed top priority on a modern highway system as the key to economic development. As a result, Congress authorized the construction of the Appalachian Development Highway System (ADHS) in the Appalachian Development Act of 1965. The ADHS was designed to generate economic development in previously isolated areas, supplement the interstate system, and provide access to areas within the region as well as to markets in the rest of the nation.

Currently, the ADHS is authorized at , including added in January 2004 by Public Law 108–199. By the end of FY 2018, —approximately 90.5 percent of the authorized—were complete, open to traffic, or under construction. Many of the remaining miles will be among the most expensive to build.

Corridor Z across southern Georgia is not part of the official system, but has been assigned by the Georgia Department of Transportation.

List of ADHS corridors

Corridor A

Corridor A is a highway in the states of Georgia and North Carolina. It travels from Interstate 285 (I-285) north of Atlanta northeasterly to I-40 near Clyde, North Carolina. I-40 continues easterly past Asheville, where it meets I-26 and Corridor B.

In Georgia, Corridor A travels along the State Route 400 (SR 400) freeway from I-285 to the SR 141 interchange southwest of Cumming.Appalachian Development Highways Economic Impact Studies
, Chapter 3: Highway and Traffic Analysis From here to Nelson, near the north end of I-575, Corridor A has not been constructed; its proposed path is near that of the cancelled Northern Arc. It begins again with a short piece of SR 372, becoming SR 515 when it meets I-575. SR 515 is a four-lane divided highway all the way to Blairsville. From Blairsville to North Carolina, the corridor has not been built, and SR 515 is a two-lane road.

The short North Carolina Highway 69 (NC 69) takes Corridor A north to U.S. Route 64 (US 64) near Hayesville. Corridor A turns east on US 64, and after some two-lane sections, it becomes a four-lane highway. Corridor A switches to US 23 near Franklin, and meets the east end of Corridor K near Sylva. From Sylva to its end at I-40 near Clyde, Corridor A uses the Great Smoky Mountains Expressway, which carries US 23 most of the way and US 74 for its entire length.

Corridor A-1

Corridor A-1 uses US 19/ SR 400 from the point that Corridor A leaves it, at SR 141 near Cumming, northeast to SR 53 near Bright. SR 400 continues northeast as a four-lane highway from SR 53 to SR 60 south of Dahlonega; this section was built "with APL funds as a local access road".

Corridor B

Corridor B is a highway in the states of North Carolina, Tennessee, Virginia, Kentucky, and Ohio. It generally follows U.S. Route 23 (US 23) from Interstate 26 (I-26) and I-40 near Asheville, North Carolina, north to Corridor C north of Portsmouth, Ohio.

Corridor B uses I-240 from its south end into downtown Asheville, where it uses US 23 (current and future Interstate 26) to Kingsport, Tennessee. The US 23 freeway ends at the Tennessee–Virginia state line, but US 23 is a four-lane divided highway through Virginia and into northeastern Kentucky.

At Greysbranch, Kentucky, Corridor B leaves US 23 to turn east on Kentucky Route 10 (KY 10) over the two-lane Jesse Stuart Memorial Bridge into Ohio. The short Ohio State Route 253 (OH 253) connects the bridge to US 52, a freeway that takes Corridor B north to Wheelersburg. US 52 continues west to Portsmouth, the proposed alignment of Corridor B continues north and northwest along Ohio State Route 823 to US 23 near Lucasville. The part of Corridor B north of SR 253 is also part of the I-73/74 North–South Corridor.

Corridor B-1

Corridor B-1 travels from KY 10 to the north end of the Portsmouth Bypass. In Kentucky, it follows US 23 and US 23 Truck; after crossing the two-lane Carl Perkins Bridge into Ohio, it uses current and planned SR 852—a western bypass of Portsmouth—and US 23. Corridors B and B-1 both end near Lucasville, where Corridor C continues north along US 23 to Columbus.

Corridor C

Corridor C is a highway in the U.S. state of Ohio. It is part of U.S. Route 23 (US 23), traveling from the north end of Corridor B near Lucasville north to Interstate 270 (I-270) south of Columbus. , most of the road is a four-lane divided highway, but there are a few gaps yet to be built. Corridor C is part of the I-73/I-74 North–South Corridor.

Corridor C-1

Corridor C-1 is a connector from Corridor C near Chillicothe southeast to Corridor D near Jackson, Ohio, along US 35. It has been completed as a four-lane highway.

Corridor D

Corridor D travels east–west from Interstate 275 (I-275), near Cincinnati, Ohio, to I-79, near Bridgeport, West Virginia. The corridor utilizes Ohio State Route 32 (SR 32) and U.S. Route 50 (US 50).

Corridor E

Interstate 68 (I-68) is a Interstate highway in the U.S. states of West Virginia and Maryland, connecting I-79 in Morgantown to I-70 in Hancock. I-68 is also Corridor E of the Appalachian Development Highway System. From 1965 until the freeway's construction was completed in 1991, it was designated as U.S. Route 48 (US 48). In Maryland, the highway is known as the National Freeway, an homage to the historic National Road, which I-68 parallels between Keysers Ridge and Hancock. The freeway mainly spans rural areas, and crosses numerous mountain ridges along its route. A road cut constructed for it through Sideling Hill exposed geological features of the mountain and has become a tourist attraction.

US 219 and US 220 travel concurrently with I-68 in Garrett County and Cumberland, Maryland, respectively, and US 40 overlaps with the freeway from Keysers Ridge to the eastern end of the freeway at Hancock.

The construction of I-68 began in 1965 and lasted for about 25 years, being completed on August 2, 1991. While the road was being built, it was predicted that the completion of the road would improve the economic situation along the corridor. The two largest cities connected by the highway are Morgantown and Cumberland, both with populations of fewer than 30,000 people. Despite the fact that the freeway serves no large metropolitan areas, I-68 provides a major transportation route in western Maryland and northern West Virginia and also provides an alternative to the Pennsylvania Turnpike for westbound traffic from Washington, D.C. and Baltimore.

There have been several major planned road projects that would affect the freeway's corridor, which, due to major funding issues, are unlikely to be completed. These include a plan to extend I-68 to Moundsville, West Virginia, and the plan to link the Mon–Fayette Expressway, a toll highway which meets I-68 east of Morgantown, to Pittsburgh, Pennsylvania.

Corridor F

Corridor F is a highway in the U.S. states of Tennessee and Kentucky. It travels from Interstate 75 (I-75) in Caryville, Tennessee, northeasterly to Corridor B ( U.S. Route 23 (US 23)) near Kentucky. Corridor F uses US 25W and Tennessee State Route 63 (SR 63) from I-75 to Corridor S ( US 25E) in Harrogate, Tennessee. There, it turns northwest along US 25E, passing through the Cumberland Gap Tunnel into Kentucky. It leaves US 25E in Pineville, Kentucky, turning northeasterly along US 119, past an intersection with Corridor I ( Kentucky Route 15 (KY 15)) in Whitesburg, to its end at Corridor B.

Corridor G

Corridor G is a highway in the U.S. states of Kentucky and West Virginia that follows the route of U.S. Route 119 (US 119) from Pikeville, Kentucky, to Charleston, West Virginia. Construction on the road began in 1972 in West Virginia and 1974 in Kentucky, but it was more than two decades before the road was completed in either state. The full length of Corridor G in West Virginia was completed in 1997, but Kentucky's last segment was not opened until 2008.

Corridor H

Corridor H is a highway in the U.S. states of West Virginia and Virginia. It travels from Weston, West Virginia to Strasburg, Virginia. In December 1999, a settlement agreement was reached, providing the framework for resumption of final design, right-of-way acquisition and construction activities on the Corridor H highway project. Corridor H is the only corridor highway that remains incomplete in the State of West Virginia. It begins at I-79 in Weston and will end at I-81 in Strasburg when complete. Virginia's portion of Corridor H runs from the West Virginia state line to I-81 at Strasburg, Virginia. The building of Corridor H was controversial, arousing strong passions for and against. Decades of public debate and legal battles aired the essential question of whether previously isolated areas should be preserved or opened to development. Despite the controversy, about 75 percent of the highway had been completed as of 2013. The highway is open from the Weston exit of I-79 to Kerens, Randolph County and an additional section of the four-lane is open from the Grant-Tucker county line to Wardensville as of July 2016.

Corridor I

Corridor I is a highway in the U.S. state of Kentucky. It travels from Interstate 64 (I-64) southeasterly along the Mountain Parkway and Kentucky Route 15 (KY 15) to Corridor F ( U.S. Route 119 (US 119)) in Whitesburg. Corridor I meets Corridor R (Mountain Parkway) near Campton and Hal Rogers Parkway and KY 80 in Hazard.

Corridor J

Corridor J is a highway in the U.S. states of Tennessee and Kentucky. It travels from the end of Interstate 24 (I-24) in Chattanooga, Tennessee, north to I-75 in London, Kentucky.

Corridor J uses U.S. Route 27 (US 27) from Chattanooga north to Soddy-Daisy. There it turns northwest on State Route 111 (SR 111), eventually curving to the north via Dunlap, Sparta, and Cookeville to Livingston. Then it turns northwest on SR 52 to Celina and northeast on SR 53 to Kentucky.

Upon crossing into Kentucky, Corridor J becomes Kentucky Route 61 (KY 61), heading north to Burkesville. There it turns east on KY 90, which it follows to Burnside. Corridor J turns north on US 27 at Burnside, quickly turning northeast on KY 914 to bypass downtown Somerset and then east on KY 80 to London.

Listed in a US House of Representatives Report in 2002, was a proposed feasibility and the planning study to establish I-175 along Corridor J. However, no allocation of monies was appropriated and no additional discussion has been made since for this briefly proposed interstate along the corridor.

Until late 2005, Corridor J was to turn west just north of Cookeville along the planned SR 451 to SR 56 north of Baxter and then use SR 56 and SR 53 via Gainesboro.

Corridor J-1

Corridor J-1 runs from Algood west to SR 56, then north to Celina via SR 53 and Gainesboro; it is proposed that the part of the corridor be renumbered as SR 451. The corridor serves as an alternate route for Corridor J, avoiding Livingston. The entire route is two-lane with wide shoulders, allowing for possible expansion if needed.

Corridor K

Corridor K is a highway in the U.S. states of Tennessee and North Carolina. Overlapped entirely by U.S. Route 74 (US 74), it also shorter concurrences with US 19, US 64, APD-40 (US 64 Bypass) US 129 and US 441. The corridor connects Interstate 75 (I-75) in Cleveland, Tennessee (northeast of Chattanooga), easterly to Corridor A ( US 23) near Dillsboro, North Carolina.

There are two gaps in the corridor, one in each state. The gap in Tennessee is the Ocoee Scenic Byway along the Ocoee River from Parksville to Ducktown. Plans outline a new alternate route for this section since the current route does not meet the purpose and need to support the regional transportation goals of a safe, reliable and efficient east–west route. Currently in environmental study, a record of decision is expected in 2017. The gap in North Carolina is located from Andrews to Stecoah. Broken in three projects, the plan outlines a new four-lane expressway that will bypass north of the Nantahala Gorge