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The Cumberland Valley Subdivision (CV Subdivision) is a railroad line owned and operated by the CSX Railroad (CSX Transportation) in the U.S. states of Kentucky and Virginia. The line runs from Corbin, Kentucky, east to Big Stone Gap, Virginia,^[3] along a former Louisville and Nashville Railroad line.

At its west end, the CC Subdivision heads north to Cincinnati, Ohio, and the KD Subdivision heads south to Etowah, Tennessee. The east end is at an interchange with the Norfolk Southern Railway Appalachia District, where CSX trains can proceed south to the Kingsport Subdivision at Frisco, Tennessee, via trackage rights.^[4][5]

In 1886, the Louisville and Nashville Railroad (L&N) began to work toward a route into the Eastern Kentucky Coalfield. Work from Corbin, Kentucky commenced on April 29, reaching the town of Pineville, Kentucky in 1888.^[6] The following year, the line was completed to Middlesboro, Kentucky. The line would reach into Southwest Virginia through a tunnel under the Cumberland Gap on September 1, 1889. The route was extended up the Poor Valley to Big Stone Gap, Virginia on April 15, 1891, then to a place called Intermont, Virginia (now Appalachia) where it connected with the Atlantic and Ohio (later Southern Railway). The route was completed to Norton, Virginia (then Prince's Flat) on May 15, 1891, completing a connection with the Norfolk and Western Railway (N&W).^[7][1]

Paralleling development of the L&N in Bell County was the building of a rail network in and around the town of Middlesboro, Kentucky. In 1886, the Middlesborough Belt Rail Road (MBRR) was constructed, encircling the town and running up Bennett's Fork to the southwest. The L&N would purchase the shortline on November 4, 1896.^[8] The Belt Line would not be long for the world, as the Middlesboro City Council would approve its removal in 1899.^[9]

The present CV main from Pineville into Harlan County, Kentucky began life in 1908 as the Wasioto and Black Mountain Railroad. Owned by local businessman T.J. Asher, construction had begun the previous year on a line further up the Cumberland River from a junction with the L&N at Harbell, Kentucky to extend into the vast coalfields owned by Asher. The L&N assisted Asher in originally building the line, and on September 1, 1909, exercised an option to purchase the line outright. At the time of the sale, the W&BM's trackage stretched 13 miles up the river from Harbell.

After purchasing the W&BM's railroad and extend it further up the river valley, arriving at Harlan, Kentucky in 1911. Service reached Baxter in April of that year, with the first passenger train arriving in the town of Harlan proper on July 17. The L&N would continue rapid expansion in Harlan County, constructing a branch up the Poor Fork to Benham, Kentucky by September 4. The Poor Fork Branch would be further extended three miles in 1917 to reach the U.S. Steel's company town of Lynch.

Construction on a branch from Clover Fork commenced thereafter, reaching Ages on May 21, 1912. Further extensions would be built, first to Kildav around March 20, 1916, and to a location named Shields on October 6, 1918. The branch would reach its greatest extent at Highsplint on June 21, 1919.^[10]

The 1920s were a boom period for the Cumberland Valley Division of the L&N Railroad. The L&N's Harlan County service would be enhanced in 1921 with the construction of a 17-track yard at Loyall, Kentucky.^[6] As many as twenty-seven daily passenger trains would stop at the station in Middlesboro in 1921.^[11]

In 1923, the L&N and the Atlantic Coast Line Railroad (ACL) entered into a joint agreement to begin operating the Carolina, Clinchfield and Ohio Railroad (CC&O). With the new agreement, plans were made to connect the Cumberland Valley Division with the CC&O mainline at Spears Ferry, Virginia, just west of Gate City. Plans were made to build the connection from the end of the L&N line in Chevrolet, Kentucky, under Cumberland Mountain, and on towards Spears Ferry. Construction on the connection began in October 1927. All told, 13.6 miles of track were constructed, along with a 6,244-foot tunnel under the mountain. The Harlan-Hagans route was opened on December 1, 1930, at a cost of $5.3 million.^[12] Further plans for the CC&O Connection were scrapped due to financial uncertainty, and the L&N opted to leave the switchback in place. As an alternative, the L&N opted would obtain trackage rights over the Interstate Railroad, now Norfolk Southern Railway, from Norton to reach the railroad.^[1] The switchback and trackage rights, now from Big Stone Gap, remain in use to this day.

By 1939, there were at least eight separate branches constructed in Bell County, including one at Fourmile; one up Straight Creek from Pineville; one that ran up Clear Creek to Chenoa; a branch up Puckett Creek at Blackmont; and another up Bennett's Fork in Middlesboro.^[13]

The year of 1952 would see the end of passenger service at Middlesboro.^[11] The L&N would replace the double-tracked portion of the line between Corbin and Harlan Junction with centralized traffic control (CTC) in 1956.

In early 1986, now-owner CSX Transportation constructed a new bridge and a connection to the Norfolk Southern Railway (ex-Southern Railway) at Big Stone Gap, Virginia, utilizing that railroad's Appalachian District as a new route to the Clinchfield main.^[6] The following year, the original mainline between Cumberland Gap and Hagans would be removed and abandoned.^[14]