markers have a green background and numbers as opposed to black, which is normally used on state Route markers. Some markers also feature the small abbreviation "CORR Z" near the top of the state outline, though this practice is being phased out. All of SR 520 from the Alabama state line to at least the eastern intersection with US 17/SR 25 near Jekyll Island is part of the National Highway System (NHS), a system of routes determined to be the most important for the nation's economy, mobility and defense. History Prior to designation The roadway that would eventually become SR 520 was established in 1920 as SR 1 from Columbus to Cusseta, SR 32 from Dawson to Sylvester, and SR 46 from Sylvester to Tifton. In 1921, SR 55 was established along a route from Louvale, at an intersection with SR 1 to Dawson, and SR 50 was established along a stretch of highway from Dawson in the west, to at least as far as Waynesville, at an intersection with SR 27, in the east. Nearly all of SR 55, and all of that stretch of SR 50, were eventually utilized by SR 520. By 1926, a portion of SR 1 southeast of Columbus and a portion of SR 50 west of Sylvester were paved. Also, US 84 was designated along the portion of SR 50 east of Waycross. Sometime around 1926, SR 27 was redesignated as SR 25. By January 1932, US 280 was designated along SR 1 from Columbus to Cusseta and SR 55 from Cusseta to Richland. All of US 280/SR 1 and nearly all of US 280/SR 55 were paved. Also, a portion of SR 55 northwest of Dawson was paved. Almost all of SR 50 from Dawson to Tifton was paved, along with a portion west of Waycross, and the entirety of US 84/SR 50 east of the city. During October of that year all of US 280/SR 55 was paved. By May 1933, a portion of SR 55 between Alapaha and Willacoochee was paved. In June, a small portion of SR 55 southeast of Richland was paved. By October 1934, a portion of SR 50 east of Tifton, as well as one west of Alapaha, was paved. By January 1935, US 27 was designated along US 280/SR 1 from Columbus to Cusseta. By October 1935, all of SR 55 between Richland and Dawson was