then traverses the hilly North Georgia terrain as it travels toward Chattanooga, Tennessee. The section of I-75 from the northern I-475 intersection to the US 11/US 64 intersection in Ooltewah, Tennessee, is one of the longest continuous multi-state six-lane freeways in the US (some segments along this corridor have as many as 16 lanes). Due to recent lane widening in southern Georgia completed in 2011, the only four-lane section of I-75 in Georgia is bypassed by six-lane I-475; along this route there are at least six lanes from the Alligator Alley portion of I-75 in Naples, Florida, to an portion of I-75 in Ooltewah (with the exception of a four-lane overpass on I-475 over a railroad track in Macon). I-75 is the only Interstate to traverse the full length of the state from north to south. The entire length of I-75 in Georgia is part of the National Highway System, a system of routes determined to be the most important for the nation's economy, mobility, and defense. History Early national highways The general routing of I-75 within Georgia was originally developed as the western routing of the Dixie Highway. The western route of the Dixie Highway as designated in 1916, followed present-day US 41 south from the Tennessee border through Atlanta and Macon south to Echeconnee, Georgia. The section that would become US 41, I-75's direct predecessor, from Echeconnee south through Perry and Valdosta to the border with Florida was paved beginning in 1919 and was later designated as a part of the Dixie Highway in 1924. In 1926, the western route of the Dixie Highway following the newer Perry and Valdosta route was officially designated as US 41. By October 1929, the majority of US 41 was paved in Georgia, the only sections that were not paved at that point were between Fort Oglethorpe and Ringgold, and another on the south side of Calhoun. 1950s The highway that would eventually become I-75 in Georgia was an unnamed expressway that was open in 1951 from the southern part of Atlanta to University Avenue. It was projected from University Avenue to Williams Street in Downtown Atlanta. This expressway was open from Williams Street to what is now the northern end of the Downtown Connector. It was also proposed from the Downtown Connector to the northwest part of Atlanta. By late 1953, this expressway was signed as US 19/US 41 as far