I-59 spans in Louisiana, the shortest distance in the four states through which it travels. The route begins at a partial cloverleaf interchange with I-10 and I-12 at the northeast corner of Slidell, a city in St. Tammany Parish. From this interchange, connections are made to New Orleans and Hammond, as well as Bay St. Louis, Mississippi. Heading north, I-59 has two exits serving the town of Pearl River, where it begins a concurrency with US 11. Immediately afterward, the highway crosses the West Pearl River and passes through an interchange with Old US 11, a portion of the pre-interstate alignment serving the Pearl River Wildlife Management Area. I-59 then travels through the Honey Island Swamp for before crossing the main branch of the Pearl River into Mississippi.
Mississippi
In Mississippi, I-59 continues to run parallel with US 11, traversing mainly rural areas, but going through or bypassing the towns of Picayune, Poplarville, Hattiesburg, Ellisville, Moselle, Laurel, and Meridian. For its length in Mississippi, I-59 either travels concurrent with, or runs close to, US 11. Between the towns of Pearl River and Picayune, US 11 travels concurrent with I-59. The highway also has concurrencies with US 98 in Hattiesburg; Mississippi Highway 42 just north of Hattiesburg; US 84 and Mississippi Highway 15 in Laurel, and US 80, US 11, and MS 19 in the Meridian area. A notoriously sharp S-curve, at milepost 96 in Laurel, was the subject of a large reconstruction project. Those sharp curves were the legacy of an overpass over the Southern Railway on a town bypass with design dating from before the Interstate Highways, and they featured a speed limit, one of the lowest anywhere on the Interstate Highway System. This work was completed in 2009. Just west of Meridian, I-20 joins I-59 and these two highways continue together for, across the border with Alabama to and through Birmingham. The exit numbers are given as those of I-59. At 4:00 p.m. on August 27, 2005, for the first time in its history, the southbound lanes of I-59 were temporarily redirected northward to accommodate evacuation for Hurricane Katrina. This was a previously agreed to joint plan by the states of Mississippi and Louisiana called contraflow lane reversal. The program began at the Louisiana–Mississippi state line and continued north to Poplarville.
Alabama
I-59 and I-20 travel together for about 40 percent of their route through Alabama, passing northeast through Tuscaloosa before finally parting ways in eastern Birmingham. In Birmingham, many wrecks and accidents occur near the cross-over interchange of I-20/I-59 and I-65. On two occasions, 18-wheelers crashed and burned fiercely enough to melt the support beams of overpasses. Beginning in eastern Birmingham, I-59 continues on its own northeast, passing by Gadsden and Fort Payne in the foothills of the Appalachian Mountains, before entering Georgia. I-59 from Gadsden at mile marker 182 to Stephen's Gap at mile marker 193 had degraded over the decades since it was opened into a rough concrete highway. Between 2010 and 2014, a construction project called "Project 59" took place between Gadsden and Fort Payne. This project consisted of reconstructing the Interstate Highway with unbonded concrete as well as modifications to the width and vertical clearance of the bridges and overpasses in the segment.
Georgia
I-59 has a short trek through Georgia, with only three exits before ending at I-24 several miles west of Chattanooga, Tennessee, in Wildwood, Georgia. Within Georgia it carries unsigned designated as State Route 406 for internal Georgia Department of Transportation purposes.
The entire length of I-59 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.
