US 78 runs along Linden Avenue, Somerville Street, E. H. Crump Boulevard, and Lamar Avenue through Memphis, Tennessee. In Tennessee, US 78 is historically known as Pigeon Roost Road, and some aborted sections of the highway in Mississippi also claim that name as well as Lamar Avenue. Throughout the Tennessee portion, US 78 is overlapped in its entirety by State Route 278, along Linden Avenue and Somerville Street, and State Route 4 along E. H. Crump Boulevard and Lamar Avenue.
Mississippi
US 78 is a freeway for its entire length in Mississippi. The section from its intersection with Interstate 269 in Byhalia, Mississippi to the Alabamastate line is designated as Interstate 22. The highway runs across the northeastern rural part of the state, connecting several population centers. Mississippi's portion of US 78 is defined in Mississippi Code Annotated § 65-3-3. The old routing of US 78 through the state is signed as MS 178.
Alabama
US 78 is a major east–west state highway across the central part of Alabama. It is internally designated State Route 4 by the Alabama Department of Transportation, though the only section of State Route 4 that is signed is along portions mainly west of Jasper. The section from the Mississippi state line to near Graysville is concurrent with Interstate 22; from Graysville south to Birmingham, US 78 takes its original routing. East of Birmingham to the Georgia state line, US 78 has been replaced as a major through-route by Interstate 20. The two routes roughly parallel each other, with junctions at Leeds and Pell City. West of Jasper, old US 78 is signed as AL 118 to Guin, and the segment from Guin northward to I-22 at Hamilton is signed as US 43/US 278.
Georgia
US 78 enters Georgia in Haralson County, and then proceeds through Carroll County and Douglas County. In Douglasville, located in Douglas County, US 78 runs through the downtown, historical part of the city. It is the original thoroughfare for these Georgia counties. There is another short freeway portion east of Atlanta, leading from just inside I-285 eastward to the suburbs of Stone Mountain, Georgia, and Snellville, Georgia. This portion is named the Stone Mountain Freeway, and has an excellent view of Stone Mountain while traveling eastbound. Along this route, US 78 is largely conterminous with Ponce de Leon Avenue. The route then continues eastward through DeKalb, Gwinnett, Walton, and Oconee counties. In Oconee county US 78 leaves Moina Michael Highway at the SR 316 interchange, turning right and running concurrent with SR 316/US 29. At the terminal eastern interchange of SR 316 both US 78 and US 29 turn right and join with SR 10 Loop, a mostly interstate-grade bypass that rings Athens-Clarke County. US 78 exits the bypass and turns right at the Lexington Road interchange. From there US 78 passes through Oglethorpe, Wilkes, McDuffie and Columbia Counties into Augusta and then onto one of the twin bridges across the Savannah River into South Carolina.
South Carolina
US 78 provides the most direct route between Augusta and Charleston, through the South Carolina Lowcountry. Crossing Savannah River into the state, it goes northeast into Aiken before going southeasterly through the cities and towns of Williston, Blackville, Denmark, Bamberg, Branchville, and St. George. East of Dorchester, it parallels Interstate 26 into downtown Charleston, where it ends.
History
In western Alabama, the historical name of US 78 is Bankhead Highway. It is also known by this name in portions of Georgia, including Atlanta, and the Bankhead neighborhood takes its name from that stretch of road. Also, the old section of US 78 that travels through downtown New Albany, Mississippi, is named Bankhead Street. Throughout the 2000s, US 78 has been gradually upgraded into a four-lane freeway in Mississippi and Alabama and signed as Interstate 22. US 78 is completely concurrent with I-22 from Byhalia, Mississippi to Birmingham, Alabama.
Future
After the completion of Interstate 22 throughout the 2010s, it is uncertain whether US 78 will be decommissioned west of Birmingham or the old route recommissioned as US 78 upon completion of Interstate 22. If the old route is recommissioned as US 78, parts of I-22 and US 78 would be forced to overlap. A stretch from just west of Hamilton, Alabama to the first exit in Mississippi, as well as a stretch from MS 25 in Fulton, Mississippi to the next exit west of Fulton after crossing the Tennessee-Tombigbee waterway will overlap. The Hamilton area overlap would be due to the old US 78 routing no longer exists west of Hamilton having been upgraded to I-22 from Weston westward into Mississippi. The second overlap would be necessary because the old US 78 no longer exists west of downtown Fulton, Mississippi due to the Tennessee-Tombigbee waterway and no bridge in place to carry US 78 traffic on the former route.
