U.S. Route 78 in Alabama
| State Route 4 | ||||
| US 78 highlighted in red | ||||
| Route information | ||||
| Maintained by ALDOT | ||||
| Existed | 1926–present | |||
| Major junctions | ||||
| West end | I-22 / US 78 at the Mississippi state line | |||
| East end | US 78 at the Georgia state line | |||
| Location | ||||
| Country | United States | |||
| State | Alabama | |||
| Counties | Marion, Walker, Jefferson, Saint Clair, Talladega, Calhoun, Cleburne | |||
| Highway system | ||||
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U.S. Route 78 (US 78) is a major east–west U.S. Highway across the central part of Alabama. It is internally designated State Route 4 (SR 4) by the Alabama Department of Transportation (ALDOT), though the only section of SR 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 (I-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 I-20. The two routes roughly parallel each other, with junctions at Leeds and Pell City.
West of Jasper, old US 78 is signed as SR 118 to Guin, and the segment from Guin northward to I-22 at Hamilton is signed as US 43/US 278.