U.S. Highway 431 (US-431), internally designated by the Alabama Department of Transportation as State Route 1 (SR-1), is a major north–south state highway across the eastern part of the U.S. state of Alabama. Although US-431's south end is in Dothan, SR-1 continues south for about 13 miles (21 km) along US-231 to the Florida state line.

State Route 1 is primarily the unsigned partner route assigned to U.S. Highway 431. The two routes are co-aligned from the southern terminus of US-431 at Dothan to the Tennessee state line. South of Dothan, State Route 1 is assigned to U.S. Highway 231. At Huntsville, US-231 and US-431 (Governors Drive) junction again as Memorial Parkway, and State Route 1 is partnered with both U.S. Highways until they cross into Tennessee.

From its point of origin in Houston County, State Route 1 is aligned very close to the Alabama-Georgia border, coming within less than one mile (1.6 km) of the border at both Eufaula and Phenix City. At Phenix City, US-431 and unsigned State Route 1 begin a concurrency with U.S. Highway 280 and unsigned State Route 38 and turn to the northwest. At Opelika, US-431 and State Route 1 divert from US-280 and resume their northward orientation.

East of Oxford, State Route 1 and US-431 merge with westbound U.S. Highway 78 and unsigned State Route 4. At Oxford, State Route 1 and US-431 begin a gradual northwestward trajectory, passing through Anniston, Gadsden and Guntersville. The two routes resume their northward orientation upon merging with U.S. Highway 231 at Huntsville.

One of the criticisms of US-431 in its entirety from Kentucky to Alabama was that it was mainly a two lane road. ALDOT has prioritized four laning the route in Alabama as a viable north–south road corridor in the eastern part of the state.

Photo of the old alignment of US 431 between Pittsview and Barbour County line, scene to many vehicular fatalities until it was bypassed in 2008.

Of particular concern was the segment from Seale south to the Barbour County line, where rolling hills along the original alignment limit the visibility of oncoming traffic, contributing to poor decisions by motorists to pass, resulting in numerous head on collisions. In this segment alone, 31 people were killed in crashes between 1992 and 2006, leading Readers Digest to proclaim it one of "America's Deadliest Highways" in 2000. After being contacted by and subsequently meeting the family of a fatal crash victim in 2003, ALDOT Director Joe McInnes decided to expedite the construction on the last remaining stretch of two lane road between Seale and the Barbour County line. This 16 mile section was completed and opened in late 2010. The old alignment in Russell County is still open to traffic and is now labeled County Route 137.

Traveling south from Tennessee, as of mid 2009, US-431 is a four lane route to Oxford, Alabama. Then it reverts to a two lane highway southward to Opelika, Alabama with a brief four lane stretch just south of Wedowee, Alabama. From Opelika southward to its southern terminus in Dothan, Alabama, US-431 is now open as a four lane highway. with the exception of a short stretch as a low speed divided avenue through the historic district of Eufaula, Alabama.