U.S. Route 31 (US 31) in Alabama runs north–south up through the heart of Alabama for 386.449 miles (621.929 km). US 31 proper begins at a junction with US 90 and US 98 in Spanish Fort and exits the state into Tennessee running concurrently with Interstate 65 (I-65) near Ardmore. US 31 enters the limits of major cities Montgomery, Birmingham, and Decatur. Throughout the state, with the exception of its concurrency with I-65 north of Athens, US 31 runs concurrently with the unsigned State Route 3 (SR 3). Today, aside from portions through major towns and cities, US 31 is largely a rural two-lane highway. The route has largely been supplanted by I-65, with which it has eight junctions and two concurrencies.