Saluda Grade was the steepest standard-gauge mainline railway grade in the United States. Owned by the Norfolk Southern Railway as part of its W Line, Saluda Grade in Polk County, North Carolina, gained 606 feet (185 m) in elevation in less than three miles (4.8 km) between Melrose and Saluda. Average grade was 4.24 percent for 2.6 miles (4.2 km) and maximum was 4.9% for about 300 feet (91 m). In December 2001, Norfolk Southern took the line containing the grade out of service for economic reasons. As of 2023, Saluda Grade is proposed to become a rail trail.

The grade (US) or gradient (UK) of a physical feature, landform or constructed line refers to the tangent of the angle of that surface to the horizontal. It is a special case of the slope, where zero indicates horizontality. A larger number indicates higher or steeper degree of "tilt". Often slope is calculated as a ratio of "rise" to "run", or as a fraction in which run is the horizontal distance and rise is the vertical distance.