Superelevation in road design is defined as the rotation in the pavement during an approach to and then through a horizontal curve. It is written as a decimal that represents the ratio of a pavement's slope to its width and has a range of 0 to 0.12 feet. Superelevation counteracts the lateral acceleration that is produced.
As of 2015, the United States Department of Transportation allows maximum superelevation rates between 0.04 and 0.12. Each state establishes its own maximum allowable superelevation, which is based on variables such as terrain, location of the road, climate, and frequency of slow-moving vehicles. For example, states that experience a high frequency of ice and snow conditions may choose a lower maximum.