L - Swell is barely visible and has a minor effect on the pavement’s ride quality. (Low-severity swells may not always be observable, but their existence can be confirmed by driving a vehicle over the section. An upward acceleration will occur if the swell is present).

M - Swell can be observed without difficulty and has a significant effect on the pavement’s ride quality.

H - Swell can be readily observed and severely affects the pavement’s ride quality.