A speed hump (also called a road hump, or undulation, and speed ramp) is a rounded traffic calming device used to reduce vehicle speed and thus sound volume on residential streets. Humps are placed across the road to slow traffic and are often installed in a series of several humps to prevent cars from speeding before and after the hump. Common speed hump shapes are parabolic, circular, and sinusoidal.[18] In Norway, speed humps are often placed at pedestrian crossings.