Smoothness New concrete pavements are some of the smoothest pavements built today. Unlike years ago, when pavements were built without any requirements on the surface smoothness, today state transportation departments specify a minimum level of smoothness with ride specifications. Most of these specifications base the requirements on a California profilograph. California Profilograph A California profilograph is a rolling straight edge. It measures vertical deviations from a moving 25-foot reference plane. A sensing or recording wheel located at the center of the frame moves freely in the vertical direction, giving the machine the ability to record surface deviations. The surface profile is logged into a computer or traced onto graph paper as the profilograph travels along the pavement. The profile is termed a profile trace and shows the location and height of bumps and dips. The profile trace of a pavement built perfectly smooth would be a straight line on graph paper. To meet the minimum smoothness requirements of the specification, contractors use a diamond grinding machine to remove bumps in the surface which are identified on the profile trace. The trace is also used to produce a profile index expressed in inches per mile (or millimeters per kilometer). When contractors and agency engineers talk about ride numbers or "the ride" they are referring to the profile index. A lower profile index represents a smoother surface than a higher profile index. Many states also successfully use incentive and disincentive payments for the degree of smoothness. FATQ: Where can I find a company that makes or sells California profilographs?