This synthesis will be of interest to construction engineers, pavement designers, contractors, and others interested in construction of new highway pavements with smooth surfaces. Information is provided on the various devices and specifications that are being used to obtain smooth pavements. The public rates a pavement primarily on its smooth-riding characteristics and highway agencies recognize that constructing smooth pavements results in fewer problems later and lower annual maintenance costs. This report of the Transportation Research Board describes the devices and specifications highway agencies use to ensure that newly constructed pavements will provide a smooth ride.

Pavement smoothness is a major factor affecting the performance of the highway surface and the safety and satisfaction of the traveling public. Smooth pavement results in better gas mileage, less vehicle wear, and less driver stress and fatigue. Pavement smoothness is the single most important indicator of pavement condition as viewed by the traveling public. Many state highway agencies, including the Kansas Department of Transportation (KDOT), have adopted specifications that set forth a goal of minimal levels of roughness for newly built pavements. Some specifications also include significant incentive/disincentive provisions to encourage contractors to concentrate their efforts on building smooth pavements. This report highlights the development of the smoothness specification for Portland Cement Concrete Pavement (PCCP) beginning in 1985 and for Asphalt Concrete Pavement (ACP) beginning in 1990. The early specifications used the 0.2 inch Blanking Band while evaluating the traces generated using the manual California type profilograph. In 1986, incentive/disincentive clauses allowed bonus payment for PCCP constructed with less than 4 in/mile of surface roughness and penalty (reduced payment) for over 12 in/mile using the 0.2 inch Blanking Band. The implementation of the smoothness specification resulted in dramatic improvement in PCCP smoothness. In 1990 the stage was set for change. The initial projects requiring the use of the profilograph with the 0.2 inch Blanking Band to measure smoothness of ACP provided a high percentage (64%) of bonus level sections thus indicating the need for a modification to the existing specification. Similarly, the PCCP projects built in 1990 also had a high percentage (63%) of bonus level sections while using the 0.2 inch Blanking Band. However, there was one PCCP reconstruction project that had achieved about 47% bonus sections but produced a high frequency vibration in the vehicle when driving at normal speed. A review of the original profilograph traces revealed a short length sine wave roughness that was slightly less than 0.2 inches in amplitude and thus was almost completely covered by the 0.2 inch Blanking Band.

The quality of smoothness of a newly constructed or overlaid pavement dictates the beginning of pavement management. Adequate acceptance testing procedures and specifications for pavement smoothness have not been available for flexible pavements. Smoothness specifications based on a 10-ft (3.05 m) straightedge has a number of limitations and is difficult to interpret and administer. This paper describes the results of a comprehensive study of several different roughness measuring devices undertaken to select a suitable device in order to develop and implement improved specifications for pavement smoothness. The candidate devices included the 690D Profilometer, Model 8300 Roughness Surveyor, Maysmeter, California Profilograph, and Rainhart Profilograph.

In its pursuit for providing smooth pavements, the Directorate General of Highways in Taiwan is developing and implementing ride quality specification as part of the construction assurance program. The straightedge and the profiler were used to measure pavement smoothness on 561 test sections. Probability distribution analysis showed that measurements of pavement smoothness of both devices follow the normal distribution. Smoothness specifications for construction quality control were developed for straightedge and profiler, respectively. The full-pay range is 1.36 to 2.45 mm and 2.16 to 3.65 m/km for straightedge and profiler, respectively. The smoothness relationship between straightedge and profiler was developed.