Friction Study of Long-Term Pavement Performance Special Pavement Study 9A Sections in Connecticut

Abstract

Pavement surface friction is one of the most important contributing factors in highway safety. It is a function of a pavement's micro- and macro texture. Therefore, tracking changes in pavement surface friction and texture depth during a pavement's service life is critical for maintaining driving safety and comfort. As part of FHWA's Long-Term Pavement Performance (LTPP) study, many state highway agencies have been collecting friction data to track these changes on designated test sections. In Connecticut, six LTPP sections were constructed in 1997 to serve as Special Pavement Study 9A sites for the characterization of Superpave® asphalt mixtures. This paper presents an analysis of pavement friction and texture data collected by the Connecticut Department of Transportation on these sections. Friction numbers were obtained with an ASTM E274 locked-wheel pavement friction tester by using smooth (ASTM E524) and ribbed (ASTM E501) tires and a GripTester fixed-slip pavement friction tester. Estimated texture depths were obtained in accordance with ASTM E1845 at each site with a Dynatest laser texture device mounted to the friction tester. In addition, mean profile depths were measured with a Circular Track Meter in accordance with ASTM E2157. The analysis of the results targeted three main objectives. First, the variability of the skid number values, measured by the locked-wheel and the braked-wheel, fixed-slip methods, was evaluated. Next, some empirical relationships between friction number and texture depth developed in previous studies were verified. Last, the friction and texture data were analyzed to correlate the measurements with surface material properties.