Effect of Water, Speed, and Grade on Continuous Friction Measurement Equipment (CFME)

The regional pooled-fund project known as the Pavement Surface Properties Consortium is a research program focused on enhancing the level of service provided by the roadway transportation system by optimizing pavement surface texture characteristics. The program was set up in 2006 with support from the Federal Highway Administration (FHWA), and six departments of transportation. The Consortium provides a practical mechanism to conduct research on pavement surface properties and explore their relationships with ride quality, friction, and noise. Complementing this effort, additional research focuses on the review, testing, and evaluation of emerging technologies. Some of the technologies tested have been Continuous Friction Measurement Equipment (CFME) operating with fixed-slip ratios. In 2010, it was decided to run comparisons of all the units to validate and establish a database and perform repeatability and sensitivity evaluations at the Virginia Smart Road. In this paper, we evaluate CFME equipment with tests conducted at different speeds and a fixed 0.5-mm water-film-thickness flow rate. A second comparison was also made in which the water-film thickness was varied, while the speed was kept constant at 65 km/h (40 mph). All of the devices were tested back to back to eliminate the effect of temperature differences on the pavement and on the water. Preliminary results show that at greater speeds, the measured friction coefficients measured are lower. Likewise, the greater the water-film thickness used, the lower the measured friction coefficients. There is also evidence that some of these units might be affected by the longitudinal grade.