In 1996, the Danish Road Directorate decided to replace its existing method of measuring friction, using a stradograph. In an experiment during Summer 1996, the stradograph was compared with two other devices. As a result, the ROAR device was bought in 1997, to replace the stradograph. This article compares the stradograph and ROAR, and discusses tests made during 1998. The stradograph operates with a side force measuring system, calculating friction as the ratio between the vertical load applied to the measuring wheel and the horizontal force acting on the measuring wheel from the pavement. The ROAR uses fixed and varible measuring techniques on the measuring wheel, which runs in the direction of travel. One disadvantage of the stradograph is that prewearing of its tyre must be performed fist. Comparative tests of the two devices were conducted on 22 sections in Denmark, and other roads in Germany and Holland. A very good correlation was found between measurements by both of them. Additional tests of the correlation between them, conducted in 1998, focused on the ability of the ROAR to identify subsections of roads with friction problems and thus needing maintance to meet Danish friction standards. Very good repeatability was found in the results of both devices. The ROAR was thus considered a suitable new device to use.
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