ASSESSMENT OF RUT DEPTH MEASUREMENT ACCURACY OF POINT-BASED RUT BAR SYSTEMS USING EMERGING 3D LINE LASER IMAGING TECHNOLOGY

Point-based rut bar systems are commonly used by transportation agencies. However, potential measurement errors exist in these systems because of the limited number of sample points (e.g. 3 to 31 points). Now, advanced sensing technology can acquire high-resolution transverse profiles of more than 4,000 points using 3D line laser imaging technology (termed the 3D line laser hereafter). This study, sponsored by the United States Department of Transportation (USDOT) Research and Innovative Technology Administration (RITA) program, is a) to explore the feasibility of using the 3D line laser to accurately and reliably measure rut depth, and b) to quantify the potential rut depth measurement errors using point-based rut bar systems. The rut depth measurement accuracy and repeatability of the 3D line laser were validated in laboratory and field tests. Results show that the absolute rut-depth measurement error is less than 3 mm, and, therefore, the transverse profiles acquired by the 3D line laser can be used to quantitatively evaluate the accuracy and reliability of point-based rut bar systems. Rut bar systems having 3 to 31 sensors were simulated using transverse profiles acquired by the 3D line laser. Test results show that the relative rut-depth measurement error generally decreases with the increasing number of laser sensors. However, the trend is unclear for rut bar systems with fewer sensors because the rut shape affects the rut depth measurement error more than the number of sensors. Thus, a 3-point rut bar system could outperform a 5-point system occasionally. Test results also show that the commonly used 3-point and 5-point rut bar systems can underestimate rut depth by 16% to 51% and 22% to 64%, respectively. The relative rut-depth measurement error is less than 10% only when the number of sensors is greater than 29.