Investigation of Locked Wheel Skid Tester Practicability on Horizontal Curves: A Camera-Based Field Implementation

Abstract

The locked wheel skid tester (LWST) has the capability to perform efficient on-site pavement skid resistance tests without traffic control. A LWST friction test measures the longitudinal friction force and vertical load taking place at the tire–pavement interface of a standard locked wheel at a specified test speed. However, the test is specified only for straight and level pavements. Possible reasons that the LWST may fail to provide reliable friction data during vehicle cornering are biased tire speed and force measurements, missing information of vehicle side friction, and risky trailer fishtailing. Horizontal curves are widely distributed in the highway network and have a higher crash rate compared to straight segments. This paper developed a camera-based setup to monitor instant cornering behaviors of a LWST traversing on horizontal curves. Along with data from the standard LWST speed sensor and force transducer, the upgraded tester can also operate as a vehicle side friction sensor and an oversteering alert system. The dual-camera-equipped experimental vehicle was employed in field friction tests on different types of pavement horizontal curves. The captured video frames were then utilized in image processing algorithms for real-time test tire speed, sideslip angle, and articulation angle measurements with high accuracies during tests. The impact of pavement horizontal alignment design on LWST friction measurements and the result performance were assessed. The investigation extends LWST practicability on highway horizontal curves with evaluated restrictions.