A contribution to non-contact skid resistance measurement

Over the past decades a wide range of routine measurement devices has been developed, all of them measuring the friction force between a rubber wheel and the (wetted) road surface. At the same time, many efforts have been undertaken to predict skid resistance solely from texture measurements. This paper presents a concept of contactless skid resistance measurement which is based on optical texture measurement and consists of two components: (1) measurement of the pavement texture by means of an optical measuring system and (2) calculation of skid resistance based on the measured texture by means of a rubber friction model. The basic assumptions and equations underlying the theoretical approach are presented. Two skid resistance-measuring devices were chosen to prove the theoretical approach: one laboratory device called Wehner/Schulze machine which corresponds to a locked-wheel braking test and another, the ViaFriction((R)) device of ViaTech AS which measures the skid resistance under controlled longitudinal slip and corresponds to ABS braking conditions. The results are very promising although in the case of the ViaFriction((R)) device only a few surfaces could be tested. A close relation between measured and predicted friction coefficients could be found. Thus, a strong indication can be provided that skid resistance could be measured without contact in the future.