Systems capable of measuring the individual multi-dimensional (3D) tyre-road contact stresses (the tyre profile) under moving tyres are generally called Stress-In-Motion (SIM) systems. Stress in motion measurement is a relatively new development that offers applications in advanced pavement design, detailed vehicle classification, tyre management and road safety.
The first SIM sensors were developed in South Africa and were mainly used in research projects to study the multi-dimensional tyre-road contact stresses and their effect on pavements. The system consists of a matrix of sensors, each sensor measuring the vertical forces from the tyre when the wheel passes slowly over the system. This type of SIM technology provides a detailed insight into the multi-dimensional contact stresses between tyres and the road surface. This may be used in the protection of road infrastructure through the advanced mechanistic design of road pavements.
Recently other SIM-systems have become commercially available, using fibre optic or piezo electric strip sensors. These new SIM systems provide tyre footprint data that is less detailed than the previous research systems. However, they are more robust and suited for day to day operation under normal traffic conditions.
Besides the pavement design applications, these systems are also used for tyre management, commercial vehicle safety and toll road applications. Here the systems will detect abnormalities in the tyre thread, the tyre pressure (under or over inflated tyres) of all tyres on a vehicle and the load distribution over the different wheels on one axle.