A road's skid resistance - especially if the road is wet - is critical to a vehicle's handling and braking performance, and correspondingly important in investigating and assessing causes of accidents. Skid resistance measurements (sub-project 2 [TP 2] of ZEB) also serve as a basis for making decisions concerning conservation management and acceptance of construction measures.
Skid resistance is registered and evaluated by means of the skid resistance measurement system (SKM - sideways force measurement) system.
Measurement system, measurement principle and friction as a condition indicator
The SKM skid resistance measurement system employs the principle of a measurement wheel slanted with respect to the direction of driving and rolling at a side-slip angle of 20°.
The wheel is mounted about 1.5 m in front of the carrier truck's rear axle. On a wet road surface, a treadless tire (at an internal pressure of 3.5 bar) rolling in the truck's right-hand track is used to measure the lateral friction coefficient at a defined target speed (federal highways: 80 km/h; federal roads: 60 km/h; urban roads: 40 km/h). In the event of a deviation between the measured and target speeds, the determined skid resistance values are converted in accordance with ARS 24/2003 using the target speed as the reference (as prescribed for projects in Germany).
For wetting the measurement track, our carrier vehicles are furnished with a 10m³ water tank enabling continuous registration for up to 200 kilometres given a defined water-film thickness of 0.5 mm.
The sideways force coefficient (μ SFC) is formed to characterize roadway traction. This value is the ratio between the lateral force exerted by friction on the measurement wheel and the wheel's normal force under a load of 200 kg.