Explains a method for determining the wet road skid resistance of a surface by measurement of the longitudinal friction coefficient LFCN.

This Technical Specification describes a method for determining the wet road skid resistance of a surface by measurement of the longitudinal friction coefficient LFCN. The described method is also used to determine the skid resistance on a surface covered by ice or snow.

The method provides friction coefficient measurements of the pavement by using an electrically braked test wheel.

ViaFriction can operate in the following modes:

• Fixed slip: The slip ratio is fixed. The slip ratio can be set to a value from 1 % to 75 %.

• Fixed slip speed: The slip speed is fixed. The slip speed has to be lower than the vehicle speed.

• Variable slip: The test wheel is braked from 0 % to 75 % slip ratio recording F 30, F 60 and the slip ratio/friction curve.

The test tyre is dragged over a pre-wetted pavement under controlled speed conditions while the test tyre is parallel to the direction of motion and perpendicular to the pavement. Skid resistance measurement on winter roads do not require pre-wetted pavement.

To determine the macrotexture of the pavement surface a laser system can be added. This system is placed in front of the towing vehicle in order to measure the macrotexture (mean profile depth — MPD) on dry pavements and on the same path as the skid resistance measurement is done. The standard for this measurement and the device is described in EN ISO 13473-1.