Friction (Skid) Testing
The MnDOT Office of Materials and Road Research operates one Dynatest Pavement Friction Tester. This device measures skid resistance, which is the force that prevents a non-turning (i.e. locked-up) tire from sliding on the pavement’s surface. Skid resistance is an important parameter because inadequate skid resistance may lead to higher incidences of skid related accidents. It may also be an important parameter when evaluating materials and construction practices.
The device consists of a tow vehicle and a two-wheeled trailer and conforms to ASTM E-274 “Standard Test Method for Skid Resistance of Paved Surfaces Using a Full-Scale Tire” specifications. The MnDOT device has one smooth tire and one ribbed tire and can perform testing with either tire. The device is driven on the road to be tested at a constant velocity of 40 mph. When a test is taken, pumps are activated and spray water in front of the test wheel. Then, the brakes on the test wheel are activated and the horizontal and vertical forces acting on the wheel are measured. This data is then used to calculate the ‘Skid Number’.