Friction Improvement by Use of Graders on Winter Roads.

In the winter season 2000/2001 a preliminary study was carried out on theeffect on friction by using graders to improve the friction on snow and ice covered surface as a part of the Norwegian Winter Friction Project. Theresults from the study indicated that there was little or no effect on friction by use of grader on a snow and ice covered surface. There have beenraised questions to the validity of these results due to the fact that the friction was quite high in beforehand under the trials and that the results from the study therefore are not representative for the potential friction improvement by use of graders. On this background Tieliikelaitos in Finland and Norwegian Public Roads Administration, Road Directorate agreed upon making a new grader study as a joint project. The new study was carried out in Norway in February 2003. The field trials included four of the most common types of blades to study possible differences between blades normally used: System 2000, Ice scratch blade, 6 mm plain blade, and P300 (grid type). To register the effects and evaluate the performance of the different blades the following measuring methods were used: Friction measurements; and Track depth and structure of the snow and ice layer. The overalleffect from the test of different type of blades is that the friction is unchanged after grading and there is no significant difference between thetypes of blades tested. There is no support for the hypothesis that grading on a slippery ice surface gives a higher rise to the friction compared to surfaces with a higher initial friction. The grading however results ina reduction in the track depth and also creates a more even surface (IRI value) compared to an untreated snow and ice layer. The results from the study support the importance of grading to create better driving conditions, but will not influence on the need for other measures as sanding to meetthe friction requirements. The type of blade seems to be of secondary importance for the quality of the grading process and should therefore be chosen from other reasons than the resulting effect concerning friction, track depth and roughness. For the covering abstract see ITRD E143097.