Abstract
It is very often forgotten that the vehicles drive on surfaces, very different from each other with a large area of qualities and defects revealed in particular under bad weather conditions. These surfaces are always very important for the active vehicles safety. Within the framework of a LCPC (the French Laboratoire Central des Ponts et Chaussées) research programme and of the VERT (VEhicle Road Tyre interaction) European research programme (1997-2000), the LRPC (Laboratoire Régional des Ponts et Chaussées) in Lyon (Part of the CETE in Lyon), made use, with the help of TRL (Transport and Road research Laboratory) in Great Britain, of the VERT data base with the aim of establishing the relative influence of the parameters affecting road surface friction. The tyre-road contact surface for a light vehicle is quite limited (A4 sheet). On a dry road, the aforementioned surface enables a vehicle, under normal driving conditions, to mobilise all the energy it needs to move (acceleration, braking, stable trajectory). On the other hand, in the presence of contaminants, and especially in the presence of water, this contact surface will be reduced according to various parameters amongst which can be noted :
-surface of the road (microtexture and macrotexture),
-type, size and wear of the tyres,
-water depth,
-speed of the vehicle,
-tyre-road slip ratio,
-wheel load.
These are the parameters that will be studied in the present document. Within the framework of the VERT programme, numerous tests were carried out in order to have a better understanding of the influence of these parameters on road-tyre skid resistance. These tests were carried out with various devices on different surfaces. Approximately 99 800 readings were made during these tests. The present document refers only to tests for which parameters 1 to 6 mentioned above presented the most significant variations. We have therefore used the results of measurements obtained on three different surfaces presenting different texture characteristics. The importance of the following points can be noted :
-availability of a road surface with a good compromise between micro- and macrotexture. We have noticed that with high water depth, the drag effect encrease with the texture of the surface.
-a good lateral drainage capacity of the wearing courses to prevent areas of water accumulation
-use of tyres in good condition which should be changed if their tread mark depth reaches 2 mm and if they have a large width,
-avoiding the use of winter tyres in summer,
-avoiding overloading of vehicles.