RELATIONSHIP BETWEEN FRICTION SURFACE CHARACTERISTICS AND RAIN INTENSITIES TO EVALUATE ROADWAY SAFETY

It is a well known fact that the effective friction available in the contact area between tyre and road surface is influenced by vehicle speed, road surface characteristics and water film thickness. Italian Standards, as well as the ones currently in use in most of European countries and in the USA, characterise friction by measuring skid resistance and texture in standardized conditions in terms of speed and water depth (WD). For instance, in Italy, skid resistance measurements are carried out with a SCRIM equipment at a speed of 60 km/h on a 0.5 mm WD and texture is measured by means of the sand patch method. The main objective of this work is the evaluation of the effective friction available during the occurrence of heavy rainfalls when the vehicle runs at the road design speed and the pavement offers variable values of skid resistance as measured according to present standards. To reach this final aim the WD is evaluated in function of the geometric characteristic of the road section (cross section width, variable longitudinal and transversal slope, road geometric alignment) and the design value of rain intensity. The available friction at the road design speed is evaluated using the Penn State Model in function of the SCRIM value and the texture of the pavement. The determined value is afterwards modified to account for the influence of the effective values of WD, present on the pavement surface. This is carried out by means of a model developed on the basis of the available experimental data got from researches on hydroplaning potential. The proposed procedure is applied to a road section including a transition curve and aims to identify the concerned skidding hazard. (A) For the covering abstract of the conference see IRRD 493717.