Gholamali Shafabakhsh - Assistant Professor, Department of Civil Engineering, Semnan University, Iran
Mahdi Akbari - Ph.D. Candidate, Road and transportation Eng., Semnan University, Iran

As pavement surface characteristics play an important role in road safety, more agencies are specifying minimum requirements for surface friction. In most cases, these requirements are specified in terms of surface macro and microtexture. Recently a method has been developed and published that uses the International Friction Index (IFI) to determine a design vehicles stopping distance and potential for loss of control. This method relies on the use of the both the IFI and the macro and micro-texture measurements of a pavement surface to calculate a vehicle stopping distance requirements. The advantage of this method is that a lack of macro-texture can be substituted by increasing micro-texture and vice versa giving significantly more options to the maintenance programs. For design of asphalt mixtures, it is proposed to incorporate the macro-texture in terms of the mean profile depth (MPD) that determined from the aggregate gradation and binder content, with the micro-texture determined from the polished aggregate friction value (PV) of the coarse aggregate. An iterative procedure is then used to determine the combination of macro and micro-texture required for meeting the stopping distance requirements, these values are then used to determine the required aggregate type and gradation and binder content, in the design process. This paper Introduce a method for estimating the macro-texture in terms of the mean profile depth determined from the aggregate gradation and binder content, with the micro-texture determined from the polished aggregate friction value (PV) of the coarse aggregate. At first stage of this method, the required mixtures macro and micro-texture should be determined. There are two steps to determine the required mixtures macro and micro-texture including estimating in-service asphalt micro texture and estimating texture depth from mix gradation and binder content. At last, stopping distance of design vehicle will be calculated. By determining the required mixtures macro and micro-texture, the stopping distance of design vehicle could be calculated. This stage has three steps that include converting values to IFI friction values, determining standard vehicle response from presented charts and complete the design process.

Skid Resistance, Asphalt Mix Design, International Friction Index (IFI), Polished Aggregate Friction Value (PAFV)