کریم نصیر احمدی

Skid resistance and road conditions are the common indices of road safety, therefore providing adequate skidding resistance will reduce the incidence of road accidents. The surface macrotexture has a large effect on the characteristics of road surface skidding, which is the focus of this research. During the study, the mean texture depth of the road surface was measured, in order to determine the conditions that ensure the maximum contact area between the vehicle tyres and road surface during wet conditions. The Pavement Guideline No. 234 was consulted for the test procedure and road surface composition, which used open and dense graded crushed lime aggregates with varying percentages of bitumen applied to the mix design. The samples were then tested to assess their stability using the Marshall and Gyratory Tests. The results showed that with the application and evaluation of the sand patch method, where the effect of the macrotexture on skidding resistance was analyzed with various gradations, there was an improved higher skidding resistance and a subsequent projected reduction of accidents with an increased safety.

One of the effective parameters for road safety is to provide a non slippery surface to reduce the road accidents. Friction of pavement condition are the most common indexed of safety issue, but the skid resistance of surface is an important issues of asphalt mixture which plays an effective role on the road safety. Road accident reports show that casualties due to low skid resistance on asphalt surface do occur on the Iranian road. The main inefficiency is due to lack of guideline. Skid resistance is one of the primary factors for determination of pavement safety especially in accident which is arising from skidding on the wet surfaces. Pavement surface texture is defined by two types of texture, micro-texture and macro-texture. Micro-texture is the main factor which has a direct effect on the pavement surface. Skid resistance is determined by micro-texture on the road surface. The characteristics of mineralogy of materials and other factors such as traffic, climatic condition would have an effect on the skidding. In the present research asphalt samples with dense graded (No. 4&5) and open graded (No. 4&5) were prepared following the Iran Road Pavement Regulations and the samples were tested using the British Pendulum Machine. The binder used was grade 60-70 and crushed sand used to prepare the samples. The results of test carried out on the samples shows that pendulum number obtained from open graded are higher than the dense graded samples, which proves that the skid resistance have an effective role on the highway safety.