What are some of the factors which affect the skid resistance of pavements? A list of the more obvious ones would include the age and condition of the surface, type of aggregate and binder, the surface texture, climate and other factors which affect weathering, temperature, moisture, and the presence of foreign materials. Even more important, however, is the surface texture built into concrete pavements. Water trapped between the vehicle tires and any smoothly polished pavement surface becomes a highly effective lubricant capable of reducing the coefficient of friction to dangerously low levels. This danger can be considerably diminished by deliberately producing a textured surface having slight closely-spaced grooves and a finish not unlike that of sandpaper. Like the grooves in the tire itself, the grooves in the pavement provide a means for water to escape from between the two surfaces thus keeping them in the intimate contact which reduces skidding. The resistance of aggregates to wear is also an important consideration. In general it may be said that the harder, more wear-resistant aggregates retain their excellent skid resistant characteristics longer then softer aggregates. Limestone is not overly resistant to the polishing action of traffic and it may be desirable to improve long range skid resistance by introducing a polishing-resistant materials as a replacement. However, since any uniformly polished material will become slippery when it is wet, it is important that the aggregate's incorporated materials have different wearing characteristics by blending different types of stones for the aggregate.