This project presented guidelines and recommendations for managing and designing for friction on highway pavements and emphasized the importance of providing adequate levels of friction for the safety of highway users. As part of this project, a guide document that deals with frictional characteristics and performance of pavement surfaces and considers related tire-pavement noise and other relevant issues was prepared and provided to AASHTO for consideration and adoption. Following review and revision, the document was published by AASHTO as the Guide for Pavement Friction (Item Code: GPVF-1).
Pavement friction is an important consideration in pavement performance. Microtexture and macrotexture are extremely important to the development of surface friction. The microtexture is the critical component for surface friction, and macrotexture is the primary means for removing water in order to obtain better surface friction from the microtexture at high speeds. Surface treatment techniques have a large impact on these parameters; macrotexture is often increased in order to increase surface friction. However, increasing macrotexture may result in greater noise generation and propagation. Similarly, noise-reduction techniques sometimes adversely affect surface friction. Therefore, the relationship between friction and noise generation must be considered when designing pavement surfaces.
The "Guidelines for Skid Resistant Pavement Design," published by AASHTO in 1976, recognized the importance of providing skid- resistant pavements. However, these guidelines have not been updated to reflect recent changes in vehicle characteristics, methods of collecting data, construction techniques, use of materials, and other factors that affect pavement surface frictional characteristics. Other issues (e.g., noise pollution, legal concerns, and economic impacts) associated with improving friction characteristics have not been addressed. Thus, there is a need to develop a Guide for Pavement Friction that identifies technologies, processes, and practices suited for designing and constructing pavements with good frictional characteristics while recognizing the effects on noise generation and other relevant issues.
Research examined the current state of the practice regarding pavement friction and presented findings, identified the test methods available for assessing aggregate's potential to provide adequate frictional characteristics and the test methods available measuring pavement friction and texture in the field. The research also reviewed pavement friction management systems and friction design policies available in the United States and the identification of friction investigatory and intervention levels. This information provided a basis for developing guidelines and recommendations for managing and designing for friction on highway pavements. NCHRP Research Results Digest 321: Guide for Pavement Friction: Background and Research summarizes the findings of the research. The agency final report titled "Guide for Pavement Friction: Final Report," gives detailed account of the project, findings, and conclusions including further information on the current practices regarding pavement friction and the research performed to prepare the AASHTO Guide for Pavement Friction. The report, which was distributed and distributed to Program sponsors (i.e., state Departments of Transportation) is available online as NCHRP Web-Only Document 108.
