AGGREGATE TYPE AND TRAFFIC VOLUME AS CONTROLLING FACTORS IN BITUMINOUS PAVEMENT FRICTION

The New York State Department of Transportation's (NYSDOT's) Pavement Friction Inventory program has collected friction data on 155 pavement sites since testing began in 1980. The data gathered were analyzed and the adequacy of the current high-friction aggregate specification, in place since 1970, was determined. Data from another 66 sites, gathered as part of a previous NYSDOT study, were included. Together, the 221 sites tested represent most combinations of coarse aggregate rock types and traffic volumes normally encountered in New York State. The coefficient of friction for a pavement at terminal polish, as determined by a drag-force trailer in accordance with ASTM E274, was found to be controlled mostly by coarse aggregate rock type and daily traffic volume, expressed as lane average annual daily traffic (LAADT). Mineral aggregates used in New York State were divided into three rock-type categories -- homogeneous, sandy, and blended -- each having a distinct polishing mode. Semilog plots of friction number versus LAADT were constructed for each rock type, showing whether each rock type is performing adequately and, if not, under what traffic conditions its use must be restricted.