The dramatic increase in the volume and speed of automotive vehicles in the 1950s and 1960s in Ontario resulted in the need for safer and better quality highways. The increased traffic also created rapid deterioration of frictional and durability characteristics of the road system that was originally designed for lighter traffic. The need to upgrade urban freeways and to rehabilitate other highways led to the development of friction course mixes. In the process of formulating policy for safer and better quality highways, in 1974 a major installation of 18 test sections of bituminous overlays on one ofthe most heavily trafficked roads in Ontario was undertaken, and a task force was set up to review the performance of friction courses and make recommendations on their use. The developments that led to the adoption of a policy of using friction course mixes in Ontario are outlined. The design, construction, and results of the experimental sections and the findings of the task force on friction course mixes are discussed. The experience gained and the annual program of friction courses are also discussed. One important finding of the experiment is that the most effective way to improve the level of friction on a wearing course is by using harsh, angular, fine aggregates such as traprock or slag screenings and a sufficient proportion of curshed good-quality coarse aggregate in the bituminous mixes to maintain the micro- and macrotexture of a surface. These characteristics can best be provided by open friction course and dense friction course mixtures. Friction courses are accepted by the Ontario Ministryof Transportation and Communications as the most suitable surface course mixtures for freeways and accident "black spots". The volume of friction course mixes laid each year verifies this commitment.(A).
Abstract