The physics of friction and traction are reviewed. Hypotheses are presented. Use of a scanning electron microscope to detect and identify polishing aggregate is presented.

Size reduction (crushing) produces greater concentrations of sharp edges, reducing flat and plane surfaces not otherwise contributing to traction.

Surface permeability and drainage through macrotexture was evaluated by an air-percussive device. An air-efflux device was contrived for evaluating hydroplaning potential and for evaluating open-graded surface courses. In-filling has been observed where road debris is abundant.

Grippers and sharpness are needed for wet traction . Drainage is needed to lower hydroplaning potentials. Sand-sizes optimize the concentration of grippers; open-graded chip-sized surfaces maximize drainage and dissipation of pressure under tires.

Report Date


Report Number


Digital Object Identifier



The contents of this report reflect the views of the author who is responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the University of Kentucky. the Federal Highway Administration, or the Kentucky Transportation Cabinet. This report does not constitute a standard, specification, or regulation.