Citation

Moyer RA. Highw. Res. Board bull. 1962; 348: 44-77.

Copyright

(Copyright © 1962, National Research Council (U.S.A.), Highway Research Board)

DOI

unavailable

PMID

unavailable

Abstract

Data are presented for many different types of pavements when dry, set, and snow- and ice-covered, with the latest types of rubber tires indicating the importance for precise measurements of coefficients of friction for the design of modern streets and highways and for developing programs for the prevention of skidding accidents. The large increase in volume and the increased speeds of present-day traffic is contributing to an increased amount of aggregate polishing, contributing to a marked increase in the skidding hazard of wet pavements. The tests reported indicate the large decrease in the coefficients of friction with an increase in speed on wet pavements. A nationwide program for the precise measurement of coefficients of friction of wet pavements is proposed using standardized skid test equipment and testing procedures. A series of correlation skid tests is further proposed. It was found that the testing units designed to measure the road friction forces using a drawbar-type measuring system introduced an error for the coefficients of friction of as much as 20 percent lower than the true coefficients of friction. A brake reaction torque meter skid test unit developed in the test program is described which provided a measurement of the coefficients of friction with an accuracy of plus or minus 1 percent. The results of the skid rests on the various types of pavements covered a wide range of values from the low friction values of 0.17 to 0.30 at 40 mph for the slippery-when-wet pavements with a dense-graded, polished aggregate-type finish, to values in the high friction range of 0.40 to 0.60 at 40 mph for surfaces with a coarse-textured, open-graded type of finish.

RESULTS of tests with 4 different tires also varied considerably in tests on the same surface and at the same speed. The highest friction values were measured with the butyl rubber tire for which the friction values were found to be 15 percent to 40 percent higher than for the smooth tread tire which yielded the lowest friction values. The high friction values measured with the butyl rubber tires were so promising that in future programs for preventing skidding accidents, improvements in tire types may be more economical and fully as effective as the proposed improvements in skid resistance of pavements.