Citation

Moyer RA, Shupe JW. Highw. Res. Board bull. 1951; 37: 1-37.

Copyright

(Copyright © 1951, National Research Council (U.S.A.), Highway Research Board)

DOI

unavailable

PMID

unavailable

Abstract

RESULTS are presented of measurements of road roughness and skid resistance for more than 50 different road surfaces in california. It is believed that the basic design of the bureau of public roads roughness trailer used in these tests is fundamentally sound and it provides the simplest and most accurate measure of road roughness. Skidding resistance measurements were made on dry and wet surfaces by three different methods: (1) towing a trailer with a truck at constant speed and recording the speed and braking effort with one trailer wheel locked, (2) locking all wheels of the passenger car and measuring the total stopping distance, and (3) locking all wheels of a passenger car and recording the speed and rate of deceleration by means of electronic and oscillograph equipment. The high type pavement surfaces on rural state highways in California were found to have the best riding qualities of all the various types of surfaces tested. The roughness of asphalt surfaces with seal coats was almost double the roughness measured on the high type pavements. The widest spread in roughness values was obtained in the measurements of the roughness of city streets. Friction values for rounded aggregate were about 25% lower than for angular aggregate in the wet skid resistance test. Slightly higher friction values were obtained on open-graded surfaces than on dense-graded surfaces although the sharpness or grittiness of the aggregate was a major factor influencing the test results. Friction values on open-grid steel bridge floors were very high in the dry test but were dangerously low in the wet test. Friction values for synthetic rubber tires with a good tread were about 5% higher than for natural rubber tires in the wet test and on the various paved surfaces. These tests indicated that the greatest skidding hazard is encountered when braking a car with smooth tread tires with all wheels locked or skidding on a wet glazed asphalt surface.