Variations in the Skid Resistance of Highway Surfaces 650261
Wide variations in skid resistance can exist on wet highway pavements. Locked wheel skids started from 40 MPH may vary from 90’ to over 200’. The principal causes of variation in skid resistance include: (1) polishing of the aggregate that comprise either portland cement concrete or bituminous pavements; (2) glazing of bituminous pavements; or (3) foreign films. The polishing of the aggregates constitutes the most widespread cause of low wet traction and is the most costly to overcome.
Skid resistance tests by many investigators have shown that the limestone-dolomite type of stone is more prone to polish than granites, greenstones, diabases and siliceous gravels and sands. More extensive testing throughout the country is needed to determine the extent to which many other types of stone will polish under traffic.
Unfortunately road surfaces with low skid resistance do exist and for the following reasons: (1) lack of awareness on part of some highway officials; (2) lack of economical polish resistant aggregate within reasonable hauling distance; (3) use of those types of bituminous surfaces that although economical are nevertheless, susceptible to becoming glazed; (4) increase in intensity of traffic that causes polishing of aggregates that did not do so formerly.
The emergence of a standard test method from ASTM Committee E-17 on Skid Resistance will undoubtedly encourage more widespread testing programs. Once this information is available, engineers can encourage highway officials to go to the added expense of providing road surfaces with high skid resistance. This assumes, of course, that no appreciable changes in the interest of longer tire wear will be made in tire composition.