Where BPNt= Skid resistance value obtained at pavement sureface temperature T degree
BPN20 = Skid resistance value obtained at pavement sureface temperature 20 degree
T = Pavement surface temperature degree
In ASTM E303-93, it is required that the rubber compound for the slider pad shall be natural rubber meeting the requirement of the RRL or synthetic rubber as specified in ASTM E501-94 and ASTM E524-88 in the british standard 7976 standard simulated shoe sole rubber and TRL rubber are the two most common types of slider pad material. If the TRL rubber slider is used, a temperature correction factor is applied to correct the test results to a standard temperature of 20 degree because natural rubber friction is temperature dependent. The ASTM-specified synthetic rubber was formulated to be independent of temperature and therefore no temperature correction is made