Feb 18, 2021 · Constants k, a, b, c, and d can be found in AP-42, Section 13.2.2, Table 13.2.2-2. Table 13.2.2-3 contains the range of values for surface material silt content, mean vehicle weight, surface material moisture content, and mean vehicle speed. Table 13.2.2-4 presents the emission factor for 1980s vehicle fleet exhaust, brake wear and tire wear.