As part of a federally funded research project to update vehicle noise emission levels, the California Department of Transportation (Caltrans) examined heavytruck noise emission levels on grades in California. Nearly 1,800 noise measurements were taken at 6 locations along Interstate and state freeways with grades ranging from+ 3 to+ 7 percent. The six sites were located far enough upgrade to allow heavy trucks to decelerate from free-flowinq speeds of 55 to 60 mph to sustained crawl speeds before measurement. The noise data showed no direct grade dependency at any observed speed. This may have been caused by the inverse relationship between grade steepness and truck weight for a given speed. In order to maintain the same crawl speeds, trucks must be carrying lighter loads on steeper grades, and vice versa, possibly resulting in offsetting effects on noise emission levels. Further research into the exact cause is recommended. Speed dependency, however, was significant. A second-degree polynomial equation for noise energy versus log10 speed was found to represent the best curve fit. A combined speeddependent curve for+ 3 to+ 7 percent grades was developed. Observed speed distributions were found to be grade dependent and appeared to agree with those typically found for trucks on grades in California. This information was used to develop" default" reference energy mean emission levels for heavy trucks on grades up to+ 7 percent in 1-percent increments. For 3 to 5 percent grades, these values are 1.4 to 0.5 dBA higher than those developed by the currently used NCHRP 117 method; above 5 percent grade the default values are 0.2 to 2.1 dBA lower than those· of NCHRP 117.

This study was part of a federally funded research project to measure vehicle noise levels and develop speed-dependent reference energy mean noise emission levels for highway traffic noise prediction models in California. The California vehicle noise (Calveno) reference energy mean emission levels for level roads were developed, published (1), and approved by FHWA for noise studies involving federal-aid highway projects. They conform with the requirements set forth by the Federal-Aid Highway Program Manual (~)• In March 1985, the Calveno curves were implemented