Coast-down studies of Class 6 trucks (19,500 to 26,000 lb gross vehicle weight) were conducted at near-zero road grade and wind conditions. Speed-versus-time data were recorded, smoothed to a quadratic equation to calculate deceleration rates and reduced by the ordinary least-square method using two-, three-, and five-parameter linear models. The estimated parameters were analyzed statistically and compared to the U.S. Environmental Protection Agency (EPA) recommended procedure. The averages of the individual truck road loads for the two-, three-, and five-parameter models were consistent within 4% when reference conditions of 40 mi/h, 15,000 lb weight, and 65 ft sq. projected frontal area were used. (Copyright (c) 1983 Society of Automotive Engineers, Inc.)