Abstract:The objective was to determine the effect of several variables—vehicle operation, weight, and accessory use—on emissions production during common on-road heavy-duty vehicle operations. Oxides of nitrogen (NO_x), hydrocarbon, and carbon monoxide emissions from a heavy-duty diesel tractor equipped with a 1999 engine were measured continuously during on-road tests. The vehicle was operated at predetermined steady-state modes of 25, 55, and 65 mph as well as full-throttle accelerations from 0 to 25 mph and 0 to 55 mph and decelerations from 65 to 0 mph. Vehicle weight (payload) and accessory use (air-conditioning) were varied. In general, increases in gross vehicle weight from 52,000 lb to 80,000 lb resulted in approximately 40% or greater increases in NO_x grams per mile (g/mi) emissions during the accelerations and higher-speed steady-state operations. These results were consistent with simulation model results from the National Renewable Energy Laboratory's ADVISOR model. Analysis of variance (ANOVA) and regression models were used to identify relationships between the variables and emissions. With the use of ANOVA, it was found that mode explained most of the variation in emissions and had a significant impact on all species of emissions tested. With the use of regression, a strong relationship was confirmed between steady-state modal NO_x emissions per hour and horsepower (r² = 0.89, P < .0001). When mode and weight were added as factors in the regression model, the overall precision of NO_x emissions prediction was increased and horsepower became nonsignificant.