Reducing aerodynamic drag and tire rolling resistance in trucks using cooled EGR engines meeting EPA 2004 emissions standards has been observed to result in increases in fuel economy and decreases in NOx emissions. We report here on tests conducted using vehicles equipped a non-EGR engine meeting EPA 2004 emission standards and an electronically-controlled engine meeting EPA 1998 emissions standards. The effects of trailer fairings and single-wide tires on fuel economy and NOx emissions were tested using SAE test procedure J1321. NOx emissions were measured using a portable emissions monitoring system (PEMS). Fuel consumption was estimated by a carbon balance on PEMS output and by the gravimetric method specified by test procedure J1321. Fuel consumption decreased and fuel economy increased by a maximum of about 10 percent, and NOx emissions decreased by a maximum of 20 percent relative to baseline. This compares with NOx reductions of up to 45 percent reported in the earlier test on the cooled EGR engine. The reduction in power requirements in the current test did not result in a corresponding reduction in brake specific NOx emissions, as it did in the earlier test. These results provide further evidence that reducing parasitic losses in heavy-duty highway vehicles will not only reduce fuel consumption and greenhouse gas emissions, but will also provide NOx reductions that pay for themselves through reduced fuel use.