Improvements in aerodynamic efficiencies of heavy-duty, on-highway commercial vehicles can result in lower fuel consumption. However, aerodynamic treatments, whether as original design concept or in the form of add-on devices, will only be most effective when overall vehicle road speed is controlled. GELCO Truck Leasing's years of experience clearly demonstrate the validity of the following: Aerodynamic improvements can lower operating costs for operators of heavy-duty, on-highway commercial trucks when road speed is controlled. Formal on-highway test procedures yield accurate predictions of in-service performance for aerodynamic components or packages-provided that in-service road speed is controlled. Computerized predictive programs are reliable indicators of in-service performance for aerodynamic enhancements when vehicle road speed is controlled. Aerodynamic efficiencies can help reduce engine horsepower requirements and open up a wider range of equipment component options to the vehicle user.