The results of a technology verification study are presented. The study focused on undercarriage aerodynamic drag reduction devices that improve the operational fuel economy of tractor-trailer vehicles and increase undercarriage access for maintenance and inspection. The Split Skirt (SS) and Wheel Cavity Cover (WCC) concepts were tested to obtain Environmental Protection Agency (EPA) SmartWay (SW) verification, California Air Resources Board (CARB) acceptance and to address the needs of the industry. Fuel consumption tests were performed in accordance with the Society of Automotive Engineers (SAE) J1321 Test Procedure as modified by the EPA SW Interim Test Method. To further minimize sources of error the test employed identical tractor-trailer combination vehicles and constrained the test to wind velocity less than 10mph. Test results were obtained on nine (9) SS variations and two (2) WCC based concepts. Three SS concepts were EPA verified to provide fuel savings greater than 5% and four SS concepts had EPA verified fuel savings between 4 and 5%. To develop an understanding of the in-service fuel savings of the Split Skirt concept various skirt gap settings were evaluated. For the 18-foot SS the data show a 2-foot gap reduces the fuel savings from 4.5% to 4.3% and a 4-foot gap reduces fuel savings from 4.5 to 4.2%. In a worst-case scenario, slider in the full aft position, fuel savings is reduced from 4.5% to 3.8%. EPA verified WCC test data were obtained for the WCC installed with and without the SS aft panel. WCC test results show a fuel savings of 1.3% and 2.4% for the WCC based concepts.