The importance of fuel economy and emission standards has increased rapidly with high fuel costs and new environmental regulations. This requires analysis techniques capable of designing the next generation long-haul truck to improve both fuel efficiency and cooling. In particular, it is important to have a predictive design tool to assess how exterior design changes impact aerodynamic performance. This study evaluates the use of a Lattice Boltzmann based numerical simulation and the National Research Council (NRC) Canada's wind tunnel to assess aerodynamic drag on a production Volvo VNL tractor-trailer combination.Comparisons are made between the wind tunnel and simulation to understand the influence of wind tunnel conditions on truck aerodynamic performance. The production VNL testing includes a full range of yaw angles to demonstrate the influence of cross wind on aerodynamic drag. Results are also presented for the same production truck in a simulated open road environment to highlight the influence of wind tunnel conditions on aerodynamic drag predictions.The effects of moving ground and rotating tires are shown to have an influence on the truck's aerodynamics. A half-scale test model is used to study this influence by investigating static ground and moving ground conditions. Comparisons are also made back to the production truck to illustrate the impacts of model scale and geometrical detail on aerodynamic performance.