Vehicle-to-vehicle (V2V)-based cooperative heavy-duty-vehicle (HDV) platooning systems are nearing commercialization. One of the major benefits of vehicle platooning is the aerodynamic drag reduction associated with the close coupling of the two vehicles. Various projects on truck platooning have been undertaken in recent years by research groups in North America, Europe, and Japan, many of which have documented road or track testing demonstrating the effect of separation distance on the fuel savings potential of such systems. The fuel savings associated with HDV platooning arises primarily from the aerodynamic interaction of the multiple vehicles, resulting in possible fuel savings for the leading and following vehicles. The aerodynamic benefits will generally be sensitive to the size and location of the low-speed air-wake behind the leading vehicles, and the size and location of the high-pressure zone generated ahead of the trailing vehicles. In addition to separation distance, the vehicle configuration, the lateral stagger, and cross-winds are expected to influence these flow-field characteristics and therefore the potential drag reduction of a truck platoon. To put into context the aerodynamic efficiency of HDV platooning, it is also important to understand the aerodynamic behaviour of a single vehicle operating in typical traffic environments, as a baseline condition. This paper documents an experimental wind-tunnel study to evaluate the aerodynamic efficiency of HDV platooning, in the context of enhancing the reliability of fuel savings estimates of HDV platooning and understanding the true potential fuel savings in standard vehicle operating environments. A wind-tunnel test program was performed at 1/15-scale for a two-truck platoon configuration to investigate the influence of separation distance, lateral stagger, vehicle configuration, cross winds, and ambient traffic on the drag of each vehicle in the platoon, along with the influence of ambient traffic on a single truck. I would like for this written paper to be considered for a presentation at COMVEC 17.