This paper examines how commercial vehicle aerodynamic improvements can be influenced by regulation particularly with respect to size and weight policy. It discusses the potential use of performance based standards (PBS) first introduced to optimize vehicle configurations in terms of vehicle stability and control and compatibility with highway geometry.There are several vehicle treatments that can be used to reduce aerodynamic drag, some of which lengthen or widen the vehicle without increasing cargo capacity. One such solution is referred to as ‘boat tails” consisting of a light weight external extension of the trailer allowing the air flow to remain attached as the vehicle cross section diminishes resulting in a reduction in the area of negative pressure at the end of the vehicle which reduces drag force. Aerodynamic treatments of this type extend the length of the vehicle in the order of 30 to 60 cm which will contravene prescriptive size and weight regulations unless regulatory flexibility can be introduced to accommodate such innovation. There are other aerodynamic treatments which may alter classic vehicle design and form in a way that may violate prescriptive regulations. For example in Europe there are limited options for truck manufactures to include front end aerodynamic treatments given regulated length constraints. This paper will discuss regulatory measures being developed in Europe and the potential for the use of PBS to support aerodynamic innovation.