The U.S. Environmental Protection Agency (EPA) has several methods in use to determine the overall fuel economy of a vehicle which is one of the mandatory fields on the Monroney sticker (better known as window sticker) of new cars and trucks. The fuel economy of a typical vehicle depends on many design properties physically known as the inertial-, wind- and rolling resistance. Each of these resistive forces is determined by several key design parameter (such as mass, frontal area, drag coefficient and rolling resistance coefficient) which are predetermined quite early in the design process. These design parameters, to a large extent, cannot freely be determined, are considerably co-dependent and have a large amount of interaction with other vehicle properties including overall vehicle costs. To optimize the design, careful consideration of the cost/benefit analysis for each of the design parameters must be made. A simplified model was developed to calculate various vehicle driving cycles and to study the sensitivity of assorted key design parameters on the fuel economy estimates. Different vehicles representing different categories (a typical light-duty pick-up truck, a mid-size sedan, and an all-electric vehicle) were benchmarked and vehicle parameter sensitivities with regard to the various driving cycles have been determined. Furthermore, fuel economy improvements through energy regeneration (braking) have been addressed.