The amount of energy saved as a result of drivers observing ALL speed limits and never exceeding 55 MPH will increase over time as the vehicle fleet of large units is replaced by smaller "downsized" models. While slowing down reduces energy consumption for all vehicles, smaller vehicles fuel economy suffers more at high speeds than larger vehicles do. In fact, as the following chart shows, at speeds over 70 MPH a small vehicle will use nearly as much energy as larger ones, negating the benefits of its smaller size and weight!