There is no reason under the sun a car or truck the size and weight of a Lincoln Navigator or a Toyota Tundra can't achieve 30+ MPG highway. There is no excuse for a Tacoma 4-cyl. to not exceed 30 MPG.
Until practical replacements for fossil fuels come along, the automobile industry should be forced by governments to develop the maximum possible fuel efficiency for the vehicle size and weight class.
Much-higher-MPG cars and trucks, even larger ones, can be achieved a number of ways.
1. advanced hybrid technology
2. developing the most efficient turbodiesel motors possible
3. developing the most fuel-efficient supercharged-gasoline engines possible