I have several friends who drive minivans because they get better fuel economy than SUV's. While true in concept, they don't go far enough. I have a sedan that gets 30mpg. Unfortunately, most of the time, I am alone in the car, therefore, I get 30 seat miles per gallon (I will discuss motorcycles shortly). I have three children and a wife, so taking the family anywhere means filling all of the seats. When the seats are full, that equates to 150 seat miles per gallon. A friend has a Toyota Prius and averages 50 mpg. He and his wife (they are without children) usually travel in this car, so they get 100 seat miles per gallon.
Taking the number of full seats into consideration when making a trip would help a person to realize the true fuel economy of a vehicle. If a Chevy Suburban was traveling with all 7 seats full for every trip, the economy would be quite good, but not as good as a minivan (126 based on 18 mpg).
My motorcycle gets 60 mpg. I don't carry passengers because I am an inexperienced rider. Although limited, I can carry some things on board. Motorcycles, combined trips, fuel efficient cars and alternative fuels have led to a lower demand for petroleum. The more people adopt these methods, the better things will be for us as consumers. The farther reaching benefit of these methods is a lower number of gallons burned, therefore less soot & CO2 released into the atmosphere.
When you see the soccer-mom who has one child, or the insecure guy alone in that 'Burb, feel sorry for him or her. When you see the guy on the bike, don't tailgate. He's helping to keep your fuel costs down while reducing greenhouse gas emissions.