The overall main learning point was:  A car engine burns fuel to generate power.  Power is needed to roll the car on the ground and push it through the air.  When the engine is efficient and the gears keep the engine in its optimal operating range, the car should get good mileage.  If it's too heavy or awkwardly shaped, or both, the mileage will be worse because the engine will have to fight those elements harder.  The first key point addressed rolling resistance.  Rolling resistance is the resistance to motion due to the tire gripping the ground under it.  The car tire must stick to the ground to ensure it rolls and doesnt slip on the ground under it.  Good tire grip is especially important in turning corners and changing lanes.  Among the factors that affect rolling resistance are vehicle weight, tire inflation and size.  Next is aerodynamics, or the study of air and motion.  Aerodynamic resistance is due to the vehicle having to push air out of the way, around the car.  When we examine both types of drag, we understand how they complement each other.  The third key point is that rolling resistance is the predominant cause of drag at slow speeds and aerodynamic drag is the predominant cause of drag at higher speeds. 

Of course, you know now that most new cars are quite aerodynamic, but this has not had a noticeable positive effect on fuel economy.  Although many modern cars are more aerodynamic than ever before, and their engines are decently fuel efficient over a wider range of speeds, few of them are very efficient.  The reason that fuel economy hasn't gone up dramatically in the last 15 years is that the engines are designed for better power throughout the rev range, and make much more power when revved high and this has had a nullifying effect on mileage.  Car engines must satisfy many requirements, and good fuel economy is just one of about a dozen.  Perhaps the most prevalent new type of engine is the multi-valve engine.  This type of engine can rev to 7,000 or higher revolutions per minute and make decent torque from 1,500 rpm all the way to redline.  Unfortunately, this type of engine does not have a "sweet spot" or a particular range of engine speed in which it is very efficient.  Therefore, the car's mileage is decent over a wide speed range, but not as good as many that have simpler engines with the traditional two valves per cylinder.  Finally, in looking at cars 10 and 15 years ago compared to new models, we see a clear trend towards more powerful, better performing cars, and gas mileage results that defy logic because they have not improved and in some cases, have gone down.  That is my major disappointment with what the automakers have done.  They are not, in my opinion, seriously concerned with preserving natural resources.