Automobiles are energy conversion devices. The driver buys the energy in the form of gasoline. Essentially all the energy is eventually transferred to heat in the surrounding atmosphere. Essentially all the energy is "loss" to inefficiencies. No energy is required to transport a vehicle from one point to another point if the two points are at the same altitude. Drivers have a great deal of control over the size of the losses incurred in operating a vehicle.

Let me explain some of the losses involved:

Air friction loss. This is probably the one of the biggest drains on fuel consumption. Air friction loss increases with the square of the speed. This is true for "slick" cars (with low drag coefficients) as well as less slick cars. That means that when a car's speed doubles, say from 40mph to 80mph, the amount of energy lost to air friction goes up by a factor of four. The slower one drives, the less overall energy is lost to air friction.

Rolling friction loss. The amount of loss in the rolling gear of a car is independent of speed and is generally minimal. The exception is tire "rolling resistance"; the tire flexs as it rolls, this flexon of the sidewall creates internal friction and heat. Under inflated tires are subject to failure from heat buildup. Over inflated tires are also subject to failure due the increased stress. Over inflated tires also give a harsher ride. To minimize rolling friction loss, tires should be inflated to the maximum acceptable safe pressure.

Brakes. Brakes convert the vehicle's kinetic energy (that you have paid for by burning fuel to attain your velocity) into hot air. Essentially, every time you touch your brakes you are wasting energy. The exception is a hybrid vehicle that converts some of the energy that would otherwise be lost to heating air into electrical energy that is stored for future use. It is a myth that rapid acceleration wastes fuel. However, rapid acceleration is likely followed by higher velocity and rapid deceleration, both of which does waste fuel. A heavy vehicle does not necessarily use more fuel than a light one. Unless brakes are used.

Why do I take the time to write this? Because of the way I see people driving. I see vehicles that are two or three times the necessary size driving around town carrying one passenger. Two or three times a reasonable weight, with engines that are three or four times a reasonable size. Driven aggressively, rapid acceleration, rapid deceleration, 45mph in a 30mph zone, 80mph in a 70mph zone. And on. And on. What are those people thinking? Do they understand what they are doing. Probably not.