The more weight that a vehicle has, the more kinetic energy it needs to reach a given speed. Kinetic energy that is all lost again when the vehicle brakes to a stop. Weight reduction is one of the most important and effective ways to make a car more fuel efficient. The University of South Australia developed an ultralight car that has space for two people. The car has a mass of only 64kg, which corresponds to a weight of only about 140 pounds! Imagine that. In a normal car, almost all of the weight is just the car. In this case, the majority of the kinetic energy is going to move the passengers and not the car. And after all the point of a car is to move people, not metal.
This low weight was achieved by building the car using panels made of layered fiberglass and aluminum. These panels were used to build a basic box like shape. Then an aerodynamic form was constructed by layering styrofoam cut to an aerodynamic shape on top. A layer of fiberglass was then placed over the styrofoam to secure and protect it.
This is another example of a vehicle that would be perfect for neighbourhood driving or one person commutes. The heavy steel cars we drive are overkill for a lot of uses to which they are put. This overkill has a cost that shows up at the gas pump. Choosing the smallest, lightest vehicle that can serve a given function is one of the best ways to save on gas.