They drive to work and go to the store to buy this and that. All this activity uses energy, and all the things they buy consume energy. One aspect of interest is in developing and encouraging the use of the diesel engine. Diesel engines are far more efficient than gasoline engines because they are unthrottled, have higher compression levels, and are turbocharged, which significantly increases thermodynamic efficiency. The fact that the diesel engine is unthrottled is its greatest asset.
Internal combustion engines breathe air into their cylinders via the intake manifold.
When the pressure in the manifold is at atmospheric level or greater, the engine can breathe freely. There is a partial vacuum in the manifold of gasoline engines under most operating conditions, but the manifold pressure in a turbocharged diesel is always equal to or greater than atmospheric pressure. The gasoline engine is throttled by how much air is allowed to enter the engine, while the diesel engine is throttled by how much fuel is injected into the cylinder. When the engine does not have to work to breathe, it is more efficient. Volkswagen currently makes a 1.8-liter diesel engine with excellent fuel economy, but it's not popular in the U.S. because it offers less performance than Americans generally prefer.