Among the factors of energy consumption by transportation, vehicle fuel efficiency plays a significant role. With an increase in fuel efficiency (in miles per gallon), marginal fuel consumption decreases. The most important fuel consumption benefits are achieved in the lower ranges of improvements. For instance, an improvement from 10 to 20 miles per gallon reduces fuel consumption by 50%, while an improvement from 20 to 30 miles per gallon will further reduce fuel consumption by 33%. Thus, vehicle-wise a significant fuel economy is reached if a consumer switches from a Sport Utility Vehicle (15 miles per gallon) to a regular car (25 miles per gallon).
Although switching to a more fuel-efficient vehicle such as a hybrid (35 miles per gallon) results in fuel economy gains, they are not marginally that significant for an individual consumer, but much more at the aggregate level (fuel consumption by the society). This is particularly the case if the higher price of a more energy-efficient vehicle does not compensate for the gain in fuel efficiency, then it is not a rational choice from an economic standpoint. Therefore, for fuel efficiency to be beneficial for society, the price of the vehicle should remain similar as its fuel efficiency increases, or at least its fuel efficiency should compensate for its higher price. Significant gains in fuel efficiency are also achieved when vehicles operate in conditions with less congestion.