Fuel consumption measures the amount of fuel a car consumes to go a specific distance. It is expressed in liters per hundred kilometers—or in countries that use the imperial system, gallons per 100 miles. For example, a Volkswagen Golf TDI Bluemotion has one of the best fuel consumption ratings, requiring just 3.17 litres to go 100 kilometers. Therefore, the smaller the value, the better the rating is.
Not all the fuel consumed is being used to directly power the car. About 3-11% of the fuel being consumed is used to overcome rolling resistance. Since the consumed fuel will not be all directly used to power the car, its good to implement driving techniques to reduce fuel consumption. Some techniques include: accelerating gently, maintaining a steady speed, and coasting to decelerate. Using these methods could reduce CO2 emissions by up to 25%.
This is a chart of average fuel consumption of all cars on the road in the United States, by year. Comparing these results to the averages for new vehicles, listed below, there is a large discrepancy. There are three reasons for this. Most importantly, new cars achieve better fuel consumption than older cars, and the older cars on the road bring down the average efficiency.
Secondly, EPA regulations (CAFE - Corporate Average Fuel Economy standards) dictate that the average fuel economy across a manufacturer's line of vehicles must be above a certain number - from 1985 to 2010 this number was 27.5 MPG. Unfortunately, while CAFE standards may seem like a simple number, the reality is much more complex. CAFE standards are based off of vehicle footprint (area between the wheels), meaning that a vehicle with a smaller footprint will have to achieve higher fuel efficiency than one with a larger footprint (ie. a compact hatchback vs. a truck). As if this was not confusing enough, CAFE standards also only apply to vehicles under a Gross Volume Weight Rating (GWVR) of 8500 pounds. This means that companies like Ford and Dodge, who make three-quarter ton vehicles like the F-250 and the Ram 2500 have an incentive to make those vehicles heavier, so that they don't have to conform to CAFE standards. This means that the real-world economy of car company's new cars is actually less than the stated fuel economy.
Finally, the average taken is called a "harmonic average," which means that it partially takes number of units sold into account, but not at a 1:1 ratio. This means that manufacturers can use all their models to balance out fuel efficiency, and that the companies can disproportionately increase their average with small cars that don't sell many units—and electric cars—which throw a wrench in the averages. This leads to a decrease in the real-world fuel efficiency of the average car.
Average fuel consumption of new cars in the USA. Values are listen in gallons of fuel per 100 miles driven. This allows for direct comparison of improvement.
This is a chart of average fuel consumption for new cars and trucks being sold in the USA. It highlights a few trends. The first being that imported cars tend to get significantly improved gas mileage over domestic cars. In addition, the gas mileage improvements have been fairly stagnant, showing around 21% improvement average for cars, and only 16.8% improvement for trucks, over the course of the past 22 years.
It is an important thing to note, that the engines in trucks and SUVs are generally just as efficient as the engines in cars. The main difference in their fuel economy comes from the fact that trucks and SUVs are significantly heavier than cars, as well as far less aerodynamic. Trucks are very necessary for contractors, or in construction. However, buying a truck as a commuting vehicle because of an occasional need to tow a boat will end up costing a lot of money in fuel, and increase an individual's CO2 footprint significantly.