Fuel Economy
When you go into a store, to buy a car, you'll always find the fuel consumption for almost every new car. Here we'll try to explain how the tests are done, so you'll have a picture about how much more (probably not less) gas you'll use.
Most and least fuel efficient cars - fuel consumption rated
Which cars are tested
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Manufacturers are not required to test each individual new vehicle offered for sale. They are only required to test one representative vehicle—typically a preproduction prototype—for each combination of loaded vehicle weight class, transmission class, and basic engine (size, number of cylinders, fuel system, etc.). In addition, some vehicles are exempt from these requirements:
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How are cars tested
Fuel economy is measured under controlled conditions in a laboratory using a standardized test procedure specified by federal law. Manufacturers test their own vehicles—usually pre-production prototypes—and report the results to EPA. EPA reviews the results and confirms about 10-15 percent of them through their own tests at the National Vehicles and Fuel Emissions Laboratory.
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In the laboratory, the
vehicle's drive wheels are placed on a machine called a
dynamometer that simulates the driving environment—much like an
exercise bike simulates cycling.
The energy required to move the rollers can be adjusted to account for aerodynamic forces and the vehicle's weight. |
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On the dynamometer, a
professional driver runs the vehicle through a standardized
driving routine, or schedule, which simulates “typical” trips in
the city or on the highway.
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Each schedule
specifies the speed the vehicle must travel during each second
in the test.
Right: The driver watches a computerized display that shows his driving statistics compared to the specified schedule. |
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A hose is connected to the tailpipe to
collect the engine exhaust.
The amount of carbon in the exhaust is measured to calculate the amount of fuel used during the test. This is more accurate than using a fuel gauge. |
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How do they drive the car during the tests ?
The EPA fuel economy test consists of two driving routines, or schedules, performed in the laboratory.
City: Represents urban driving, in which a vehicle is started with the engine cold and driven in stop-and-go rush hour traffic. The driving cycle for the test includes idling, and the vehicle averages about 20 mph (~32 km/h).
Highway: Represents a mixture of rural and Interstate highway driving with a warmed-up engine, typical of longer trips in free-flowing traffic. Average test speed is about 48 mph (~77km/h) and includes no intermediate stops or idling.
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The city schedule represents
low-speed driving in stop-and-go |
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The highway schedule simulates non-metropolitan driving at higher speeds, with no stops and negligible idling. |
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Test Schedule
Characteristics
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Adjusting Estimates
In the 1980s, an EPA study found that drivers were typically achieving lower fuel economy than predicted by EPA laboratory tests. As a result, EPA required the laboratory-derived city and highway fuel consumption estimates posted on the labels of new vehicles to be adjusted downward by 10 percent for city estimates and by 22 percent for highway estimates to better reflect the fuel consumption real-world drivers can expect.
Source: Fuel Economy.gov
Most and least fuel efficient cars - fuel consumption rated
