However, these "official" ratings rarely reflect our own real-world driving experience. Depending on what, how, and where you drive, the differences can be huge. Many consumers often complain that the EPA's numbers are substantially higher than what an average owner might expect to experience in real-world driving.
Why is this the case? It has a lot to do with the way new cars and trucks are evaluated for their energy consumption. While it would seem logical to determine a vehicle's fuel economy simply by filling up the tank, driving it on the road or a test track for a set number of city or highway miles, refilling the tank, and dividing the number of miles driven by the number of gallons consumed, this is not how the experts do it.
In fact, tested vehicles don't reach the pavement at all. Rather, a car or truck's fuel economy is measured under rigidly controlled circumstances in a laboratory using a standardized test that's mandated by federal law.
Automakers actually do their own fuel economy testing and submit the results to the EPA, which reviews the data and confirms about 10 to 15 percent of the ratings itself at the National Vehicles and Fuel Emissions Laboratory.
In this article, we'll detail how vehicles are tested, what the difference between the EPA's fuel economy figures and real-world fuel-economy numbers are, and why the EPA's fuel-economy findings are still important. Here's a summary of what we'll cover:. The EPA doesn't just drive the vehicle to determine how many miles per gallon it gets.
Each new car and truck is tested on what's called a dynamometer, which is like a large treadmill. While the engine and transmission drive the wheels, the vehicle never actually moves -- just the rollers upon which the wheels are placed. A professional driver runs the vehicle through two standardized driving schedules, one each to simulate city and highway driving conditions, and ensures he or she is maintaining the mandated pace via a real-time computer display.
The "city" program is designed to replicate an urban rush-hour driving experience in which the vehicle is started with the engine cold and is driven in stop-and-go traffic with frequent idling.
The car or truck is driven for 11 miles and makes 23 stops over the course of 31 minutes, with an average speed of 20 mph and a top speed of 56 mph. The "highway" program, on the other hand, is created to emulate rural and interstate freeway driving with a warmed-up engine, making no stops both of which ensure maximum fuel economy.
The new Government of Canada test methods will better reflect everyday driving in Canada. Manufacturers will use 5 different tests designed to simulate different road conditions:. The testing is done in laboratories to make sure every car is tested under identical conditions in order to ensure consistency. Despite the new methodology no test can simulate all the possible combinations of conditions that Canadian drivers experience. Visit vehicles. A vehicle is driven about 6, km before testing.
Then the test vehicle is placed on a machine called a chassis dynamometer, which is like a treadmill for vehicles.
The dynamometer is adjusted for things like the weight and aerodynamics of the specific vehicle. A driver runs the vehicle through standard driving cycles that simulate trips in the city and on the highway. City and highway fuel consumption ratings come from the emissions generated during five laboratory driving cycles:.
The first test cycle, which sought to mimic rush-hour traffic in downtown Los Angeles with an average speed of 21 mph, is called the FTP, or city cycle, and is still in use today. This dyno test is 11 miles long, takes just over 31 minutes to complete, involves 23 stops, reaches a top speed of 56 mph, and has maximum acceleration equivalent to a lazy, second 0-tomph run.
A second cycle to measure highway driving was added in the late s as part of the introduction of corporate average fuel-economy CAFE regulations. This As a result, and even though the test figures were adjusted downward starting in the early s in an attempt to produce more realistic sticker values by 10 percent for the city test and 22 percent for the highway , the EPA numbers gave drivers too optimistic an expectation of fuel economy for decades.
In , Congress allowed the states to increase highway speed limits from 55 to 65 mph, but it would take another 21 years for the EPA to adopt tests that provide more realistic projections. To accomplish this, the EPA added three additional test cycles to the original two for model-year cars.
Until the model year, however, automakers may use results from the two old fuel-economy cycles and then plug those numbers into an elaborate equation developed by the EPA that approximates the new five-cycle procedure.
For , all fuel-economy figures will derive from the results of the While piloting a Honda Insight at the lab, we found the high-speed US06 cycle impressively aggressive. The cycle still averages only 48 mph but has bursts of acceleration similar to a 7. To keep pace, the Insight required at least three-quarters throttle, which made us appreciate the realism of the new tests and wonder if some underpowered cars may have a tough time keeping up with their acceleration demands.
The imperfection of human drivers is a big problem with repeatability of the tests, and hybrid vehicles in particular are very sensitive to throttle inputs—which, in turn, control engine starting and stopping and the amount of battery assist.
Measuring fuel economy during the tests is likewise hugely complex, which is why the automakers and the EPA both follow precisely the same protocol.
Before being used, the gas is analyzed to measure its properties, and fuel economy is then calculated based on the measured carbon content of the various tailpipe emissions—unburned hydrocarbons, carbon dioxide CO2 , carbon monoxide CO , methane CH4 , and oxides of nitrogen NOx —that are collected in bags made of a special Kynar plastic.
The one-percent accuracy of this machine from Japanese company Horiba is amazing considering the minuscule amounts of some of the exhaust constituents—some in quantities as low as a half-dozen parts per million.
The final city and highway ratings are calculated by taking the fuel-economy results from specific portions of each of the five tests and piecing them together.
The EPA maintains a repository of ratings from to the present at www. Skip to Content Skip to Footer. Share this on Twitter Share this on Facebook Email. How to buy an electric car. Electric cars. Buying an electric car can be easier than you think, we spoke to EV specialists to answer the most common EV related questions.
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