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How The EPA Performs Fuel Economy Testing

Why The Window Sticker Lies

Alex Steele
Jul 1, 2015
Fuel economy estimates are an essential part of comparison-shopping when buying a new car or light-duty truck in the U.S. Since the mid-'70s, city and highway mpg ratings published by the Environmental Protection Agency (EPA) have been posted on new-vehicle window stickers. The sticker itself is titled the Monroney, after Oklahoma Senator Almer Stillwell "Mike" Monroney, who played a pivotal role in the Automobile Information Disclosure Act of 1958. This was before the EPA came into existence, and the label was originally meant to disclose MSRP, options, destination charge, assembly plant, etc.
Fuel economy and emissions estimates are determined with the use of a dynamometer, which simulates driving conditions in a laboratory, under highly specific circumstances. A dyno uses the vehicle's drive wheels, spinning on top of a dual set of heavy steel rollers in an attempt to mimic the speed and load (resistance) of normal driving. Dynos are also used to measure the force, power, and torque produced by an engine.
Federal law mandates manufacturers to perform standardized testing, typically on pre-production models, and submit the data to the Environmental Protection Agency. Due to insufficient budget and manpower, the National Vehicles and Fuel Emissions Laboratory (NVFEL) in Ann Arbor, Michigan, only confirms 10-15 percent of this information. If a discrepancy is found, an EPA investigation takes place, and mpg figures are eventually corrected. This has only occurred twice since 2000. However, recently a large number of '12-'13 Hyundai and Kia model estimates were typically off by a significant margin, the Kia Soul was rated as much as 6 MPG too high on the highway. The breach was unprecedented and surfaced following a rash of consumer complaints to the EPA. The inaccuracy was claimed by the manufacturer to be a testing error, which resulted in fines, lawsuits, and quite possibly a knock to their reputation with American buyers.
Emissions testing is similar and is performed by manufacturers on a dyno under strict guidelines, with a small percentage confirmed or disproved at NVFEL as well. Instead of projecting fuel economy, analyzers are measuring the amount of harmful emissions coming out the tailpipe. A relative part of fuel economy testing is the method in determining the amount of fuel used, not by measuring the liquid fuel drawn from the tank, but a remarkably more accurate technique involving the capture of emissions and calculating the volume of fuel burned by the amount of carbon in the subsequent sample.
Through the '07 model year, two Federal Test Procedure (FTP) tests were performed, consisting of city and highway driving programs. The city dynamometer schedule began with a cold engine (cold engines require more fuel), included 23 stops, had an average speed of 20 mph, and topped out at 56 mph over a period of 31 minutes. The highway schedule entailed a warm engine, no stops, 48 average mph, and high of 60 mph covering a 10-mile distance. The fuel economy numbers were then adjusted down: 10 percent city and 22 percent highway to allow for realistic driving.
There was consistent criticism on the accuracy of these estimates, especially when fuel costs soared. New-car Monroney numbers were almost always higher than the mpg achieved during real-world on-road driving.
Things changed in 2008 with the implementation of three new Supplemental Federal Test Procedure (SFTP) tests by the EPA. The SFTP included faster driving speeds, harder acceleration, colder temperatures, and additional use of air conditioning. Complaints aren't going to stop, but these new procedures brought down the MPG estimates to a realistic range. The percentage of reduction in fuel economy ratings were also applied to '07 and prior EPA statistics.
Now here's the thing. No matter what "average" fuel economy estimates the EPA comes up with, everyone drives differently, on varying roadways, and under different climate, maintenance, and traffic conditions. So it's not feasible to hit dead-on what your miles per gallon will be in the real world. A driver traveling consistently—and aggressively—in stop-and-go traffic may come in below the EPA city rating. However, a conservative driver, staying below the speed limit throughout long-term highway travel, can produce an mpg figure above the highway mark.
How To Improve Fuel Economy
Driving Habits
  • Accelerate and brake as gradually as possible without inhibiting drivers behind you. Picture a full cup of coffee on top of the dash and be careful not to spill it.
  • Speed kills gasoline. Gas mileage typically begins dropping rapidly above 50 mph.
  • Engines get zero mpg at idle. If avoidable, don't let your car sit there and warm up for extended periods of time.
  • Cruise control maintains vehicle speed steadily and makes a positive difference.
  • Cargo on the roof creates wind resistance, and unnecessary weight in the trunk or bed also forces the engine to work harder.
  • Turn the A/C button OFF (disengage the AC compressor) when not needed for passenger compartment cooling or defog.
If the Malfunction Indicator Lamp (MIL) is on and/or the vehicle failed a state emissions inspection—forget it—don't talk to me. Keep the engine's air filter clean, replace sparkplugs, and perform a valve adjustment (if applicable) according to manufacturer's recommendations.
Low tire pressure can hurt more than you might think. You can lose 0.3 percent in gas mileage for every one psi that tires are low, and tires can be underinflated by 10 psi or more without you even noticing. So check regularly with a gauge. Correct inflation pressure is usually displayed on a decal inside the driver's doorjamb.
Use the correct motor oil. 10W-30 is thicker than 5W-30. Using higher viscosity oil than recommended increases resistance to engine rotation.
What Is CAFE?
Corporate Average Fuel Economy (CAFE) was enacted by congress in 1975 following the Arab Oil Embargo. CAFE involves manufacturer regulations measured by the EPA and regulated by the Department of Transportation (DOT) and the National Highway Traffic Safety Administration (NHTSA). The standards are becoming more complex, individualizing specific size (or footprint, which is wheelbase times average track width) models to different mpg requirements. But in general, each manufacturer must maintain an average fuel economy of the majority of its cars and light-duty trucks at or above an mpg standard established for that upcoming model year. If a manufacturer exceeds the CAFE mpg standard for a given year, they receive credits, which may be applied to an upcoming fleet coming up short. No credits to work with? The current penalty is $5.50 per 0.1 mpg below the standard, multiplied by total production for U.S. sale. Emissions requirements are enforced in accord with fuel economy.
CAFE mpg standards are significantly higher than EPA fuel economy estimates deemed for consumers. All passenger cars (excluding light-trucks or SUVs) with an EPA combined mpg rating of 22.5 or below are subject to a gas-guzzler tax.
What's On The Window Sticker?
The Monroney has come a long way. The latest edition of the EPA label began in 2013. First thing you'll notice is the "combined city/hwy" mpg rating. It has much larger text, situated before both city and highway ratings. This is a weighted average presuming 55 percent city driving and 45 percent highway. Again, it's an estimate. You or I could be way off on our own respective daily commutes, but the prominent combined statistic may simplify comparing the efficiency of one new car or truck to the next.
The EPA/DOT sections of current Monroneys are categorized by powertrain type:
Gasoline (Including Non Plug-In Hybrid)
Compressed Natural Gas
Hydrogen Fuel Cell
Flexible-Fuel: Gasoline-Ethanol (E85)
Plug-In Hybrid: Electricity-Gasoline
Photo 2/2   |   Gasloine Label
1. Helpful recent additions (Gasoline)
2. Vehicle rated fuel economy numbers, city, highway and combined rating 3. Range and best mpg for the vehicle class (ex: Small SUVs)
4. How much you save or lose in fuel cost compared to the class average over 5 years.
5. How many gallons used per 100 miles.
6. Model-specific annual fuel cost.
7. Fuel economy and greenhouse gas ratings (1 worst, 10 best). This is determined by the amount of carbon dioxide emitted from the tailpipe each mile driven. As fuel economy increases, carbon dioxide (greenhouse gas) output decreases.
8. Grams of carbon dioxide (CO2) emitted per mile, and best in class.
9. Smog rating (1 worst, 10 best): Vehicle emissions standards on nitrogen oxide, non-methane organic gas, carbon monoxide, particulate matter, and formaldehyde.
10. A note explaining why these estimates may not match your particular vehicle's mpg.
11. QR Code (gotta have an app): Barcode to obtain additional information when scanned with a smartphone.
12. Fuel economy website:
Typical hybrids fall under the gasoline category because there's no other fuel used to generate forward motion. A plug-in hybrid or electric vehicle uses a different formula to determine fuel economy. A plug-in hybrid label will show fuel economy in both modes of operation, whether powered by the gasoline engine or electric motor. Gasoline mode displays typical miles per gallon, while all-electric range reads MPGe. This refers to miles per gallon of gasoline-equivalent, meaning the equal amount of energy produced from electricity, as in a gallon of gas. Both are a combined city/highway value. Similar to gallons used per 100 miles, plug-ins and EVs use kilowatt-hours (KWh) per 100 miles. There's also a mileage range on a full electric charge.
Electric vehicles use MPGe alone, and of course score 10 on fuel economy and greenhouse gases, 10 on smog, and 0 for carbon dioxide emitted. However, keep in mind that the electricity used to charge the battery costs money and the power plant producing the electricity (aside from nuclear, water, solar, or wind) disburses emissions into the atmosphere. So, it's by no means a free ride.
Greenhouse gases are a major concern due of their effect on global warming. The transportation industry is the second highest contributor of greenhouse gases, behind electricity production. And the largest transportation sources are passenger cars and light-duty trucks, with their foremost pollutant, carbon dioxide, coming from the internal combustion of fossil fuels.
After The Sale
I couldn't help but contact an EPA source with what I consider a personal question. What happens when a vehicle that had previously met CAFE fuel economy standards is modified (post-sale) by the manufacturer through a campaign, technical service bulletin, or extended warranty and no longer meets the requirements?
Prior to '12 production, vehicles were required to maintain the CAFE mpg standard for 1 year of on-road use. After that, regulations no longer applied. '12 and newer production requires vehicles to maintain greenhouse gas standards (primarily carbon dioxide, which goes hand in hand with fuel economy) for a duration of 120,000 miles, with allowance for normal engine degradation.
This could be a drawback to manufacturers previously making changes after the fact, and with the limited EPA budget and capacity for follow-up testing, it makes you wonder what's going to fall through the cracks?
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