Fuel Economy Numbers Gone Wild


It has been a tough couple of months for the window sticker. An EPA investigation found that Hyundai and Kia, the two automakers most responsible for making "40 mpg highway" an industry mantra, don't hit that number at all. As of this writing, the agency may also look into whether Ford has been inflating the numbers on some of its hybrids. The embarrassing shortcomings raise some important questions, starting with, "What the hell happened?" More important, considering how much is riding on fuel-economy numbers and tougher standards, can the EPA still keep automakers in line?

The most obvious source of concern with the testing is how little the EPA actually does itself. It's more or less common knowledge that the EPA doesn't independently certify every car: automakers develop fuel-economy numbers according to the EPA's procedure, but the agency audits only ten to fifteen percent of them every year at its facility in Ann Arbor, Michigan. What's less well known is that there's another part of the test, called "coast down," which is checked even less frequently. In order to account for a vehicle's unique drag profile -- something that won't show up on a stationary test bed -- carmakers time how long a vehicle takes to coast from 70 mph to 10 mph in neutral. As EPA compliance engineer Linc Wehrly explains, that's not an easy procedure for the EPA -- not to mention some smaller automakers -- to perform. "You have to do it at an outdoor track that has at least a two-mile-long straightaway. And it has to be flat. There are only a handful of those facilities in the country -- or, for that matter, in the world." The EPA is thus usually forced to rely on numbers that automakers supply -- even on the cars it audits on its own test beds. "Even if we wanted to, we couldn't do nearly the amount of throughput for [coast down] as we do with regular testing," Wehrly says.

Hyundai and Kia submitted coast-down results that were forgiving -- a procedural error, the company says -- resulting in fuel-economy-rating exaggerations of as much as 6 mpg on the highway. The exaggerations appeared legitimate on the EPA's dynamometers. Could other automakers be doing the same?

"Well, that's a good question," says Wehrly.

Even if other automakers are playing by the rules, there are several ways to take advantage of them. Manufacturers have learned to exploit the tiniest loopholes in the EPA's requirements to gain the crucial marketing advantage that a single mile per gallon can afford.

For instance, the EPA doesn't require distinct certifications of every vehicle variant. That makes sense, because it would be unwieldy and expensive for, say, Chevrolet to individually test every wheel-and-tire combination on the Silverado. What makes somewhat less sense is when a model variant such as the Camaro SS 1LE, with its numerically higher gearing and sticky tires, flies under the radar and wears the same window sticker as its more common -- and surely more efficient -- linemates.

Another source of inconsistency and possible inflation is the person who actually "drives" during the test cycle. The route, mapped out on a computer screen set in front of the windshield, is designed to cause spikes in the throttle. "You're not supposed to anticipate and smooth your route; you're supposed to follow it exactly," explains Robert Bienenfeld, senior manager of environment and energy strategy for Honda. In practice, an automaker could employ a more savvy driver, someone who could subtly smooth out throttle applications and, as a result, get better mileage. "If you do a lot of throttlings versus a steadier driver, you'll get a three-, four-, or five-percent variation... which is probably one of the more frustrating aspects of the test," Bienenfeld says. Hybrids may be particularly sensitive to this practice. Bienenfeld adds that Honda has pushed for robots to replace human testers.

As any racing fan can tell you, there will always be engineers and new technologies capable of beating the system. The difference is that federal regulators can hardly react with the swiftness of Formula 1's Bernie Ecclestone. That's not to say there haven't been changes. Wehrly points to window sticker adjustments in the early 1980s that cracked down on rampant mileage inflation. More recently, the EPA added test cycles to account for increased air-conditioner usage, colder temperatures, and more aggressive driving, all of which had an especially profound effect on keeping hybrids honest. But these tweaks generally come only once a decade or so, and they're limited by what the EPA can do independently of Congress. In practice, that ties the window-sticker numbers to much older, easier tests for Corporate Average Fuel Economy.

"Congress locked in that the standards have to be based on these forty-year-old tests that have nothing to do with the way people drive," says David Friedman, senior engineer and deputy director of vehicles program for the Union of Concerned Scientists. "The fundamental test needs to change."

Friedman advocates a clean-sheet approach that uses data collected from the cars of real owners. Onboard computers, which barely existed in the 1970s, now make it possible to observe how people actually drive, and the information could be used to develop more realistic and sophisticated tests. This information could supplant fuel-economy tests altogether.

"What we need to do is essentially throw away this old paradigm -- that we're going to test a car on a test cycle...because it's just a test cycle," says David Greene, a researcher with the Oak Ridge National Laboratory who oversees the official EPA website fueleconomy.gov. "It's not the way I drive."

Greene envisions personalized window stickers -- a system in which you could input data from your car and then see how you would do in other cars. "We're some way from that, but the technology exists," he says.

Such comprehensive change would not be easy or quick -- and not because of the technology. It would likely require a coordinated effort from the EPA and automakers to convince owners to share information from their cars and then, perhaps, to convince Congress to rework fuel standards. And for all that work, there's no guarantee that the new system wouldn't have its own problems. "Real-world data is not a panacea," says Honda's Bienenfeld, pointing out, for instance, that such data might disadvantage automakers (like Honda) that sell lots of cars to younger, more aggressive drivers.

It's also worth noting that the current system, creaky though it may be, worked the way it was supposed to -- the EPA caught Hyundai, and Hyundai is paying a heavy price. So will Ford, if its numbers prove inaccurate (the company says it's confident it followed EPA procedures properly). Watchdogs like Consumer Reports and Internet forums where drivers are able to share observed mileage also play a role in curbing exaggerated numbers. So, too, do the automakers themselves. They're more than willing to question their competitors' results and, if necessary, complain about those who don't seem to be playing by the rules. Indeed, other automakers raised a red flag with federal regulators regarding Hyundai. The consequences for the Korean company -- an expected $100 million annually in compensation to owners and a badly dinged image -- sends a message to the industry.

There's also the age-old but often overlooked disclaimer: your mileage does vary. "If you drive 75 mph instead of 65, you would lose about 7 mpg in our new Fusion Hybrid," says Raj Nair, Ford's global product chief, adding that cool weather and break-in miles similarly affect observed economy. Wehrly quips that he's fielded calls from angry drivers wondering why they didn't achieve the ratings while towing trailers. This variance is more obvious in high-mpg cars due to the fact that mileage is inversely related to fuel consumed. That means falling 2-mpg short in a car that's rated at 24 mpg is roughly the same, in terms of extra fuel consumed, as falling 7-mpg short in a car rated at 47 mpg. Of course, neither math nor context play as well on billboard advertisements as a big number.

In the short term, smart tweaks, rather than wholesale changes, are likely. More funding for the EPA to enforce the rules already in place -- and, in particular, to audit coast-down numbers -- would help, as would more improvements to the cycles to eliminate the loopholes and wiggle room.

"I think in the next few years, you can expect the EPA to take a look at the tests we use to generate the [fuel-economy] labels to see whether we need to fine-tune those tests," says Jeff Alson, a senior policy advisor at the EPA.

Regardless of the measures, both automakers and the EPA have an interest in making sure consumers trust the window sticker, especially on higher-efficiency models.

"The world doesn't stand still; your tests can't stand still," Friedman says.

Behind the sticker: How automakers test for fuel economy
In order to ensure consistent comparison across vehicles, the EPA developed a relatively simple and repeatable procedure with strict guidelines. Here's how it's done.

The EPA specifies how much air the cooling fans can blow. Some tests use fans that blow at a constant rate, while other tests vary it depending on wheel speed.

The driver's aid graphically displays the speed the car needs to hit at every second of the test.

The driver is trained to follow the drive trace within 2 mph of the specified speed. Going outside that limit invalidates a test.

The dynamometer is uniquely calibrated to each vehicle, based on coast-down tests, to apply the correct resistance.

Tailpipe emissions are collected in large bags. Gas samples are taken from the bags to measure the fuel used and the pollutants produced.

Sherman S.
I'm seeing all kinds of articles about the EPA tests, but they never mention that some cars normally beat the EPA numbers...specifically diesels.  My Passat TDI is rated at 30/40, but I get 40 in suburban driving and about 46 at 75mph.  And I don't play hypermiling games, just normal driving.  Consumer reports backs these numbers up, they got 51 HWY with theirs.  The tests don't allow diesels to shine.  If you live in the stop and go city with 35mph speed limit get a hybrid, but in the suburbs or if you drive high speed hwy diesels win.
the existing procedure is not accurate at all. It needs to be overhauled but automakers have no reason to support making the necessary changes because FE figures would drop substantially- especially in the city. the EPA city ratings for many of todays cars are totally inflated and if you look at testing by various publications you will often see that most cars today register real world mixed MPGs that are close to their EPA city figures. Cars like the Altima are rated at 29-30mpg in EPA combined mpgs but real world testing has not come close to those lofty numbers.
"falling 2-mpg short in a car that's rated at 24 mpg is roughly the same, in terms of extra fuel consumed, as falling 7-mpg short in a car rated at 47 mpg"as this line exemplifies, not only do we need a change in the testing procedure, but also that the metric itself could use an adjustment. it would take some getting used to, but highlighting consumption in gal/100mi (or something similar) would be far more illustrative.

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