The Environmental Protection Agency’s National Vehicle & Fuel Emissions Laboratory has quietly gone about its business on Plymouth Rd. since 1971, writing emission standards and testing cars and fuels sold in the United States.

In that business, the lab has unquestionably succeeded. “We’ve removed lead from gasoline, so kids are smarter,” says Chris Grundler, director of the EPA’s Office of Transportation and Air Quality since 1995. “We’ve removed sulfur from diesel fuel. Automobiles are 98 percent cleaner now than when we started.” They aim to get to “practically 100 percent” in ten years, and they’re now working on standards for medium- and heavy-duty trucks plus oceangoing vessels.

The lab also developed an important sideline in rating cars’ fuel efficiency. They tell manufacturers how to test new cars’ mileage–and also do their own tests to make sure the manufacturers’ numbers are accurate.

That sideline recently put the north-side laboratory in a global spotlight. In the 2013 model year, Hyundai-Kia claimed that five of its models would deliver forty mpg on the highway, while Ford said its new C-Max hybrid would get forty-seven mpg overall–but drivers couldn’t duplicate those results in the real world.

“Ford launched the C-Max in later September, early October 2012,” recalls Byron Bunker, director of the lab’s compliance division, “and we first heard about problems from media reports in October. I read the first article, and my reaction was ‘hmm, that’s interesting.’ But by the fourth article, it was clear there was something there.

“We started testing early the next year,” Bunker continues. “When we first looked at it, we thought it was a different problem: that our test procedures weren’t good for hybrid vehicles.”

In fact, Grundler says, the real problem was that Ford based its mileage estimate for the tall C-Max hatchback on the sleeker Fusion sedan. “In our fuel economy regulations from 1970, manufacturers were told they could group certain vehicles together [if they had] the same engine and transmission and were in the same weight class. That makes complete sense and worked well–until recently.

“The Ford C-Max, Fusion Hybrid, and Lincoln MKZ Hybrid all have the same engine and transmission and are in the same weight class, so Ford put the same [mileage] label on them. But because they use so little fuel, little things make a huge difference.”

“This was the first time someone had a family of hybrids,” explains Bunker. “Before this, hybrid powertrains were used on just one model, like the Prius and the Escape. But the C-Max has a way different profile from the Fusion, and with very, very efficient engines, a change of profile made a big difference.”

When the lab tested a C-Max, it came up with an overall figure of forty-three mpg–and that’s what Ford’s window sticker now claims. The company gave buyers who purchased their cars before the label changed $550 to compensate for their higher-than-expected gas costs.

“For Hyundai-Kia, it was a matter of how they tested the vehicles,” Grundler says. “They have a process they call ‘coast-down testing’ that’s done outside the laboratory.” Hyundai’s website says “coast-down testing measures a vehicle’s aerodynamic drag, tire rolling resistance and drivetrain frictional losses, and provides the technical data used to program the dynamometers that generate EPA fuel economy ratings.”

The problem was that the Korean automaker’s coast-down figures weren’t precisely replicable–nor were they obtained using EPA-sanctioned procedures.

What Hyundai-Kia’s exact error was and how they’ve corrected it, Bunker can’t say “until it’s all wrapped up, which could be up to six months or longer.” But the company has retroactively lowered the mileage estimates for most of its 2012 and 2013 models. And it’s compensated 900,000 buyers for the difference between the mileage they were promised and the mileage they actually got.

The EPA also has changed its own procedures. “We’re doing coast-down testing on a regular basis now,” Grundler says–though not in Ann Arbor: “We’re renting Air Force runways in Arizona and northern Michigan.” Though they regularly drive cars outside the lab to break them in, the lab had not previously tested cars in the real world.

That’s not all that’s different. “We’ve changed how [vehicle] labels look and what information is on them,” Grundler continues. “And we’re doing more testing. Though the sequester was rough on us, we’ve shifted our resources, and where we did 10 to 15 percent of new vehicles in the past, in the last two years we’ve done 16 to 19 percent.” In all, nearly 400 cars passed through the Ann Arbor lab last year.

The 202,000-square-foot lab is secured behind spike-capped fences and gates. I enter through the office building after passing by two guards and through a metal detector. I’m escorted down gray halls and across a parking lot locked behind tall wire fences topped with barbed wire to the laboratory building, where director David Haugen meets me in the lobby.

“The lab was located here because the center of the universe for cars was southeast Michigan,” Haugen says. “But after we opened, a whole new industry, the emission measurement industry, developed around it. And it used to be that imports were shipped in to be tested here, and some of the manufacturers decided to go local. Today Toyota, Nissan, Hyundai- Kia, and Mercedes all have offices plus engineering services here.”

The lab itself is a huge garage with pristine cars stacked on metal racks in the center, rows of smaller garages on each side, and a fuel bay at the far end. Everything is brightly lit, incredibly clean, and amazingly quiet–with only a few casually dressed folks around.

“Friday is quiet day,” explains Haugen. “Monday is set-up day, Tuesday through Thursday we do the bulk of the testing, and Friday is finishing day. More than 150 people work in the lab running tests, and there’s 200 to 250 more working over in the office building writing policy based on our data.”

Haugen says the lab is clean because clean is safe. “Cars are dangerous. Fuel is very dangerous. And we store a lot of fuel here.”

They do. The fuel bay has seventeen pumps in it, and beside, behind, and beneath the bay are rooms full of fuel barrels attached to the pumps. “Remember, we also test fuel,” says Haugen, “and we have forty or fifty different kinds of fuel here.”

The smaller garages are called test cells, sealed rooms fitted with heating and air-conditioning units that can take the temperature from twenty to ninety-five degrees, plus a wind machine at one end. During tests, the car is driven onto a chassis dynamometer, four forty-eight-inch rollers mounted on massive hydraulics in the basement that simulate changing speeds and road conditions. Tubes attached to the exhaust pipe lead to transparent bags hung in the attic above, where emissions are measured by equipment made by either Horiba or AVL, both of which have facilities in the Ann Arbor area.

“We capture everything that comes out of the tail pipe,” says Haugen. “Then we measure the carbon atoms in the exhaust. We also have sealed rooms that measure emissions even when [the cars are] not moving by measuring hydrocarbons.”

Haugen says the results are rigorously repeatable. “Despite what the label on a new car says, our mileage does not vary. We test representatives of the fleet [because] in here we have the same conditions every time, and with careful measurements we get very refined data.

The lab tests not just cars and car fuel but “everything from weed whackers to fuel for oceangoing vessels,” Haugen says. “We’re now working on gas standards for trucks to increase fuel economy and reduce greenhouse gas emissions.”

The EPA is also adding a gigantic new facility on the side of the lab to test trucks and buses on even bigger rollers. “It’ll take nine months to a year to finish the building, and then they’ll install the equipment,” says Haugen. He estimates the new facility will cost $12 million and begin testing in the summer of 2015.

Since the EPA lab opened four decades ago, it’s worked its way through everything that moves with an engine. It began with cars, because they outnumber everything else on the road, and has been moving down through the rest, from light-duty trucks to heavy-duty trucks to backhoes and locomotives.

On the way out, Haugen shows off the chemistry labs where they test fuel. “These days, we’re testing fuel from large oceangoing vessels for sulfates to determine the risks to the coastal environment.

“This is the place where policy is developed that will have a huge reach and a big impact in many industries: the automobile industry, the transportation industry, the fuel industry. There’s not another federal lab like this anywhere!”

“There’s no other facility like this in the world,” Chris Grundler confirms. “I’ve been to the one in China. It’s quasi-state owned, and they don’t deal with fuels. The European lab is 10 percent our size, and they don’t do any testing.” But even with the best facility in the world, Grundler says there’re some things they can’t test.

Can consumers trust manufacturers’ and EPA’s mileage claims? “Yes,” replies Grundler without hesitation. “The integrity of the label is paramount to us. The industry and the EPA have common cause: our reputation and integrity are at stake. I believe the EPA’s estimates are the best estimates consumers have to make an informed decision about mileage.

“But as to how will it do in the real world, well, it will vary–so we say: [your] mileage may vary.”