Taking A Detailed Look At Why 'Your Mileage May Vary'

Hyundai Elantra window sticker

It's safe to say that mileage claims are controversial at best, and often inaccurate.

"There are three types of lies: lies, damned lies and statistics," goes the old quote variously attributed to Mark Twain, Benjamin Disraeli and other wits. Were they writing today, they'd probably add a fourth: fuel economy numbers.

As regular readers have heard, Hyundai is being sued for allegedly misleading mileage ads. Honda, meanwhile, beat back one Civic Hybrid owners mileage lawsuit upon appeal but also agreed to a settlement covering thousands of others who didn't get nearly what the automaker promised.

Without taking sides in these individual cases. it's nonetheless safe to say that mileage claims are controversial at best, and often inaccurate, at least in terms of what real world driving is likely to yield.

"Your mileage may vary" is a disclaimer we've all heard, and certainly there are enough variables that impact what your car, truck or crossover will deliver: such factors as the speed you drive, what altitude the vehicle is operated at, what fuel you use, whether your tires are properly inflated and how many passengers you've got crammed into the backseat. And considering the added bulk too many of us carry around our middles, even that can play a role.


Paul EisensteinPaul A. Eisenstein is Publisher of TheDetroitBureau.com and a 30-year veteran of the automotive beat. His editorials bring his unique perspective and deep understanding of the auto world to Autoblog readers on a regular basis.



The challenge has been to come up with valid test procedures that come anywhere close to replicating real-world conditions.

But there's no question that manufacturers clearly want to put the best face possible on their products and, like that speed-talking spokesman for FedEx some years back, fuel economy disclaimers may be overlooked entirely.

The so-called Monroney sticker, the window label found on all new automobiles sold in the States, dates back to 1958 and legislation sponsored by Oklahoma Senator Almer Stillwell Monroney. Fuel economy numbers were added in the 1970s when Congress authorized the Environmental Protection Agency to oversee the new Corporate Average Fuel Economy [CAFE] standard and to begin testing every new vehicle entering the market.

The challenge – then and now – has been to come up with valid test procedures that come anywhere close to replicating real-world conditions. To help individual motorists adapt the numbers to their own driving styles, the EPA went to a three column approach, with city, highway and combined ratings.

The EPA employs only about 20 staffers to run mileage tests and they process barely 15 percent of all the new products that come to market each year.

In reality, the EPA employs only about 20 staffers – less than 0.1-percent of its staff – at its Ann Arbor, Michigan outpost to run those tests and they process barely 15-percent of all the new vehicles that come to market each year. For the rest, they take the manufacturers at their word, though random testing – much like the more extensive screening travelers occasionally experience at the airport – is intended to keep everyone honest.

For the 200+ vehicles that are subject to actually testing, the federal agency uses a dynamometer, the automotive equivalent of a treadmill. The computer-controlled devices can simulate such factors as road friction and wind resistance – but specially trained staff actually do the "driving," carefully obeying instructions displayed on a computer monitor to ensure uniform speed, acceleration and braking behavior that can be readily duplicated from one vehicle to the next.

The raw data goes through an incredible amount of finessing to account for such things as the use of air conditioning and other accessories. And the EPA has routinely tweaked the results to reflect increased highway speeds and changes in driving patterns.

Given the choice, it's no surprise that automakers flaunt the high-mpg highway results.

It's also had to adapt to technological changes, such as the increased use of all-wheel drive and, most recently, the emergence of battery-based powertrains. The numbers you see on the Monroney today reflect big changes that went into effect for the 2008 model year – driven by the fact that early-generation hybrids routinely performed significantly better in EPA testing than on the road – despite what those hyper-milers might tell you.

Those changes over the years add up. Without these corrections, the unadjusted mileage for the typical vehicle sold in the U.S. in June would have been an even 29.0 mpg. The average Monroney sticker was just 23.6, however – though both figures represent a 17-percent increase from when the University of Michigan Transportation Research Institute, or UMTRI, began tracking the data in October 2007.

Anyway, that's how we wind up with the numbers you see. Or should see. But given a choice of promoting a 28 mile per gallon city-cycle figure, a 32 mpg combined number or the highway-rated 40, well, it's probably no surprise that most (read: "all") car companies flaunt the open-road results. (The exception being hybrids, which typically do better in stop-and-go driving that recharges their batteries.)

"We'd like to advertise the figures closest to what an owner should get... but if we did that we'd be at a competitive disadvantage."

And that's where the debate that could land Hyundai in hot water comes in. And it's not alone.

"We'd like to advertise the combined numbers because those are the figures closest to what an owner should get day-to-day," said an official with a major Japanese competitor who asked not to be identified by name, "but if we did that we'd be at a competitive disadvantage."

That's also why makers will continue to use whatever the EPA reports even if they know the figure is inflated. In May, California Superior Court Judge Dudley Gray II overturned a small claims court judgment that originally went in favor of Civic Hybrid owner Heather Peters. "Federal regulations control the fuel economy ratings posted on vehicles and advertising claims related to those fuel economy ratings," he wrote in his verdict.

An automaker is legally entitled to lower the figures if it believes they are inaccurate. Fat chance.

In fact, that is not the correct interpretation of the law, according to the EPA itself. The figures the agency quotes are the maximum a maker can use but it is legally entitled to lower the figures if it believes they are inaccurate.

Fat chance. Unless someone blinks, or the courts or regulators step in, it's likely you'll continue to see automakers focus on the biggest numbers they can get away with using – putting the rest in the smallest print they also can get away with.


Paul EisensteinPaul A. Eisenstein is Publisher of TheDetroitBureau.com and a 30-year veteran of the automotive beat. His editorials bring his unique perspective and deep understanding of the auto world to Autoblog readers on a regular basis.