New EPA Fuel Economy Ratings Are Not The Answer

- by Atul H. Patel, Editor-in-Chief

It seems as though the EPA is trying to get more realistic with its fuel economy ratings by revising how the figures are calculated.  It's admirable that they attempt this, but I'm afraid it won't make much difference in the way we collectively behave with our purchases.  In converting from 2007 fuel economy labels to the 2008 ones, the average vehicle loses around 2-3 mpg (combined).  Unless the person buying the vehicle is good at doing math in her head, it's not going to stop her from buying the vehicle she would have bought if she had only seen the 2007 label.  "It's only 3 mpg" is what will be thought. The phrase "3 mpg is 15% more gas I have to buy," will never be spoken.  So then the conversion to dollars won't happen either.  To those that already own vehicles, realizing that the sticker numbers have gone down may make the buyers feel a little better that they're getting fuel economy closer to "what they're supposed to get".  So there is some positive there, but then it may prevent people from trying to conserve fuel to try to match the sticker ratings.  Also, this new scheme doesn't account for the many people that surpass the fuel economy ratings.  I've done it with nearly every car I've owned, but some people never have.  For examples of people that do this regularly, go to  http://www.cleanmpg.com and see how some people have turned hypermiling into a science.  Part of it is the way the vehicles are tested for fuel economy figures; the other part that accounts for real world fuel economy is the way they are driven.

I don't have scientific proof, but only logic to explain why certain vehicles exceed the fuel economy ratings, while others do much worse.  Heavier vehicles take more energy to move and this disparity compared to lighter vehicles only increases as the rates of acceleration are increased.  So a 3-ton SUV driven with a lead foot will miss the sticker by a higher percentage than a light compact driven with a lead foot.  And at high speeds, tall vehicles don't fare well.  They tend to have large frontal areas which hurt their ability to cut through the air.  As vehicle speed doubles, aerodynamic drag quadruples, (based on scientific formulas).  So if you're bad to begin with, the high speeds have a much worse effect.  Add to that tires that have aggressive off-road oriented treads and you're heading for a career as a part-time gas station attendant whose job responsibility is to fuel your own vehicle. 

One other area that is frequently not looked at is a vehicle's tendency to coast.  This is inconsequential in the real world if you are cruising at a steady speed.  You're going to hold the gas pedal steadily for any vehicle at a steady speed on flat ground.  However, in decelerating, you're going to use a combination of engine braking and braking from your brakes.  When it comes to fuel economy testing, vehicles that engine brake significantly, will require the throttle to be applied longer to maintain the rate of deceleration that the fuel economy cycle calls for.  The test driver must follow the speed versus time profile closely.  So the rating for vehicles that engine brake a lot will seem artificially low on the highway rating.  Contrastingly, those that coast a lot will have artificially high numbers.

Having worked in the field of fuel economy simulation, I know that real vehicles aren't tested on roads for EPA figures.  Rather, a coast-down value from a real car, (time to coast from one speed to another), is "dialed in" as resistance for a vehicle powertrain hooked up to a dynamometer, (basically rollers for the wheels to spin on without the vehicle actually moving).  The test driver follows arbitrary speed versus time routes which have been around for ages and have little relation to the way we drive.  We do more stop and go and higher speeds on the highway than the creators of the cycle ever envisioned.  At least with the 2008 ratings, they're correcting some of the flaws by introducing colder cold starts, more air conditioning usage and higher speeds.

In the end, no matter how "realistic" the sticker ratings are, nothing can make up for the fact that somewhere in the ballpark of 10% to 30% of fuel economy difference is caused by driver behavior.  Perhaps the government should educate the public about ways to conserve fuel with the vehicles they already have.  At least some people would listen and it would be a relatively painless way for us to reduce our oil consumption in a short amount of time.  Here's an idea for something more compelling than an environmental or conservation message.  If the average driver drives 12,000 miles a year at $2.50 per gallon, the difference between getting 20 mpg and 25 mpg could add up to $30,000 in 40 years of driving if the money in the bank earns just 4% interest.  If one were to switch to a vehicle that gets an average of 30 mpg, the amount jumps to nearly $50,000!  Perhaps this will be more compelling than the revised EPA fuel economy labels.  Whatever the message, we should all think a little more before we buy.  Wasteful fuel consumption hurts not only the environment but also your pocketbook.

+ Atul

Comments

[Michael Karesh]

Actually, I think the 2-3 MPG change will make a difference, and not necessarily a good one in the short term. I know I was shocked when I drove a Dodge Avenger R/T recently and it was rated 16/26. Then I remembered the change...

Most consumers won't be aware of the change. They'll just think the new numbers look really bad.

In the long run, though, I suppose they'll be an improvement if only because they're more realistic.

For those interested in the impact of driving style, my site's real-world fuel economy survey is here:

http://www.truedelta.com/fuel_economy.php

It includes questions about driving conditions and driving style.

[Atul]

Michael,

Perhaps you're right that 2-3 mpg will make a difference to some people in the short term, but they will become desensitized to it in a few years. Even so, how many people monitor their fuel economy? TrueDelta contributors who do this are a rare breed. Most people just consider how often they fill up and how much they pay to fill up. I looked through some GM market resarch that supports this phenomena.

As you mention, driving style is the key, the government and people like us need to educate the public more about this. What an easy way to reduce fossil fuel usage and emissions. Proper maintenance is also low hanging fruit.