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2 In 3 Misunderstand Gas Mileage; Here's Why 1042

Posted by kdawson
from the bad-at-math dept.
thecarchik sends in this piece, which was published last March but remains timely: "OK, so here's a little test: Which saves more gasoline, going from 10 to 20 mpg, or going from 33 to 50 mpg? If you're like most Americans, you picked the second one. But, in fact, that's exactly backwards. Over any given mileage, replacing a 10-mpg vehicle with one that gets 20 mpg saves five times the gasoline that replacing a 33-mpg vehicle with one that gets 50 does. Last summer, Duke University's Fuqua School of Business released a study that shows how much damage comes from using MPG instead of consumption to measure how green a car is. Management professors Richard Larick and Jack Soll's experiments proved that consumers thought fuel consumption was cut at an even rate as mileage increased."
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2 In 3 Misunderstand Gas Mileage; Here's Why

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  • by Tumbleweed (3706) * on Tuesday June 08, 2010 @06:36PM (#32503188)

    News at 11!

    • by Fluffeh (1273756) on Tuesday June 08, 2010 @06:47PM (#32503356)
      Yup, the average person is mathematically still an infant (or has forgotten all they learned and reverted back to infancy).

      What they need to start doing is standardizing how they mark vehicles fuel consumption. Here in Australia, they label most electric appliances with a sticker [energyrating.gov.au] in the shops that shows you just how much energy it consumed compared to other similar alliances. It's not perfect, but it's a start in the right direction, and it has been running for a long time.

      Perhaps they could start doing something like this with cars?
      • Re: (Score:3, Insightful)

        by cibyr (898667)

        Here in Australia, they label most electric appliances with a sticker [energyrating.gov.au] in the shops that shows you just how much energy it consumed compared to other similar alliances. It's not perfect, but it's a start in the right direction, and it has been running for a long time.

        One of the really crazy aspects of this system is the units used. You couldn't expect a normal person to understand "Watts" or "kW", so I've seen air conditioners labelled in "kWh per hour". As in "kiloWatt-hours per hour". I wish I took a photo.

        One of the things we get right is how we label fuel consumption: litres per 100 km. Half the number means you use half as much fuel to drive the same distance. Twice the number means twice as much fuel to drive the same distance.

    • Re: (Score:3, Funny)

      by fishexe (168879)
      But only seven fifths of people have trouble with fractions...
    • by nmg196 (184961) on Tuesday June 08, 2010 @07:13PM (#32503744)

      > 3 people in 2 don't know math

      Wow that's scary. That's nearly half!

      • by zooblethorpe (686757) on Tuesday June 08, 2010 @07:23PM (#32503890)

        Clearly, what we need here is a car analogy!

        Anyone?

        Cheers,

      • by Dragonslicer (991472) on Tuesday June 08, 2010 @07:46PM (#32504214)

        > 3 people in 2 don't know math

        Wow that's scary. That's nearly half!

        Seriously? Are you really that stupid? 3 divided by 2 is 1.5, which isn't even close to 50. What the hell do they teach kids in school these days?

  • Solution? (Score:2, Insightful)

    by aliquis (678370)

    I don't know if changing the units will help much ..

    • Re:Solution? (Score:5, Informative)

      by Tuidjy (321055) on Tuesday June 08, 2010 @06:40PM (#32503256)

      In Europe, or at least every country I've lived in, people measure fuel consumption in Liters-Needed-For-100-kilometers. I think that it works better than the way we are doing it here in the US.

    • Re:Solution? (Score:5, Insightful)

      by selven (1556643) on Tuesday June 08, 2010 @06:40PM (#32503260)

      Yes, changing the units will most definitely help. The units we should change to are the ones we already use here above the border: liters per 100 km. Going from 20 L/100k to 15 L/100k saves just as much as going from 10 L/100k to 5 L/100k. In most people's lives, the distance you need to travel is constant, not the amount of money you have to spend on fuel, so fuel per distance is much more logical anyway.

      • by Anonymous Coward on Tuesday June 08, 2010 @06:54PM (#32503434)

        True, but you're one of those people who want to use the metric system and hate America, so I won't listen to what you say.

        • Re:Solution? (Score:5, Interesting)

          by Ken_g6 (775014) on Tuesday June 08, 2010 @07:54PM (#32504312) Homepage

          So let's use English units (even though England doesn't even use them anymore!)

          There are 128 fluid ounces (oz) in a gallon. So oz/mile (let's call it OPM) is equivalent to gallons/128 miles.

          This also happens to be about half the European value. (5 L/100km == 2.72 OPM == 47 MPG)

      • by Dishevel (1105119) * on Tuesday June 08, 2010 @07:17PM (#32503826)
        No. Here is why. I consider it a stupid tax. Like the lottery. We need more stupid taxes. Down with the stupid.
  • by alexandre (53) * on Tuesday June 08, 2010 @06:36PM (#32503198) Homepage Journal

    I get that the 1st one is a 100% increase while the other is only 50% but you still get a better deal and less pollution by buying the 50 mpg car (if the price is the same).

    So which saves more gasoline? the 2nd one ...

    • Re: (Score:2, Insightful)

      by welcher (850511)
      The point is that the number of miles driven is assumed fixed. Say you drive 100 miles, then in the first case you could potentially save 10 gallons. In the second case, you can save at most 3 gallons.
      • Re: (Score:3, Insightful)

        Car A gets 20 MPG and car B gets 50 MPG and both drive 100 miles. Car A uses 5 gallons of gasoline and Car B uses 2 gallons of gasoline.

        Who gives a care about % savings and if anyone misunderstands what this waste of science research reports if you ultimately understand basic facts about gasoline consumption.

        This is like saying Americans are dumb because they should realize that an SUV/Truck is more efficient than a Toyota Corolla.
      • Re: (Score:3, Informative)

        by hedwards (940851)
        Which is a mistake. Barring the government intervening like WA has, the amount of driving tends to increase as the fuel economy does, meaning that there's a tendency for a very small decrease if any in the fuel consumption. The paradox of efficiency is pretty well established with data.
    • by SleazyRidr (1563649) on Tuesday June 08, 2010 @06:46PM (#32503346)

      There was one comment on TFA which pretty much summed it up for me. Imagine a 2 car family. They have a small car that gets 33mpg for zipping around the city, and a big car that gets 10mpg for more serious work. Would they be better off upgrading the 33mpg car for a 50mpg car, or upgrading the 10mpg car for a 20mpg car. if they upgrade the small car they'll save 1 gallon for every hundred miles it drives, but if they upgrade the big car they'll save 5 gallons for every hundred miles they drive.

      Of course the answer depends on how much each of them is used, upgrade price etc. but the fuel usage is an important piece of information.

    • by nosilA (8112) on Tuesday June 08, 2010 @06:47PM (#32503350)

      Not really. A typical suburban American family has 2 cars - one sedan and one minivan/SUV and may be looking at deciding which one to replace.

      Also, it's not the ratio between the gas mileages - it's the inverse that you have to look at. A car that gets 30 mpg uses 333 gallons for 10,000 miles. A car that gets 40 mpg (a "33% improvement) goes 250 miles - a savings of 88 gallons. A SUV that gets 12 mpg uses 833 gallons but one that gets 15 mpg (a mere "25%" improvement) uses 667 - a savings of 166 gallons.

      If you are replacing one car this year, is it the civic or the Yukon?

    • by betterunixthanunix (980855) on Tuesday June 08, 2010 @06:50PM (#32503376)
      It really depends on the comparison you are making. If you currently have a 10MPG vehicle, and you have a choice between 20MPG and 50MPG, clearly the 50MPG car is the winner. On the other hand, if you have two families, one driving a 33MPG compact, the other driving an old 10MPG station wagon, and you can choose to encourage the first to buy a 50MPG hybrid or encourage the second to buy a 20MPG SUV, which policy should you pursue?

      The point TFA is trying to make is that there are a lot of people out there who need a large vehicle, perhaps because they have a large family, or because they need to transport some sort of equipment around for their work, or whatever. Such vehicles are not going to get 50MPG (at least not with the current state of car manufacturing), but 20MPG is not unreasonable.
      • Re: (Score:3, Insightful)

        by Idiomatick (976696)
        "...a lot of people out there who THINK they need a large vehicle.."

        Really, the biggest savings in America to be had are convincing people to give up their giant trucks and SUVs of all kinds. If you aren't uprooting trees with your truck on a weekly basis you don't need a vehicle where the HOOD is 3m off the ground.

        Exagerated example [mlblogs.com] (The owner is a pitcher, he could probably drag a small stadium around with the thing.)
        • by betterunixthanunix (980855) on Tuesday June 08, 2010 @07:24PM (#32503908)
          Actually, there are millions of people who really do need a larger vehicle. There are plenty of workers who carry their equipment around in vans and pickup trucks, and who could not possibly fit that equipment in a smaller car. I do not just mean people who uproot trees -- anyone who needs to carry a ladder around, or a portable generator, or heavy supplies (pipes, large cable spools), and so forth. You can stand around a typical urban streetcorner and see dozens of vans go by, and a lot of them are owned by small businesses and independent contractors.
          • by dakameleon (1126377) on Tuesday June 08, 2010 @07:43PM (#32504182)

            You don't exactly see your local plumber driving his supplies in an Escalade, though. GP's point is about SUVs etc owned by people who don't use that extra "utility", not actual utility vehicles used for actual utility.

          • Re: (Score:3, Insightful)

            by Dragonslicer (991472)

            Actually, there are millions of people who really do need a larger vehicle.

            Okay, let's say that "millions" is 10 million people. That's approximately 3% of the population. Are SUV's only 3% of the vehicles on the road?

    • by A. B3ttik (1344591) on Tuesday June 08, 2010 @06:50PM (#32503388)
      You fail, hard. The first scenario goes from 0.1 gallons per mile to 0.05 gallons per mile. You're saving 0.05 gallons of gas with that switch. The second scenario goes from 0.03 gallons per mile to 0.02 gallons per mile... or only 0.01 being save. Making the first switch saves 5x as much gas as the second.

      If raw numbers are too hard to understand, imagine going from a two-liter of gas per mile to a coke-can of gas per mile, vs. going from a thimble of gas per mile to half a thimble of gas per mile.
    • by Anonymous Coward on Tuesday June 08, 2010 @06:51PM (#32503400)

      I get that the 1st one is a 100% increase while the other is only 50% but you still get a better deal and less pollution by buying the 50 mpg car (if the price is the same).

      So which saves more gasoline? the 2nd one ...

      I think the point they are making is that a 100 mile trip takes:

      10 gallons for a 10 mpg car
      5 gallons for a 20 mpg car (saves 5 gallons over the 10 mpg car)
      3 gallons for a 33 mpg car
      2 gallons for a 50 mpg car. (saves 1 gallon over the 33 mpg car)

          So, creating incentives to get rid of the lowest mpg car saves the most fuel (five times as much).....as opposed to creating incentives to squeeze more mpg out of already efficient cars.

          That is their point. However, in context, if you create incentives to build 20 mpg cars...you actually create a DISINCENTIVE for people to adopt ultra high 33 or 50) mpg cars....effectively reducing the overall fuel savings.

          Changing units will not help Americans understand math...especially when those units are based on 100% gasoline, and not this Ethanol filled crap they sell us at the pump, which DESTROYS gas mileage.

          That, to me, is the biggest "misunderstanding" in the USA today: The addition of Ethanol significantly destroys fuel mileage, destroys engines and components (requiring new parts constructed of Petroleum), AND it makes the gasoline MORE EXPENSIVE THAN IT WOULD BE WITHOUT THE ETHANOL ADDED (once you factor in all the tax money that is given to Ethanol producers...coming right out of our pockets). In short, ETHANOL DOES NOTHING TO REDUCE OUR PETROLEUM CONSUMPTION OR COSTS....it is simply a giveaway to the powerful corn lobby.....

          Also? The use of Ethanol in gasoline drives up the local and worldwide prices for meat (fed with corn), corn, sugar, milk, and a host of other agricultural products that we eat every day.

          If we want to help reduce our Petroleum consumption, step one is to BAN THE USE OF ETHANOL in GASOLINE.

      • by SEAL (88488) on Tuesday June 08, 2010 @07:29PM (#32503986)

        Addition of 10% ethanol, which is common, does not have a significant impact on gas mileage and it certainly does not "destroy" it. A quick look at Wikipedia on energy density shows that a 90-10 gasoline-ethanol mix produces about 93% of the energy of pure gasoline. Now if you're talking about "flex-fuel" E85, then yeah, you're going to see a noticeable mileage drop. But that is not a common fuel.

        Also ethanol acts as an oxygenate, to make the gas burn more completely and reduce carbon monoxide emissions. Pricewise - prior to oxygenating with ethanol, we were using MTBE anyhow, which has health risks and is a ground water contaminant.

        So your post is mostly over-hyped nonsense. Now in a general sense, should corn be used to produce ethanol? No, and that's a result of the lobby that you mentioned. But they've affected much more than ethanol usage (see: high-fructose corn syrup and how they essentially killed sugarcane production in Hawaii).

        Ethanol production from sugarcane, and to a lesser extent, beets, is much more energy efficient than corn.

        • by MightyYar (622222) on Tuesday June 08, 2010 @09:09PM (#32504984)

          Now in a general sense, should corn be used to produce ethanol? No, and that's a result of the lobby that you mentioned.

          There IS a benefit to using corn (for now). If we encourage ethanol use, then an infrastructure gets built up which can handle ethanol. When the cellulosic ethanol starts to become more widely available, that can replace the corn-based, and the infrastructure will be in place. It is a bet, to be sure, but seems to be much more realistic than the hydrogen proposals out there. Bio-diesel is also a strong contender, but there's already a infrastructure in place for that, and you still need a fuel for the cold-weather states.

        • by electrosoccertux (874415) on Tuesday June 08, 2010 @10:30PM (#32505602)

          90-10 gasoline-ethanol mix produces about 93% of the energy of pure gasoline

          In other words, the last 10% only gives you 3% more power?

    • by AmberBlackCat (829689) on Tuesday June 08, 2010 @07:27PM (#32503954)
      While working Cash For Clunkers in the United States, a lot of people were griping about how (people who got some new pickup truck with a 2mpg increase over told one) were getting the same credit as people who replaced their old car with a new one that gets like 10 or 15mpg more. Maybe if they had known about this, they'd understand.
  • Breaking! mlpm (Score:5, Insightful)

    by drDugan (219551) * on Tuesday June 08, 2010 @06:37PM (#32503212) Homepage

    Breaking: In an astounding fit of partial international cooperation and scientific rationality, the US adopts a mostly metric measure of resource use: the milliliter per mile, or the mlpm

    For example:
    10MPG = 378 mlpm
    20MPG = 189 mlpm
    33MPG = 115 mlpm
    50MPG = 76 mlpm
    90MPG = 42 mlpm

    The unit is linear, easy to understand, with numbers everyone can grasp (40-400 ish), and most important, it slowly creeps the US mind toward the metric system, one small step at a time! What a breakthrough! When the cars fly, we can try for using km, not miles.

    Also, mlpm helps put the idea that gasoline is a great resource, to be used sparingly, by the milliliter, as opposed to "by the gallon" like 7eleven slurpies.

    Sadly, in all seriousness, from TFA "Consumption instead of mileage? Nah. Dumb idea. Never work. [sigh]" Probably have to agree with this. Not because it's a dumb idea, but because Americans with the social and business systems in place have shown repeatedly that they will hold onto current ideas so strongly even in the face of overwhelming and obvious evidence showing them to be wrong. Only the real American idol will effect real change in the US system, the dollar.

  • There are always proposals to replace MPG with gallons per hundred miles or something of that sort, since the latter would show the even decline. That said, it's mostly immaterial; the measurement doesn't match naive expectations, but it's still accurate. Increasing MPG means using less gas, and people aren't likely to think about it in terms more detailed than that.
  • GP100M (Score:5, Insightful)

    by ceeam (39911) on Tuesday June 08, 2010 @06:38PM (#32503222)

    I always thought that measuring it Euro-way - in, for example, gallons per 100 miles - would me more practical and clear.

    • Re: (Score:2, Insightful)

      by Anonymous Coward

      As a European, I ask myself: What the fuck is a mile? Is that some UK and/or USA thing?

      I think most Europeans would be talking about liters per 10 or 100 km.

  • by JesseL (107722) * on Tuesday June 08, 2010 @06:38PM (#32503234) Homepage Journal

    Though it may not be obvious why to someone in a metropolitan area or Europe.

    MPG is the more useful number when you need to figure out what the range of a vehicle is (and perhaps if you'll be able to reach the next station). In the western US it's not unheard of to find yourself 100 miles from any gas station.

  • News at 11.

    An alarming number of folks suck at everyday math, and the worst part is that most don't even realize it. Instead we see them taken in by false sales, and easy to see through misinformation all the time.

    I'm not sure if I should call them fools, or try to sell them something?

  • by farble1670 (803356) on Tuesday June 08, 2010 @06:40PM (#32503266)

    Which saves more gasoline, going from 10 to 20 mpg, or going from 33 to 50 mpg?

    people answer incorrectly because the question is academic. what matters is that people know a higher MPG is better, which i think almost everyone does.

    • by fishexe (168879) on Tuesday June 08, 2010 @07:34PM (#32504052) Homepage

      Which saves more gasoline, going from 10 to 20 mpg, or going from 33 to 50 mpg?

      people answer incorrectly because the question is academic. what matters is that people know a higher MPG is better, which i think almost everyone does.

      I don't think it is academic, and I don't think most Americans find it academic either, because we have finite money. The question is not "is higher better?" but, rather, "how much higher is worth the extra price?" If you're choosing between replacing the family pickup truck or replacing the family sedan, and each of these replacements has a different cost, and each will also save a different amount of gasoline, how do you resolve that choice without knowing how much one option will save relative to the other? If you replace both, which do you pay a higher premium for? If you're willing to pay more for that 17mpg increase for the car than for the 10mpg increase for the truck, you're probably losing money. That's important in the real world.

  • My zoned high school (which I thankfully did not attend) boasted a 30-40% "at or above grade level" scoring rate on the statewide basic algebra exam, at least as recently as 2005. This was considered an improvement over the rate from the 90s, which hovered around 25%. I am not at all surprised that so few people can see through a basic ratios problem like the one given in TFA, even though my high school is (hopefully) not representative of the norm.
  • by 101010_or_0x2A (1001372) on Tuesday June 08, 2010 @06:44PM (#32503306)
    If you go from 10 to 20 mpg, youre still less than the 33 mpg lower limit in the second case, so the second option "saves more gas". If the question is "which is a bigger improvement in fuel economy", then the answer is the first one.
    • Actually, no (Score:4, Insightful)

      by betterunixthanunix (980855) on Tuesday June 08, 2010 @06:54PM (#32503438)
      In fact, the two cases are not interchangeable. Suppose the problem is dressed up a little: you have two cars that you use on a regular basis (this is not negotiable), but only enough money to replace one of them. One car gets 33MPG, and the other gets 10MPG. If you replace the 33MPG car, you can get a 50MPG vehicle. If you replace the 10MPG, you can get a 20MPG vehicle. Which would save more gas, replacing the 33MPG car or the 10MPG car?
    • by bledri (1283728) on Tuesday June 08, 2010 @09:24PM (#32505104)

      Unfortunately, the slashdot summary of the blog paraphrasing of the Duke study failed to spell out the real question which is: Given a two car family that have (and presumably needs) both an SUV and a commuter and both are driven 100 miles per week. Does it save more fuel to replace the 10 mpg SUV with a 20 mpg SUV, or the 33 mpg commuter with a 50 mpg commuter. Most people pick the wrong combination. Here's an example online test: MPG Illusion [mpgquiz.com]

  • mpg vs g for 100m (Score:3, Informative)

    by obarthelemy (160321) on Tuesday June 08, 2010 @07:12PM (#32503724)

    The European way:

    Gazoline need for 100 miles:

    @10 mpg: 10 gallons
    @20 mpg: 5 gallons... saved: 5 gallons, 50%

    @33 mpg: 3 gallons
    @50 mpg: 2 gallons .... saved: 1 gallon, 33%

    kinda more intuitive.

  • by richardkelleher (1184251) on Tuesday June 08, 2010 @07:24PM (#32503898) Homepage
    How much fuel is saved by replacing a vehicle that gets 10 MPG with one that gets 50 MPG?
  • Forget mpg. (Score:5, Funny)

    by gklinger (571901) on Tuesday June 08, 2010 @07:30PM (#32504008)
    My car gets 40 rods to the hogshead and that's the way I likes it.
  • Who cares? (Score:4, Insightful)

    by Eskarel (565631) on Tuesday June 08, 2010 @08:16PM (#32504518)

    Don't get me wrong, if you're looking at replacing a perfectly good car with a new car, knowing how much better that car is is compare to your old car is a very useful thing.

    That said, if you need a new car anyway, it really doesn't matter that the difference between a 10 mpg car and a 20 mpg car is higher than the difference between a 50 mpg car and a 33 mpg car. I 50 mpg car is still the best choice. No you probably shouldn't throw out your 6 month old 33 mpg car to get a 50 mpg car, and no you shouldn't say "I can't afford the 50 mpg car so I'm going to stick with the 10 even though I can afford the 20", but while mpg doesn't scale linearly, 50 is still better than 33.

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