Qu’est-ce qui réduit le plus les émissions?

Traduction par Véronique Pagé

A. Quelqu’un qui échange son vieux véhicule utilitaire sport (VUS) qui fait 12 miles au gallon (mag) pour une version hybride qui fait 18 mag, ou

B. quelqu’un qui échange sa voiture compacte (25 mag) pour une Prius neuve (46 mag)?

(Ignorons pour l’instant les questions de fabrication ou d’habitudes de conduite et considérons le cas où les distances parcourues sont les mêmes.)

Étonnamment (du moins, si l’on ne fait pas le calcul), la réponse est A. On peut expliquer ceci facilement: si on considère une distance parcourue de 100 miles, l’économie d’essence (et donc la réduction d’émissions) en A est de 100/12-100/18 = 2.8 gallons alors qu’en B elle n’est que de 100/25-100/46 = 1.8 gallons.

Pour la plupart des gens il est plus naturel de raisonner de façon linéaire que de façon inverse; pour cette raison plusieurs croient qu’une modification du mag amène une modification similaire de la consommation d’essence. Ce n’est pas le cas: une amélioration de l’efficacité au bas de l’échelle mag réduit beaucoup plus les émissions qu’une réduction semblable à haut mag. En fait il s’agit d’une observation générale: pour améliorer l’efficacité, il vaut toujours mieux commencer par les processus les moins efficaces.

Il y a quelques mois, cette erreur fréquente se retrouvait sous les projecteurs suite à étude publiée dans Science

par Larrick et Soll. Ils y rapportaient que la plupart des gens interprètent mal une variation du mag, ce qui affecte leur prise de décision. Ils ont aussi testé une manière différente de présenter la consommation d’essence – la quantité d’essence (en gallons) utilisée pour chaque mile parcouru. Comme cette quantité varie linéairement avec les émissions, la plupart des gens ont interprété correctement le lien entre les deux quantités (notons qu’à plusieurs endroits en Europe le standard de mesure pour la consommation d’essence est déjà le litres/100 km). En terme de gallons par miles, les choix de réponse à notre question de départ deviennent:

A. Quelqu’un qui échange son vieux VUS, qui utilise 8,3 gallons d’essence pour parcourir 100 miles, contre une version hybride, qui utilise 5,6 gallons pour faire la même distance, ou

B. quelqu’un qui échange sa voiture compacte (4 gallons /100 miles) pour une Prius neuve (2,2 gallons /100 miles)?

Beaucoup plus clair, non? Les auteurs de l’étude tentent présentement de convertir les fabricants de voitures américains et l’EPA (U.S. Environmental Protection Agency) à ce nouveau standard de mesure (ils privilégient gallons/10 000 miles). Ceci nous semble judicieux.

356 comments on this post.
  1. SecularAnimist:

    Here’s what I think is eminently sensible: my 1991 Ford Festiva which gets 38 MPG in stop-and-go city driving and 48 MPG on the highway (approaching 2 gallons/100 miles), using the technology that was available 18 years ago.

  2. Ethan:

    I note that mileage is quoted in Canada (and I think elsewhere in the world) in liters per 100 km, which makes this much clearer.

    How about the person who gets rid of their old SUV and buys a hybrid compact?

  3. Leonard Evens:

    Of course someone switching from his old (8.3 gallon fir 1oo miles) to either a compact (4 gallons for 1000 miles) or a Prius (2.2 gallons for 100 miles) will do even better. Or, suppose the auto manufacturers produced larger vehicles for those who need the space which could get go 100 miles on 3 gallons.

    In passing, I saw Frank Lutz on The Colbert Report, who was explaining why GM was producing the Volt when he still doesn’t believe in global warming. Lutz came up with the old story about the 30,000 scientists who agreed with him that human activity wasn’t the cause of the warming. Colbert didn’t challenge him on that, which I think was a shame, but he did ask him just whom he expected to buy this new car if global warming was a myth.

  4. Peter Coates:

    People have a hard time comparing inverses, so gallons/10,000 miles is a step in the right direction. But 400 gallons/10,000 miles remains an abstract concept.
    4 gallons/100 miles is a concrete concept. It means something immediate.
    I do not see what the attraction is of gallons/10,000 miles. Is it just a gratuitous rejection of the (familiar to some) litres/100km measure?
    I wanted to use the word “reci…cals” instead of “inverses”, but hte spam filter saw a bad word imbedded in it.

  5. Richard:

    The argument loses some of its weight if we have to ignore manufacturing issues (i.e. the CO2 generated in the manufacture of a new car).

    Going a little off topic… it’s a bit like the solar energy discussions where the the CO2 generated in the manufacture is almost always completely ignored (along with the extra costs associated with regular cleaning required for both solar panels and mirrors)

    [Response: All analyses need to use the full lifecycle in order to be useful for decision making. However, this point is simpler than that. – gavin]

  6. Nash:

    Yes yes, but the absolute amount of fuel required to travel those 100 “miles” still makes for a good anti-SUV argument. So what’s the point of showing that efficiency gains are more for a small improvement in a very inefficient system, rather than for a larger improvement in a very efficient system? Michaelis Menten graphs, saturation curves etc.

  7. Maya:

    How to account for things like PZEV, SULEV, ULEV? Are the emissions from a 15 mpg engine actually double those from a 30 mpg engine? What about the age of the engine? What about gas vs. “clean diesel” vs ethanol blends? I’ve even known someone who ran his pickup on propane, and I have NO idea what the emissions from that are like. What about oxygenating the fuel? What about someone who replaces part of his driving with riding a motorcycle or scooter? What about a vehicle (like the upcoming Volt) that gets some of its power from plugging into the grid? How do you calculate the impact of that?

    I know, I digress somewhat, but as fuel choices get more diverse, the general public probably gets more confused …

    [Response: Emissions are very closely tied to the fuel usage. Different fuels have different emissions per gallon (depending on the molecular structure – i.e. how many carbons, denisty etc.), so you need to be careful comparing mpg from a diesel than from a petrol engine. Hopefully someone knows a good source on this? As for ethanol blends, it all comes down to where the ethanol comes from. If it’s from corn in the US, emissions are basically the same as if it was pure gasoline (due to the fossil fuel use during production), if it’s from sugarcane in Brazil, net emissions are significantly lower. Plug-in hybrids benefit from the more efficient use of fossil fuels in electricity generation even now and so have lower emissions than internal combustion engine cars, and if they get their juice from renewables, emissions would be very low indeed. – gavin]

  8. rpauli:

    What an excellent idea. Totally fresh view for evaluating mileage. Thanks for getting us thinking in that way.

    Of course total energy costs to manufacture that Prius should be considered. So I will keep my old Isuzu Pooper – and just drive it fewer miles. Because that saves all the energy that goes into a new car manufacturing.

    The next measurement consumers need is to know how much energy goes into products and services. Take for instance a cup of coffee. Measure the growing, picking, shipping, roasting, grinding, brewing, containers etc – all are energy intensive. I am sure that Starbucks knows precisely how much energy goes into a typical cup of coffee. I bet it is surprisingly high.

    All products need to show a rating of this energy – we might make a Starbuck the moniker for a standardized energy measurement.

    So any item could be rated by the starbuck standard… or without a brand name – just to think of how many coffee-cup-energy-units are in any item.

    Think of how much better decisions we could make.

  9. RichardC:

    Good post. In a related matter, the exclusion of vehicles “expected” to be used for business from CAFE (Light trucks – all before, now over 8,500 lbs GVWR) is bad policy for the reasons you gave as well as because business vehicles travel far further! Thus, the argument for excluding business-type vehicles from CAFE is backwards. They should have been regulated first. Consider taxis, for example. They should all get absolutely the best mileage possible.

    Ethan, perhaps everyone should get a set amount of gas at normal prices, and as much over that as desired with a $10 a gallon tax tacked on. That might get a few folks to downsize. Too bad it would take record-keeping or ration cards or whatnot. Then again, the planet just *might* be worth the inconvenience… Captcha agrees: to permitting

  10. Samson:

    I think liters per 100 kilometers would be better than gallons per 100 miles (why 10,000 miles?). We from europe have a few problems with miles and gallons ;-)

  11. Richard Harvey:

    Please be advised that we in Quebec and the rest of Canada already use liters/100km. So it’s not only in Europe!

    Richard H.

  12. Chris Dudley:

    The person switching to the Prius is going to be saving a factor of 1.84 on fuel while the other switch only saves a factor of 1.5. If fuel cost is what is bothering you, you are probably already driving the compact and you have more motivation. If we really want to tackle bulk fuel use, we should go to rationing. This works better than price signals when the ability to pay is so broadly spread. It can also make an energy trasition much much less costly: http://mdsolar.blogspot.com/2008/06/oil-is-too-expensive.html

  13. Mark:

    What’s always puzzled me is the “need” for a huge great big car. “So we can drive in comfort with the kids when we go on holiday”.

    So rent a big car.

    Especially in the US when there are so few holidays, they are spent like gold dust, they aren’t going to be highly contested on any one week.

    Rent it.

    Borrow it.

    And have a car appropriate for the normal use. With the *possibility* of sub-optimal use of the smaller car for transporting all the kids.

  14. Mark:

    rpauli, #8.

    Do you know what the most recycled (and most efficiently recyclable) part of a normal car is?

    The batteries.

    The prius batteries WILL be re-used.

    Heck, the reason why electric cars as expensive is because the batteries are expensive. WHO THE HELL is going to throw THAT away???

    Especially when you know that a big current theft is taking the copper lines used for telecoms and selling the copper. DIGGING UP THE COPPER IS WORTH IT!!!

  15. Samson:

    Richard, I didn’t say that. I suppose that there are a lot of countries besides Canada and the EU which use litres per 100 km. As far as I know only the USA uses mpg. From my point of view a change from mpg to gallons per 10,000 miles is only a small step in the right direction (I had to look up the conversion for gallon in litre and mile in km).

  16. Kjartan Bleie:

    Perhaps it is easier to measure the emission of CO2 produced in grams of CO2 per distance. The European Union had a voluntary agreement to reach an average of 120 g/km for all new passenger cars by 2012.

  17. mugwump:

    RE #13 Mark:

    What’s always puzzled me is the “need” for a huge great big car. “So we can drive in comfort with the kids when we go on holiday”.

    I’m with you, man. We got rid of all our cars and cycle everywhere now. Just strap a kid to each thigh, one across the pannier racks and another on my back and we’re away (I only make the wife carry one kid).

    Of course, visiting the relatives on the weekend can be a bit of a chore. By the time we’ve ridden the 135 miles there, it’s almost time to turn around and go home again. But it’s worth it for the warm inner glow I get from knowing our family’s carbon footprint is almost negligible.

  18. Ike Solem:

    Well, there is a better choice – but let’s take the lifecycle approach:

    1. Set up a solar PV manufacturing factory that derives all of its power from solar panels.

    2. You will also need a polysilicon plant to feed high-quality silicon wafers into the solar PV plant, such as this one:

    3. Now, we have ourselves a solar breeder facility. In goes silica ore, out comes finished PV panels, and no fossil fuels are involved in the PV manufacturing process.

    4. Take those solar panels and set them on top of carparks or home garages, or feed the electricity directly into the grid.

    5. Build an electric car manufacturing factory, and surround it with enough solar panels to power the manufacturing process.

    6. Take your electric car, charge it up with your solar panels, and you have a fossil fuel-free transportation system.

    Zero emission transportation. All the elements already exist – they just have to be put together.

    Now, we can port this concept to agriculture systems, which are heavily dependent on fossil fuels – solar / wind powered water pumps, electric farm equipment, even fertilizer.

    Currently, fertilizer is made using natural gas (steam reforming of methane to generate hydrogen to feed into the Haber process) – but with the new advances ( http://www.greencarcongress.com/2008/07/researchers-at.html ), it should be possible to generate that hydrogen directly from water using sunlight; feed the hydrogen into the Haber process (energy expensive, true, but doable), and then you have your ammonia, convert half of that to nitrate, and there you have your ammonium nitrate fertilizer, which currently accounts for about 1/2 of all agricultral fossil fuel use.

    So, now you have your fossil fuel free agricultural system, zero net emissions, with equivalent productivity. Whatever you grow that you don’t use for food can then be fed into biofuel production (as well as biochar production, as a soil amendment, meaning NEGATIVE emissions), and then you have some amount of ethanol, biodiesel, or bio-based hydrocarbon product. This lead us to:

    7. Take your hybrid Prius, fill it up with that zero-emission biofuel, and you have the equivalent of a solar-powered electric car, emission-wise.

    So, those are two routes to zero-sum-emission transportation, as well as route to zero-sum-emission agriculture.

    Here’s a good question, though: how do you transport container-loads of raw materials all around the world without access to cheap fossil fuels? By sail?

    Well, ideally you don’t do that at all. Instead, you only ship high-value goods (laptops, refined chemicals, solar panels) and you eliminate the global trade in raw materials – because it is just too expensive.

    Those are the kinds of approaches that will be needed to get past the Fossil Fuel Age, which will end due to replacement by superior technology, which is also how the Stone Age ended.

    I bet the makers of stone tools were just as upset about their loss of market share to the bronze tools as our fossil fuel CEOs and investors are about their own eventual downfall. Did they also carry out massive PR campaigns in the hopes of holding off the inevitable?

  19. Karen Kohfeld:

    Interesting post. I passed it on to my SUV-loving family members…

    Gavin, I realize that the life-cycle analysis was not the point of this post, but I think it would be a great future post. Do you have access to some good articles on this topic?

    Does the life cycle analysis of a prius vs a hummer actually give the hummer a smaller carbon footprint? (I doubt this, but I’ve seen an article suggesting that it is true). I know I know, not exactly climate science…

  20. Mark Schaffer:

    So Mugwump…

    Did you miss the rest of Mark’s post on renting or borrowing a vehicle when you need more capacity or is your sarcasm of the lightweight variety???

  21. ouini:

    Another confounding factor is that, except for inexpensive staples, people use less when a product becomes more expensive, and use more when the product is cheap. Essentially, people spend more money when they make more money.

    So I suspect the answer isn’t as clear cut as it was stated in the blog post. The answer if a study were done might amaze Gavin. That is, it might not be ‘A’.

    If the driving distance is 100 miles for a person in a 12mph SUV, then the driving distance might drastically increase to 130 miles for a person in a 18mph SUV. If the driving distance is 100 miles for a person in a 25mph car, then the driving distance might only become 110 miles for a person in a 46mph hybrid.

    Then for case A the saving in fuel used is 100/12-130/18 = 1.1 gallons, while for B, you have 100/25-110/46 = 1.6 gallons.

    The confusion arises because people like to think statically about demand, not dynamically, and so tend to assume that a set relationship between change in effective supply (mpg) has identical (or no) impact on change in demand (car usage). This is not however the case – huge drops in cost for a staple that uses a perceived significant portion of income drive up usage more than they do for a huge drop in cost for a relatively cheap staple.


  22. Tony:

    This analysis reminds me of relative risk versus absolute risk in risk assessment. Your analysis is certainly correct but the relative change in gas mileage for the SUV example is 33.7% (2.8/8.3) compared to 45.0% (1.8/4) for the Prius example. In relative terms, the compact-to-Prius change is greater. Did I get that right? There are many different ways to think about this, but the instincts of linear thinkers are correct in terms of environmental outcomes: assuming equivalent CO2 etc. output per gallon of gas burned, the final outcome of the SUV change is two and a half times more damaging to the environment than the outcome for Prius change.

    [Response: I disagree. The issue is the total amount of emissions, not how important the relative improvement is. – gavin]

  23. Oxnardprof:

    I think that this is a good transition to make. The framing of the energy consumption will help consumers make more effective decisions on their fuel use.

    The decision of whether to switch should be separate from when to switch vehicles. If a vehicle is replaced at the end of its service life (or near it), then the issue of energy cost in its manufacture are less important. I would guess that energy costs of production of vehicles is related to the mass of the vehicle.

    I think this concept could be stretched to show the fuel consumption per 100 miles at various speeds. Over the past two weeks, I tried driving on the freeway at 60 mph instead of 65 mph. Traffic conditions allow this easily. I travel 45 miles each way on the freeway, and my fuel consumption in mpg went from 50 to 55.
    (or 2 gallons / 100 miles to 1.8 gallons per hundred miles). The cost in time: about 5 minutes. (I drive a Prius, in case anyone is wondering.)

    In addition, it would be useful to know the energy cost (or relative energy cost) of more consumer items. The EnergyStar program has some severe problems, but it is a start. Energy consumption of other items is usually ignored (computers, for example).

    Finally, I think we need some concept of a level of energy consumption, or carbon footprint (take your measurement) that is acceptable with reference to preventing AGW.

    Measuring carbon footprint is complex – if you have not tried to do this, try it. It is complicated. How do you account for the aspirations and goals of folks – often related to a standard of living measured by wealth?

    One example: if I believe that AGW is real (I do) and I should minimize my carbon footprint (I try) how much air travel can I justify for pleasure and / or business?

    [Response: One of things I’ve noticed with drivers of hybrids is how their driving habits change if they have the mpg numbers on a real time display on the dashboard. That is, they drive to keep the numbers up (like a video game). I’m pretty certain that increasing the use of such displays in all cars would improve overall efficiency without any change in the fleet. – gavin]
    […though it might also increase accidents. I find I’m often looking at the darn screen instead of the road in my Prius…–eric

  24. tom delor:

    Efficient driving is secure, easy and fun!
    A New Fuel Saving Device Can Change the Way We Use Fuel Driving Our Car.
    Using the momentum of your car will reduce your fuel consumption; The U.S. Patent Office issued a Patent for Moment-O-Meter.
    When Tom presented me his work, I was skeptical because it was utterly simple and logical, thus not new. It took thousands of years to put wheels on our luggage because nobody thought about it.

    Clearwater, Fla. (PRWEB) August 20, 2008 — GREEN TECHNOLOGY MFG manufactures the long awaited Moment-O-Meter, a consumer friendly device that helps to reduce fuel consumption (patent # 7,411,140).

    “It may take ten years for car manufacturers to create and redesign higher fuel efficient cars, fifteen years to find and exploit fuel fossil reserves in the US and maybe twenty more years to develop safe nuclear energy providing 50% of our electricity,” said the inventor, Tom Delor.

    It takes only a few seconds to stick Moment-O-Meter to your windshield and plug it in your cigarette lighter to upgrade your car to a fuel efficient car. “Moment-O-Meter was developed and tested during the last three years, and we now manufacture it in Clearwater, Florida,” added Delor, a retired ex-aeronautical engineer who co-invented this device to help his school teacher daughter to save gas. “It all started with my daughter and I’m always looking for a good reason to spend some time in my workshop,” added Delor.
    As Speed-O-Meter indicates the speed of a vehicle, Moment-O-Meter indicates its inherent momentum allowing users to coast by, moving their car effortlessly by force of the inertial mass generated. Green light indicates you can coast, red light indicates you need to use fuel to maintain the car’s speed. It’s like a personal trainer telling you what to do.
    “Every driver can take advantage of their car’s momentum to drastically increase their fuel efficiency if they are shown how,” the inventor said. “You will save 20% to 50% gas the very first time you use it. To make it work for everyone, it had to be simple and visual. Moment-O-Meter is very simple; just react to the device’s lights to save gas. I personally save 50% but my wife saves only 32% … It still depends on the driver’s skills, but improvement is expected as driving efficiently will become second nature,” concluded Delor.
    GREEN TECHNOLOGY MFG, located in Clearwater, Florida, is the developer and manufacturer of this long awaited new instrument for cars. The device uses simple visual cues to allow drivers to take advantage of the moving vehicle’s momentum. It really does not matter if the vehicle uses gas, ethanol, or electricity or if the vehicle is a small or an eighteen wheelers. Retired ex-aeronautical engineer Tom Delor is the co-inventor, and patent attorney John Rizvy from Fort Lauderdale, Florida said: “When Tom presented me his work, I was skeptical because it was utterly simple and logical, thus not new. It took thousands of years to put wheels on our luggage because nobody thought about it.” Comparatively, nobody thought about showing the momentum of a moving vehicle until now, replied Delor. With the energy crisis, necessity became the mother of all inventions and the United States Patent Office by issuing the patent confirmed that Moment-O-Meter is a genuine new invention.
    More information:

  25. oxnardprof:


    RE: Number 19 – Hummer vs Prius. the linked post discusses this illusion that is floated about on the web

  26. David W:

    Instead of changing the car, why don’t we change the town. High density housing in the city, then farms and parkland. No suburbs.
    Would that fit the American dream?

  27. Karen Street:

    I agree that it’s easier for me and others to compare cars in gallons/hundred miles.

    Re the GHG cost of manufacturing, there may be a newer analysis, but I use this one: On the Road in 2020 (pdf)

    Re the cost of flying, there are lots of assumptions around because of different ways of using or ignoring a 1999 report on aviation’s role in global warming [Aviation and the Global Atmosphere] for the Intergovernmental Panel on Climate Change—the effects of flying are much worse than would be predicted by just burning the oil.

    Atmosfair calculates GHG emissions for flying, multiplying the effects of time at high altitude by 2 (IPCC said 2 – 4) and incorporating information about whether the flight was nonstop.

    Life cycle cost of a hummer is a great deal more than for a Prius.

  28. Johnno:

    The embodied energy requirement (not just fuel economy) for replacing the entire fleet will be crucial when things get tougher. As others point out it may be difficult to produce enough metal and glass in a solar economy to even make cars let alone finding energy for propulsion. So far as I’m aware no-one has done a life cycle analysis of the Pickens plan as it affects cars. Under one scenario existing SUVs could get a $2000 conversion to compressed natural gas. Drive those cars for another 10-20 years and that saves a whole lot on replacing them with Priuses with an embodied energy equivalent to say 900 USgall or 3400L of fuel. I’ll omit the calculations.

  29. Francis Massen:

    #3: I could very well be an anthropogenic global warming skeptic and buy a GM Volt. I think driving a noiseless e-car and possibly saving on traditional fuel could be a strong incentive, with no need to push it up with climate considerations. BTW New Scientist (20 Sep.2008) has an interesting comparison showing that plug-in hybrid electrical vehicles (PHEV) will emit about the same 95 g CO2eq/km regardless if the electric power comes from nuclear or renewabels. Greenpeace and others are trying to impose a still stricter 80g/100km maximum here in Europe, what makes me wonder if these enviros will ever be happy with an achievement, or continue to ask for the impossible , regardless of the difficult job of the scientists and engineers who made the first reduction happen.

  30. Larry Coleman:

    Oxnardprof wrote about the improved mileage at lower highway speeds. He notes that it took only 5 minutes longer on his 45 mile commute. Recently, I wondered how much one would “earn” as an hourly wage in terms of the money saved per hour of extra travel time due to the lower speed. For some typical cars I looked up the mpg vs speed graphs, and assumed $4/gal gas. In the end I was kind of disappointed because the hourly “wage” was only $8-9 for a 20 mpg car and less for a 40 mpg vehicle, something like minimum wage. So you save more per hour with the gas guzzler, a fact that is closely – but not obviously – tied to the original question in this post. I was hoping for a higher hourly wage because it could be a strong incentive for people to slow down. In the end I decided that a better way to present the message is to cast it in terms of dollars saved per 100 miles…or maybe in terms of a reduced effective cost of a gallon of gas. People are very sensitive to the latter.

  31. Figen Mekik:

    If hybrid (or eventually all alternative fuel) cars and hybrid commercial airplanes (imagine that!) were made more affordable than the traditional vehicles, I would imagine more people would take that route regardless of how much they understand or care about global climate change.

  32. Geoff Russell:

    #27, the link “On the Road in 2020” is broken.

  33. Ed Davies:

    Miles per gallon: ug! Gallons per hundred miles: a bit less bad. Litres per hundred kilometres: better still. Kilograms per hundred kilometres, best.

    kg/100 km is an improvement because the volume of a given mass of petrol changes (very slightly) with temperature and it’s the mass (not volume) burnt which determines both the energy available and the emissions produced.

    Airliners (747-400s, I believe) flying Hong Kong/London have their fuel chilled before loading to be able to get a larger mass into the fixed volumes of the tanks.

    The UK still mostly uses miles per gallon but l/100 km is used a bit.

  34. Mark:

    Larry, #30.

    That would only be lost OPPORTUNITY cost.

    How much would he earn if he didn’t go for a number one and wore incontinence pants?

    How often would he lose 5 minutes from a productive work day? Would he lose *any* pay over it?

    If he’s salaried, he’d earn exactly nil.

    If he’s on hourly, he has to spend 10 minutes at work. IF anyone is minuting him that closely. Which they aren’t.

  35. tharanga:

    At the risk of swamping people with numbers, I’d like to see no less than three numbers quoted:

    miles/gallon, cost/mile, g CO2/mile.

    energy density, cost efficiency, and carbon intensity are three separate topics, yet all are relevant to the driver.

    This becomes more important as we begin to see a variety of fuels and blends available.

  36. KiwiInOz:

    But, when upgrading to a more fuel efficient car, you tend to sell your old car to someone else. So the effect is actually additive. There are now two cars on the road rather than one, irrespective of whether one is more fuel efficient than the other.

    So really we should be crushing and recycling our old cars, rather than trying to recoup some financial return by selling them on and feeling smug about our new hybrids. :^)

  37. Karen Street:

    On the Road in 2020: http://lfee.mit.edu/public/el00-003.pdf

    Re the Pickens plan, I heard Lee Schipper talk a couple of weeks ago. Compressed natural gas does 10% better than gasoline re GHG emissions, except that the natural gas will come from Indonesia and there will be a lot of leakage if there are a lot of vehicles. Such was reported in a recent bus/train collision in LA.

  38. Oxnardprof:

    Another benefit of reducing driving speed, if all drivers reduced speed, is a reduction in traffic congestion. This was discussed in the NY Times not long ago, but if there is an incident blocking traffic, and highway speeds are reduced, then fewer cars will get caught in the delay, and traffic jams are reduced. Thus reduced highway speeds in urban areas would reduce fuel consumption both by reducing gallons per mile consumed when traffic is flowing, and by reducing the duration and intenstiy of congestion when traffic is blocked.

  39. Lowlander:

    Gavin #7
    “so you need to be careful comparing mpg from a diesel than from a petrol engine. Hopefully someone knows a good source on this?”

    Maybe this can help: http://www.epa.gov/oms/climate/420f05001.htm
    Gasoleum is a heavier oil and therefore has a higher carbon density per litre than gasoline. However, on average a diesel engine tends to be between 30% to 40% more eficient in fuel consumption than its equivelant engine size petrol counterpart, therefore, per km the diesel engine will emit less.
    The caveat here are the new hybrid gasoline engines which dramatically improve petrol fuel consumption, which coupled with the lower carbon density of the fuel make them lower emitters than an equivelant engine size diesel.
    I imagine that if a viable hybrid diesel engine is developed this will outperform the current toyotas and hondas by an equivelant margin of the other conventional engines.

  40. Aaron Lewis:

    I do my best thinking while walking, so I walk to the market almost every day. I like to bicycle for exercise, so many of my “round about town” chores are done on my bicycle. If I have to be at the EPA in SF at 9:00 in the morning, bike/BART is far and away faster considering traffic and parking. My bike will get me to BART, and BART will get me to both airports, so “round about town” includes day trips by plane. (in nice weather)

    My point is the real measure of transportation efficiency is pounds of carbon per task, and for that, even the Prius comes out way down the list.

  41. Ike Solem:

    China and the U.S. have a similar level of net emissions, but China’s population is four times as large.

    If everyone in the U.S. had the same per capita emissions as your average Chinese citizen, we’d reduce our emissions by 75%.

    However, that would only slow the rate of increase in atmospheric CO2 by about 16%.

    Frugal dependence on fossil fuels just won’t do it. The only option is to cut out fossil fuels entirely, starting with coal and heavy crude.

    Anyone who claims otherwise is just ignoring the obvious. The carbon can’t be buried in the ground; you just have to stop burning the stuff.

    If you buy a Prius and reduce your emissions by 50% and congratulate yourself on the good deed you are doing – well, sorry, that’s delusional. All you are really doing is keeping your gasoline bill a bit lower.

  42. Rick Larrick:

    We appreciate people’s interest in this idea.

    As one of the authors, I wanted to answer a question that has come up a few times, which is “why gallons per 10,000 miles?”. In short, we think any measure of GPM would help car buyers recognize gains in efficiency more accurately. Shifting to “gallons per 100 miles” would be a big improvement over MPG.

    But we think there are a few advantages to gallons per 10,000 miles. Our main premise is that we’re trying to help people recognize efficiency gains at the time they’re buying a car—that’s the moment at which a car owner makes a commitment to a given level of efficiency for the next 5 to 10 years. Let’s help buyers see the magnitude of their gas consumption over longer (but realistic) periods of time.

    As a concrete illustration, here are gallons per 10,000 mile levels, at 100 gallon increments, and the corresponding MPG levels (with rounding):

    1000 = 10 MPG
    900 = 11 MPG
    800 = 12.5 MPG
    700 = 14 MPG
    600 = 16.5 MPG
    500 = 20 MPG
    400 = 25 MPG
    300 = 33 MPG
    200 = 50 MPG

    We believe that thinking in terms of gallons per 10,000 miles during the car purchase decision helps in the following ways:

    It is a distance that is close to what many people drive in a year’s time and makes total gas use for a year salient (it directly quantifies the wastefulness of the inefficient cars and helps buyers think about cost and payback).

    The base is round, which makes it (reasonably) easy to scale up or down (and preferable to other large, realistic distances such as 12,000 miles or 15,000 miles).

    And, most importantly, it makes savings in gas between two vehicles large and obvious. For example, the MPG gain from 16 to 20 looks small, as does a gain in gallons per 100 miles from 6 to 5. But stating the improvement as reducing gas use from 600 gallons to 500 gallons is large and clear. That 100 gallon savings is about $400 and a ton of carbon.

    We think having gallons per 10,000 miles on car stickers, at Consumer Reports, and at fueleconomy.gov would reach buyers at the right time in the decision process.

    Following up on a few of the earlier comments:

    More metrics–such as cost/mile and CO2/mile–would be extremely helpful. This reinforces the shortcoming of our current reliance on MPG–MPG isn’t directly useful for knowing gas consumption or its consequences(cost and CO2) without more calculations.

    The ultimate goal, proposed by an earlier commenter, is to have a single meaningful CO2 metric for comparing a range of activities (driving, flying, upgrading an air conditioner, reducing meat consumption, etc.).

  43. The Wonderer:

    I think it would be great to see a ZipCar type concept on a larger scale, and for renting pickup trucks and SUVs rather than just compacts. Or maybe just some community cooperatives. It will become more difficult to borrow one on occasion once all my friends downsize. Daily rentals from large companies are too expensive, and the taxes are ridiculous.

  44. Jim:

    in addition to the comments on #23 – I have a prius in Canada where all the gauges are in liters per 100km and a friend recently bought a new prius from the States so all the gauges are in mpg. It seems to me (maybe just the bias from looking at it for so long) that having an absolute bottom of zero and the linear y axis makes it far easier to discern relative difference in efficiency – filling up the entire top quarter of the guage from 75mpg to 100mpg is only a small change from 3.13 l/100km to 2.35 l/100km (assuming google has done my math correctly… using the correct gallons.)

    Just another small reason to change it.

  45. Hank Roberts:

    > moment-o-meter
    > “… In-house tests CONFIRMED THAT the USE OF moment-o-meter

    I’d like to see your data, and your analysis. Will you provide these?
    It sounds like you’re asking $250 for information I can get with a bobblehead doll on the dashboard.

  46. Richard:

    Perhaps it is time for the United States to get into the 19th Century and go metric. In Australia we measure consumption in Litres/100 km. Makes a lot more sense.

  47. Jim Eager:

    Re ouini @21: “If the driving distance is 100 miles for a person in a 25mph car, then the driving distance might only become 110 miles for a person in a 46mph hybrid.”

    Then again, it might not. Our annual milage went down when we sold our 10 year old Subaru and bought a Prius.

  48. RichardC:

    10 Samson, because 10,000 miles is a year’s worth of driving. I think 1,000 is better, though, since folks usually budget by the month.

    17 mugwump (ahh, an appropriate BS in Humour name) I’m guessing you own TWO vehicles. Your argument fails miserably, even without the rental option.

    19 Karen, the Hummer VS Prius spin assumed that GM’s vehicle would outlast the Toyota by perhaps 3 to 1 (they took the battery guarantee as the date the whole car would fry, yet strangely, didn’t take the Hummer’s guarantee for fry-time, even though GM products fry far faster than Toyotas.), and included tremendous fake recycling costs for the Toyota. (The Prius is built to make recycling easy, and Toyota gives a $200 refund for returning the battery.) The spin doctors then took the development cost for a hybrid system and leveraged it onto the few Priuses that had been built by then. The whole “analysis” was a pack of lies. Turns out 3 year old Prius resells for near its original price while the Hummer loses 54%! Turns out Toyota is making money off the development by spreading it throughout their line and also selling the tech to Nissan.

    21 Ouini, you’re right. That’s why gas prices must be artificially inflated. Another way to do it is a $10 a gallon tax, with all proceeds refunded equally per adult legal resident. Ya don’t burn gas, you get free money. Cool, eh?

    23 Gavin, I agree. I wonder when someone will come out with a video game with that premise. Pick different drivers (Little Old Lady, Eco-nut, Speed Demon), and score based on different parameters. Eric, I doubt displays cause a net increase in accidents. Folks get in the habit of leaving lots of space between themselves and other cars to allow for coasting. And accidents would be more :boinks: than ::BOOMS::.

    30 Larry, add in lives saved, wear and tear, and the fact that cruising to tunes is better than slaving in a cube, and driving a bit slower makes ECOnomic sense. Plus, it’s “found” money (no taxes) and you save time by not pumping gas as often. A chip in the car that communicates with the speed limit signs would save lots of lives and gas. Speed limit is 65? Your car CAN’T go faster and society stops wasting gas on cops. OTOH, plenty of folks adore the rush given by pounding 300 ponies to their limit.

    31 Figen, Airplanes can’t be hybridized (though I guess a 4 engine plane could have two tuned for efficiency and two for power, with the power engines turned off during cruise), but either inclined runways or launching vehicles could reduce the size of engines needed. Some safety reduction would result, and folks have shown an amazingly intolerant view of air-danger when considering their flip attitude towards car-carnage. Cars that increase danger are coveted!

  49. George Marshall:

    Speaking from the UK, another problem with gallons is that the US gallon is only 0.83 of an Imperial (UK) gallon. In the UK, where we still think in mpg, this has led to a widespread belief that US cars are incredibly inefficient and a sense of self righteousness that Euro cars are greatly more efficient. It’s not particularly true.

  50. Urs Neu:

    re 7, 39, diesel-gasoline comparison, other emissions (!)

    1 gallon diesel leads to 15% more CO2 emissions than 1 gallon gasoline.

    diesel engines are about 25% more efficient in fuel use (litres per 100km)

    Thus: if you just compare the litres per 100km of a gasoline and a diesel car, you have to add 15% to the diesel number to get a comparison of CO2 emissions.
    If you focus on a certain type of car, CO2 emissions are about 10% lower (25% less fuel use, 15% more CO2 emissions) for the diesel car.

    But: CO2 is not the only thing! A diesel car without particle filter emits in the order of 100 to 1000 times more particulate matter (which is not a good thing) and about 3 times more NOx (which is a precursor of ozone) than a gasoline car with catalyst.

    Thus: When chosing between diesel and gasoline, do not forget the lungs of the people around and only take the diesel if it is with particle filter.

    These numbers are for the Swiss car fleet, but probably is not very different from other countries (we have no car industry of our own…)