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The mpg confusion

Filed under: — gavin @ 23 September 2008 - (Español) (Français)

What reduces emissions more?
A. Someone swapping their old SUV (which gets 12 miles per gallon) for a hybrid version (18 mpg) or
B. someone upgrading their 25 mpg compact to a new 46 mpg Prius?
(ignore for a minute manufacturing issues or driving habits and assume the miles driven are the same).

The surprising answer (for those who don’t work it out) is A. It’s easy enough to see why this is the case. If the driving distance is 100 miles, then for case A the saving in fuel used (and hence emissions) is 100/12-100/18 = 2.8 gallons, while for B, you have 100/25-100/46 = 1.8 gallons. The confusion arises because people like to think linearly about numbers, not inversely, and so tend to assume that a similar change in mpg has a similar impact on fuel usage. This is not however the case – improvements in efficiency at the low end of the scale are much more useful at reducing emissions. This is actually a very general point – when trying to raise efficiency it is always sensible to start with the least efficient processes.

This confusion got some attention a couple of months ago after a piece that was published in Science by Larrick and Soll. They tested peoples instinctive reactions to changes in mpg numbers and found that people very often got it wrong, leading to less than optimal decisions. They also tested a different way of giving fuel usage information (the number of gallons used per mile), and since this is linear in emissions, people made the correct judgment much more often (it’s worth noting that the standard in most of Europe is already litres per 100 km). Rewritten in those terms, the choices above become:

A. Someone swapping their old SUV (which takes 8.3 gallons to go 100 miles) for a hybrid version (5.6 gallons/100 miles) or
B. someone upgrading their 4 gallons/100 miles compact to a new 2.2 gallons/100 mile Prius?

Much easier, right? The authors of the Science piece are trying hard to get US manufacturers and the EPA to switch over from mpg to this new standard (though they prefer gallons/10,000 miles). It all seems eminently sensible to us.

356 Responses to “The mpg confusion”

  1. 51
    Tele2Dave says:

    re 17

    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).

    Not so stupid – I visited friends over the weekend (by bike and train) My friend gave me a lift to the rail station on his school run. We cycled in on a triple (him on the front, me in the middle and his daughter on the back. Strapped my rucsac on the back on top of the paniers – worked fine for the 10 miles into town. I commute by bike myself 15 miles eachway. I save the car for longer journeys or where I have too much gear for the bike. So far this year I’ve saved 2200 miles by commuting on the bike.

  2. 52
    Herwig Ranner says:

    Your calculation is of course correct, but in general it makes more sense to get the most mileage out of your liter/gallon. Driving SUVs is certainly fun but I suppose 90% of the poeple using them do not need them. Here in Europe we have a growing tendency to of using bicycles and public transport for short distances. A recent study showed that the average distance people travel in their cars is less than 5 kilometers.

    The other bloggers are right of course that it is difficult for the public to compare different fuel standards. But the real message we should get across is: only use your car when you really have to. i guess that could save a huge amount of CO2 emissions, regardless of the mileage per litre of fuel. :)

  3. 53
    mugwump says:

    RE #42:

    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).

    Why is a bigger car wasteful and inefficient?

    And I doubt you want people thinking too deeply about that cost and payback. Most hybrids have a much higher total cost of ownership than their purebred cousins.

  4. 54
    Northern Plains Reader says:

    Doesn’t driver A only reduce their fuel consumption by 33 percent, while driver B reduces their fuel consumption by 45 percent? Sure, driver A reduces their consumption by 2.2 gallons per 100 miles, but they are not reducing their fuel consumption (on a percentage basis) as much.

    It is my opinion that Driver B made more of a sacrafice.

  5. 55
    pete best says:

    I did 90 miles yesterday in a Audi A3 2.0 TDI and got an average of 60.2 MPG. As the average MPG in the USA us 22 MPG and only 33 MPG in Europe there is a lot of scope for improving liquid energy use but a lot of people probably need to start walking again.

  6. 56
    Dean says:

    Another variable that would be considered when building a “more efficient” fleet of cars is the market size. Right now, the SUV market is tumbling. In a few years, increasing the SUV efficiency may only affect a few people whereas increasing the Camry efficiency would make a dramatic impact on overall fuel usage.

    Oh, and I personally like the gallons per 100 miles. I can relate to 100 miles. 10,000 miles is a bit too abstract unless you’re sitting down and looking at yearly expenses (which sadly too few of us do).

  7. 57
    Tom Prugh says:

    Re #17: though your tongue was clearly in cheek, allow me to point out that while cycling (and walking) can easily be superior to vehicular transport in CO2 emissions per passenger mile, it depends on the diet that produces the energy used by the muscles. The Pacific Institute has studied this; see

  8. 58
    Bob North says:

    I like the gallons/mile (or 1000 miles or 10,000 miles) idea. I do own a large SUV for business needs. As gas prices skyrocketed the last year and a half, I took the concept one step further and began thinking in terms of $$/mile. As in the 33-mile trip to the jobsite is going to cost me ~$8. It definitely helped me focus on the necessity of a trip and looking at ways to combine multiple travel needs to reduce my overall expenses.

    Maybe in addition to gallons or liters per mile, efficiency should be posted in $$/year, assuming some standard yearly mileage, e.g., 12,000, and whatever the average price of gasoline is for that quarter.

  9. 59
    Uli says:

    I don’t believe that there is any emission reduction in both cases.
    The cumulative emissions will depend on the extraction of oil, not on the MPG.
    Of course you can drive more miles per gallon (or per $) with a car with a higher MPG value. But this is an economic benefit.
    To reduce the (cumulative) emissions we would need to keep some oil or coal in the ground.

  10. 60
    Ike Solem says:

    It is a mistake to ignore the upstream costs of fuel production, measured as energy input and CO2 released.

    Thus, one should compare the energy demand for gasoline derived from crude oil to that of gasoline derived from tar sands oil to that of ethanol and biodiesel derived from biomass.

    Ignoring the life-cycle analysis is not at all justified, and is highly misleading as well.

  11. 61
    robert says:

    has anyone figured out a way of measuring how much oil (carbon) is used in making a car?

  12. 62
    catman306 says:

    Any gasoline powered vehicle can be easily and cheaply converted to run on compressed natural gas or propane. I’ve had the Jay Storer book for 20 years.

    We could create a network of conversion shops (think muffler shops) across the country. How badly do we want to get away from foreign oil and use domestic natural gas?

  13. 63
    Mark says:

    Well mugwump shows in #53 how little he thinks if that thinking may point out his lifestyle to be wrong in ANY way.

    Muggers, when you’re driving a 3L SUV you’re driving yourself and a ton of extra car that isn’t needed to carry you forward.

    A smaller car is still more than ample for carrying you where you wish to go.

  14. 64
    Dave Rado says:

    Re. Mugwump, #53:

    Most hybrids have a much higher total cost of ownership than their purebred cousins.

    This is disinformation – see here.

  15. 65
    RichardC says:

    53 mugwump claimed, “Most hybrids have a much higher total cost of ownership than their purebred cousins.”

    Totally ludicrous. In 2008, 55% of all hybrids sold were Toyota Priuses. So that single model represents MOST hybrids. A 2005 Prius (private party 40k miles) sells for around $21k, That’s $2300 total depreciation for a car four model years old! Add in gas savings, and it’s a slam dunk. Drive a hybrid, save tons of cash.

    61 Robert, “The British auto industry trade group estimated in their 2006 sustainability report that life cycle CO2 emissions – a strong proxy for energy – are allocated 10% to manufacturing; 85% to use; and 5% to disposal.” Note that the 5% for disposal is overstated, and could be a negative carbon cost, since the results of the disposal is raw steel, etc, which eliminates the need to mine and refine more steel.

  16. 66
    tom delor says:

    Reply to Hank Roberts.

    You wrote: > 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.

    ANSWER: It took us 3 years to succeed to display the momentum of a vehicle and you want believe you cab=n do it with a “bobblehead on you dash board”. I give you a free Moment-o-Meter if you prove me you can do it. Our data are backed up with a money back guarantee.

    Tom Delor, Inventor.

  17. 67
    Maya says:

    #57: for the link to work, remove the trailing period.

  18. 68

    I drive an electric car with a 6KW AC traction motor and 6 220AH 12 Volt gel cell batteries. Even with the DC to AC conversion its still quite efficient and I get speeds up to 55MPH. At $19K costs less to buy than a Prius, and the lead batteries can be completely recycled.

    I have a solar array to charge it partially, though I still connect to grid while at work.

    Perfect for everyday around town…cost to operate per mile, including, cost of grid electricity and battery replacement every 4 years is less than 5 cents per mile.


  19. 69
    Larry Coleman says:

    Mark – #34
    No, it’s not opportunity cost I’m talking about. Do you think drivers are thinking of arriving at their Dilbert jobs earlier so they can get to work earlier?

    Not me. But beyond that, a lot of people driving on the freeways are not commuting. Yet, they are still resistant to slowing down even to the speed limit. They are simply impatient. They need incentives to slow down.

    My point is that not enough thought has been given to the question of what will influence people to change their driving habits. As many posts here have shown, it is a fertile field, and there are better ways than giving mpgs, the knee-jerk response. It has been suggested that some form of gpm, e.g., would be better. I think so. Maybe dollars saved per gallon. But not what they are being paid per hour to slow down because the wage is too small. People might be moved by $50/hr, but not by $9/hr. Who is motivated by minimum wage?

    Others have suggested to me that dollars saved per 100 miles would be more meaningful because it is how much will he save on a specific trip that matters to the driver. It would be relatively easy to scale up or down from 100 miles, easier than figuring out the trip savings from an hourly “wage” which is a two-step calculation.

    Or, knowing that people will drive 5 miles out of their way to get save 2 cents/gal, perhaps the effective reduction in cost of a gallon of gas would be persuasive. I don’t know. I do know that a lot of people are driving with no apparent consideration of the effect on mileage.

    I have tried driving the speed limit on recent trips of 3500 miles (RT) and 2000 miles. This is now possible as trucks have mostly slowed to the speed limit or just below (at least in the center of the country where I was driving – the Mississipi R to Arizona). So they have discovered the savings in lower speeds. It was relaxing to settle in the righthand lane with the trucks and let others jockey around each other and the trucks.

    And yes, Mark, I wore incontinence pull-ups as you suggest I should. I recently had prostate surgery and am still on the road back.

  20. 70
    Jim Eager says:

    Re Ike Solem @41: “Frugal dependence on fossil fuels just won’t do it. The only option is to cut out fossil fuels entirely….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.”

    Ike, unfortunately, for the time being we’re stuck with the infrastructure we have, and one can not currently buy a fossil fuel-free car. Until one can, the Prius is an interim step that at least uses less fossil fuel.

    Captcha: warning send

  21. 71
    Ike Solem says:

    Jim Eager, I would instead recommend holding off on the purchase of any new car whatsoever until the electric and added-range electrics (i.e. an electric with a internal combustion engine for charging the battery) are available.

    Second, consider the fact that tar sand crude oil generates around 35% more CO2 emissions per gallon of gasoline than does conventional crude.

    However, it does appear that a few of our politicians are aware of that issue:

    The U.S. Energy Independence and Security Act passed last December, without a fuss on this side of the border.

    Yet Section 526 of the 822-page piece of legislation should have set Canadian alarm bells ringing. The section forbids any federal agency — such as the Defense Department or the U.S. Postal Service — from buying “synthetic” fuel from non-conventional sources for any “mobility-related” uses.

    The section was authored by Congressman Henry Waxman, a California Democrat, and chair of the House of Representatives committee on oversight and government reform.

    In a letter to the U.S. Department of Defense, Waxman made the law’s intent clear:

    “This provision ensures that federal agencies are not spending taxpayer dollars on new fuel sources that will exacerbate global warming,” Waxman wrote. “This provision is also applicable to fuel derived from tar sands, which also produce signficantly higher greenhouse gas emissions than are produced by comparable fuel from conventional petroleum sources.”

    Edmonton Journal, Canada, Sept 16 2008

    Such laws should be extended to ban the import of tar sand oil to the United States, period.

  22. 72
    dhogaza says:

    I would instead recommend holding off on the purchase of any new car whatsoever until the electric and added-range electrics (i.e. an electric with a internal combustion engine for charging the battery) are available.

    That’s what I’m doing, trying to nurse my 1990 Acura to at least 275K miles before replacing it with some form of plug-in/internal combustion engine combination.

  23. 73
  24. 74
    Mike Donald says:

    What’s best? Swapping your SUV for the prius! C! Or maybe not. Steve Koonin – Chief Scientist BP claims that US car engine efficiency went up 23% in the decade 1990-2001. Americans responded by buying heavier vehicles and driving more. Result – more fuel burnt.

    Plenty of food for thought in this clip.

    OK – public transport D or bike E.

  25. 75

    RE #71 & “tar sand crude oil generates around 35% more CO2 emissions per gallon of gasoline than does conventional crude”…

    I was wondering if either the tar sand crude or perhaps some types of biofuels might actually entail more energy (measured in calories or BTUs) in their production than the energy (calories or BTUs) gained from them. If such endeavors are being heavily subsidized, it’s possible that could happen, and people would be subsidizing boondoogles, not to mention grossly harming the environment.

    Of course, ALL energy input in the process of production would have to be accounted (including workers driving to work and eating), not only the more obvious and direct energy used.

    I know this sounds preposterous, but, well, it could conceivably happen.

  26. 76
    Hank Roberts says:

    > Our data are backed up with a money back guarantee.
    > Tom Delor, Inventor.

    Yeah? I’d like to see your data and your analysis. Where can we look at the data and the analysis?

    I’d like to see exactly what is in this data that you say is backed up by a money back guarantee.

  27. 77
    David B. Benson says:

    According to an IEA paper, in 2005 CE the world produced 5.9 billion tonnes of coal, two-thirds of that for electric power production.

    That’s a lot of CO2 every year.

  28. 78
    Mark says:

    Larry, #69.

    So how is “wasting” 5 minutes a day in traveling to work costing them anything? The work schedule isn’t 100% full and 5 minutes out of a 10 hour day is 0.83%. The work schedule isn’t timed to achieve 100% efficiency. They cannot “sell” 5 minutes of their time for ANY amount.

    So how, in any sense of the word “earn”, would they lose any money by taking five minutes longer to get to work at their hourly base rate? Or even minimum wage?

  29. 79
    Andy Simpson says:

    Re #42

    This is an important thing to get right if you want to dislodge mpg.

    I understand your motivation for using gallons per 10,000 miles, but I think that gallons/100 miles is a far easier figure for average drivers to comprehend (and slightly easier to calculate).

    Most drivers probably (IMHO) don’t keep a close tab on how far they drive in a year, but they are aware of how far any of their regular round trips are (20 miles, 50 miles etc) and the gallons/100 miles figure is on the same scale. They can easily figure out what their existing gallons/100 miles figure is, which is important when they come to compare with the efficiency of a new vehicle.

    Determining gallons/10,000 miles sounds like too much math[s].

    Test it out, it would be a shame to not displace the mpg metric just because you picked a big number.


  30. 80
    Lowlander says:

    Urs Neu #50

    Thank you for yor clarification, it puts clear solid figures to my vague statements. However I feel that:

    “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.”

    Is not an honest comparison, firstly because it is not fair to compare unfiltered diesel emissions with petrol emissions submitted to catalytic filtering process. Comparisons must be like with like in order to be valid. And would even challenge you to find automobile markets where the regulator (introduction of such devices is never a result of a “free market”) imposes catalysts in petrol without imposing filters in diesel.
    Comparing like with like, the total amount of toxic polutants is equivelant in both engines, with the difference that petrol emits mostly small particulates and diesel emits mostly large particulates, these will have impacts different points of your respiratory organs but remain nevertheless toxic and carcnogenic, in other words, different flies…

  31. 81
    Jim Eager says:

    Re Ike Solem @71: I would instead recommend holding off on the purchase of any new car whatsoever until the electric and added-range electrics (i.e. an electric with a internal combustion engine for charging the battery) are available.”

    Ike, I would agree with your recommendation if I were thinking about replacing a vehicle and there was no compelling reason that I had to buy sooner, but we bought our Prius a year and a half ago to replace a 10 year old car with 200k on it and doubled our mpg, and I have absolutely no regrets.

    As for thinking about gasoline source, how exactly is a consumer to know where the source crude came from when they pull up to the pump?

  32. 82
    Larry Coleman says:

    Mark #78
    Either I am doing a lousy job of explaining what I mean, or you are not paying attention, Mark.

    Who said anything about the driver “wasting” time. You did, not me. It’s your term, not mine.

    The sense in which I am using “earn” is the ordinary, garden variety sense in which you get a return for the investment of your time. Just like in most everyday situations, the time spent in earning that money is not, repeat NOT, in competition with other ways you might spend that time, unless as you point out the boss is unusually time-on-job conscious.

    No, the sense of “earn” here is the same as getting a return for clipping coupons and redeeming them at the grocery. It is not in competition with other ways of earning money so there is no opportunity cost…nor is there any OC in driving more slowly (ordinarily: but if it would make you late for an appointment with the President, all bets are off). But again, Mark, most driving does not even involve commuting, so can we quit talking about arriving five minutes late to work? By driving more slowly, no matter the destination a driver saves money, which is indistinguishable from earning money (except no taxes!) for the extra time spent on the road. That’s it.

    Once again, the real question is what would motivate drivers to slow down. I would love to hear your thoughts on THAT.

  33. 83
    Lab Lemming says:

    If congress is mandating efficiency standards, they could easily also require all cars to have fuel use monitors. Our European turbo diesel has one, and we generally ‘video game’ it to try to stay under 6 l/100k (39 mpg) in town and 5 l/100k (47 mpg) on the road.

    Obviously liters aren’t directly comparable, since diesel has both a higher specific gravity and a slightly higher C-H ratio.

  34. 84
    Prof. Bleen says:

    The same point was made on a while back, in an article attempting to defend the “need” for huge SUVs. My reaction is that if someone who is concerned about emissions feels a “need” for an unnecessary, overpriced status symbol like the Chevy Tahoe, they’d be much better off buying something like diamond jewelry (fair-trade, of course), which emits no carbon dioxide at all when kept away from very hot flames.

  35. 85
    Chris Dudley says:

    Gavin in #22:

    Dean (#56) makes the crucial point. It is really the ubiquity of the low efficiency vehicles that make them a better target for first improvements. There are military reasons to improve the fuel efficiency of the Bradley Fighting Vehicle so that supply line needs are reduced, but there is not a big CO2 emissions urgency even though they burn more fuel than an SUV.
    The fighting vehicles are rare so they can’t contribute much.

    If SUVs become rare, then we want to look elsewhere. Ultimately though, we need a way to leave carbon in the ground. Shifting off of carbon entirely is more important and it is encouraging that one of the car manufacturers is planning to introduce a plug in minivan soon:

  36. 86
    matt says:

    I think the best way to educate the consumer would be a meter on the dash that showed $ of gas used that day for the first few seconds the car was on, followed by a trip cost that measured the cost of gasoline used since the car had been started. When the car pulls into the gas station, the prices are downloaded to the car via bluetooth (which is already in many new cars).

    Most people see fractions, energystar ratings, etc, and just tune out. They don’t want to be bothered with these things.

  37. 87
    Nigel Williams says:

    We are dealing here with a threat that is gradual and a long way off compared with our Fight or Flight response. So it has to ba a very solid wall folk need to come up against to change driver behaviour. Speed limiters will make people slow down, like Lab Lemming probably has on his euro diesel, and we have on our Citroen C4. Set (using a transponder) the limiter at the city limit to 30 kph, and on the open road to 80 kph and the country would immediately meet its savings target, and crank it down as things get worse. Draconian, maybe, but the alternative is to go without.

    Good to see this discussion happening, and for most of us non-USA types its faintly amusing really, as we’ve had this ‘confusion’ resolved some decades ago! But feel free to catch up anytime! :)

  38. 88

    I understand why lifecycle analysis wasn’t included because this article is making a simple point. But since since there is a lot of disinformation out there, some repeated here, an article on this topic would be good. In particular, I find it boggling that people are gullible enough to believe that engineers with a sharp environmental and energy-saving focus would neglect to do lifecycle analysis. It’s a whole lot more likely that engineers without either focus would neglect to do this.

    In the meantime the WikiPedia page on Net Energy Gain may interest some though it needs some work at time of writing.

  39. 89
    Mark says:

    Larry, 82. No, the attempt to say “your five minutes spent extra is less than the minimum wage” only makes sense when you’re trying to show that they are wasting this time.

    If you’re thinking about the money you could make, then you can’t sell your time in five minutes.

    If you mean that the time could be spent in something else, well, the best way of getting time back isn’t driving faster to work. Instead of driving forty minutes fast, get a job that’s closer. You could save forty minutes a day.

    Basically, I don’t understand why you are trying to work out the “wage” of driving slower.

  40. 90
    Mark says:

    Further Larry.

    Why compare it to the earnings of “cutting coupons”? Cutting coupons isn’t “a job”. Anything you earn is because you bought the product. Cutting out 150,000 coupons for 10p off “feminine products” will save a single man exactly nil pounds. If they wanted to spend their time playing games or on their hobby then they don’t think “this will cost me $150 for the evening!!!” nor even “I could be saving money by cutting coupons for 25p off a pot of jam!!!”.

    Your “point” has nothing to say about why you aren’t saving money by driving slower to work each day. Nothing relevant anyway.

  41. 91

    mugwump writes:

    Why is a bigger car wasteful and inefficient?

    1. Kinetic energy is:

    Ek = (1/2) m v^2

    where m is mass and v velocity. To accelerate a car to a given speed that masses twice as much, you need twice as much energy.

    2. Air drag is:

    D = (1/2) rho A v^2 Cd

    where rho is density of the medium, A cross-sectional area, v velocity, and Cd the coefficient of drag, which varies with shape. Other things being equal, a car with twice as much cross-sectional area will exert twice the drag force, requiring twice the energy to overcome the drag force.

  42. 92
    Bruce Tabor says:

    In Australia we use litres per 100km along with the rest of the metric system. We changed from the old Imperial units in the early 1970s.

    Why wont the US make the change? Come on in the waters fine! And life is so much easier and more logical.

  43. 93
    Larry Coleman says:

    Geez! I’m not talking about driving to work.

    You don’t get it. No one else is interested. I give up.

  44. 94
    Rod B says:

    Ike (71), what is “synthetic” fuel that Waxman prohibited from imports? Oil from tar sands? Refined gasoline from oil from tar sands? Did the referenced section ban such from only Canada, or did it ban such imports from anywhere?

  45. 95
    Ed Beroset says:

    The idea mentioned about putting mpg (or other measure) display on a dashboard has been recently made in one of the car magazines I read recently (Automobile? Car and Driver? I’m afraid I don’t recall.) But his point was that Prius drivers tend to pay attention to it because it’s understandable and it’s displayed, while Hummer drivers have no such display.

    Interestingly, there’s been a similar push in the electric utilities. Most people don’t really have any feedback on how much power they’re using until the bill comes at the end of the month. The new idea is to try to give users of electricity some kind of usable way that they could be more aware of their own usage, and take steps to manage it.

    Ultimately, perhaps, the most useful display for either vehicles or homes might be a $/day (or whatever local currency might be useful) to make it extremely concrete even for those who might not otherwise care much about NOx emissions or kW demand.

  46. 96
    JCH says:

    Just curious, did the used vehicle disappear? At my local most excellent taco stand (seriously, the best tacos on the planet and I am always the only white guy there) I’ve noted a trend. The parking lot is full of Escalades and Hummers. Used SUVs have become so cheap that immigrants are buying them like hotcakes. Last year I decided that since I drive my Honda Pilot so little, around 5000 miles per year, that it was best to just keep it. If I trade it, it’s likely the new owner will drive it a whole lot more. Our other car is a Civic. Throughout our marriage we have always selected places to live that are very close to work (no more than 15 minutes on city streets), and have always had one car that will haul the family on long vacations, and one car that gets high mileage. I know people look down on my SUV, but at the end of those noses there are a lot of people who have racked up a whole bunch more CO2 because of where they’ve chosen to live.

  47. 97
    matt says:

    #84: Prof Bleen The same point was made on a while back, in an article attempting to defend the “need” for huge SUVs.

    The SUV won’t go away. In fact, alt energy is a certain way to increase the proliferation of large cars. The cost for energy has fallen at amazing rates over the last 200 years, even when $150/bbl oil is factored in. There is no reason to expect the cost of energy will not continue to fall at amazing rates. Nuclear, wind, locally generated solar, etc, will all play a role.

    If moving to electric allows me to reduce my operational costs by 80%, and if my monthly energy budget stays the same, you can bet that driving larger and even more luxurious cars is coming. When gas prices rise, they drive less. When energy prices fall, they drive more. When energy costs tumble, they get a new car.

    Build more roads. They will be needed. Increase the sprawl. It will be demanded. In 30 years expect that electric “smart cars” will be able to travel in closely packed caravans traveling at 130 MPH with computers running the show. You can sleep or read while on these super freeways and you’ll only need to drive on the legacy roads.

    Sprawl is limited today by time and energy costs. Those barriers will fall.

  48. 98
    Urs Neu says:

    Re 80 Lowlander

    “And would even challenge you to find automobile markets where the regulator (introduction of such devices is never a result of a “free market”) imposes catalysts in petrol without imposing filters in diesel.”

    This is e.g. the case for Switzerland (and other European countries). Catalysts are mandatory here for about 30 years now, while particle filters still are not. Catalysts are much more common than particle filters, at least in Europe.

    “Comparing like with like, the total amount of toxic polutants is equivelant in both engines”

    This is new to me. A catalyst does not eliminate particles, as far as I know. I am not aware of any reports confirming this. I only have sources giving a factor of 100 to 1000 more for diesel, irrespective of catalysts. There is only one new technology for gasoline motors (direct fuel injection) which produces similar amounts of particles. What are your sources?
    It is well known that diesel soot is very toxic and is also relevant for climate (warming effect).

    I agree for NOx which is about the same for Diesel and Gasoline without catalyst. The problem here is that there is a (very common) technical solution for the gasoline NOx but only first tries for the diesel NOx



  49. 99
    Rich Creager says:

    Collectively, substantial decreases in fuel use could be accomplished pending the replacement of the entire motor vehicle fleet. How about local traffic engineering depts making reducing idling time a priority in all planning. How about a cruise control which maintains throttle setting rather than speed. How about a reevaluation of the need for every overhead roadway light, and outdoor lighting in general for that matter. And on and on. What’s needed is that the issue be taken seriously and addressed simultaneously by all levels of society, from individuals right up through international organizations. Thanks to RC and all others who press the issue.

  50. 100
    Paul says:

    The original post and the whole discussion is not relevant to cutting emissions.

    1. If you buy a car, you are supporting a massive industry that is committed to selling millions of vehicles to millions of people. A few mpg saved here or there is going to be wiped out by the fact that these companies want to sell more and more cars to more and more people across the world.

    2. The primary issue with cars is that in order for them to be used efficiently, every seat in the vehicle has to be filled. But this effectively makes them into a pseudo public transport system where the owner/driver has to schedule journeys around other peoples requirements in order to make sure the emissions per passenger is the optimum minimum. The other consequence of this way of using a car is that far fewer of them would be required.

    What do these two basic facts mean?
    No matter how you view the subject, you can only reduce passenger transport emissions by operating scheduled services that are less convenient.