Improving the fuel efficiency of U.S. light vehicles

I recently highlighted grounds for pessimism about the ease with which the U.S. could significantly change our oil consumption habits. Here I highlight some interesting new research by U.C. Davis economics professor Christopher Knittel which offers a more optimistic assessment.

Knittel’s paper notes that although U.S. fuel economy has shown only a modest improvement over the last 30 years, vehicle weight and horsepower have increased substantially. For example, the diagram below shows weight, horsepower, torque, and fuel economy for the Honda Accord since 1980.

Attributes of Honda Accord over time. Top row: weight and horsepower. Bottom row: torque and fuel economy. Source: Knittel (2009).

Knittel argues that manufacturers could produce cars with different combinations of these attributes, and that technological improvement has allowed them to give consumers more of everything. For example, the figure below shows combinations of fuel economy and horsepower offered by different passenger cars. The circles correspond to cars sold in 1980, and the squares to cars sold in 2006. A typical car improved on both dimensions– the production possibilities set has shifted out over time, with consumer preferences opting to take more of the technological improvement in the form of higher horsepower rather than better fuel economy.

Fuel economy versus horsepower for U.S. passenger cars in 1980 and 2006.
Source: Knittel (2009).

Knittel estimated an empirical relationship between fuel economy, horsepower, size, torque, and other characteristics such as whether the vehicle uses automatic transmission, based on a panel data set of different models sold over time, allowing the intercept of this relation also to change over time. That changing intercept is a key magnitude of interest, since it captures the extent of overall technological improvement due to features such as more efficient engines and transmissions. Here is what Knittel concludes about the magnitude of the outward shift over time in the production possibilities set:

if weight, horsepower and torque were held at
their 1980 levels, fuel economy for both passenger cars and light trucks could have increased by nearly
50 percent from 1980 to 2006; this is in stark contrast to the 15 percent by which fuel economy actually


57 thoughts on “Improving the fuel efficiency of U.S. light vehicles

  1. Frank the salesforecaster

    The public voted with their money that more torque/hp was better than increased fuel efficency. The interesting question to me is one pertaining to how fast we can replace the vehicle parc. Given current prices and mpg, going from existing gasoline to new electricity powered vehicles will only save the owner a small percentage of the addition money it would cost to buy a new vehicle.

  2. BH

    My family owned an early 80′s Accord. In terms of size and power, it was much closer to my 2000 Corolla or a Civic (although I think those have gotten larger as well).
    It’s amazing that the Accord has gained 1000 pounds. It’s also amazing that they’re putting a 200+ HP V6 into a mid-sized sedan. An engine like that is less fuel efficient to begin with AND adds weight to the car.

  3. TexFinEcon

    Moved to Texas driving a sporty compact. Last purchase considered lesser fuel consuming sporty compact. However, driving amongst the large pickups, land yacht Yukons and Suburbans, quite a number of Hummers, and the ubiquitous 18 wheelers, I chose an Exterra for higher road vision and more protective mass. Now my choice is contributing to similar size choices by others.

  4. Ronald Calitri

    It would have been useful to weight the range of models weighted by sales before arguing that consumers prefer horsepower over fuel efficiency. By all means keep a bango-zango in the window, it helps when selling zut-puts. Judging from the cluster, the mean path seems about 45 degrees.

  5. Watt D Fjark

    Why has vehicle weight been increasing?
    Air bags (plus necessary electronics), pretensioning seat belts, heated mirrors, stainless steel exhaust systems, traction control/ABS, crumple zones, power everything, AC essentially a standard item (where in 1980 it was an “option”)…
    All these things have benefits, but there is no such thing as a free lunch. Added features means, in many cases, added weight.
    People have voted with their dollars…even now, the well-advertised under $10K base models of some cars are very poor sellers. Manual windows?? Right.
    The first Accord, 1984 I believe, is similar in size to a present-day Civic. Hence Honda brought in the Fit, to slot in under the Civic. Almost every vehicle redesign results in a larger vehicle.
    We like our cars big and well equipped, at least for now.

  6. rj

    1. Get rid of all automatic transmissions, everyone drives a stick unless they’re a pariplegic. Automatic transmissions take energy away from the engine in order for them to operate, they are parasitic. If a person doesn’t know how to drive a stick, he or she shouldn’t have a driver’s license anyway. (can be done…now)
    2. People buy diesels instead of gasoline engine cars. Diesels are more efficient than gasoline, the technology is out there and infrastructure exists for people to drive them instead, and diesel fuel requires less refining. (can be done now)
    3. All extra emissions regulations in California are banned. By enforcing tighter emissions, fuel efficiency goes down. If you want more bang for your buck in terms of fuel efficiency, you want to achieve as much horsepower with the minimum amount of fuel to propel the car, which means you want to combust as much as fuel as possible. However, by combusting more fuel, emissions go up. So current CARB regulations lessen fuel efficiency. (can be done now)
    4. Spinners are banned. These are the things you see on wheels that are attached as accessories by almost entirely African-Americans that when a person is stopped at a stoplight give the impression the wheel is still spinning. What it does though is increase the moment of inertia on the tire, meaning that more energy is required to turn the wheel, meaning that fuel efficiency decreases. (can be done now)

  7. Lyle

    On Watts point #1 the this is true for the traditional automatic but no longer true for the 6 speeds and the Continiously variable automatic. For example a a Nissian Versa with the CVT beats the fuel economy of the same vehicle with a stick.
    The CVT as noted in the paper keeps the engine at a nearly constant rpm by having an infinite number of speeds.
    The modern digital automatic with auto clutch gives the economy of the stick with auto shifting as well. Note that this beats a driver shifting as the shifts are done at the absolute right points, and when combined with 6 speed transmissions makes a difference. (These are available today). t

  8. Cedric Regula

    The first step automakers (excluding hybrid cars) are taking is going to turbocharged 4 bangers. There is supposed to be ultra-lean burn IC engines coming soon.
    Diesel is 35% more efficient than gasoline and 60% of the cars in Europe are diesel now. But refineries crack a percentage of gasoline and diesel, you can’t make 100% diesel fuel.
    Natural gas is an option.
    All electric makes a good city vehicle, but better/cheaper batteries would be welcome.
    Upsizing of passenger vehicles is a major problem, and I view it as a civilian arms race. We got to get back to driving cars, not assault vehicles.

  9. David White

    Actually, some new cars with 6 speed electronically controlled automatic transmissions get better mileage than the same vehicle with a manual.

  10. James

    I am amazed that the engineers who design cars don’t take into account that the more stuff you add to a car, decreases its efficiency. I am sure they are fully aware of what they do to a car affects its efficiency. However, money seems to talk nowadays. As long as customers keep ignoring Peak Oil and pay for all the “stuff” on cars. The engineers will oblige them. When Peak Oil finally starts to rear its head, then it will make people start to become more practical. I, for one, would like a small basic car with no power “stuff” on it and gets good mileage (30+ per gallon. I would only use it to go to work, or to get to places not drivable by bicycle. The rest of the time I would use mass transit, ride my bicycle, or walk. I truly hope that the price of gas goes through the roof and stays there. This will finally make people start to conserve, live within their means, and force lifestyle changes that will have influence on the U.S. to start doing things differently, instead of ignoring the problems and trying desperately to keep living an unsustainable lifestyle.

  11. J

    In response to the last (ridiculous) post:

    1) People are generally bad enough at operating a manual transmission that autos do just as well these days. Look at the EPA estimates for cars with the option and you’ll see.

    2) This is a decent point.

    3) Improve fuel efficiency at the expense of emissions… genius! Also in terms of combustion completion and emissions, I’d check your chemistry as you have it exactly backwards.

    4) The idea that removing spinners from cars, which are probably currently on 1/50th of 1% of cars and only negligibly, if at all, affect efficiency, is the 4th most important feature of a policy improving fuel mileage is simply preposterous. The aside that they are primarily owned by blacks is borderline racist.

  12. Dan Weber

    As a consumer that doesn’t really care about power, I haven’t voted with my dollars at all for higher power vehicles at the expense of less mileage. I don’t even know the horsepower of my current cars my family owns.

  13. Christian

    It’s surprising to me that so many Americans would choose a vehicle in the 200+ hp range considering the relatively low speed limits.
    Living in Germany, I’m doing quite fine with my 10 year old VW Diesel that gets 90 hp and a max speed of 112 mph (I average around 50 mpg). And at least I can at times use that max speed legally although with Diesel around $6.50, I tend to avoid that … mileage drops from 29.4 mpg to 23.5 mpg between 100 mph and 112 mph!
    Personally, I believe the trend in the USA hasn’t been so much towards more horsepower, but heavier cars. Some of that is due to more airbags, more electronics, etc. But I do wonder if it’s really all that necessary.
    It may be convenient, but I suspect that if we see a sustained rise in gas prices again, we might see a pretty rapid shift towards lighter cars again.

  14. Cedric Regula

    Drag coefficient is another problem besides just weight and horsepower. It doesn’t have anything to do with handicapping beauty contests in San Francisco, but indicates that if you try and power something down the freeway with the frontal area of the Santa Maria, it takes more horsepower.
    The drag force goes up at the square of velocity, and becomes a big factor at freeway speeds.
    So big trucks and SUVs brought us another factor in poor national fuel efficiency.

  15. sfbicyclist

    James is on he right track. We would be able to greatly reduce transportation fuel use and the obesity problem just by going low tech. Walking, cycling, transit are all feasible now for large portions of our population. Even many suburbs are workable if people are willing to cycle short 5 mile distances. It requires a cultural shift not an technical solution. Of course, as is clear of this site it is unclear how the consumption driver of the economy is going to work when we stop wasting our money on cars.

  16. Steven Kopits

    I think people are sensitive to their budget constraints. Thus, if people are used to paying $30 to fill their car, they continue to be willing to pay that. If their cars becomes more efficient, they will prefer to take more features and leave the budget constraint, the $30 per fill up, essentially unchanged.
    If that $30 rises to $50, then a series of interesting questions arise. How does the consumer respond? Will they maintain consumption and pay more and reduce savings or incur debt? Will they maintain consumption and reduce some other item of their consumption portfolio? Or will they reduce fuel consumption, either tactically (conserve) or strategically (buy a more efficient vehicle)?
    Prior to the recession, the statistics suggest that US consumers accepted higher prices and reduced savings or debt.
    During the recession, consumers reduced consumption of oil, as well as other items.
    In the recovery, given relatively high oil prices, consumers appear unwilling to increase consumption of oil…perhaps we’re seeing greater elasticity in oil demand, and that’s why oil prices seem stuck around $80. When prices exceed that threshold, consumers in the advanced economies refuse to fight for their share.
    And we may be seeing greater efficiency as consumers buy higher mileage vehicles. So increased efficiency may be something specifically associated with recovery from a recession.
    Don’t really know.

  17. don

    TexFinEcon has it right. It is the arm’s race on the highway that has resulted in the fad for big vehicles in the U.S. A good example is parent’s buying their newly-driving teenage kids SUV’s for ‘safety.’ (Yes, my family reacted to the incentives in the predictable manner. Just looking back on our small children in the backseat of a light, delightful-to-drive Camry while driving through a sea of behemouths was enough.) Ms. Summers has done some good work on this topic. The net effect of the fad has been to increase traffic deaths compared with what they would have been without the SUV’s (including pedestrians, but not small children backed over in dreiveways, as these are not ‘traffic’ accidents.) It is, quite simply, outrageous.
    Since 1970, population has increased from about 200m to about 300m, whereas vehicle miles have increased three-fold. With no imagination and the worst tendencies, we see the results of allowing people to ‘vote with their dollars’ with no external guidance as regards the total social costs of their choices (pollution, congestion, climate). We need Pigou taxes so people cna see and be encouraged to pay the true social cost of theri choices. Europe is quite a bit ahead of us on this, which is why Christian pays so much for his fuel.

  18. Doc at the Radar Station

    “Personally, I believe the trend in the USA hasn’t been so much towards more horsepower, but heavier cars. Some of that is due to more airbags, more electronics, etc. But I do wonder if it’s really all that necessary. ”
    This is true. Engineers have been able to squeeze a lot more horsepower from the same sized engine-making it far more efficient. I think the heavier vehicle trend is a combination of a lot of logical factors: 1) Cheap and declining gas prices in the 80s and 90s, 2) People have more stuff that they want to haul around, 3) CAFE requirements got circumvented with SUV’s, 4) Artificially low interest rate environment encouraging financing of heavier and more expensive vehicles., etc. I disagree with the idea of power equipment and comfort options contributing significantly to declining fuel economy. It’s primarily gross weight of the vehicle, period. I recall my parent’s fully optioned New Yorker in the mid 80s getting nearly 30mpg (with a turbocharged 4 cylinder engine).

  19. Cedric Regula

    If you add up the weight of some power window motors, door lock actuators, and an aluminum air conditioning compressor, and even throw in the mpg player, like sfbicycle says, it probably weighs far less than the big butt that gets in the car and drives it.
    And when I bought my new car in AZ (after researching cars thoroughly before setting foot on a car lot)the first question I asked was “how good does the air conditioning work?”
    The salesman said “Great! And it may even save your life someday!”
    So I don’t think we need to drive econo-boxes to get good mileage. I do see a whole lot of very large vehicles on the road with only one occupant, however. As far as consumer behavior/preferences go, I thought of one easy change. Buy a small car. The few times you may need a large SUV or truck, rent it for the occasion!

  20. mulp

    The weigh increase is amazing given the major reduction in component weight. Car for car, a 1970s car would weigh probably close to twice as much as the same car in 2000 design. Frame plus shell replaced by unibody. Steel bumpers replaced by plastic. cast iron block replaced by alloy block. Heavy DC generator replaced light weight alternators. Component by component, the weigh has been significantly reduced.
    My guess is power windows are a weight reduction over the handle crank and its levers and gearing. A/C improves fuel economy on the highway from reduced drag, so the weight of the A/C reduces the weight of body trim and window complexity to offset window drag cost.
    My guess a big reason for the bigger vehicles is the same as the bigger burgers, bigger portions, bigger everything. Lack of satisfaction drives the quest for more. Driving in the US doesn’t have the joy of fifty years ago, the joy of the open road and scenic territory, or the community on the road – people talked and shouted and had fun within and between cars it was recreation. Today, driving is work nearly all the time.
    So, driving alone for hours in a car makes the car a home, and people want cars to have the comfort of home.
    I started hating cars about two decades ago. I resented the fact I had to have one and spend so much time in one. It wasn’t like this when I was a kid. When a family had one car.

  21. wally

    horsepower, per se, doesn’t have a lot to do with mileage ratings. If you check listings in a magazine like Consumer Reports, for example, you’ll see little difference in going from a 4 cyl to a 6 cyl in any given car. The load the engine needs to overcome (weight during acceleration, air and mechanical resistance in steady-state driving) are the issues.

  22. Cedric Regula

    Engines produce the horsepower that the load requires. Load components are:
    2)Air resistance proportional to the square of velocity.
    3) Drive train friction and tire rolling resistance proportional to the velocity.
    Gasoline IC engines have a narrow speed range over which they get their peak efficiency of 25% (pretty crappy) and efficiency drops off rather dramatically outside this range. That is why a 6 speed or CVT transmission can improve mileage over a manual transmission by shifting so the engine stays in its peak efficiency band.
    Then GM did develop 8 cylinder engines that would shut off 4 cylinders under light load and improve mileage a little bit. But going with a turbo 4 cylinder saves significant engine weight and internal friction, while boosting power when needed.
    They say better tires are coming which reduce rolling resistance.
    But the low hanging fruit is still weight and drag coefficient.
    Then an all electric motor and electronic control is 75% efficient. This is why you can come out ahead in cost even though electricity cost per BTU is much higher than gasoline. But the battery packs are costing upwards of $10K, which could use some improvement.

  23. Sasparilla

    The weight increase is easy to understand. While air bags ect. added some – the big increase is because our cars have gotten much bigger. And we started buying big heavy SUV’s.
    The 2006-2010 Civic is as big as a 2000 Accord. A Corolla now is as big as a Camry from 10 years ago. An SUV is even heavier than a similar size car. For the last decade and a half every new version of a vehicle model resulted in a size increase (with associated weight increase). We bought all these big heavy SUV’s.
    Until 2007-2008, there wasn’t an economic penalty for this behavior in the US. In 2007-2008 as the price of oil approached and exceeded $4 gallon in the US, sales of SUV’s and large vehicles in the US went off a cliff. Dealers could not get small efficient cars in fast enough. There were newspaper articles talking to dealers about people trading in Tahoe’s for Corolla’s. Once the economy crashed, oil demand was destroyed and its price cratered, but its coming back up already.
    This is how you get people to have smaller/efficient vehicles, let the price of oil get back up (its through $3 gallon, should be approaching $4 gallon summer 2011) and people will buy more small efficient vehicles again. No need for a tax, world crude oil production plateaued since 2005 – 2008 and the market is taking care of things.

  24. GNP

    TexFinEcon: We followed the same reasoning a few years ago and continue to drive a gas-guzzling ’93 Nissan Pathfinder, the older version of your Nissan Xterra. Among other factors, I want to be high enough so I can see people juggle cell phones, cigarettes and make-up.

    I have been increasing the portfolio’s exposure to overseas oil companies predicated on the assumption that benchmark oil prices stay over US$60/b until early 2011. Christopher Knittel’s research and the ensuing discussion confirm my bullish bias. I’m glad to see that wide consumer choice remains a priority for educated American liberals, at least in this small sample. I’m particularly happy about the support implied for emission regulations.

    Thank you.

  25. GK

    The Civic of today has almost the same weight and volume as the Accord of 1980.
    Of course, the Civic of today has much better fuel economy.
    At a 20 mpg level, Horsepower has increased 3x.
    The problem is, size is increasing, and I am of the belief that oil will never get above $120/barrel for any length of time, since demand destruction happens, and alternatives like plug-in hybrids, cellulose ethanol, etc. are arriving.
    While I am normally a low-tax, small government zealot, a tax on all cars above a certain weight would be a net positive. Less carnage in accidents, less wear and tear on roads, less tire wear, less pollution.
    A progressive tax :
    Better than 40 mpg gets a REBATE of $1000
    30-40 mpg : no tax
    20-30mpg : $300/year
    under 20 mpg : $600/year.

  26. GK

    People are buying bigger and bigger tanks for the highway for ‘safety’ reasons.
    But the biggest safety increase for the least money, of course, is to wear a light, strong, wide-field helmet while driving.
    Of the 40,000 deaths and 2 million serious injuries a year, about 80% of these would be greatly reduced with just a tiny helmet.
    In a crash between an SUV with no helmet and a Civic where the driver is wearing a helmet, the Civic driver’s injuries will still be less severe.
    Of course, none of us do it, because it would ‘look funny’.

  27. grooft

    The consumer choices were narrowed in the cheap gas era. Almost all the “wagons” disappeared, replaced by the SUV. The Honda Civic wagon, gone. The Accord wagon; gone by 2000. Camry wagon, gone.
    Only Subaru (and the expensive Euro imports, Volvo, Saab, VW, Audi) kept the wagons in the US product line. And all of them made significant “improvements” in horsepower with resulting loss of MPG.
    The wagons turned into SUVs — the Honda CRV or the Element for the sports minded; the RAV4. Subaru upsized the Legacy to the Forrester.
    Now the Honda Fit is the (size equivalent) of the Civic circa 1990.

  28. GK

    200 hp should be enough for anyone.
    Many 30 mpg options exist at 200 hp.
    I am in favor of a heavy-vehicle tax/light vehicle rebate. It would save money in many other ways. It costs $1-$10 million per mile to redo a road.
    Oil is now two-thirds of the US trade deficit. Reducing oil consumption by just a little will bring our trade deficit much closer to balance.

  29. GK

    No need for a tax, world crude oil production plateaued since 2005 – 2008 and the market is taking care of things.
    I don’t think so. It will be extremely hard for oil to stay about $120 for any length of time.
    India/China consumption per capita will still be lower than Europe even 20 years from now.
    Oil discovery technologies are unlocking billions of barrels that could not have been recovered before.
    $40 is more likely than $120.

  30. GK

    The rise in US obesity since 1980 means that a family of 4 now weighs 100 lbs more than in 1980 (25 lbs/person).
    That is also a drag on cars.

  31. GK

    I would also add that average car size has risen even though average household size has fallen.
    A 4-door family car now easily seats 5 adults. How often are 5 people all over the age of 13 in a car?

  32. GK

    When I was young and stupid, I got a used 1990 V-6 Pontiac Firebird. It was considered a fast muscle car at the time, despite having just 140 hp and mileage of 18/24.
    Now, just 16 years later model-wise (2006 model), even a Honda Civic has the same 140 hp. Fuel efficiency, of course, has risen to 30/40.
    And don’t get me started on the chasm between the mechanical reliability of the two.

  33. Dan Weber

    The real benefit of electric cars is yet to come. If a substantial fraction of cars on the road are electric, it makes sense to electrify the road, like a subway line. Cars can cruise without using up any on-board fuel, but still have the flexibility of driving around at will when they leave the electric lane.
    This could be a billed service, or it might be something that municipalities do to reduce gasoline combustion in their physical area.

  34. Steven Kopits

    Some indications that $80-ish oil is what the global economy can take before it begins to shed oil consumption:
    From the FT Energy Source blog:
    “Some recent themes in oil futures markets have returned rather sooner than some expected. Brent is once again trading at a premium to WTI, when the opposite is normally the case. And contango is again strengthening, not long after talk that markets could actually slip into backwardation.
    On Thursday both these characteristics were enhanced by a bearish report on US crude oil stocks from the EIA, which included a 20-year-plus record high for the mid-West area.”
    …and this…
    “Yesterday, it was Taxi drivers in Lebanon that were blocking the cities in protest of high fuel prices, early this week it was Taxi drivers in South Africa doing the same. Last week Taxi and truck drivers went on strike in Ivory Coast over high fuel prices and the government was forced to lower prices after the Cocoa exports were put at threat. Next week (April 27th) it is the turn of India to organize mass protests against the fuel prices in an effort to force the government to reverse the price increases.”
    Definitive, no. Suggestive, yes.

  35. fred schumacher

    There was an incentive to manufacturers to increase vehicle size: increased profit margins. The larger vehicle could be sold at a higher markup justified by consumers feeling they were getting better value with the larger vehicle. This kept Detroit attached to the SUV long beyond its point of usefulness.
    The largest cause of automotive deaths is a single vehicle running off the road. The vehicles most likely to cause these deaths are high center of gravity pickups and SUVs. The perception that SUVs are safer is only a perception, not reality, but it has had a huge impact in consumers making bad vehicle choices.
    Consumers base their purchasing choice on ultimate need, and then use their vehicles lightly loaded the vast majority of the time. Vehicle morphology is a rarely discussed major component of fuel efficiency. Most of the time we use the wrong automotive “tool” for the task at hand.
    By not focusing on vehicle morphology, that is, shape, we find ourselves in the position of making incremental efficiency improvements rather than accomplishing a paradigm shift. This includes battery powered cars, the design of which is sticking to established morphology.
    Seven-eighths of the time we drive alone. We don’t need a 4,000 pound machine to move a 200 pound payload. We have numerous multi-purpose vehicles, but no single purpose cars to accomplish our primary transportation task: the daily commute from Point A to Point B and back with only the driver in the car.
    Such a single purpose vehicle could be made small enough and light enough to quadruple present fuel economy, while costing half as much as a standard sedan, allowing a two-earner family to buy two of them for the price of one 5-seat car. Two such vehicles could fit into one standard garage slot, while leaving a sedan or minivan in the other slot for multi-purpose, non-commuting, use only.

  36. GNP

    The largest cause of automotive deaths is a single vehicle running off the road. The vehicles most likely to cause these deaths are high center of gravity pickups and SUVs. The perception that SUVs are safer is only a perception, not reality, but it has had a huge impact in consumers making bad vehicle choices. -fred schumacher

    Interesting. Can you point to data that supports high-centred vehicles being more dangerous?

    Would point out in passing that some of us actually use SUVs for the purpose they were originally designed for, i.e., travelling off-road in rural and wilderness situations that would rip up the uni-body chassis of a typical passenger car.

    Moreover, here on the wet Pacific coast in SW British Columbia, heavy rain is the most dangerous natural element most of us encounter. For that reason I run expensive 4-season 6-ply mud & snow Michelin tires on the ’93 pathfinder. A heavier vehicle cuts through the pools of rain water better than light passenger cars and minimizes the hydro-planing.

    Would also point out that the regular tread 4-season tires work just fine in all the horrible places I drive the vehicle, the same places where others with bigger vehicles and knobbier tires get frequently stuck. Most people put noisy, fuel inefficient All Terrain (AT) tires on their SUVs and light trucks that they do not need. But I guess it looks cool and macho. I would guess that the foregone aggregate wealth in North America from the inappropriate tire choices alone is in the hundreds of millions if not billions of dollars.

    Would love to upgrade to a modern diesel engine but that option is not yet available in a continent that seems to prefer politburo-style emission regulations.

  37. GK

    I am perfectly happy to get a fair amount of my local driving (non-highway) done with something as small and cheap as a Tata Nano.
    If they actually do sell the Nano in the US for $6000, it could sell. People would use it to complement their usage of existing cars.

  38. Cedric Regula

    “Would love to upgrade to a modern diesel engine but that option is not yet available in a continent that seems to prefer politburo-style emission regulations.”
    Clean Diesel is ready. Ultra low sulfer fuel is now the rule. This enabled use of NOX cat converters and particulate traps which solve the major pollution problems old diesel had.
    VW has a diesel car available in the US, but I haven’t seen any SUV/Truck yet. I think it’s mostly the Germans pursuing diesel, so selection may be limited for some time.

  39. Pch101

    Cars are heavier because of consumer demands for safety, sound insulation and luxury devices. Without expensive, lighter materials that provide the same safety benefit, cars are not going to get much lighter than they are today.
    Of course, if weight is added, more power is required to move it while delivering the same acceleration and sensation of power. We would have to increases taxes to a point that consumers would prefer to go less quickly at a lower price, than pay a premium for improve acceleration.
    Automatic transmissions take energy away from the engine in order for them to operate
    This is no longer accurate. Today’s automatics choose better shift points than do most drivers, resulting in similar or even better fuel economy to their manual counterparts. I drive a 6-speed stick myself, but I do it for the driving experience, not for the fuel economy.
    Diesels are more efficient than gasoline
    This is mostly false. The primary reason that diesel cars get higher mpg is because diesel has more oil in it.
    If a barrel of oil was refined to produce more diesel, the offsetting loss in gasoline production would exceed the increased production of diesel.
    In the macro, there is minimal difference between gas and diesel; if we bought our fuel by the pound, it would be obvious how wrong these promotions of diesel happen to be. MPG is not a useful measure of efficiency when comparing the results of one fuel type over another, as it ignores the difference in energy content between the fuels.
    Diesels are a bit more efficient than gas engines because they run at higher compression ratios. But this benefit increases overall efficiency by just a few percent, nothing close to the inflated claims made by scientifically ignorant diesel fans who misunderstand what “mpg” actually measures.

  40. John S

    “The first Accord, 1984 I believe, is similar in size to a present-day Civic…”
    The Accord appeared in 1976 and was considerably smaller than the present day Fit. It weighed under 3,000 lbs and in today’s cellphone driving SUV-choked 100 mph highways, it would be a grossly underpowered death trap.

  41. GNP

    Good points Pch101. I like a manual shift because I believe it gives me more control (or so I believe) but note that many keen, competent recreational off-roaders have graduated to automatic transmissions. (I’m not one of those; I always park, and self-propel.)

    Right-side steering wheel equipped Japanese, diesel-powered SUVs are available but I’m not interested because of the right-side steering wheel.

    By going to a light-truck-based SUV a modern diesel engine, I would hope for a small fuel efficiency improvement. I would also hope for more torque at the low end which is sometimes important in off-road situations.

    Pch101: In your opinion, will technology ever evolve to the point that natural gas can be cost-effectively substituted for current industrial diesel applications?

  42. Cedric Regula

    “Pch101: In your opinion, will technology ever evolve to the point that natural gas can be cost-effectively substituted for current industrial diesel applications?”
    Science and engineering haven’t given us the proper tools to evaluate that question yet. In the mean time, look at mpg ratings and pump price. As far as NG goes, we are still waiting on something better than mpg to help us make up our minds.
    I’m still trying to look at the energy/global warming thing from a mile per resource exploitation cost, but they are making that difficult for me.

  43. Pch101

    In your opinion, will technology ever evolve to the point that natural gas can be cost-effectively substituted for current industrial diesel applications?
    We’re starting to deplete our natural gas resources, and it would be difficult to integrate natural gas as a motor fuel into our existing gas/diesel infrastructure (it isn’t as easy to transport long distances as is conventional motor fuel), so no, I doubt it. The technology itself, though, works fine, so the vehicles aren’t the issue.
    I don’t believe that there are any magic bullets here. The US is energy dependent and always will be; our appetite exceeds our resources. We should be trying to diversify and reduce our demand and conserve whatever we have, but we don’t have the political will needed to make real sacrifices, (i.e. raise fuel taxes to the point that demand is fundamentally reduced.) Those who are hoping for a return to the days of the low horsepower 1,800 pound Accord are going to be disappointed.

  44. aaron

    I suspect the increase in weight is what drives the demand for more horse-power, and that that is what is bringing down fuel economy.
    People paying for horse power they don’t actually use is a problem, but higher horse power itself isn’t a problem. It’s that our roads have gotten congested because of poor planning, traffic management, and education. If people actually used that horse-power they’d get better fuel economy.

  45. fred schumacher

    Re: “Can you point to data that supports high-centred vehicles being more dangerous?”- GNP
    High center of gravity vehicles roll when they encounter uneven terrain when running off the road. Roll-overs are something like 3% of accidents and produce over 40% of deaths. Check out the book Traffic.
    Here in Minnesota, in the past couple of days we’ve had some horrific roll-over accidents involving pickups and teenage drivers.
    Earlier this spring, I was driving between Mankato and Minneapolis during high winds causing drifted snow to melt and refreeze in the driving track, forming black ice. Over the 75 miles, there were half a dozen SUVs and pickups on their roofs. No cars or minivans that had slid off the road had flipped.
    Re: “A heavier vehicle cuts through the pools of rain water better than light passenger cars and minimizes the hydro-planing”
    It’s not the weight, but the design of the tread siping and the ratio of weight to tire width. The trend toward wide, “rubber band” tires is not conducive to inclement weather road holding. If you want to go racing on dry pavement, get wide tires, otherwise, narrower is generally better.
    Re: diesel efficiency
    Gasoline weighs 6 pounds per gallon and diesel weighs 7.2 pounds. Much of the efficiency gain of diesel is in the higher energy content of diesel. However, higher compression produces greater efficiency. Diesels also run on an excess of air, something not possible with spark ignition. At idle, a diesel will use one-sixth the fuel of a gas engine. Whereas gasoline engines are about 25% thermally efficient, the new generation of marine diesels have reached 50% thermal efficiency, the same as fuel cells.
    New spark ignition technology, such as direct injection, throttleplate-free air intakes, turbocharging are improving the thermal efficiency of gasoline engines. Homogeneous charge compression ignition (HCCI) has the potential to greatly increase efficiency and reduce emissions.

  46. Cedric Regula

    Thermal efficiency isn’t the whole story of course. Refineries make a certain amount of diesel and gasoline and they have some latitude to shift the percentage. I asked a Exxon Chem E once if you designed a brand new refinery from scratch, could it produce all diesel fuel? He hemmed and hawed a bit, but then said he didn’t think so.
    Now they say a diesel can run on almost anything, so maybe you could pipe Saudi high sulfer crude from a oil tankers hold into it’s marine diesel engine, but that’s not done for some reason.
    So utilization of the resources we have is a big factor.
    Next we could weigh a pound of water to see if fuel cells are a good idea, but that gets much too confusing. Then on to electric cars….

  47. Pch101

    I suspect the increase in weight is what drives the demand for more horse-power, and that that is what is bringing down fuel economy.
    That is certainly part of it. A heavier car requires more power just to move it to and fro and the same pace as a lighter car.
    But part of it also comes from the consumer’s desire for better performance. Since the Honda Accord is one of the subjects du jour here, consider this:
    -A 1976 Accord accelerated from 0-60 mph in about 14 seconds, and ran the quarter mile in about 20 seconds.
    -A 2009 Accord 4-cylinder accelerated from 0-60 mph in about 9 seconds, and ran the quarter mile in less than 17 seconds.
    To be sure, some of it is size and weight. As noted by others here, the modern Accord is a heavier, larger car that bears little resemblance to the earlier version — the newer car has a wheelbase that is a whopping 16.5 inches longer, which places it in an entirely different size class from its original namesake.
    At the same time, the newer car is certainly quicker off the line. Today’s 4-cylinder Accord delivers better acceleration than did many 8-cylinder sedans back in the mid- to late-70s.
    These modern cars would get better fuel economy, even without shedding any pounds, if we would accept the slower acceleration of the olden days. But now that every soccer mom has tasted power, I doubt that we’re going to lose our desire for acceleration. Even today’s minivans are performance cars by yesteryear’s standards, and it’s going to take very expensive fuel for us to ever go back.

  48. GNP

    Cedric: If I understand correctly, ocean-going freighters will burn cheap bunker fuel in their engines at sea and then switch to cleaner fuel closer to port, at least in some jurisdictions.

    Thanks to Fred, Pch101, CR for informative comments. Apologies to others for the auto-tech turn the discussion took.

    Incidentally, a friend informs me that Subaru will delay bringing some diesel models to North America until the [relative] price of diesel decreases. Jeep Patriot and Grand Cherokee SUV now offer diesel engine models. Some preliminary estimates of total costs show little or no gain for a VW Golf diesel over a VW Golf gasoline model. I would expect fuel efficiency to be capitalized into the prices of both new and used vehicles.

  49. Pch101

    In the interest of economics, I’m going to plagiarize myself and post a comment that I made previously on a different forum re: Professor Knittel’s research –
    There is a basic economic answer here: The consumer is willing to devote some portion of his budget to fuel costs, and will buy a vehicle that fits within that budget.
    When fuel is cheap, people will happily trade fuel economy for size, safety, comfort, luxury or whatever else they want, while they will give up at least some of those things up when fuel gets more expensive, just so long as it stays within their budgets.
    Since 1946, consumption dollars devoted to fuel has comprised an average of 3.2% of total consumption, with a standard deviation of 0.6%, so it hasnt varied much over time. The SUV boom occurred during a period when total fuel costs were below the historic norms as a percentage of consumption, which tells you that a lot of people felt that their fuel budgets went a long way and could be stretched into much larger vehicles. Now were back to something close to the long-run average, so well see what happens.
    Thats a nice summary of why CAFE legislation is a failure. The way to inspire lower consumption is to make fuel more expensive. If the price goes up, people will buy vehicles that get them back to their fuel budget happy place, whatever that is. If youre too impatient to let the free market get you there, then youll just have to tax it.

  50. Cedric Regula

    I don’t know for sure if ships sometimes burn crude oil. They do burn the heaviest, dirtiest stuff yielded from cracking to distillate. Seems like injector nozzle sizing for major differences in viscosity would matter, and burning really bad stuff would foul up the engine oil and be a maintenance nightmare. But that’s just off the top of my head guesswork. And it sure wouldn’t be clean diesel auto fuel.
    Check the VW site on Golf gasoline vs. Golf TDI mileage. I think the comparison was 22/30 vs 30/40, so there is a significant improvement for diesel. However comparing the Golf TDI to a gas Honda Civic doesn’t look like an impressive gain.
    Also, the title of the post was “Improving the fuel efficiency of U.S. light vehicles”. We just added how.

  51. Cedric Regula

    Just re-read your post and realized you said “total cost”, meaning the increase in mileage doesn’t pay back the increase in vehicle cost.
    That may be, but it depends what you define the goal to be. My version is to reduce energy usage and thereby reduce the trade deficit and global warming. I’m assuming we will drive the same number of miles we always do.
    It will take more expensive technology to do that. If we can offset part of that cost we are doing good. We need CAFE because the automakers won’t take the risk of developing and bringing to market more expensive technology unless the government provides a level playing field. We just nationalized the world’s largest car company because the vagaries of consumer preferences changed with the wind.
    So that’s the immediate term. But we can be pretty sure fuel prices will steadily increase from Asian demand(hopefully they will have trouble affording it too) and we will get an additional bump from Cap&Trade or carbon taxes. So we may see economic payback in the not to distant future. But don’t try and hurry it. You have an expensive car payment to make.

  52. aaron

    It’d be interesting to see what these vehicles get in the real world. I doubt the difference is as big as the rating.
    I think we’re looking at the wrong end of the issue, driving behavior is the big bottleneck in fuel efficiency; People not putting the power they have to use, accelerating too slowly and causing congestion.

  53. aaron

    It might have more to do with cellphones and texting, but since fuel prices became an issue in 2005 fuel economy has declined. James has shown us truck and SUVs mostly sat on lots during this time, and the rating of the newly manufactured fleet increased some.
    (the graph is total gasoline consumption for the US from the EIA over total vehicle miles traveled from the FHWTA)
    We saw some improvement in 2008, but because people stopped driving altogether.

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