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Oxford University Study Finds Downscaling of Vehicle Size and Weight the Best Way to Reduce Transport GHG Emissions in the Short Term

An new study from the Smith School of Enterprise and the Environment at Oxford University suggests that best way to reduce transport greenhouse gas (GHG) emissions in the short term is a “drastic downscaling of both size and weight” of conventional gasoline and diesel cars.

The study editor Sir David King (former Chief Scientific Adviser to the UK Government) and lead author Dr. Oliver Inderwildi urge the government to impose higher taxes on drivers of large, inefficient vehicles and reinvest the money in better public transport and measures to get more people cycling and walking.

“The most significant impact that can be made in reducing CO2 emissions from automobiles in the coming decades is reducing the average weight and engine size of vehicles.”
—Future of Mobility Roadmap

The report “Future of Mobility Roadmap” assesses the potential for low carbon transport on land, by air and sea. Among its findings for land transport—the largest contributor to the transport sector’s greenhouse gas emissions—are:

  • In the short-term, turbocharging and downscaling in combination with weight reduction of current vehicle technology offer a significant opportunity for reductions.

  • In the medium-term, hybrid systems, those using internal combustion engines and regenerative electric systems such as the Toyota Prius, offer significant savings and will help the evolution to a purely electric drivetrain.

  • While purely electric vehicles are not zero emission vehicles due to electricity and hydrogen generation they will be important low carbon transport in the long term.

  • Plug-in electric vehicles are restricted by battery technology, fuel cell systems are limited by power density of the unit and both systems are challenged by limited rare material availability.

  • First generation biofuels, those derived from food stocks, have proved the viability of such fuels, but remain a localized solution, as in Brazil.

  • Second generation biofuels synthesized from inedible cellulosic biomass have the potential to be true low carbon fuels but are constrained by land availability.

  • Algae-based fuel show promise as they exclude land use and food security issues, but they require a mass production break through to be viable.

  • Both electric and diesel rail systems have low operating emissions but high embedded infrastructural costs and lack route flexibility.

In the short-term a significant impact that can be made in reducing CO2 emissions from automobiles by blunt down-scaling the physical vehicle size and engine capacity. In the medium-term, alternative powertrain technologies such as HEVs and PHEVs, by combining the advantages of ICEVs and battery electric vehicle (BEV), offer perhaps the best interim step. In the long-term it is envisaged that all electric drive vehicles will be the man source of transportation. These can be split into two distinct groups, fuel cell vehicles (FCV) and BEV.

...As with technology, economic policies also have an important role to play in reducing GHG emissions from transport. An efficient mobility model for the future must take into account the true costs of transport and its regulatory framework needs to create incentives for people to make sustainable transport choices. In order to achieve this economic instruments can be used to correct road transport externalities such as environmental and road damage, accidents, congestion, and oil dependence. CAC [command and control] policies and incentive-based policies can be used to reduce the negative impact of transport externalities. Physical policies, soft policies, and knowledge policies can be used in combination in an integrated framework with taxes and permits in order to move towards a sustainable transport model.

—Future of Mobility Roadmap

Myth Busting
The report identifies a number of myths surrounding low-carbon road transport:
  • “Diesel cars are highly polluting.”
  • “We should just use fuel cells.”
  • “Electric vehicles are zero-emission.”
  • “Corn ethanol is an environmentally friendly fuel.”
  • “Biofuels compete with food sources.”
  • “Biofuels will save the day.”
  • “Policy X is the only solution.”
  • Air. For the air sector, the report finds that technical changes, such as improvements to propulsions systems and reduction to aerodynamic drag could reduce emissions by up to 50%, in the short term. However, the rate of uptake of new technologies is restricted by fleet lifetimes.

    Longer term developments require change to the current aircraft architecture from “tube and wing” to “flying wing” systems, offering 32% reduction in GHG through drag reduction alone. Biofuels and operational improvements could also reduce the GHG emissions from aviation.

    Sea. Sea or maritime transportation accounts for 3% of global GHG emissions while transporting 70% of the world’s cargo by volume, leading to the lowest emission per tonne kilometer of all modes discussed in the report. Through both technical and operational change, reductions of up to 75% of GHG emission are possible in the medium to long term, the authors conclude.

    Behavioral Change. The report throughout emphasizes the need for behavioral change to achieve low carbon transport:

    • Either top-down or bottom-up polices are required.

    • Top-down methods include command and control polices, such as regulation and incentive based polices, such as taxes and charges.

    • Top-down methods are not efficient from an economical perspective but are when drastic changes in activity are required.

    • Bottom up methods or complementary polices can be used in combination with top down methods.

    • Complementary polices fall into one of three broad categories: physical polices, soft polices and knowledge polices.

    • Bottom-up methods are economically efficient but do not always achieve their full potential for change.

    The study warns that action must be taken immediately to have any impact on climate change because of the long lifetime of transport fleets and subsequent delays in technological impact.




    "..a significant impact that can be made in reducing CO2 emissions from automobiles by blunt down-scaling the physical vehicle size and engine capacity."

    While including the weight of airbags, can auto firms actually make the scores of millions of under 2000 lb. cars that VW, Toyota, Honda .. sold for decades?


    Why no mention of improving aerodynamics?


    Myth Busting
    "Biofuels compete with food sources.”
    “Biofuels will save the day.”
    “Policy X is the only solution.”

    This is a very practical report. You can make a car lighter and stronger without making it a lot smaller..that is not a myth.
    People in the U.S. like a roomy car. That can be done. Cellulose biofuels are not Policy X, but come close in conjunction with other solutions.


    The best way is to tax emissions or fuel consumption at time of purchase, and back this up with "trade zone wide" fuel economy / CO2 mandates.

    This has been done in the EU and is bringing about a rapid reduction of CO2 output and fuel consumption.

    [ In Ireland they have steep purchase taxes based on the car's CO2 band reaching 32% for > 219 gms/km ]

    You might also back off on car safety testing - i.e. reduce the speed of tests, or at least freeze the standards.

    In Ireland now the percentage of cars in the < 140gms sector has gone to about 50% (and noone is any the worse off (except petrol retailers)).

    Action such as this has to be taken at a large level - the Eu or the US can act, but individual countries are too small to make car manufacturers change their designs.

    But if you keep up a steady pressure, (as the EU has), you will see results.


    EU politics is different from the U.S. The EU can set goals and the politicians of the individual countries to not face the ire that the U.S. politicians do, they can say it is the EU doing all of this.


    Reads much as you would expect given the subject.

    In the Behavioral Change suggestions they write 'polices' several times where I expected to see 'policies'.

    But maybe 'polices' is really what meant. As in 'cats and mices'. They will be the cats.

    Somewhat more seriously. I agree with mahonj about this. The best way is to tax consumption at the time of fuel purchase. That doesn't require new bureaus, etc. They can just increase the existing tax rate.

    Collecting more tax when a vehicle is sold is also a simple approach. These transactions are already taxed. Just boost the rate.


    Mahonj: Excellent way to deal with oversized gas guzzlers and high pollution makers.

    However, in many (advanced democracies), where lobbies and interested groups have taken over from people and elected representatives, common sense regulations and laws have become impossible to introduce and apply.

    This is not realy new. Most well known democracies went through similar distortions periods, specially in the latter years of their existance.


    Downscaling of size, but also reducing resistance, for instance the should get much more support.


    Very perceptive Ken. We might wonder how our Oxford scholars have become so Freudian. The misstated goal here is energy independence.


    Or at least less dependent on imported oil. Biopolymers, bio jet fuel, it all helps eliminate middle eastern oil and maybe all OPEC oil some day.

    Baby Fishmouth

    If we can fake a moon landing, why can't we make a lighter and more efficient ICE?



    Lighter and more efficient ICEs are being made. Improvements come to market every year. I expect this to happen for another five to ten years.

    Eventually there there will be little or no profit to be gained from further ICE refinements and capital will not be invested.

    Fifty, or even twenty, years ago manufacturers felt there was very little profit potential in improving efficiency or reducing weight. So they didn't.

    They concentrated on reducing engine production cost instead.


    They did a heck of a job producing engines with all those precision parts cheaply. If they can to that they can make motors, batteries and fuel cells as well.


    There is a very easy way to convince manufacturers to build lighter more efficient vehicles.

    We should STOP buying inefficient heavy weights. There are many new lighter, more efficient vehicles in the show rooms.

    Some, like the Chev Equinox, Ford Fusion HEV, Toyota Prius III, etc are even built locally.

    Hummer (and similar type vehicles) could and should stay on retailers parking lots. After a few months, most, if not all, manufacturers would stop making them.

    A simple general boycott would do it.


    Yes, but as long a huge gas guzzling vehicles are available for sale some people will believe it is their "freedom" to buy them and drive them with NO regard for anyone else.

    CAFE will put an end to those vehicles. If they continue to offer them for sale. I would suggest a premium fee to make the buyers aware of the hidden costs of using those products. If you had to pay a $5000 purchase fee for a $50,000 huge SUV getting 10 mpg, they would think twice before buying one.

    fred schumacher

    Theissue is morphology: use the right tool for the task. Most of the time we drive alone, yet we use a 4,000 pound machine to move that 200 pound payload. This is like using a 12 inch crescent wrench to pound nails.

    We have lots of general purpose vehicles but no single purpose vehicle, the one that's required most of the time. We buy a vehicle for its ultimate use and then use it lightly loaded 90% of the time. A very small vehicle, designed primarily to haul one person, and an occasional two, costing less than half as much as a standard sedan could rapidly reduce fuel consumption without sacrificing primary task functionality.

    Note: the Tata Nano Europa gets Prius level fuel economy at one-fourth the price. Low cost is essential toward rapid fleet replacement, and rapid fleet replacement is more important than maximizing high tech fuel economy measures.


    Fred, that is an excellent point. It's similar to a family buying a moving van because they think they might move in the next few years. Or, a city like Atlanta buying a fleet of snow removal trucks.
    We should only purchase vehicles for what they are used for 90% of the time.
    Rent something for the other 10%.
    I'm glad to see Home Depot and Lowe's offering very reasonable rates for truck rental. I'm guilty of buying a vehicle because i might want to bring a piece of plywood home once a year.


    That is the point I make to people that buy trucks, SUVs and even RVs. Drive a nice efficient car all year and if you need or want to use a larger vehicle, RENT ONE!

    Will S

    SJC - spot on!


    Or tow a trailer.  I get ~38 MPG bobtail, ~28 towing a 4x8 U-Haul, ~24 towing a 5x8 U-Haul (packed with cargo).  I'd like to see a 3/4 ton pickup get 24 MPG empty.

    Stan Peterson

    Autos have been downsizing for 40 years. We have reached or past the reasonable limits with 'A' segment cars.

    I suggest with all the money being tossed around that that there ought to be a government sponsored R & D effort to breed the human race as dwarfs. By shrinking full size people to 3.6" at best, than further downsizing for cars is possible.

    fred schumacher

    Re: "Autos have been downsizing for 40 years. We have reached or past the reasonable limits with 'A' segment cars. "

    The inside of a car and the outside are not the same thing. There are cars that are big on the outside and small inside, and vice versa.

    Back in the mid-70s I had a 1969 Simca 1204 GLS. This is the car that inspired the Omni/Horizon and brought front wheel drive to America. I once gave a ride to a co-worker. He was stunned at how much more room the Simca had than his Camaro. And he was talking about the front seat. The rear was no contest. Only a double amputee could sit comfortably in the back of a Camaro. In 1976, I lived inside that Simca as I drove all over North Dakota as a photographer for the Dakota Photo Documentary Project.

    Jeremy Clarkson of the Top Gear TV program likes the Fiat 500 because he fits comfortably into it. Clarkson is 6'6" tall. The Fiat is shorter than my old Simca, which was smaller than any American car.

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