MIT Study: Vehicle Weight Gains Have Offset Potential MPG Improvements

Although it’s true automakers have improved average miles delivered per gallon to meet government fuel economy mandates here and around the world, between 1980 and 2006, efficiency for U.S. market vehicles increased only around 15 percent.

Not so great you say? Perhaps, but while those gains might seem modest, according to a research paper by MIT economist Christopher Knittel, they don’t account for the fact that vehicle offerings – not unlike fast food restaurant menus – have been tending toward a preference to supersize. That is, during this same 26-year period, vehicle curb weights increased by 26 percent, while engine power output grew by a whopping 107 percent.

The paper, titled, “Automobiles on Steroids,” said that given technological advancements we’ve seen in automobiles in the last three decades, if Americans today were driving cars that were equivalent in size and power to those on the road back in 1980, the fleet fuel economy average would be approximately 37 mpg – 10 mpg above the current average of 27 mpg.

“Most of the technological progress [we’ve seen] has gone into compensating for [weight and horsepower],” said Knittel, who observed that despite gains garnered from introduction of features such as electronic fuel injection, multi-cam engines and transmissions with an ever increasing number of speeds, Americans in particular continue to favor, larger, more powerful and better equipped vehicles. Further, the situation is not helped by the fact that in real terms, U.S. gas prices today are on average, some 30 percent lower than they were in 1980.

“I find little fault with the auto manufacturers, because there has been no incentive to put technologies into overall fuel economy. Firms are going to give consumers what they want and if gas prices are low, consumers are going to want big, fast cars.”

Although the Obama administration has committed to increasing Corporate Average Fuel Economy (CAFE) requirements from 35.5 mpg in 2016 to 54.5 mpg (about 40 mpg on the window sticker) in 2025, Knittel believes this won’t be enough by itself to significantly boost fuel economy and reduce fossil fuel dependence. He, like many environmental policy analysts, said he believes that in the long run, a fuel surcharge would be more effective.

Mileage regulations like CAFE “end up reducing the cost of driving,” he said. If you force people to buy more fuel-efficient cars through CAFE standards, you get what’s called “rebound (a concept where people actually end up driving more and consumption increases).” On the other hand, he said a fuel surcharge would, in his view, spur demand for more fuel-efficient vehicles without resulting in such a rebound scenario.

Further reading


  • Van

    The question we must ask ourselves is how much added weight was mandated by Government regulations. How much of the price of Gasoline is mandated by Government regulations and taxes.

    In the 1970″ we created the Energy Department to take actions to reduce our dependence on foreign oil. But with all those regulations, what has been the result, we are more depend now, and our dependence is growing.

    We have tried a government run economy, see history of Soviet Union, and found a too centralized control leads to poverty and corruption.

    We need better batteries, that is for sure, but the New Fusion Plug-in, due in about 12 months, plus the Prius PHV due next month, should provide an ability to reduce gasoline consumption without harming the economy. Take a drive in a new Camry Hybrid or a Kia. These are great cars that get that 10 MPG better than the currant fleet average of 27.

    Rather than mandating high fuel costs, how about lowering fuel costs by providing alternatives. Duh

  • Libertarian Don

    I was thinking about this exact same issue last night while walking my dog. My Datsun 210 I drove in the 1980′s averaged 27 mpg, took ~15 seconds to get to 60 mph, and weighed ~2000 lbs. My 2007 Honda fit averages 30 mpg, takes ~8.5 seconds to 60, and weighs ~2600 lbs.

    From my understanding of the weight issue is most is derived from safety hardware include side impact beams, air bags (the Fit has 8 air bags) and other reinforcements. I’ll keep my safety thank you.

    Hybrids lead to even more weight gain from the batteries, extra electric motor and additional hardware required to make it all work.

  • Van

    Hi Libertarian Don, your willingness to increase our dependence on foreign oil and government regulation would need to be actually offset with improved safety. Have you seen a study where injury per collision is compared, 1985 vehicles with 2005 vehicles that demonstrates an improvement.

    I believe Government mandates lock in old design and make innovation difficult. Remember the first air bags actually injured small front seat passengers, and when it was discovered that the bag inflation rate was a one speed fits all design set for high speed crashes when most were at lower speeds? We could not make the design change but had to get the government to modify its regulation? And this one example is just the tip of the iceberg.

    Not to mention the change in the lending rules during the Clinton era which gave birth to the housing bubble. Over-regulation even with best intentions leads to more poverty and corruption, not less.

  • Van

    A little bit on weight and safety. We have small cars and their passengers are more at risk of injury than passengers of heavier cars.
    However, not much safety gain is achieved once you reach 2900 lbs, in today’s mix of vehicle sizes. And once you reach 3600 lbs, no significant safety improvement is seen with heavier vehicles. Thus anything over 3600 lbs simply wastes gas and adds to the hazard of small car drivers.

    A Prius weighs about 2900 and a Camry hybrid weighs about 3600.

    Thus vehicles over 3600 lbs with horsepower over 200, simply waste gas.

    We do not need regulation, we need education based on sound science, not agenda driven briefs aimed at political goals.

  • Libertarian Don

    The weight gain was not done for safety purposes, but instead was a result of government mandated safety devices that add roughly 25% to the weight of a small vehicle like my Fit.

    These safety devices are important in a small vehicle when getting clobbered by a 6000 lbs SUV. Simple physics. So while as a libertarian I am usually against government mandates I do appreciate some of the resultant safety devices (air bags. side impact bars, etc) Recent proposed mandates are just going to add to the cost and weight (e.g.- blackboxes)

    The death rate per mile driven has fallen to an all time low. A ten mph accident in 1970 could often result in death while now it will more likely result in bruises. I was hit head on by a Caprice classic going 50 mph in my Saturn SL2. My brother was hit head-on by a Ford E350 sliding on its side at 70 mph in a Saturn SL1. My wife, my brother, and I walked away with minor injuries (both cars were totalled). If not for the airbags our injuries would have been severe and I have little doubt my brother would be dead.

  • Not So Libertarian Don

    You can find some estimates of the sources of weight growth in another study from MIT:

    http://web.mit.edu/sloan-auto-lab/research/beforeh2/files/Zoepf_MS_Thesis.pdf

    Basically, it finds that for cars (excluding light trucks) there was about 200 lbs of weight increase attributable to safety and emissions equipment between 1980 and 2010. Over the same period, there was about 260 lbs of weight increase attributable to comfort & convenience features.

  • veek

    Good article and postings. The automotive marketers have done their homework, and can apparently read our collective minds far better than the legislators. Not all is bad, though. The size for new homes seems on its way down, fast food franchises are offering more healthy choices, and car makers offer excellent choices for those wanting to downsize. Maybe supersizing is not an inevitable trend.

    Good point about increasing the cost versus implementing the mandates (and the CAFE numbers will us so much voodoo math they wouldn’t be credible anyway). European and Asian drivers probably use less fuel largely because it costs far more, not because their governments make any better regulations than ours does.

  • Blonda

    This is a very interesting article! The subject is very..fragile and i like a lot the way the author chose to treat it! It’s a really good point that implementing the mandates means in the same time increasing the costs!
    Parfumuri Originale

  • derek

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    that someone decided to say something like this stuff .

  • greg45

    I think the study has really paid off here. I think it is so important to try improve the MPG for the future. The benefits will definitely pay off in the long run. Keep up the good work. Medical Depot Canada