Study:Car supersizing explains small MPG gains
http://dervishcom.blogspot.com/2012/01/studycar-supersizing-explains-small-mpg.html
Cars haven't improved their miles-per-gallon much in recent decades, but fuel efficiency is not to blame. A new study quantifies the real culprit: super-sizing.
The average auto, which now gets 27 miles-per-gallon, would have seen its mpg jump from 23 in 1980 to about 37 had it retained the same weight and horsepower, according to a study by economist Christopher Knittel at the Massachusetts Institute of Technology.
That didn't happen. Between 1980 and 2006, the average curb weight increased 26% and horsepower soared 107%. So even though fuel economy jumped 60%, Knittel says the average gas mileage of vehicles sold in the United States rose only about 15%.
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"Most of that technological progress has gone into [compensating for] weight and horsepower," Knittel says, citing innovations such as fuel-injection systems and variable-speed transmissions. He says his "Automobiles on Steroids" study, published in the American Economic Review, is the first to calculate what could have happened if vehicles hadn't been souped-up.
Knittel says safety features, such as side-curtain air bags, don't explain the bulk of the added weight. Rather, he says the main cause is the shift from cars to light trucks, including SUVs, prompted partly by the less stringent federal fuel efficiency standards for trucks.
In 1980, light trucks represented about 20% of passenger vehicles sold in the U.S. but accounted for 51% by 2004. Last month, Americans' appetite for trucks of all kinds rebounded strongly to a combined 54.8% of new vehicle sales.
How much of a difference will new fuel economy standards make?
In November, President Obama proposed that the Corporate Average Fuel Economy of cars and trucks increase to a fleet-wide average of 35.5 mpg by 2016, and 54.5 mpg by 2025.
"They're not as aggressive as they appear," Knittel says, noting the 54.5 mpg standard equates to about 40 mpg in actual driving. He says automakers could achieve that simply by maintaining their current rate of technological innovation and curbing vehicle weight and horsepower 25%. If they shifted back to the vehicle weight and power of 1980, he says they could achieve a fleet-wide average of 52 mpg by 2020.
Knittel says more fuel-efficient vehicles may actually prompt people to drive more, thus negating the environmental benefits. He says hiking gas taxes is the most effective way to reduce the greenhouse gas emissions associated with driving.
He knows that's not a politically popular idea. "No one's ever been elected on a a campaign of raising gas taxes."
The average auto, which now gets 27 miles-per-gallon, would have seen its mpg jump from 23 in 1980 to about 37 had it retained the same weight and horsepower, according to a study by economist Christopher Knittel at the Massachusetts Institute of Technology.
That didn't happen. Between 1980 and 2006, the average curb weight increased 26% and horsepower soared 107%. So even though fuel economy jumped 60%, Knittel says the average gas mileage of vehicles sold in the United States rose only about 15%.
FOLLOW: Green House on Twitter
"Most of that technological progress has gone into [compensating for] weight and horsepower," Knittel says, citing innovations such as fuel-injection systems and variable-speed transmissions. He says his "Automobiles on Steroids" study, published in the American Economic Review, is the first to calculate what could have happened if vehicles hadn't been souped-up.
Knittel says safety features, such as side-curtain air bags, don't explain the bulk of the added weight. Rather, he says the main cause is the shift from cars to light trucks, including SUVs, prompted partly by the less stringent federal fuel efficiency standards for trucks.
In 1980, light trucks represented about 20% of passenger vehicles sold in the U.S. but accounted for 51% by 2004. Last month, Americans' appetite for trucks of all kinds rebounded strongly to a combined 54.8% of new vehicle sales.
How much of a difference will new fuel economy standards make?
In November, President Obama proposed that the Corporate Average Fuel Economy of cars and trucks increase to a fleet-wide average of 35.5 mpg by 2016, and 54.5 mpg by 2025.
"They're not as aggressive as they appear," Knittel says, noting the 54.5 mpg standard equates to about 40 mpg in actual driving. He says automakers could achieve that simply by maintaining their current rate of technological innovation and curbing vehicle weight and horsepower 25%. If they shifted back to the vehicle weight and power of 1980, he says they could achieve a fleet-wide average of 52 mpg by 2020.
Knittel says more fuel-efficient vehicles may actually prompt people to drive more, thus negating the environmental benefits. He says hiking gas taxes is the most effective way to reduce the greenhouse gas emissions associated with driving.
He knows that's not a politically popular idea. "No one's ever been elected on a a campaign of raising gas taxes."
