Weight Gain Of U.S. Drivers Has Increased Nation's Fuel Consumption

Americans are now pumping 938 million gallons of fuel more annually than they were in 1960 as a result of extra weight in vehicles. And when gas prices average $3 a gallon, the tab for overweight people in a vehicle amounts to $7.7 million a day, or $2.8 billion a year.

The numbers are added costs linked directly to the extra drain of body weight on fuel economy. In a paper to appear in the October-December issue of the journal The Engineering Economist, the scientists conclude that each extra pound of body weight in all of today's vehicles results in the need for more than 39 million gallons of extra gasoline usage each year.

"The reason we looked at this issue was that gas prices hit an average exceeding $3 per gallon in September 2005," said Sheldon H. Jacobson, a professor of computer science and director of the simulation and optimization laboratory at Illinois.

"This was the highest recorded level in the United States. We thought there must be some way that we could determine how to quantify the effect of being overweight on fuel consumption. We felt that beyond public health, being overweight has many other socio-economic implications."

Jacobson presented the challenge to Laura A. McLay, who was a doctoral student in his laboratory at that time and is now on the faculty at Virginia Commonwealth University, and they pursued the issue through his funding with the National Science Foundation.

Their conclusions are based on mathematical computations drawn from publicly available data on U.S. weight gain from 1960 to 2002, a period in which the weight of the average American has increased by more than 24 pounds, according to data from the U.S. Department of Health and Human Services.

By 2002, 62 percent of adults were overweight with a body mass index of between 25 and 30; more than 30 percent were considered obese with a BMI exceeding 30.

The fuel-consumption calculations apply only to passenger vehicles, including cars and light trucks driven for non-commercial reasons. Ruled out were other factors such as increasing the weight of cargo or decreasing fuel efficiency through poor maintenance. Driving data collected in 2003 were used to gauge fuel consumption based on weight gains during the last four decades.

The researchers used three different scenarios that considered not only beefier drivers behind the wheel but also their passengers, accounting for individual characteristics such as ages, numbers of people in the vehicle, and expected weights.

Since 1960, McLay and Jacobson said, the consumption of no less than 938 million gallons of gasoline annually can be attributed to weight gains of drivers and passengers. Of that total no less than 272 million gallons are consumed annually as a result of weight gains since 1988.

"The key finding is that nearly 1 billion gallons of fuel are consumed each year because of the average weight gain of people living in the United States since 1960 -- nearly three times the total amount of fuel consumed by all passenger vehicles each day based on current driving habits," McLay and Jacobson wrote.

"Although the amount of fuel consumed as a result of the rising prevalence of obesity is small compared to the increase in the amount of fuel consumed stemming from other factors such as increased car reliance and an increase in the number of drivers, ... it still represents a large amount of fuel, and will become even more significant as the rate of obesity increases.

The conclusions, Jacobson said, should be considered conservative because they do not consider many indirect consequences of obesity nor the increase in the number of vehicle miles linked to more people living in the United States and owning cars.