reached a saturation point despite predictions, by the International Energy Agency, of 1.5 percent annual growth through 2030. The researchers concede the findings are not conclusive but say they could mean projections of fuel consumption and CO2 emissions will be lower than previously believed.

“A major factor behind increasing energy use and carbon dioxide emissions since the 1970s has ceased its rise, at least for the time being,” Lee Schipper, one of the study’s two authors, told Miller-McCune. “If it is a truly permanent change, then future projections of carbon dioxide emissions and fuel demand should be scaled back.”

Schipper is a researcher at Global Metro Studies at the University of California, Berkeley, and at the Precourt Energy Efficiency Center at Stanford University. He was joined in the research by Adam Millard-Ball, a doctoral candidate at Stanford. They analyzed travel trends between 1970 and 2008 in the United States, the United Kingdom, Canada, Sweden, France, Germany, Japan, and Australia. In each case they plotted the distance traveled per capita per year by car, pickup, bus, airplane, train, light rail, streetcar, and subway. Then they compared the data to the country’s gross domestic product per capita.

They found a correlation between rising prosperity and passenger travel from 1970 to 2003. But passenger travel stopped growing after 2003 even as GDP per capita continued to rise. Motorized travel has plateaued at about 16,155 miles per year per person in the United States, 6,213 miles in Japan and between 8,077 and 10,563 miles in the other countries.

“Since 2003, motorized travel demand has leveled out or even declined in most of the countries studied, and travel in private vehicles has declined,” the authors wrote in their study. “Car ownership has continued to rise, but these cars are being driven less.”

More than rising fuel prices are at work here, as the researchers say. They did not delve too deeply into the reasons why motorized travel has plateaued, but they speculate on several factors:

• Saturation in vehicle ownership. There are about 700 cars per 1,000 people in the United States, which is more cars than licensed drivers. The figure is about 500 cars per 1,000 people in most of the other countries. Car ownership in the U.S. has declined since 2007 due to the recession.
• Rising fuel costs.
• An aging population that doesn’t commute as often or as far.
• Traffic congestion. People spend an average of 1.1 hours per day traveling. Schipper told Miller-McCune, “My basic thesis is, ‘There ain’t room on the road.’”

The authors note that if passenger travel remains the same even as automobiles become more fuel efficient, reducing transportation emissions may not be as daunting as previously believed. They concede the findings are by no means conclusive and more research is needed but their findings should not be dismissed.

“The assumption of continued, steady growth in travel demand, which is inherent in many transport models and energy use projections, is one that planners and policy makers should treat with extreme caution,” they write.

Photo of Atlanta traffic: jandclindenbaum photos / Flickr

Authors: Chuck Squatriglia

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