Amid the planes, trains and automobiles of the holiday season comes a surprising finding from transportation scientists: Passenger travel, which grew rapidly in the 20th century, appears to have peaked in much of the developed world.
A study of eight industrialized countries, including the United States, shows that seemingly inexorable trends — ever more people, more cars and more driving — came to a halt in the early years of the 21st century, well before the recent escalation in fuel prices. It could be a sign, researchers said, that the demand for travel and the demand for car ownership in those countries has reached a saturation point.
"With talk of 'peak oil,' why not the possibility of 'peak travel' when a clear plateau has been reached?” asked co-author Lee Schipper, who shares his time between Global Metro Studies at the University of California, Berkeley, and the Precourt Energy Efficiency Center at Stanford University.
Schipper and Adam Millard-Ball, a doctoral candidate at Stanford University, looked at the gross domestic product per capita of the United States, Canada, Sweden, France, Germany, the United Kingdom, Japan and Australia from 1970 through 2008 and plotted it against the distance traveled per capita per year in each country by car, pickup truck, bus, train, light rail, streetcar, subway and plane.
Beginning in 1970, they found, motorized passenger travel grew rapidly in all eight countries as greater prosperity led to rising car ownership and domestic air travel. But after 2000, when per capita GDP in the U.S. hit $37,000, passenger travel stopped growing here. In the other countries, passenger travel leveled out at a GDP of $25,000 to $30,000 per capita.
“A major factor behind increasing energy use and carbon dioxide emissions since the 1970s has ceased its rise, at least for the time being,” Schipper said. “If it is a truly permanent change, then future projections of carbon dioxide emissions and fuel demand should be scaled back.”
The peak travel study runs counter to government models predicting steady growth in travel demand well beyond 2030. Schipper and Millard-Ball say that their own findings are “suggestive rather than conclusive.” They speculate that highway gridlock, parking problems, high prices at the gas pump and an aging population that doesn’t commute may be contributing to peak travel. People already spend an average 1.1 hours per day traveling from one place to another, and driving speeds can’t get much faster.
“You can’t pronounce one single factor for the slowdown in travel,” Schipper said. “The most important thing will be to see what happens as the economy recovers. Everybody expects oil prices to go up. But with new fuel economy standards, more hybrids and higher oil prices competing against a recovery in which people buy old-fashioned gas-guzzlers, the question is, what is going to win?”
Most of the eight countries in the study have experienced declines in miles traveled by car per capita in recent years. The U.S. appears to have peaked at an annual 8,100 miles by car per capita, and Japan is holding steady at 2,500 miles.
There are signs of saturation in vehicle ownership, too, at about 700 cars per 1,000 people in the U.S. — more cars than licensed drivers — and about 500 cars per 1,000 people in Japan and most of the European countries. Car ownership has declined in the U.S. since 2007 because of the recession.
“You get to a point where everybody who could possibly drive, drives,” Schipper said.
Finally, researchers found, the energy intensity of cars and light trucks has declined in all eight countries since 1990. (Energy intensity is the amount of fuel expended per passenger-mile, or one passenger moving one mile.)
At the same time, though, vehicle occupancy declined, as more and more people drove alone. In the U.S, the average vehicle occupancy is 1.7 people per car, down from 2.2 in 1970, reflecting a likely shift away from carpooling. So, for example, in 2007, car travel in the U.S., with two-thirds of the seats empty, was more energy-intensive than U.S. air travel, because the planes were more than 80 percent full, on average.
There’s no question that the task of reducing carbon dioxide emissions in transportation is daunting. According to one estimate, vehicle travel in the U.S. would have to fall by half by 2050, or fuel efficiency would have to improve to 130 miles per gallon, or biofuels would have to make up most of the fuels on the market to avoid the worst impacts of climate change.
And people still like to buy big, heavy cars that can accelerate to 60 mph in less than four seconds. In a separate study this year, Schipper found that technological improvements to vehicle efficiency drove down fuel use per unit of horsepower by 50 percent in recent years, even as most of the potential fuel savings were wiped out by consumer’s preferences for larger, more powerful vehicles, particularly in the U.S.
Still, peak travel holds a glimmer of collateral benefits for the industrialized world. Higher prices at the pump, including higher fuel taxes, could help stimulate the manufacture of smaller, less powerful cars, change people’s driving habits and foment a renaissance in walking and bicycling, reducing carbon dioxide emissions below their present levels, Schipper said.
The growth of motorized travel in China, India and Brazil will reduce the overall impact of gains in the industrialized world, but they are still gains, he said. The average American car on the road today uses a third less fuel per mile than in 1973, and 20 percent less than in 1981, he said. For European cars, the savings is between 20 percent and 25 percent.
Traffic is paralyzed everywhere, and that will be an obstacle to motorization in the developing world in the end, Schipper said.
“My basic thesis is, ‘There ain’t room on the road,’” he said. “You can’t move in Jakarta or Bangkok or any large city in Latin America or in any city in the wealthy part of China. I think Manila takes the prize. Yes, fuel economy is really important, and yes, hybrid cars will help. But even a car that generates no CO2 still generates a traffic problem.
“Sadly, what is going to restrain car use the most is that you can’t move.”