That's according to a study of more than 3,000 southern California children, published in The Lancet's online edition.
"Since lung development is nearly complete by age 18 years, an individual with a deficit at this time will probably continue to have less than healthy lung function for the remainder of his or her life," write researcher W. James Gauderman, Ph.D., and colleagues.
The study may raise "important questions for society about the structure of the transportation system, engines, fuels, combustion, and road dust in urban areas," editorialists write in The Lancet.
Gauderman works in the University of Southern California's preventive medicine department. He and his team studied 3,677 children in 12 communities in southern California.
The children were in the fourth grade (average age: 10 years) when the study started in the 1990s. They took yearly lung function tests for up to eight years.
Children 10 to 18 go through a period of rapid lung development, the researchers note.
The researchers also looked at how close the children lived to freeways and found that 440 lived less than a third of a mile from one.
Their results showed that the children living that close to a freeway had slower lung development during the study, compared with those living at least three times farther from a freeway.
The findings held after the researchers took other factors into account, including family income, race, asthma, smoking, regional air quality, and kids who moved during the study.
Local roads that weren't freeways were not associated with slower lung development. The children weren't followed beyond age 18, so it's not clear how well their lungs functioned later in life.
The concentration of pollutants in the area near major freeways may be the problem, but it's hard to rule out other influences, note Gauderman and colleagues.
It's also not clear what factors, if any, influenced the kids' lung development before age 10, say the editorialists. They included Thomas Sandstrom, M.D., Ph.D., of the respiratory medicine and allergy department of University Hospital in Umea, Sweden.
"However, these questions should not distract from the major achievement of follow-up of such a large group of children through secondary school with repeated lung function tests," write the editorialists.
The study was funded in part by the California Air Resources Board, the National Institute of Environmental Health Sciences, and the Environmental Protection Agency.
SOURCES: Gauderman, W. The Lancet, Jan. 26, 2007; online edition. Sanstrom, T., The Lancet, Jan. 26, 2007; online edition.
By Miranda Hitti
Reviewed by Louise Chang, M.D