Traffic fumes from motorways can seriously impair the lung development of children, new research suggests.
A large-scale study in California found that 10-year-olds who lived within 500 metres of a motorway suffered a "substantial" loss of lung function by the age of 18.
The effect became less the further away a child lived from the road.
A similar impact was seen on both boys and girls, and there was little influence from social background, other pollution sources, or exposure to tobacco smoke.
Between the ages of 10 and 18, a period of rapid lung growth occurs. This can be assessed with tests which measure the amount of air a child can blow into a tube.
The scientists carried out annual lung function tests on 3,677 Californian children for eight years.
Those living at least 1,500 metres from a major road were used as a baseline. Compared with them, children living closer to motorways had less "puff" at the age of 18.
The researchers, led by Dr James Gauderman, from the University of Southern California in Los Angeles, reported in The Lancet medical journal: "Pronounced deficits in attained lung function at age 18 years were recorded for those living within 500 metres of a freeway."
For one test, their average performance was 3% lower than that of the baseline children. Another test showed an almost 7% reduction, but individual children had deficits of up to 10%.
The scientists said their findings pointed to diesel pollution as being a prime culprit.
