It said there was “strong evidence” that exposure to traffic helped cause variations in heart rate and other heart ailments that result in deaths. But among the many studies that evaluated death from heart problems, some did not separate stress and noise from air pollution as a cause, it said.
The institute, based in Boston, is jointly financed by the Environmental Protection Agency and the auto industry to help assure its independence. Its reports are peer-reviewed but are not published in a scientific journal.
The researchers noted that proving that air pollution from vehicles caused illness was difficult. The pollutants studied often come from sources like industry in addition to cars and trucks, they said, and many of the studies failed to rule out factors like income levels that could contribute to the illnesses studied.
Many people who live near major roads fall into lower-income categories. Vibration and noise rather than air pollution could also cause some health damage, the report said.
Nonetheless, “we see a strong signal that says traffic exposure seems to be causing effects,” said Dan Greenbaum, the president of the institute.
The study found that the biggest effects occurred among people who lived within 300 to 500 meters — about two-tenths to three-tenths of a mile — from highways and major roads. That applies to 30 percent to 45 percent of the population of North America, the authors said.
The pollutants studied in the report do not include ozone, the chemical for which the Environmental Protection Agency proposed new regulations last week. Ozone is more prevalent in places distant from highways.
For many categories of health effects, the authors concluded that the studies completed so far suggested that air pollution from vehicles was the cause, without establishing that as fact.
Contacted for comment, the environmental agency said it welcomed the study. The agency added that it was taking steps to cut toxic materials in gasoline and that the federal recovery act included $300 million for cleaning up diesel engines.
Outside experts briefed on the study had mixed reactions.
“Like the issue of second-hand smoke, it’s very difficult to understand the exact mechanisms that make it bad — but it’s easy to understand that it is in fact bad,” said Rich Kassel, an expert on diesel engines at the Natural Resources Defense Council, an environmental group. “This study underscores that difficulty.”
“Despite 40 years of building ever-cleaner vehicles, we still have a vehicle pollution problem in this country,” Mr. Kassel said.
Howard J. Feldman, the director of regulatory and scientific affairs at the American Petroleum Institute, noted that the evidence of a causal factor was inconclusive for some ailments.
“The only conclusive thing that was found was with the asthma,” Mr. Feldman said. “Nothing else was found to be conclusive, which to me was interesting in itself.”
“These are epidemiological studies, which by definition reflect past exposures with past fuels,” he added.
As emissions from traffic decline, Mr. Feldman predicted, exposures from other sources will become more important.