It turns out those big concrete barriers put up along busy highways to shield neighboring residents from the roar of traffic also reduce how much air pollution they get from the passing vehicles.
That's what a new government study found, anyway. Researchers with the National Oceanic and Atmospheric Administration and the Environmental Protection Agency released harmless "tracer" gases along highways to track how they were dispersed through the air - and by extension, indicate what happens to harmful pollutants such as carbon monoxide, soot and benzene that are emitted by cars and trucks going by.
The researchers found that in addition to blocking out sights and sounds of traffic, the barriers apparently channel air flow - and many of the pollutants - up and away from nearby residential areas.
"We also found that the barriers tend to trap pollutants in the area of the roadway itself, especially at night in low wind-speed conditions," said Dennis Finn, a NOAA meteorologist from Idaho, and lead author of the study, published in the journal Atmospheric Environment.
That ought to be an added relief to residents sleeping in homes shielded from highways by those barriers - though if you're on the highway you may not want to breathe too deeply or stay long if you find you have to stop your car on the shoulder in one of those concrete sound-barrier canyons.
(1998 Baltimore Sun photo by Lloyd Fox of sound barrier being built on I-695 near US 40)