Every commuter who's ever been stuck in traffic behind a diesel-powered bus or truck knows that it's a stinky, dirty place to be, and a new report shows that it's also very unhealthy.

The report by the nonprofit Clean Air Task Force says that although commuters spend only a tiny portion of their day -- usually less than an hour -- traveling to and from work, they get more than half of their daily exposure to unhealthy soot during that time.

The Boston-based environmental research and advocacy group's report also says commuters are exposed to high levels of airborne particles from diesel exhaust regardless of whether they commute by bus, train, car, bike or on foot because commuting corridors they use are so heavily polluted by diesel vehicles.

"Exposure to diesel exhaust during commutes poses a serious public health risk that can and must be fixed," said Rachel Filippini, executive director of the Group Against Smog and Pollution, which joined Clean Water Action in releasing the report yesterday in Pittsburgh.

Publication of the report is part of a campaign by those groups and more than a dozen others to reduce all sources of diesel-produced small particle pollution. When inhaled, those small bits of unburned carbon and chemicals permanently lodge deep inside lungs, and can cause lung cancer, strokes, heart attacks and infant deaths and trigger asthma attacks and allergies.

Locally, diesel exhaust causes thousands of asthma attacks and hundreds of heart attacks and shortens the lives of about 240 residents each year.

"The study shows that increased exposure to diesel exhaust is associated with health problems," said Dr. David Eibling, chief of otolaryngology at the VA Medical Center in Oakland. "The authors have shone a light on the problem. It's our challenge to redesign the commuter system."

The study, which measured diesel exhaust levels during commutes in Boston, New York City, Austin, Texas, and Columbus, Ohio, documented diesel particulate levels inside commuter cars, buses and trains that were four to eight times higher than the ambient outdoor air in those cities. And biking or walking to work is not necessarily healthier because those commuters are exposed to high levels of diesel pollution in the thoroughfares.

Ms. Filippini said such exposure could be greatly reduced by retrofitting the 13 million diesel vehicles in use today with filters that can reduce fine particle emissions by 85 percent or more.

Each filter, installed in place of the truck or bus muffler, costs $5,000 to $7,000.

"The technology is available now and particulate filters will be installed on all 2007 vehicles in the factory. But the transition to replace all the old diesels will take 30 years," said Ashleigh Deemer, Clean Water Action program organizer. "We need to retrofit as many vehicles as possible as soon as possible."

Ms. Deemer said the local environmental groups are working with Pittsburgh to set up a $130,000 pilot program to retrofit 10 vehicles in its fleet, and are calling on the city, Allegheny County and the Port Authority to retrofit all of their vehicles.

The county has committed $500,000 from its Clean Air Fund, which is funded by polluter fines, to a program that will help school districts retrofit their buses. The program pays all the costs of retrofitting buses for poorer school districts and three-quarters of the costs for more affluent districts.

North Allegheny School District, which used a federal funding source, and Penn Hills School District, which used the county money, have completed retrofits. Plum and Deer Lakes school districts have retrofitted their buses using money from a Toyota penalty settlement.

The Allegheny County Health Department is accepting applications from other school districts now, and has set March 15 as the deadline to submit a letter of interest and July 15 as the application deadline.