The good news about air pollution doesn't mean everyone fares better.
Greg Pratt, a Minnesota Pollution Control Agency (MPCA) research scientist, said a growing body of evidence shows that people living in high-traffic corridors are at higher risk for certain diseases.
That makes road-expansion projects such as on I-35W through Southwest environmentally controversial.
A paper published in 2001 in "JAMA," the Journal of the American Medical Association, found that efforts to reduce downtown Atlanta congestion during the 1996 Olympics resulted in less traffic and less ozone, and correlated with lower rates of childhood asthma acute care events.
Pratt has a stack of studies suggesting negative health effects from vehicle-generated pollution.
A February 2003 paper published in "Environmental Health Perspectives" suggested a 10 to 20 percent increased risk of preterm births for women potentially exposed to high-traffic-related air pollution levels.
A February 2000 paper in the "Journal of the Air and Waste Management Association" suggested children living near heavily traveled roadways have a higher childhood cancer risk. The study found elevated risks for children living within 750 feet (slightly more than one long city block) of roads carrying 20,000 vehicles or more per day -- similar to flows on Hennepin Avenue through Southwest, or Lake Street near I-35W.
Making comparisons with high-volume Southwest byways is difficult, however. For instance, pollution from 20,000 cars a day could vary depending on a number of conditions, such as congestion: the more congestion, the more pollution, traffic engineers say.
Pratt said some people cite the studies while others criticize them.
Dave Thornton, MPCA's manager of policy and planning for air issues, said people who live near freeways or factories are probably exposed to higher concentrations of air pollution, but area freeways such as I-35W are recessed, perhaps minimizing exposure.
Thornton could not say what the health effects might be. "We haven't done enough work here to be able to make any conclusive statements," he said.
University of Minnesota researchers may find an answer. They have applied for $300,000 to better understand how pollution -- notably extremely tiny particles called nanoparticles -- might affect the health of residents living by high-traffic corridors.
Prof. David Kittelson of the University Center for Diesel Research and Winthrop Watts, research associate and industrial hygienist, want to study nanoparticles in and around places such as I-35W and I-94.
The federal government regulates fine particles, called PM2.5, the size of fine dust. Nanoparticles are 50 times smaller than the largest of the fine particles, said Kittelson.
Commuters and people within 1,000 meters of the freeway -- approximately six-tenths of a mile -- can get significant nanoparticle exposures, Kittleson said. The closer to the freeway, the higher the exposure.
While studies show people living near roadways have higher rates of health problems, scientists do not understand why, he said.
"There are concerns that nanoparticles are dangerous," Kittleson said, but "it might be something else near the roadway."
If they get the grant, Kittelson and Watts would use a large mobile laboratory -- a truck with a 20-foot container -- to drive busy metro freeways to identify nanoparticle hot spots, so that health researchers could do focused follow-up studies.
Mayor R.T. Rybak wrote the U.S. Environmental Protection Agency to support the project.
"This research is critical to help us better understand the air quality implications of slated highway expansion in and around Minneapolis," he wrote.