Aging Vehicle Fleet Polluting The Air

May 17, 1999

With six years of emissions data on more than 2 million metro Atlanta vehicles, researchers have determined the city's fleet is growing old and polluting the air.

The average vehicle in Atlanta has about 90,000 accumulated miles on it, and there are a significant number of vehicles with more than 200,000 miles on them, according to Georgia Tech's Air Quality Laboratory. Researchers analyzed emissions inspection and vehicle registration records to make these estimates.

"Atlantans drive more per day and keep their vehicles longer than drivers in many other major U.S. cities, particularly those in the North where vehicles don't last as long because of salt on the roads," says Dr. Michael Rodgers, director of the Air Quality Laboratory. "Our concern is that we expect this trend to continue, and as vehicles get older, there is degradation. Their emissions control systems become less efficient, and the vehicles release more pollution into the air."

Rodgers and his research team are entering their seventh year of a long-term vehicle emissions monitoring program of Atlanta and short-term studies in other eastern U.S. cities. The Georgia Department of Natural Resources has funded the Atlanta study with about 25 cents of the $25 emissions inspection fee charged per vehicle in the metro area. The U.S. Environmental Protection Agency funds other parts of the program.

The researchers use remote sensing, vehicle registration data, roadway observation studies and laboratory testing to compile emissions data that provides insight into ozone pollution problems.

"Previously, there was not a systematic methodology for determining the effect of aging on a vehicle fleet over time with on-road measurements," Rodgers says. "The Atlanta study is now the oldest monitoring program of its type in the world."

Short-term studies conducted in New York City, Boston, Baltimore, Nashville and Raleigh, N.C., complement the findings of the Atlanta monitoring program. Studies are planned for parts of Oregon, Utah and California this year. Altogether, they are giving researchers cause for concern, they say.

"Most vehicles gradually increase their emissions, but with aging vehicles, there are some catastrophic failures, such as holes in catalytic converters," Rodgers explains. "Some estimates show that vehicles with catastrophic emissions systems failures can be responsible for 50 to 70 percent of emissions."

Fuel-injected vehicles manufactured since the mid-1980s tend to deteriorate more slowly than the previous generation of vehicles, Rodgers says. But people are driving their vehicles longer now, even in excess of 300,000 miles. So Atlanta can expect to see an increase in catastrophic failures in vehicle emissions control systems as its fleet ages, Rodgers explains.

Emissions inspections presumably detect vehicles with catastrophic failures. In reality, however, only 1 percent of vehicles manufactured in the past six years has failed an emissions test. "It's like looking for a needle in a haystack," Rodgers says. But the search is worth it because of their significant contribution to air pollution.

Researchers in the Air Quality Laboratory regularly conduct remote sensing and roadway studies along the metro Atlanta area's interstate highways. In remote sensing studies, researchers gather vehicle information at entrance and/or exit ramps. In just seven-tenths of a second, remote sensing equipment measures a vehicle's emissions as it breaks an infrared beam in its path. Other equipment photographs the vehicle's tag; researchers later use this photo to correlate emissions data with registration data.

In a typical day, researchers gather information on 4,000 vehicles. In Atlanta, researchers gather data on 30,000 vehicles a month. Since 1993, they have collected data on more than 2 million vehicles in the 13-county metro Atlanta area. Augusta, Ga., Macon, Ga., and Nashville, Tenn., are the control cities where researchers collect data they compare with their findings in Atlanta.

In roadway observations, researchers determine the total emissions released on a particular roadway. For example, a recent study was conducted on Interstate 20 near Bremen, Ga. Researchers measured emissions from commercial trucks overnight. They monitored emissions and weather conditions both upwind and downwind.

The Air Quality Laboratory also conducts vehicle tests in its new dynamometer lab, which is being donated to Georgia Tech this spring by Atlanta Gas Light Company. There, researchers determine when and why vehicles release high and low amounts of emissions. This detailed information complements the less detailed data gathered in remote sensing studies. Researchers also conduct dynamometer equivalent tests on vehicles they purchase and equip with emissions instrumentation. They monitor these vehicles for two to nine months at a time.

"Georgia Tech is one of a very few places in the United States to do both remote sensing and dynamometer testing," Rodgers says. "So we probably have the most comprehensive, university-based vehicle emissions testing program in the country."
For technical information, contact:
1. Dr. Michael Rodgers, 404-894-5609; e-mail:
2. Leisha Davis, 404-894-9345; e-mail:
3. Mikhail Fogelson, 404-894-8103; e-mail:

Georgia Tech Research News and Research Horizons magazine, along with high resolution JPEG images, can be found on the Web at

Georgia Institute of Technology

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