Vehicle Emissions Modeling Researchers develop model to better predict vehicle emissions and ozone pollution formation.

It's been more than five years in the making at Georgia Tech. This fall, it is expected to make its debut. It is a new motor vehicle emissions model that can be used in developing transportation plans and air pollution control strategies.

photo by Stanley Leary Transportation researcher Dr. Billy Bachman uses geographic information systems (GIS) technology to integrate data in a spatial format. Researchers are using this GIS framework to predict vehicle operating profiles and subsequently estimate emissions. (300-dpi JPEG version - 540k)

main traffic story Getting Out of the Heat Vehicle Emissions Modeling Viewpoints Growing Old and Polluting the Air Air Pollution Facts Correlating Travel and Land Use Patterns Georgia Transportation Institute Understanding and Predicting Ozone Pollution Commercial Vehicle Operations On the Road

The Mobile Emission Assessment System for Urban and Regional Evaluation (MEASURE) estimates vehicle production of carbon monoxide, volatile organic compounds and oxides of nitrogen in space and time. MEASURE differs from the U.S. Environmental Protection Agency's current model in that it estimates vehicle emissions as a function of vehicle operating modes — such as cruise and idle — rather than average vehicle speeds. Because it is a modal model, researchers believe MEASURE more accurately reflects on-road emissions.

"The current emissions model says to reduce emissions, you need to reduce total vehicle miles traveled or have vehicles operating at an optimal speed of 45 miles an hour," says Dr. Billy Bachman, a MEASURE researcher in Tech's Center for Geographic Information Systems.

"But the new models tells us what we really need to do is reduce stop and go activity and the amount of driving under conditions that demand greater engine power output — for example, high speed and hard acceleration driving. These operating conditions often result in high fuel-to-air ratios in the engines, significantly increasing tailpipe pollution levels."

MEASURE works within a geographic information systems (GIS) framework that predicts vehicle operating profiles and subsequent emissions. GIS is a valuable research tool that integrates a variety of data in a spatial format. Using GIS, the MEASURE model can distinguish emissions for many vehicle technology groups (engine, fuel and emission control technology combinations) across a variety of vehicle operating modes. These modes include cruise, acceleration, deceleration, idle and others that cause high fuel-to-air ratios, which pollute the air.

Viewpoints... return to main story "We will never 'solve' our air quality problems as long as we're an industrial society. What we must do is manage our air quality, and that starts with making countless small decisions, both public and private. It starts with individuals and the decisions they make about combining trips, the type of vehicles they buy, whether they drive for fun or not, and whether they move closer to their jobs." — Dr. Michael Rodgers director of Georgia Tech's Air Quality Laboratory ****** "We need to reduce our automobile dependence. That is the long-term solution. . . . In the short term, we need to develop technological strategies, such as alternative fuels. We need both long- and short-term efforts. We're just chasing our tail if we only seek the short-term solutions." — Dr. Larry Frank assistant professor of city planning, Georgia Tech College of Architecture ****** "The most important thing we can do is get the public involved. Once they become a partner, they feel like they have ownership of not only the problems, but also the solutions. One way to do that is to use high-tech systems and package the information in such a way that people can make better, wiser, smarter, safer decisions. That's where it's at. That's my focus. I think it's going to affect the most people." — Dr. John Leonard assistant professor, Georgia Tech School of Civil and Environmental Engineering

Development of MEASURE has presented researchers with significant challenges. "Determining the reasons for emissions behaviors and determining how much of the vehicle fleet might exhibit similar behaviors is a great challenge," says Dr. Randall Guensler, an assistant professor of civil engineering and co-director of the project.

The MEASURE model, which is statistically based, uses vehicle activity data obtained from laboratory and on-road tests. Examples of vehicle activities analyzed in the model are: the number of vehicle starts when the engine is cold (because engines emit more pollutants when the catalytic converter is cold); and distribution of vehicle speeds and accelerations (because quick accelerations yield more pollution, accounting for more than half of the emissions output during a trip for some vehicle technologies).

The model combines this information with data on the characteristics of vehicle fleets (e.g., what percentage of vehicles are older and thus emitting more pollutants); traffic flow data; and external conditions, such as weather, that affect the production of ozone pollution from emissions. By tying model development and validation into ongoing real-world monitoring, such as the Georgia Tech Air Quality Laboratory's remote sensing studies, the MEASURE model will continue to evolve with the on-road fleet.

Because MEASURE operates in a GIS framework, it is compatible with the analytical and decision-making tools used by most state departments of transportation and metropolitan planning organizations. Researchers see this factor as a distinct advantage. For example, with MEASURE, local traffic engineers could determine areas with the highest emissions and decide how they might stagger vehicle starts, Bachman says. MEASURE output could also be used to model the air quality benefits of improving traffic flow with intelligent transportation systems, Guensler says. For example, traffic signal timing that reduces vehicle stop and go could significantly decrease emissions.

"When this model is complete, we will be able to determine the answers to a number of 'what-ifs'," says Dr. Michael Meyer, head of the School of Civil and Environmental Engineering, which spearheads the project. "What will happen if we increase vehicle occupancy or restrict use of lanes? What will happen to air quality if we do X, Y or Z?.... So this model could be used for transportation planning."

The various components of MEASURE are undergoing evaluation and validation testing at Georgia Tech. Researchers expect that by this fall, it will gain EPA's official support, though in a restricted capacity initially. When the Georgia Tech model receives initial approval, cities that choose to use MEASURE instead of the current vehicle emissions model may do so in conducting transportation analyses related to implementing traffic control strategies. MEASURE will be distributed to users as a software package. Guensler expects that Atlanta, Chicago, Los Angeles, San Francisco, Baltimore and Washington, D.C., will be among the first cities to use MEASURE to analyze traffic flow measures.

Initially funded by the U.S. Environmental Protection Agency and the Federal Highway Administration, the MEASURE project has now received research support from the Georgia Department of Transportation and the Atlanta Regional Commission.

— Jane M. Sanders

For more information, contact Dr. Randall Guensler, School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0355. (Telephone: 404/894-0405) (E-mail: randall.guensler@ce.gatech.edu)

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Last updated: May 28, 1999