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Multi-Pollutant Emissions Benefits of Transportation Strategies-FHWA

8. Conclusion

This report has provided an overview of traditional and innovative transportation-related control strategies intended to assist transportation practitioners in considering a broad range of strategies to reduce transportation-related emissions of concern. Specifically, this report has focused on identifying the effect of strategies on seven major pollutants - CO, PM-10, PM-2.5, NOx, VOCs, SOx, and NH3 - through the calculations of emissions impacts for sample projects. It is increasingly relevant for transportation agencies to understand the effects of emissions reduction strategies on a range of these seven pollutants since many regions are facing multiple air quality objectives. Additionally, in some cases, control strategies successful in reducing one pollutant may actually increase emissions of another pollutant. In other cases, control strategies may effectively reduce multiple pollutants.

In summary, the strategies examined within the document demonstrate the following general emissions effects, based on type of transportation system effect:

The findings are limited somewhat by the current state of research and limitations in the established motor vehicle emissions model, MOBILE6.2, in regard to speed effects of PM, SOx, and NH3. EPA's new MOVES model, as a modal emissions model, will more accurately be able to capture the effects of changes in traffic flow, and speed implications for the various pollutants. EPA guidance should be consulted for information on calculating emissions impacts for use in SIP development, and methods and assumptions for use in a conformity determination should be determined through the interagency consultation process.
Cost-effectiveness of these strategies is not evaluated as part of this report. Resources are available that provide a rough indication as to how strategies compare with respect to cost effectiveness. Provided below is a list of recommended resources for further discussion on this topic. By no means is this list intended to be comprehensive, but rather serve to highlight useful and relevant sources of further guidance.

"8-Hour Attainment: Control Strategies: On Road," prepared for North Central Texas Council of Governments by ENVIRON Corp., 2006,

"The Carl Moyer Memorial Air Quality Standards Attainment Program Guidelines," California Air Resources Board, 2005,

"Clearinghouse for Inventories and Emissions Factors," U.S. Environmental Protection Agency, 2006,

"Congestion Mitigation and Air Quality (CMAQ) Improvement Program," Federal Highway Administration, 2006,

"Costs and Emissions Impacts of CMAQ Project Types," prepared for U.S. Environmental Protection Agency Office of Policy by Hagler Bailly, Inc., September 1999,

"Mobile Sources," U.S. Environmental Protection Agency, 2006,

"A Sampling of Emissions Analysis Techniques for Transportation Control Measures," prepared for Federal Highway Administration by Cambridge Systematics, Inc., October 2000,

Updated: 6/28/2017
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