Assessment of Emission Reduction Potential of Truck Freight Diversion to Other Transportation Modes and Development of Improved Methods for Estimating Air Quality Benefits of Freight Modal Shifts

Focus Area

Air Quality


Air Quality






1-2 years

Research Idea Scope


Truck freight operations are a major source of air pollutants, including criteria pollutants, toxic air pollutants and greenhouse gas emissions. Although the 2008-2010 recession has led to recent reductions in freight shipments, growth projections for future freight volumes are enormous. Truck freight volume is projected to grow 26 percent by 2020 according to the American Trucking Association. The growth in container shipments to the nation’s ports is expected to be significant over the next twenty years. The widening of the Panama Canal will likely lead to large increases in the numbers of container ships using Gulf Coast ports and ports along the Atlantic coast.
The rate of fleet turnover for heavy-duty trucks impacts the level of emissions associated with the movement of freight. Overall, sales of new heavy-duty diesel trucks are down 30-40 percent compared to 2008. EPA’s MOVES model will reportedly produce higher emission estimates for some major pollutants emitted by heavy duty trucks, including higher NOx and somewhat higher particulate matter (PM) emissions. The new emissions model has also significantly increased the estimate of the number of existing diesel engines (i.e., the so-called “legacy fleet”) from 11 million to 20 million engines. 
EPA classifies diesel exhaust as a probable human carcinogen. Recent health studies are providing more evidence of the human health effects of living near major freight corridors and facilities. These health effects include statistically significant increases in leukemia and asthma rates in areas very near areas with high volumes of diesel traffic. The location and distribution of these areas of elevated risk often raise environmental justice concerns.
One major strategy for reducing emissions from truck freight operations is to divert truck freight to other transportation modes, such as rail and river transportation (e.g., barges). These modes are generally thought to be more efficient and that diverting truck freight to these modes will lead to lower emissions than if the freight were hauled by truck. Transportation and air quality agencies also need an improved, more accurate methodology or package of methods for estimating the emission reductions that may be achieved by a project designed to divert freight volumes to other transportation modes.
Research Objectives

The purpose of this research is to develop an improved emission estimation methodology or methodologies that would provide more accurate and reliable estimates of the air quality benefits that could be achieved by projects designed to shift truck freight to other modes.
The second purpose of the research is to identify and recommend an improved methodology for estimating the emission benefits of truck freight diversion. There may be a need for more than one methodology. On one hand, transportation agencies need improved methods that will produce more accurate and reliable estimates for truck freight diversion. For example, the standard equations used to determine emission reduction benefits assume that trucks that divert freight to rail are then removed from service and cease to emit air emissions. That is very rarely the case. Typically, the truck just ends up hauling freight along a different route.
On the other hand, most agencies need a methodology that is easy to use and that does not require the agency to gather a great deal of information to use it. A spreadsheet analytical tool would be very helpful, but may not be able to significantly improve the quality of emission estimates. The research may lead to a decision to develop a easier to use and less data-intensive method that would be appropriate for some projects, and a more robust and data-intensive method that would be appropriate for larger or more ambitious projects.
The research should begin with a literature survey of methods that have been developed and used, and then proceed with a critical evaluation of the strengths and weaknesses of the alternative methods that are identified. After selecting the strongest published method, the researchers should attempt to identify possible improvements in that method that would reduce its identified weaknesses. Describing this best, improved method and how to use it will be the primary deliverable for the research.

  1. Conduct a literature search on available methods to estimate the air pollution emission reductions associated with truck freight diversion projects.
  2. Compare the strengths and weaknesses of the various methods and select the strongest overall method.
  3. Identify, test and apply potential enhancements that could improve the accuracy and reliability of the emission reduction estimates produced by the strongest emission reduction estimation method.
  4. Develop and describe the improved analytical method for estimating the emission reduction benefits of a truck freight diversion project. This method should address criteria pollutants, toxic air pollutants and greenhouse gases. To improve the accuracy of emission estimates, it may be necessary to increase the complexity and difficulty of the emission estimation method. If this is the case, the researchers should also develop a second method that is easier to use and less data-intensive. This second method may be appropriate for use with smaller projects.
  5. Provide a summary report based upon Tasks #1 through #4 that describes the methodology or methodologies developed for estimating air quality benefits of truck freight diversion. The report should provide sufficient information that the reader will be able to understand and use those models. The report should also describe the facts and issues related to estimating these air quality benefits, and how those contributed to the choice, enhancement and development of the methodologies that are recommended.


Urgency and Payoff

Suggested By

Ron Pate, WSDOT, Telephone: 360-705-7950 John Zamurs Chair Air Quality, Climate Change and Energy Subcommittee

[email protected]