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1 SUMMARY Representing Freight in Air Quality and Greenhouse Gas Models The purpose of NCFRP Report 4: Representing Freight in Air Quality and Greenhouse Gas Models is to review and evaluate current methods used to estimate air emissions from freight transportation activities and determine their suitability for decision making and public education. All freight modes are represented, including heavy-duty trucks, rail, ocean- going vessels, harbor craft, cargo handling equipment, and air freight. To the extent possible, three geographic scales are analyzed for each mode, namely at the national, regional, and local/project levels. This report is organized by transportation mode since many emission models and methods used to estimate freight emissions are specific to each mode. Methods, models, and para- meters are discussed for each freight mode. The accuracy of models to estimate emissions is described for each mode as well as the data collection process and system boundaries. Pol- lutants of concern include greenhouse gas emissions, criteria pollutants, and air toxics. The application of freight emission models in influencing government decisions is also discussed. Freight emissions can directly affect decisions over how public (and private) funds are spent on infrastructure projects and associated mitigation measures. They are used in the preparation of environmental documents to satisfy National Environmental Policy Act (NEPA) and related state statutes, and in analyses required under the General Conformity regulations. Emission estimates also can serve as inputs to dispersion models that use mete- orological information to simulate the atmospheric dispersion of pollutants and estimate resulting spatial concentrations. The examination of accuracy and uncertainty of methods and models in this report is done mostly on a qualitative basis, identifying strengths and weaknesses, as well as evaluat- ing the parameters that have the largest impact on final emissions and highest uncertainty relative to others. The evaluation of methods, models, and parameters is done for each trans- portation mode at the national, state, and local/project-level scales. At the national level, the report examines the Inventory of U.S. Greenhouse Gas Emissions and Sinks (1) and the National Emissions Inventory (2). These approaches differ from other mode- specific transportation methodologies in that they span all modes, and are better analyzed independently of individual modal methodologies. For regional and project-level scales, the analysis is mode specific. For heavy-duty trucks, the report examines MOBILE6.2 and EMFAC2007, which are the currently approved models for preparing SIPs, conformity analyses, and project-level analysis to fulfill NEPA/CEQA requirements. In addition, MOVES2009 and CMEM also are examined. Issues regarding the application of these models to regional and project-level scales also are discussed. (Note, MOVES2009 will soon replace MOBILE as the approved emissions model for these applications.)
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2 For rail, this report examines methods at the regional and project-level scales that esti- mate fuel consumption from different rail parameters. These include allocation techniques from traffic density, active track, number of switchers or hours, number of employees, and time-in-notch calculations. The uncertainties in these estimation techniques and the input parameters are discussed. For ocean-going vessels, three basic methods for calculating emissions at ports are dis- cussed, namely (1) a detailed methodology where considerable information is gathered regarding ships entering and leaving a given port, (2) a mid-tier method that uses some detailed information and some information from surrogate ports, and (3) a more stream- lined method in which detailed information from a surrogate port is used to estimate emis- sions at a "like" port. Uncertainty in both methodology and input parameters is discussed. For harbor craft, there are no established models. Emissions are estimated by a number of techniques depending upon geographic scale. Uncertainty in freight-related harbor craft emission estimates from these methodologies can be attributed to process uncertainty (i.e., degree to which the methods accurately represent actual emissions) and parameter uncer- tainty (i.e., uncertainty in the individual elements used for calculations). These are discussed in this report. Generally, cargo handling equipment (CHE) emissions at ports are estimated using either the NONROAD or OFFROAD emission models--or methods similar to those in the mod- els. Two general categories of methods are used to estimate CHE emissions. These are referred to as the "best practice" and "streamlined" methodologies. Both methods are discussed and the relative uncertainties examined. The representation of freight activity in air transportation is perhaps the most challenging among all modes because air freight, unlike other modes, also is transported in passenger aircraft. Emissions associated with the transport of freight by aircraft were analyzed using two modeling approaches, namely FAA's System for Assessing Aviation's Global Emissions (SAGE) and the Emissions and Dispersion Modeling System (EDMS), which also was devel- oped by FAA. These methods and the variety of input parameters are discussed and analyzed. The report discusses air quality models and how air quality concentrations are assessed from the emission estimates for each transportation mode and scale. The associated uncer- tainties are examined as well. The report includes a Conceptual Model that offers a comprehensive representation of freight activity in the United States, covering all modes and relationships between modes. For this model to be effective in improving emissions estimates, it captures the factors in freight movements and freight equipment that most influence emissions. The Conceptual Model provides the link between economic activity, freight transportation activity, freight- related emissions, and associated health effects. Finally, the report presents five recommended areas for research that offer great promise for improving freight emissions estimates.