EXPANDING METROPOLITAN HIGHWAYS: IMPLICATIONS FOR AIR QUALITY AND ENERGY USE. APPENDIX A: EMISSION AND ENERGY CHARACTERISTICS OF HEAVY-DUTY DIESEL-POWERED TRUCKS AND BUSES

Heavy-duty diesel-powered trucks are major contributors to oxides of nitrogen (NOx) emissions and combustion-derived particulate emissions in many urban areas. This appendix provides a brief review of the energy use and emissions characteristics of heavy-duty diesel vehicles (HDDVs) and reviews the effects of expansions of highway capacity on emissions. The structure of the HDDV fleet, which encompasses a wide range of vehicles [from 8,500 lb gross vehicle weight (GVW) to more than 80,000 lb GVW], is discussed. Data on sales, populations, and use of the HDDV fleet are presented. Historical and future emissions regulations for HDDVs are reviewed. Since California has been the leader in new emission standards and in-use controls, particular attention is given to the California standards and the proposed low-emission truck standards. Fuel standards and in-use requirements are also discussed in detail. The data that have been used to construct emission factors and speed correction factors for HDDVs are reviewed. In particular, U.S. Environmental Protection Agency (EPA) emission factors and speed correction factors are contrasted with the findings on these issues from other data or engineering analyses. HDDV fuel economy data are reviewed, with emphasis on average fuel economy derived from surveys. Data on the change of fuel economy with speed derived from simulation models or on-road tests are presented. These data and their relationship to the conversion factor used to convert emissions expressed in units of work to the more familiar units of grams per mile are explored. Finally, the findings are summarized in the context of the National Research Council's project goals of estimating the effects of expansions of highway capacity.