The general approach to quantifying the emissions-related benefits or disbenefits of a transportation project involves the following steps:
emission models, such as the EPA's MOVES model,
California's EMFAC model and other similar mobile source emissions
models can be used to predict the per-mile vehicle emissions under
various vehicle operating conditions and location specific atmospheric
conditions. The following factors tend to affect emission rates:
The table below summarizes estimated costs per metric tonne of emissions, and unit costs per vehicle-mile, based on various studies. Some jurisdictions or government agencies have standard units to be used when evaluating air pollution costs.
Regional Pollution Studies Summary Table – Selected Studies (Litman 2009)
There are several issues that may arise when estimating emissions benefits. Assumptions and sensitivities in the results due to these issues should be noted in the presentation of the results:
AEA Technology (2005), Damages Per Tonne Emission of PM2.5, NH3, SO2, NOx and VOCs From Each EU25 Member State, Clean Air for Europe Programme, European Commission (http://ec.europa.eu/index_en.htm).
Booz-Allen & Hamilton Inc. California Life-Cycle Benefit/Cost Analysis Model (Cal-B/C) Technical Supplement to User's Guide. California Department of Transportation (Caltrans), 1999. Available at: http://www.dot.ca.gov/hq/tpp/tools_files/tech_supp.pdf.
Mikhail Chester and Arpad Horvath (2008), Environmental Life-cycle Assessment of Passenger Transportation: A Detailed Methodology for Energy, Greenhouse Gas and Criteria Pollutant Inventories of Automobiles, Buses, Light Rail, Heavy Rail and Air v.2, Paper vwp-2008-2, UC Berkeley Center for Future Urban Transport (www.its.berkeley.edu/volvocenter). Available at: www.sustainable-transportation.com.
Mark A. Delucchi (2005) A Multi-Country Analysis of Lifecycle Emissions from Transportation Fuels and Motor Vehicles, Institute of Transportation Studies, University of California Davis (www.its.ucdavis.edu). Available at:www.its.ucdavis.edu/publications/2005/UCD-ITS-RR-05-10.pdf.
DfT (2009), Transport Analysis Guidance: 3.3.5: The Greenhouse Gases Sub-Objective, Department for Transport (www.dft.gov.uk). Available at: www.dft.gov.uk/webtag/documents/expert/unit3.3.5.php.
EC (2005), ExternE: Externalities of Energy - Methodology 2005 Update, Directorate-General for Research Sustainable Energy Systems, European Commission (www.externe.info). Available at: www.externe.info/brussels/methup05a.pdf.
EDRG (2007), Monetary Valuation of Hard-to-Quantify Transportation Impacts: Valuing Environmental, Health/Safety & Economic Development Impacts, NCHRP 8-36-61, National Cooperative Highway Research Program (www.trb.org/nchrp). Available at: www.statewideplanning.org/_resources/63_NCHRP8-36-61.pdf.
Environmental Valuation Reference Inventory (www.evri.ca) is a searchable storehouse of empirical studies on the economic value of environmental benefits and human health effects.
Federal Register (U.S.). (2010). “Environmental Protection Agency and Department of Transportation, National Highway Traffic Safety Administration: Light-Duty Vehicle Greenhouse Gas Emission Standards and Corporate Average Fuel Economy Standards; Final Rule.” Vol. 75, No. 88 (May 7, 2010).
ITDP and CAI-Asia Center (2010), Transport Emissions Evaluation Models for Projects (TEEMP), Clean Air Initiative for Asian Cities (www.cleanairinitiative.org) and the Institute for Transportation and Development Policy (www.itdp.org); at www.cleanairinitiative.org/portal/node/6941. These Excel-based TEEMP models were developed for evaluating the emissions impacts of Asian Development Bank’s transport projects (www.adb.org/Documents/Evaluation/Knowledge-Briefs/REG/EKB-REG-2010-16/default.asp) and were modified and extended by ITDP, CAI-Asia and Cambridge Systematics for the for Global Environmental Facility (www.thegef.org) Scientific and Technical Advisory Panel (STAP). The Manual for Calculating Greenhouse Gas Benefits of Global Environmental Facility Transportation Projects (www.thegef.org/gef/GEF_C39_Inf.16_Manual_Greenhouse_Gas_Benefits) provide step-by-step instructions for developing baseline and impact estimations for various types of transport policies and projects, including transport efficiency improvement, public transport, non-motorized transport, transport demand management, and comprehensive transport strategies.
Todd Litman (2009), “Evaluating Carbon Taxes As An Energy Conservation And Emission Reduction Strategy,” Transportation Research Record 2139, Transportation Research Board (www.trb.org), pp. 125-132; based on Carbon Taxes: Tax What You Burn, Not What You Earn, Victoria Transport Policy Institute (www.vtpi.org). Available at:www.vtpi.org/carbontax.pdf.
Todd Litman (2010), "Safety and Health Impacts," Transportation Cost and Benefit Analysis, Victoria Transport Policy Institute (www.vtpi.org). Available at www.vtpi.org/tca/tca0503.pdf.
M. Maibach, et al. (2008), Handbook on Estimation of External Cost in the Transport Sector, CE Delft (www.ce.nl). Available at: http://ec.europa.eu/transport/sustainable/doc/2008_costs_handbook.pdf.
Lena Nerhagen, Bertil Forsberg, Christer Johansson and Boel Lövenheim (2005), The External Costs of Traffic Air Pollution, Report 517, Swedish National Road and Transport Institute (www.vti.se).
Nadine Unger, et al. (2011), “Attribution Of Climate Forcing To Economic Sectors,” Proceedings of the National Academy of Sciences of the U.S. (www.pnas.org): at www.pnas.org/content/early/2010/02/02/0906548107.abstract.
Urban Transportation Emissions Calculator (www.tc.gc.ca/UTEC) provides tools for estimating greenhouse gas (GHG) and criteria air pollution emissions from various types of vehicles.
US Environmental Protection Agency (EPA). (2011). MOVES (Motor Vehicle Emissions Simulator) Model. Available at: http://www.epa.gov/otaq/models/moves/index.htm.
Anming Zhang, Anthony E. Boardman, David Gillen and W.G. Waters II (2005), Towards Estimating the Social and Environmental Costs of Transportation in Canada, Centre for Transportation Studies, University of British Columbia (www.sauder.ubc.ca/cts), for Transport Canada. Available at: www.sauder.ubc.ca/cts/docs/Full-TC-report-Updated-November05.pdf.