An evaluation of criteria for selecting vehicles fueled with diesel or compressed natural gas

References

• Ahlvik, P. & Brandberg, A. 2000. Relative Impact on Environment and Health from the Introduction of Low Emission City Buses in Sweden. 2000-01-1882. Warrendale, PA: SAE International.
   Google Scholar
• Barnitt, R. & Chandler, K. 2006. New York City Transit (NYCT) Hybrid (125 Order) and CNG Transit Buses. Final Evaluation Results. Technical Report NREL/TP-540-40125. Golden, CO: National Renewable Energy Laboratory. http://www.nrel.gov/vehiclesandfuels/fleettest/pdfs/40125.pdf.
   Google Scholar
• Beer, T., Grant, T., Brown, R., Edwards, J., Nelson, P., Watson, H., & Williams, D. 2000. Life-cycle Emissions Analysis of Alternative Fuels for Heavy Vehicles, Stage 1. Atmospheric Research Report C/0411/1.1. Aspendale, Australia: CSIRO, Australian Greenhouse Office. http://www.environment.gov.au/settlements/transport/publications/lifecycle.html.
   Google Scholar
• Beer, T., Grant, T., Morgan, G., Lapszewicz, J., Anyon, P., Edwards, J., Nelson, P., Watson, H., & Williams, D. 2001. Study of Life-cycle Emissions Analysis of Alternative Fuels for Heavy Vehicle, Stage 2. Final Report EV45A/2/F3C. Aspendale, Australia: CSIRO, Australian Greenhouse Office. http://www.environment.gov.au/settlements/transport/comparison/index.html.
   Google Scholar
• Beer, T., Grant, T., Williams, D., & Watson, H. 2002. Fuel-cycle greenhouse gas emissions from alternative fuels in Australian heavy vehicles. Atmospheric Environment 36(4):753–763.
   Google Scholar
• Beer, T., Grant, T., Williams, D., Watson, H., & Olaru, D. 2004. Life-Cycle Emissions Analysis of Fuels for Light Vehicles. Atmospheric Research Report HA93A-C837/1/F5.2E. Aspendale, Australia: CSIRO, Australian Greenhouse Office. http://www.environment.gov.au/settlements/transport/publications/lightvehicles.html.
   Google Scholar
• Bose, R. & Sundar, S. 2005. Emissions Test Results From Diesel Buses, With and Without Oxidation-Catalyst and Regenerating Particle-Trap, and CNG Buses With Three-Way Catalyst in India. 2005-01-0477. Warrendale, PA: SAE International.
   Google Scholar
• Braun, A., Pakzaban, P., Toqan, M., & Beér, J. 1987. Generation of biologically active substances in a natural gas flame. Environmental Health Perspectives 72(1):297–303.
   Google Scholar
• Brinkman, N. 2001. Well-To-Wheel Energy Consumption and Greenhouse Gas Analysis. Analysis of Fuel Cell Applications Workshop. June 26–27, Cincinnati, OH: Environmental Protection Agency. http://www.epa.gov/nrmrl/std/fuelcell/fuelslides/Brinkman_GM_Session3%20Presentation.ppt.
   Google Scholar
• Brinkman, N., Wang, M., Weber, T., & Darlington, T. 2005. Well-to-Wheels Analysis of Advanced Fuel/Vehicle Systems: A North American Study of Energy Use, Greenhouse Gas Emissions, and Criteria Pollutant Emissions. Argonne, IL: Argonne National Laboratory. http://www.transportation.anl.gov/pdfs/TA/339.pdf.
   Google Scholar
• Burtscher, H. 2005. Physical characterization of particulate emissions from diesel engines: a review. Journal of Aerosol Science 36(7):896–932.
   Google Scholar
• California Air Resources Board (CARB). 2002. Briefing Paper on Interim Results and Tentative Conclusions. Sacramento: CARB. http://www.arb.ca.gov/research/cng-diesel/briefing.pdf.
   Google Scholar
• Cannon, J. & Sun, C. 2000. Bus Futures: New Technologies for Cleaner Cities. New York: INFORM.
   Google Scholar
• Chamberlain, S., Modarres, M., & Mowrer, F. 2002. Compressed Natural Gas Bus Safety: A Qualitative and Quantitative Risk Assessment. College Park, MD: Center for Technology Risk Studies, University of Maryland. http://www.enre.umd.edu/ctrs/report.pdf.
   Google Scholar
• Chamberlain, S. & Modarres, M. 2005. Compressed natural gas bus safety: a quantitative risk assessment. Risk Analysis 25(2):377–387.
   Google Scholar
• Chandler, K., Walkowicz, K., & Clark, N. 2002. United Parcel Service CNG Truck Fleet: Final Results. Oak Ridge, TN: National Renewable Energy Laboratory. http://www.nrel.gov/vehiclesandfuels/fleettest/pdfs/31227.pdf.
   Google Scholar
• Chandler, K., Eberts, E., & Melendez, M. 2006. Washington Metropolitan Area Transit Authority: Compressed Natural Gas Transit Bus Evaluation. NREL/TP-540-37626. Golden, CO: National Renewable Energy Laboratory. http://www.nrel.gov/docs/fy06osti/37626.pdf.
   Google Scholar
• Cohen, J., Hammitt, J., & Levy, J. 2003. Fuels for urban transit buses: a cost-effectiveness analysis. Environmental Science and Technology 37(8):1477–1484.
   Google Scholar
• Cohen, J. 2005. Diesel vs. CNG for school buses: a cost effectiveness evaluation of alternative fuels. Energy Policy 33(13): 1709–1722.
   Google Scholar
• Davies, C., Findsen, J., & Pedraza, L. 2005. Assessment of the Greenhouse Gas Emission Benefits of Heavy Duty Natural Gas Vehicles in the United States. Final Report to U.S. Department of Transportation Center for Climate Change and Environmental Forecasting. McLean, VA: Science Applications International Corporation. http://climate.dot.gov/documents/natgasvehic092205.pdf.
   Google Scholar
• Di Pascoli, S. & Aldo, T. 2001. Natural gas, cars and the environment: a (relatively) “clean” and cheap fuel looking for users. Ecological Economics 38(2):179–189.
   Google Scholar
• Eastlake, A. 1999. The Latest Developments in Heavy Duty Vehicle Aftertreatment Testing for Real World Emissions and Fuel Economy. 1999-01-0470. Warrendale, PA: SAE International.
   Google Scholar
• Eaves, M. 2006. Ultrafine Control in Natural Gas Engines. Ultrafine Particles: The Science, Technology, and Policy Issues. April 30–May 2, South Coast Air Quality Management District, Los Angeles, CA. http://www.aqmd.gov/TAO/Ultrafine_Presentations/Session6_4_Eaves.pdf.
   Google Scholar
• Edwards, R., Griesemann, J., Larivé, J., & Mahieu, V. 2004. Well-to-Wheels Analysis of Future Automotive Fuels and Powertrains in the European Context. Version 1b. WTW Report 220104. Ispra, Italy: EUCAR, CONCAWE, & JRC. http://ies.jrc.ec.europa.eu/uploads/media/WTW_Report_220104.pdf.
   Google Scholar
• Edwards, R., Larivé, J., Mahieu, V., & Rouveirolles, P. 2007. Well-to-Wheels Analysis of Future Automotive Fuels and Powertrains in the European Context. Version 2c. WTW Report 010307. Ispra, Italy: EUCAR, CONCAWE, & JRC. http://ies.jrc.ec.europa.eu/uploads/media/WTW_Report_010307.pdf.
   Google Scholar
• Eudy, L. 2002. Natural Gas in Transit Fleets: A Review of the Transit Experience. APTA Bus & Paratransit Conference. May 19-24, Minneapolis: American Public Transportation Association. http://www.apta.com/research/info/briefings/documents/af_eudy.pdf.
   Google Scholar
• Farrell, A., Sperling, D., Arons, S., Brandt, A., Delucchi, M., Eggert, A., Haya, B., Hughes, J., Jenkins, B., Jones, A., Kammen, D., Kaffka, S., Knittel, C., Lemoine, D., Martin, E., Melaina, M., Ogden, J., Plevin, R., Turner, B., Williams, R., & Yang, C. 2007. A Low-Carbon Fuel Standard for California, Part 1: Technical Analysis. Paper UCB-ITS-TSRC-RR-2007-2. Berkeley, CA: Transportation Sustainability Research Center. http://repositories.cdlib.org/its/tsrc/UCB-ITS-TSRC-RR-2007-2/.
   Google Scholar
• Gautam, M., Wayne, S., Clark, N., Thompson, G., Carder, D., Burlingame, T., Thiagarajan, S., Oshinuga, A., Kreeb, R., Paris, H., Tadrous, T., & Graham, L. 2004. Characterization of Exhaust Emissions from a Catalyzed Trap Equipped Natural Gas Fueled Transit Bus. Proceedings of the 14th CRC On-Road Vehicle Emissions Workshop. March 29-31, San Diego, CA: Coordinating Research Council.
   Google Scholar
• Gautam, M., Kappanna, H., John, B., Wayne, W., Carder, D., Oshinuga, A., Kreeb, R., Paris, H., Graham, L., Tadrous, T., & Brown, K. 2005. Reduction and Characterization of Exhaust Emissions from a Catalyzed Trap Equipped Natural Gas Fueled Transit Bus. Proceedings of the 15th CRC On-Road Vehicle Emissions Workshop. April 4–7, San Diego, CA: Coordinating Research Council.
   Google Scholar
• Gautam, M. 2006. Control of Toxics and Nanoparticle Emissions from CNG-Fueled, Heavy-Duty Transit Buses. Ultrafine Particles: The Science, Technology, and Policy Issues. April 30– May 2, South Coast Air Quality Management District, Los Angeles, CA. http://www.aqmd.gov/TAO/Ultrafine_Presentations/Session5_2_Gautam.pdf.
   Google Scholar
• General Motors Corporation, Argonne National Laboratory, BP, ExxonMobil, & Shell. 2001. Well-to-Wheel Energy Use and Greenhouse Gas Emissions of Advanced Fuel/Vehicle Systems–North American Analysis. Executive Summary Report. Argonne, IL: Argonne National Laboratory. http://www.transportation.anl.gov/pdfs/TA/163.pdf.
   Google Scholar
• Gragg, K. 1995. Emissions from Two CNG Fueled Buses. Report No. MTC 9405B. Haninge, Sweden: ASB Motortestcenter. Harris, J. 2006. Application of Particulate Filter Technology to a CNG Engine. Ultrafine Particles: The Science, Technology, and Policy Issues. April 30–May 2, South Coast Air Quality Management District, Los Angeles, CA. http://www.aqmd.gov/TAO/Ultrafine_Presentations/Session5_4_JonathanHarris.pdf.
   Google Scholar
• Hess, D. 2007. What is a clean bus? Object conflicts in the greening of urban transit. Sustainability: Science, Practice, & Policy 3(1):45–58. http://ejournal.nbii.org/archives/vol3iss1/0608-027.hess.html.
   Google Scholar
• Hesterberg, T., Lapin, C., & Bunn, W. 2008. A comparison of emissions from vehicles fueled with diesel or compressed natural gas. Environmental Science and Technology 42(17):6437–6445.
   Google Scholar
• Heywood, J., Borak, J., Parsley, B., Pickett, T., & Widener, M. 2002. FY 2003 Two Hundred Bus Procurement. Expert Panel Report to the Massachusetts Bay Transportation Authority. Boston, MA.
   Google Scholar
• Holmen, B. & Ayala, A. 2002. Ultrafine PM emissions from natural gas, oxidation-catalyst diesel, and particle-trap diesel heavy-duty transit buses. Environmental Science and Technology 36(23):5041–5050.
   Google Scholar
• Holmen, B. & Qu, Y. 2004. Uncertainty in particle number modal analysis during transient operation of compressed natural gas, diesel, and trap-equipped diesel transit buses. Environmental Science and Technology 38(8):2413–2423.
   Google Scholar
• Hunt, R. 2002. 100 Million Miles on CNG: The LACMTA CNG Experience. http://www.iangv.org/tools-resources/reports.html?func=fileinfo&id=156. November 7, 2008.
   Google Scholar
• Jackson, M., Unnasch, S., & Pont, J. 2003. The Impact of Alternative Fuels on Greenhouse Gas Emissions: A “Well-to-Wheels” Analysis. International Vehicle Technology Symposium. March 11–13, Sacramento: California Air Resources Board. ftp://ftp.arb.ca.gov/carbis/cc/techsem/final_presen tations/mjackson_altfuels.pdf.
   Google Scholar
• Johansson, B. 1999. The economy of alternative fuels when including the cost of air pollution. Transportation Research Part D 4(2):91–108.
   Google Scholar
• Kado, N., Okamoto, R., Kuzmicky, P., Kobayashi, R., Ayala, A., Gebel, M., Rieger, P., Maddox, C., & Zafonte, L. 2005. Emissions of toxic pollutants from compressed natural gas and low sulfur diesel-fueled heavy-duty transit buses tested over multiple driving cycles. Environmental Science and Technology 39(19):7638–7649.
   Google Scholar
• Kittelson, D., Watts, W., Johnson, J., Rowntree, C., Payne, M., Goodier, S., Warrens, C., Preston, H., Zink, U., Ortiz, M., Goersmann, C., Twigg, M., Walker, A., & Caldow, R. 2006. On-road evaluation of two diesel exhaust aftertreatment devices. Journal of Aerosol Science 37(9):1140–1151.
   Google Scholar
• Lanni, T., Frank, B., Tang, S., Rosenblatt, D., & Lowell, D. 2003. Performance and Emissions Evaluation of Compressed Natural Gas and Clean Diesel Buses at New York City’s Metropolitan Transit Authority. 2003-01-0300. Warrendale, PA: SAE International.
   Google Scholar
• Lapin, C., Gautam, M., Zielinska, B., Wagner, V., & McClellan, R. 2002. Mutagenicity of emissions from a natural gas fueled truck. Mutation Research: Genetic Toxicology and Environmental Mutagenesis 519(1–2):205–209.
   Google Scholar
• Lave, L., MacLean, H., Hendrickson, C., & Lankey, R. 2000. Life-cycle analysis of alternative automobile fuel/propulsion technologies. Environmental Science and Technology 34(17):3598–3605.
   Google Scholar
• LeTavec, C., Uihlein, J., Hallstrom, K., Vertin, K., Chandler, K., Chatterjee, S., Coburn, T., Wayne, S., Clark, N., Gautam, M., Thompson, G., & Lyons, D. 2002. Year-Long Evaluation of Trucks and Buses Equipped With Passive Diesel Particulate Filters. 2002-01-0433. Warrendale, PA: SAE International.
   Google Scholar
• Lewtas, J. 1983. Comparative approach to evaluating relative cancer risks from energy sources using short-term genetic bioassays. Developments in Toxicology and Environmental Science 11(1):23–34.
   Google Scholar
• Lowell, D., Parsley, W., Bush, C., & Zupo, D. 2003. Comparison of Clean Diesel Buses to CNG Buses. Ninth Diesel Engine Emissions Reduction (DEER) Workshop. August 24–28, Newport, RI: USDOE Office of Energy Efficiency and Renewable Energy. http://www.osti.gov/bridge/servlets/purl/829622-k8LC2V/native/.
   Google Scholar
• Lyford-Pike, E. 2003. An Emission and Performance Comparison of the Natural Gas C-Gas Plus Engine in Heavy-Duty Trucks: Final Report. NREL/SR-540-32863. Golden, CO: National Renewable Energy Laboratory. http://www.nrel.gov/docs/fy03osti/32863.pdf.
   Google Scholar
• MacLean, H. & Lave, L. 2000. Environmental implications of alternative-fueled automobiles: air quality and greenhouse gas tradeoffs. Environmental Science and Technology 34(2):225–231.
   Google Scholar
• McClellan, R. & Lapin, C. 2003. Comment on “Fuels for Urban Transit Buses: A Cost-Effectiveness Analysis.” Environmental Science and Technology 37(20):4823.
   Google Scholar
• McDonald, J., Harrod, K., Seagrave, J., Seilkop, S., & Mauderly, J. 2004. Effects of low sulfur fuel and a catalyzed particle trap on the composition and toxicity of diesel emissions. Environmental Health Perspectives 112(13):1307–1312.
   Google Scholar
• Motta, R., Norton, P., Kelly, K., Chandler, K., Schumacher, L., & Clark, N. 1996. Alternative Fuel Transit Buses. Final Results from the National Renewable Energy Laboratory (NREL) Vehicle Evaluation Program. Golden, CO: National Renewable Energy Laboratory. http://www.eere.energy.gov/afdc/pdfs/transbus.pdf.
   Google Scholar
• Nakagawa, R., Sera, N., Horikawa, K., & Tokiwa, H. 1987. A powerful mutagen dinitrofloranthene detected in diesel emissions and in incomplete combustion products of LPG. Mutation Research: Environmental Mutagenesis and Related Subjects 182(6):368–369.
   Google Scholar
• Nanzetta-Converse, M., Holmén, B., & Ayala, A. 2005. Size-Selective Measurements of Ultrafine Particle Emissions from a CNG and a Trap-Equipped Diesel Bus During Transient Operation. Proceedings of the 15th CRC On-Road Vehicle Emissions Workshop. April 4–7, San Diego, CA: Coordinating Research Council.
   Google Scholar
• Northeast Advanced Vehicle Consortium. 2000. Hybrid-Electric Drive Heavy-Duty Vehicle Testing Project: Final Emissions Report. Manchester, NH: M. J. Bradley & Associates. http://www.mjbradley.com/documents/Navc9837.pdf.
   Google Scholar
• National Center for Statistics and Analysis (NCSA). 2009. Motor Vehicle Traffic Crash Fatality Counts And Estimates of People Injured for 2007. Washington, DC: National Highway Traffic Safety Administration. http://www-nrd.nhtsa.dot.gov/Pubs/811034.PDF.
   Google Scholar
• National Renewable Energy Laboratory (NREL). 2001. UPS CNG Truck Fleet Start-Up Experience. Golden, CO: National Renewable Energy Laboratory. http://www.eere.energy.gov/afdc/pdfs/ups_cng.pdf.
   Google Scholar
• Nylund, N., Erkkilä, K., Lappi, M., & Ikonen, M. 2004. Transit Bus Emission Study: Comparison of Emissions from Diesel and Natural Gas Buses. Finland: VTT Processes. http://www.vtt.fi/inf/pdf/jurelinkit/VTTNylund.pdf.
   Google Scholar
• Oberdorster, G., Gelein. R., Ferin, J., & Weiss, B. 1995. Association of particulate air pollution and acute mortality: involvement of ultrafine particles? Inhalation Toxicology 7(1):111– 124.
   Google Scholar
• Okamoto, R., Kado, N., Kuzmicky, P., Ayala, A., & Kobayashi, R. 2006. Unregulated emissions from compressed natural gas (CNG) transit buses configured with and without oxidation catalyst. Environmental Science and Technology 40(1):332– 341.
   Google Scholar
• Pelkmans, L., Lenaers, G., & De Keukeleere, D. 2002. Evaluation of Emissions and Fuel Consumption of Heavy Duty Natural Gas Vehicles in Real City Traffic. http://www.iangv.org/tools-resources/reports.html?func=fileinfo&id=181. November 2, 2008.
   Google Scholar
• Pickrell, D. 2003. Fuel Options for Reducing Greenhouse Gas Emissions from Motor Vehicles. Final Report October 2001– August 2003. Washington, DC: Department of Transportation. http://climate.dot.gov/documents/fuel_options.pdf.
   Google Scholar
• Pont, J. 2007. Full Fuel Cycle Assessment: Well-to-Wheels Energy Inputs, Emissions, and Water Impacts. Consultant Report for California Energy Commission. Cupertino, CA: TIAX, LLC. http://www.energy.ca.gov/2007publications/CEC-600-2007-004/CEC-600-2007-004-REV.PDF.
   Google Scholar
• Ramaswamy, V., Boucher, O., Haigh, J., Hauglustaine, D., Haywood, J., Myhre, G., Nakajima, T., Shi, G., Solomon, S. 2001. Radiative forcing of climate change. In J. Houghton, Y. Ding, D. Griggs, M. Noguer, P. van der Linden, X. Dai, K. Maskell, & C. Johnson (Eds.), Climate Change 2001: The Scientific Basis. pp. 351–416. New York: Cambridge University Press. http://www.grida.no/climate/ipcc_tar/wg1/pdf/TAR-06.pdf.
   Google Scholar
• South Coast Air Quality Management District (SCAQMD). 2000. Multiple Air Toxics Exposure Study (MATES-II). http://www.aqmd.gov/matesiidf/matestoc.htm. November 4, 2008.
   Google Scholar
• South Coast Air Quality Management District (SCAQMD). 2001. Rule 1195–Clean On-Road School Buses. http://www.aqmd.gov/tao/FleetRules/1195SchoolBus/index.htm. November 7, 2008.
   Google Scholar
• South Coast Air Quality Management District (SCAQMD). 2008. Multiple Air Toxics Exposure Study in the South Coast Air Basin. MATES-III. http://www.aqmd.gov/prdas/matesIII/MATESIIIFinalReportSept2008.html. November 4, 2008.
   Google Scholar
• Schubert, R. & Fable, S. 2005. Comparative Costs of 2010 Heavy-Duty Diesel and Natural Gas Technologies: Final Report. Cupertino, California: TIAX LLC. http://www.tiaxllc.com/reports/HDDV_NGVCostComparisonFinalr3.pdf.
   Google Scholar
• Scientific Applications International Corporation (SAIC). 2006. Life Cycle Assessment: Principles and Practice. EPA/600/R-06/060. Cincinnati, OH: National Risk Management Research Laboratory. http://www.epa.gov/ORD/NRMRL/lcaccess/pdfs/600r06060.pdf.
   Google Scholar
• Seagrave, J., McDonald, J., Gigliotti, A., Nikula, K., Seilkop, S., Gurevich, M., & Mauderly, J. 2002. Mutagenicity and in vivo toxicity of combined particulate and semivolatile organic fractions of gasoline and diesel engine emissions. Toxicological Sciences 70(2):212–226.
   Google Scholar
• Seagrave, J., Gigliotti, A., McDonald, J., Seilkop, S., Whitney, K., Zielinska, B., & Mauderly, J. 2005. Composition, toxicity, and mutagenicity of particulate and semivolatile emissions from heavy-duty compressed natural gas-powered vehicles. Toxicological Sciences 87(1):232–241.
   Google Scholar
• Seaton, A., MacNee, W., Donaldson, D., & Godden, D. 1995. Particulate air pollution and acute health effects. The Lancet 345(8943):176–178.
   Google Scholar
• Seguelong, T., Coroller, P., & Plassat, G. 2003. Comparative Study on Exhaust Emissions from Diesel- and CNG-Powered Urban Buses. Ninth Diesel Engine Emissions Reduction (DEER) Workshop. August 24–28, Newport, RI: USDOE Office of Energy Efficiency and Renewable Energy. http://www1.eere.energy.gov/vehiclesandfuels/pdfs/deer_2003/session5/deer_2003_seguelong.pdf.
   Google Scholar
• Silva, C., Goncalves, G., Farias, T., & Mendes-Lopes, J. 2006. A tank-to-wheel analysis tool for energy and emissions studies in road vehicles. Science of the Total Environment 367(1):441–447.
   Google Scholar
• Thompson, N., Ntziachristos, L., Samaras, Z., Aakko, P., Wass, U., Hausberger, S., & Sams, T. 2004. Overview of the European “Particulates” Project on the Characterisation of Exhaust Particulate Emissions from Road Vehicles: Results for Heavy Duty Engines. 2004-01-1986. Warrendale, PA: SAE International.
   Google Scholar
• Tonegawa, Y., Oguchi, M., Tsuchiya, K., Sasaki, S., Ohashi, T., & Goto. Y. 2006. Evaluation of Regulated Materials and Ultra Fine Particle Emission from Trial Production of Heavy-Duty CNG Engine. 2006-01-3397. Warrendale, PA: SAE International.
   Google Scholar
• Toy, E., Graham, J., & Hammitt, J. 2000. Fueling heavy duty trucks: diesel or natural gas? Risk in Perspective 8(1):1–6.
   Google Scholar
• Toyota Motor Corporation & Mizuho Information & Research Institute. 2004. Well-to-Wheel Analysis of Greenhouse Gas Emissions of Automotive Fuels in the Japanese Context - Well-to-Tank Report. Japan: Mizuho Information & Research Institute. http://www.mizuho-ir.co.jp/english/knowledge/documents/wtwghg041130.pdf.
   Google Scholar
• Turrio-Baldassarri, L., Battistelli, C., Conti, L., Crebelli, R., De Berardis, B., Iamiceli, A., Gambino, M., & Iannaccone, S. 2004. Emission comparison of urban bus engine fueled with diesel oil and “biodiesel” blend. Science of the Total Environment 327(1–3):147–162.
   Google Scholar
• Turrio-Baldassarri, L., Battistelli, C., Conti, L., Crebelli, R., De Berardis, B., Iamiceli, A., Gambino, M., & Iannaccone, S. 2006. Evaluation of emission toxicity of urban bus engines: compressed natural gas and comparison with liquid fuels. Science of the Total Environment 355(1–3):64–77.
   Google Scholar
• Ullman, T., Smith, L., Anthony, J., Slodowske, W., Trestrail, B., Cook, A., Bunn, W., Lapin, C., Wright, K., & Clark, C. 2003. Comparison of Exhaust Emissions, Including Toxic Air Contaminants, From School Buses in Compressed Natural Gas, Low Emitting Diesel, and Conventional Diesel Engine Configurations. 2003-01-1381. Warrendale, PA: SAE International.
   Google Scholar
• Unnasch, S. 2006. Fuel Cycle Analyses Assessment. Joint Workshop on Increasing the Use of Alternative Transportation Fuels. October 16, Sacramento: California Energy Commission. http://www.energy.ca.gov/ab1007/documents/2006-10-16_joint_meeting/presentations/2006_10-16_FFCA_AB1007.PDF.
   Google Scholar
• Utell, M. & Frampton, M. 2000. Acute health effects of ambient air pollution: the ultrafine particle hypothesis. Journal of Aerosol Medicine and Pulmonary Drug Delivery 13(4):355– 359.
   Google Scholar
• Valderrama, A. & Beltran, I. 2007. Diesel versus compressed natural gas in Transmilenio-Bogotá: innovation, precaution, and distribution of risk. Sustainability: Science, Practice, & Policy 3(1):59–67. http://ejournal.nbii.org/archives/vol3iss1/0608-025.valderrama.html.
   Google Scholar
• Watt, G. 2000. Natural Gas Vehicle Transit Bus Fleets: The Current International Experience. Auckland: International Association for Natural Gas Vehicles. http://www.cleanairnet.org/infopool/1411/articles-35682_ naturalbus_watt.pdf.
   Google Scholar