This document evaluates the potential environmental impacts of increased use of alternative fuels and advanced technologies in the U.S. transit bus industry. It finds that adopting newer diesel technologies, compressed natural gas buses, and diesel-electric hybrids between 2007-2009 would reduce emissions of pollutants like CO, NMHC and PM compared to the 2003 fleet. Replacing 15% of buses with each alternative fuel/technology could provide additional emissions reductions, with conventional and hybrid diesel buses reducing CO, NMHC and PM similarly due to engine improvements.
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Environmental Benefits of Alternative Fuels and Advanced Technology in Public Transit
1. Environmental Benefits of Alternative Fuels and Advanced Technology in Public Transit Jairo A. Sandoval and W. Scott Wayne, PhD Center for Alternative Fuels, Engines & Emissions Dept. of Mechanical & Aerospace Engineering West Virginia University, Morgantown, WV American Public Transportation Association 2007 Bus Technical, Maintenance and Procurement Workshop New Orleans, LA October 29, 2007 FTA REPORT No. 26-7003-07.2
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10. Distribution by Model Year Model year bins according to applicable EPA emissions regulation
11. Emissions from Baseline Fleet (2003) Total annual VMT: 2,420.8 million miles (a) Fuel consumed is expressed in Diesel-equivalent gallons Number of Buses CO tons NMHC tons CH 4 tons NO x tons PM tons CO 2 tons Fuel Consumed (a) thousands of gallons Total Emissions Diesel 49,938 15,886 2,611 65,669 1,494 6,497,649 589,135 CNG/LNG 7,609 1,194 308 5,879 6,318 7 796,630 100,393 Diesel Hybrid 489 5 0.6 220 0.5 35,865 3,361 Total 58,036 17,085 2,920 5,879 72,207 1,502 7,330,143 692,889 Average Emissions Levels per Bus CO g/mile NMHC g/mile CH 4 g/mile NO x g/mile PM g/mile CO 2 g/mile Fuel Economy mile/gal Diesel 6.98 1.15 28.84 0.66 2,853 3.51 CNG/LNG 3.44 0.89 16.94 18.21 0.02 2,296 3.14 Diesel Hybrid 0.22 0.03 9.87 0.02 1,608 6.02
14. Estimated Emissions of 2009 Fleet Number of Buses CO tons NMHC tons CH 4 tons NO x tons PM tons CO 2 tons Fuel Consumed thousands of gallons Total Annual Emissions Diesel 50,003 9,577 1,667 53,981 843 6,289,918 573,989 CNG/LNG 10,064 1,331 364 6,902 7,229 9 1,003,149 125,818 Diesel Hybrid 1,525 12 2 489 1 107,814 9,805 Total 61,592 10,920 2,032 6,902 61,699 853 7,400,881 709,612 Relative Change 6% 36% 30% 17% 15% 43% 1% 2% Average Emissions Levels per Bus CO g/mile NMHC g/mile CH 4 g/mile NO x g/mile PM g/mile CO 2 g/mile Fuel Economy mile/gal Diesel 4.31 0.75 24.32 0.38 2,833 3.51 CNG/LNG 2.98 0.81 15.45 16.18 0.02 2,245 3.22 Diesel Hybrid 0.18 0.03 7.22 0.02 1,592 6.26 2003 - Average Emissions Levels per Bus CO g/mile NMHC g/mile CH 4 g/mile NO x g/mile PM g/mile CO 2 g/mile Fuel Economy mile/gal Diesel 6.98 1.15 28.84 0.66 2,853 3.51 CNG/LNG 3.44 0.89 16.94 18.21 0.02 2,296 3.14 Diesel Hybrid 0.22 0.03 9.87 0.02 1,608 6.02 Reductions in CO and NMHC due largely to advent of diesel particulate filters. Lower CO emissions from stoichiometric CNG buses offset the increase in number of CNG buses
15. Estimated Emissions of 2009 Fleet Number of Buses CO tons NMHC tons CH 4 tons NO x tons PM tons CO 2 tons Fuel Consumed thousands of gallons Total Annual Emissions Diesel 50,003 9,577 1,667 53,981 843 6,289,918 573,989 CNG/LNG 10,064 1,331 364 6,902 7,229 9 1,003,149 125,818 Diesel Hybrid 1,525 12 2 489 1 107,814 9,805 Total 61,592 10,920 2,032 6,902 61,699 853 7,400,881 709,612 Relative Change 6% 36% 30% 17% 15% 43% 1% 2% Average Emissions Levels per Bus CO g/mile NMHC g/mile CH 4 g/mile NO x g/mile PM g/mile CO 2 g/mile Fuel Economy mile/gal Diesel 4.31 0.75 24.32 0.38 2,833 3.51 CNG/LNG 2.98 0.81 15.45 16.18 0.02 2,245 3.22 Diesel Hybrid 0.18 0.03 7.22 0.02 1,592 6.26 2003 - Average Emissions Levels per Bus CO g/mile NMHC g/mile CH 4 g/mile NO x g/mile PM g/mile CO 2 g/mile Fuel Economy mile/gal Diesel 6.98 1.15 28.84 0.66 2,853 3.51 CNG/LNG 3.44 0.89 16.94 18.21 0.02 2,296 3.14 Diesel Hybrid 0.22 0.03 9.87 0.02 1,608 6.02 Particulate Filters “mandated” on all 2007 and newer diesel buses + increase in inherently low PM emitting CNG buses NO x reductions largely attributable to reduction in NO x limit from 2.5 g/bhpr to 1.2 g/bhphr in 2007
16. Estimated Emissions of 2009 Fleet Number of Buses CO tons NMHC tons CH 4 tons NO x tons PM tons CO 2 tons Fuel Consumed thousands of gallons Total Annual Emissions Diesel 50,003 9,577 1,667 53,981 843 6,289,918 573,989 CNG/LNG 10,064 1,331 364 6,902 7,229 9 1,003,149 125,818 Diesel Hybrid 1,525 12 2 489 1 107,814 9,805 Total 61,592 10,920 2,032 6,902 61,699 853 7,400,881 709,612 Relative Change 6% 36% 30% 17% 15% 43% 1% 2% Average Emissions Levels per Bus CO g/mile NMHC g/mile CH 4 g/mile NO x g/mile PM g/mile CO 2 g/mile Fuel Economy mile/gal Diesel 4.31 0.75 24.32 0.38 2,833 3.51 CNG/LNG 2.98 0.81 15.45 16.18 0.02 2,245 3.22 Diesel Hybrid 0.18 0.03 7.22 0.02 1,592 6.26 2003 - Average Emissions Levels per Bus CO g/mile NMHC g/mile CH 4 g/mile NO x g/mile PM g/mile CO 2 g/mile Fuel Economy mile/gal Diesel 6.98 1.15 28.84 0.66 2,853 3.51 CNG/LNG 3.44 0.89 16.94 18.21 0.02 2,296 3.14 Diesel Hybrid 0.22 0.03 9.87 0.02 1,608 6.02 Very modest increase in CO 2 and fuel consumption despite increase in number of buses and miles traveled … largely offset by increase in hybrid buses Methane emissions increase due to higher number of CNG buses
17. Estimated Emissions of 2009 Fleet Number of Buses CO tons NMHC tons CH 4 tons NO x tons PM tons CO 2 tons Fuel Consumed thousands of gallons Total Annual Emissions Diesel 50,003 9,577 1,667 53,981 843 6,289,918 573,989 CNG/LNG 10,064 1,331 364 6,902 7,229 9 1,003,149 125,818 Diesel Hybrid 1,525 12 2 489 1 107,814 9,805 Total 61,592 10,920 2,032 6,902 61,699 853 7,400,881 709,612 Relative Change 6% 36% 30% 17% 15% 43% 1% 2% Average Emissions Levels per Bus CO g/mile NMHC g/mile CH 4 g/mile NO x g/mile PM g/mile CO 2 g/mile Fuel Economy mile/gal Diesel 4.31 0.75 24.32 0.38 2,833 3.51 CNG/LNG 2.98 0.81 15.45 16.18 0.02 2,245 3.22 Diesel Hybrid 0.18 0.03 7.22 0.02 1,592 6.26 2003 - Average Emissions Levels per Bus CO g/mile NMHC g/mile CH 4 g/mile NO x g/mile PM g/mile CO 2 g/mile Fuel Economy mile/gal Diesel 6.98 1.15 28.84 0.66 2,853 3.51 CNG/LNG 3.44 0.89 16.94 18.21 0.02 2,296 3.14 Diesel Hybrid 0.22 0.03 9.87 0.02 1,608 6.02
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19. (a) Fuel consumed is expressed in Diesel-equivalent gallons (b) Implemented in the older diesel buses of the fleet Greater Use of Alternative Fuels & Technology Reductions are in addition to those shown in the previous table CO tons NMHC tons CH 4 tons NO x tons PM tons CO 2 tons Fuel Consumed (a) thousands of gallons Clean Diesel 1,723 377 - 3,291 201 35,251 2,664 CNG 689 341 422 4,239 205 220,758 2,154 Diesel Hybrid 1,776 366 - 4,418 202 491,352 50,658 Gasoline Hybrid 6,178 211 - 5,963 199 74,114 2,833 Biodiesel (B20) (a) 384 166 - 369 38 25,087 3,876 Percent Incremental Change Clean Diesel 16% 19% - 5% 24% 0% 0% CNG 6% 17% 6% 7% 24% 3% 0% Diesel Hybrid 16% 18% - 7% 24% 7% 7% Gasoline Hybrid 57% 10% - 10% 23% 1% 0% Biodiesel (B20) (b) 4% 8% - 1% 4% 0% 1% Conventional & hybrid diesel buses have similar reductions in CO, NMHC and PM emissions because they benefit from the same engine advancements. Diesel hybrid buses gain an advantage in NO x emissions over conventional diesels.
20. (a) Fuel consumed is expressed in Diesel-equivalent gallons (b) Implemented in the older diesel buses of the fleet Greater Use of Alternative Fuels & Technology Reductions are in addition to those shown in the previous table CO tons NMHC tons CH 4 tons NO x tons PM tons CO 2 tons Fuel Consumed (a) thousands of gallons Clean Diesel 1,723 377 - 3,291 201 35,251 2,664 CNG 689 341 422 4,239 205 220,758 2,154 Diesel Hybrid 1,776 366 - 4,418 202 491,352 50,658 Gasoline Hybrid 6,178 211 - 5,963 199 74,114 2,833 Biodiesel (B20) (a) 384 166 - 369 38 25,087 3,876 Percent Incremental Change Clean Diesel 16% 19% - 5% 24% 0% 0% CNG 6% 17% 6% 7% 24% 3% 0% Diesel Hybrid 16% 18% - 7% 24% 7% 7% Gasoline Hybrid 57% 10% - 10% 23% 1% 0% Biodiesel (B20) (b) 4% 8% - 1% 4% 0% 1% Conventional diesel, stoichiometric CNG, diesel hybrid and gasoline hybrid offer near identical reductions in particulate emissions.
21. (a) Fuel consumed is expressed in Diesel-equivalent gallons (b) Implemented in the older diesel buses of the fleet Greater Use of Alternative Fuels & Technology Reductions are in addition to those shown in the previous table CO tons NMHC tons CH 4 tons NO x tons PM tons CO 2 tons Fuel Consumed (a) thousands of gallons Clean Diesel 1,723 377 - 3,291 201 35,251 2,664 CNG 689 341 422 4,239 205 220,758 2,154 Diesel Hybrid 1,776 366 - 4,418 202 491,352 50,658 Gasoline Hybrid 6,178 211 - 5,963 199 74,114 2,833 Biodiesel (B20) (a) 384 166 - 369 38 25,087 3,876 Percent Incremental Change Clean Diesel 16% 19% - 5% 24% 0% 0% CNG 6% 17% 6% 7% 24% 3% 0% Diesel Hybrid 16% 18% - 7% 24% 7% 7% Gasoline Hybrid 57% 10% - 10% 23% 1% 0% Biodiesel (B20) (b) 4% 8% - 1% 4% 0% 1% Gasoline hybrids offer the largest overall NOx reductions
22. (a) Fuel consumed is expressed in Diesel-equivalent gallons (b) Implemented in the older diesel buses of the fleet Greater Use of Alternative Fuels & Technology Reductions are in addition to those shown in the previous table CO tons NMHC tons CH 4 tons NO x tons PM tons CO 2 tons Fuel Consumed (a) thousands of gallons Clean Diesel 1,723 377 - 3,291 201 35,251 2,664 CNG 689 341 422 4,239 205 220,758 2,154 Diesel Hybrid 1,776 366 - 4,418 202 491,352 50,658 Gasoline Hybrid 6,178 211 - 5,963 199 74,114 2,833 Biodiesel (B20) (a) 384 166 - 369 38 25,087 3,876 Percent Incremental Change Clean Diesel 16% 19% - 5% 24% 0% 0% CNG 6% 17% 6% 7% 24% 3% 0% Diesel Hybrid 16% 18% - 7% 24% 7% 7% Gasoline Hybrid 57% 10% - 10% 23% 1% 0% Biodiesel (B20) (b) 4% 8% - 1% 4% 0% 1% B20 used in older model buses without DPFs results in slight increase in NO x emissions and modest decrease in PM emissions. B20 also results in a modest increase in gallons of fuel consumed due to lower energy content; however biodiesel displaces use of imported petroleum.
23. (a) Fuel consumed is expressed in Diesel-equivalent gallons (b) Implemented in the older diesel buses of the fleet Greater Use of Alternative Fuels & Technology Reductions are in addition to those shown in the previous table CO tons NMHC tons CH 4 tons NO x tons PM tons CO 2 tons Fuel Consumed (a) thousands of gallons Clean Diesel 1,723 377 - 3,291 201 35,251 2,664 CNG 689 341 422 4,239 205 220,758 2,154 Diesel Hybrid 1,776 366 - 4,418 202 491,352 50,658 Gasoline Hybrid 6,178 211 - 5,963 199 74,114 2,833 Biodiesel (B20) (a) 384 166 - 369 38 25,087 3,876 Percent Incremental Change Clean Diesel 16% 19% - 5% 24% 0% 0% CNG 6% 17% 6% 7% 24% 3% 0% Diesel Hybrid 16% 18% - 7% 24% 7% 7% Gasoline Hybrid 57% 10% - 10% 23% 1% 0% Biodiesel (B20) (b) 4% 8% - 1% 4% 0% 1% Diesel-hybrid buses appear to offer the greatest overall environmental advantage.
24. Global Warming Potential (a) B20 Implemented in the older diesel buses of the fleet Tailpipe only If B100 in all the fleet: Life cycle emissions ↓ ~ 40%
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