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38 of transit expansion and land use measures on transportation TABLE 12 GHG emissions. IMPACT OF INCREASING ALTERNATIVE FUELS AND TECHNOLOGIES TO 15% OF THE TRANSIT FLEET IN 2009 Fuel Consumed EMISSIONS FROM AGENCY OPERATIONS Alternative Fuel CO2 tons Thousands of Gallons Clean Diesel 35,251 2,664 Emissions from agency operations, including emissions from CNG -220,758 2,154 transit vehicles, facilities, and construction and maintenance activities, are a standard component of emissions inventories Diesel Hybrid -491,352 -50,658 for transit agencies. In most cases, estimation of these emis- Gasoline Hybrid -74,114 2,833 sions simply requires data on the use of fuel or electricity, typically available from agencies' records or from the NTD. Biodiesel (B20)a 25,087 3,876 Standard factors of GHG emissions are applied to these data Change relative to 2009 baseline. to calculate GHG emissions. aImplemented in the older diesel buses of the fleet. Source: Wayne, W.S., Environmental Benefits of Alternative The APTA methodology provides guidance on estimat- Fuels and Advanced Technology in Transit, Federal Transit ing the following: Administration, 2007 (55). Direct emissions from stationary combustion (e.g., on- Another study sponsored by FTA examined the GHG site furnaces) emissions performance of various bus propulsion technolo- Direct emissions from mobile combustion gies over a 12-year lifespan. The study assumes that buses Indirect emissions from electricity use were purchased in 2007. In this case, the study did use life- Other indirect emissions (e.g., steam purchases) cycle (well to wheels) emission factors. Figure 17 provides the Fugitive emissions (e.g., refrigerant leaks) results of the study. The study again shows diesel hybrids as Embodied emissions from construction materials. the lowest emitting type of bus on a CO2 per mile basis. CO2 emissions per mile tend to increase in future years, presum- For a quick snapshot of an individual transit fleet's GHG ably because fuel efficiency declines as the vehicles age. emissions, agencies can visit The online transit calculator provides instant estimates for most agencies, based on 2002 NTD data. Once baseline emissions from any source are calculated, agencies can estimate the impact of specific strategies that reduce emissions. Of those strategies that reduce emissions from agency operations, alternative fuel and vehicle technol- ogy strategies have been analyzed most extensively. Changes in fuel or vehicle technologies produce measurable changes in GHG emissions on a per mile basis. Simple reduction fac- FIGURE 17 Life-cycle GHG emissions from various propulsion tors, such as those provided in Table 7, can be applied to the technologies (Source : Clark, et al., Transit Bus Life Cycle Cost and Year 2007 Emissions Estimation, Federal Transit target vehicle population to estimate emission reductions. Administration, U.S. Department of Transportation, 2007, p. 34). The Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation model, from which the factors in that table are drawn, can be used to calculate emission reduction A life-cycle emissions analysis of transit can account for factors for additional fuel types and fuel pathways. Emis- all emissions from the transit system, including emissions sions can be calculated on a life-cycle basis or on a tailpipe from building the highway or rail system, manufacturing the basis only. vehicles, maintaining the infrastructure and vehicles, pro- ducing and using the fuel, and eventually disposing of the A recent study commissioned by the FTA examined a vehicles and infrastructure (3). Comparing the same life- hypothetical case in which the proportion of alternative fuel cycle components for SOVs allows for a full life-cycle evalu- buses was increased to 15% of the entire transit bus fleet by ation of the benefits of shifting auto-based transportation to 2009. The study examined changes in emissions from this bus and rail transportation. scenario on a tailpipe emissions basis only. Results are pro- vided in Table 12. The study found that diesel hybrid tech- A study from the University of California, Berkeley, com- nologies would be the most effective by far to reduce tailpipe pared the actual life-cycle emissions of four rail transit sys- CO2 emissions from buses (55). tems with average emissions from buses and SOVs. The rail