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34
CHAPTER five
ESTIMATING GREENHOUSE GAS SAVINGS FROM TRANSIT
Transit agencies can estimate both the impacts of entire tran- CO2 is the most commonly analyzed gas, accounting for
sit systems on GHG emissions and the marginal impacts of 95% of U.S. transportation GHG emissions (5). Emissions
specific strategies on GHG emissions. Impacts of systems of CO2 are typically the easiest to calculate. CH4 and N2O
generally can be quantified using existing data and analysis are also commonly included in calculations. The remaining
techniques. Estimating the impact of specific transit strate- gases are less commonly included, although estimates of
gies is more complex in some cases. This chapter provides an these are required by some registries.
overview of analysis frameworks and some agencies' expe-
riences with quantification, as well as references to more TABLE 11
detailed calculation methodologies. TYPICAL SOURCES OF EMISSIONS
Global
Several recent studies have provided methodologies for Typical Sources for Warming
calculating the GHG impacts of transit service. The most Gas Transit Agencies Potential (GWP)
robust of these is a methodology developed by APTA's Cli- Gasoline and diesel
mate Change Standards Working Group and funded by FTA. combustion
The methodology, Recommended Practice for Quantifying Carbon dioxide Combustion at stationary
1
Greenhouse Gas Emissions from Transit, was released in (CO2) sources; e.g., maintenance
2009. This chapter draws heavily on that document. More yards
detail on many of the calculation methodologies described Electricity purchases
here is available within APTA's methodology (50 ). Gasoline and diesel
combustion
Methane (CH4) 21
Quantifying the impacts of transit systems and of transit Fugitive emissions of
strategies on GHG emissions is a relatively new effort. For natural gas
years, state DOTs, MPOs, and transit agencies have esti- Nitrous oxide Gasoline and diesel
310
mated the impact of transit strategies on criteria pollutants, (N2O) combustion
as required by the Clean Air Act; however, there is no regu- Hydrofluorocar-
Leakage of refrigerants 1211,700
latory requirement to estimate the impacts of transit on GHG bons (HFCs)
emissions. Still, transit agencies may find it useful to quan- Perfluorocarbons
tify impacts on GHG emissions for the following purposes: Leakage of refrigerants 6,5009,200
(PFCs)
Sulfur hexafluo- Leakage from electrical
· Reporting to the Climate Registry and other agencies 23,900
ride (SF6) equipment
· Preparing for possible state and federal reporting
Source: Recommended Practice for Quantifying Greenhouse
requirements (e.g., Washington State is currently Gas Emissions from Transit: Draft, APTA Climate Change
developing a rule that will require reporting by any Standards Working Group, Mar. 2008, p. 16 (50).
agency that operates an on-road vehicle fleet that emits
at least 2,500 metric tons of GHG annually). Analyses of transit's impact on GHG emissions can
· Supporting internal efforts to reduce emissions include any of the four components discussed in chapter
· Communicating the benefits of transit to the public and three. Transit displaces emissions through travel mode
to legislators shift, compact development, and reduced congestion.
· Ensuring eligibility for new funding sources Transit produces emissions from vehicles, facilities, and
· Preparing for the implementation of new state GHG regula- construction and maintenance (see Figure 5 for a diagram
tions, such as California's SB 375, which requires MPOs to of components). Analyses of individual transit strategies
plan for reduced GHG emissions from light-duty vehicles incorporate emissions produced by transit vehicles and
· Preparing for possible new federal regulations. emissions displaced by transit to measure the net impact of
strategies. Emissions displaced include, at a minimum, the
Analyses can include any of the six GHGs listed in Table impact of travel mode shift. To provide a more complete
11. Within analyses of GHG emissions from transportation, account of displaced emissions, the benefits of reduced
