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Page 106
Suggested Citation:"Glossary." National Academies of Sciences, Engineering, and Medicine. 2021. An Update on Public Transportation's Impacts on Greenhouse Gas Emissions. Washington, DC: The National Academies Press. doi: 10.17226/26103.
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Page 106
Page 107
Suggested Citation:"Glossary." National Academies of Sciences, Engineering, and Medicine. 2021. An Update on Public Transportation's Impacts on Greenhouse Gas Emissions. Washington, DC: The National Academies Press. doi: 10.17226/26103.
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Page 107

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106 Glossary Biogenic Greenhouse Gas Greenhouse gas emissions resulting from fuels sourced from plant matter and part of the natural carbon cycle. Biogenic carbon dioxide, CO2(b), is often tracked separately from other greenhouse gas emissions. Bus Rubber-tired vehicle operating on roadways. For the purposes of this report, “bus” also includes the NTD modes of “bus rapid transit,” “commuter bus,” “publico,” and “trolleybus.” Carbon Dioxide Equivalent CO2e is the sum of greenhouse gases weighted by their relative 100-year climate impact using global warming potentials. Commuter Rail Train service that is typically region wide. Commuter rail in the 2018 NTD was fueled by biodiesel, diesel, or electricity. For the purposes of this report, the mode type “commuter rail” also includes NTD modes “Alaska railroad” and “hybrid rail.” Direct GHG Emissions The CO2, CH4, and N2O emissions that occurred at the vehicle when fuel was consumed. Electric Battery Bus A fully electric bus that stores electricity in a battery pack and uses it to power the vehicle. In this report, an electric battery bus is not a hybrid electric vehicle. Electric Propulsion Bus A bus propelled by electricity through an overhead wire or other continuous external source; also called a “trolleybus.” Emissions Factor The greenhouse gas emissions associated with a unit of activity— for example, carbon dioxide per gallon of gasoline. Ferry/Ferryboat Watercraft used as public transportation. Ferryboats in the 2018 NTD were fueled by biodiesel or diesel fuel. Global Warming Potential The energy absorbed by a greenhouse gas relative to carbon dioxide. This report uses 100-year GWPs of 28 for CH4 and 265 for N2O. Greenhouse Gas Gases creating the greenhouse effect, absorbing and emitting heat in the atmosphere. Heavy Rail An electric-powered train with high capacity. Indirect GHG Emissions The CO2, CH4, and N2O emissions that occurred at the power plant when electricity was produced or in the process of pro- ducing hydrogen.

Glossary 107   Land Use Efficiency GHG Savings The GHG emissions saved by the broader impact of transit on VMT in the community, such as through shorter trips and fewer personal vehicle trips (also called indirect effect). Light Rail A lower-capacity train powered by electricity. For the purposes of this report, the mode type light rail also includes NTD modes “cable car,” “inclined plane,” “monorail,” “automated guideway,” and “streetcar rail.” Mode Shift Factor The share of public transit passenger miles that would have otherwise been personal vehicle miles, such as through driving, carpooling, ridehailing, or taking a taxi. Occupancy The number of passengers per vehicle seat. Passenger Mile One mile ridden by a public transit passenger. Personal Vehicle Automobiles and light trucks; for the purpose of this report, includes ridehailing and taxi vehicles for hire; also called “private automobile.” Ridehailing A hired car for a single trip; also called “transportation network company”; examples are Uber and Lyft. Transit Multiplier The ratio of the total VMT reduction associated with transit, including (1) the direct impacts of avoided personal vehicle travel by transit passengers and (2) the indirect effects of avoided travel in the communities with transit due to factors such as shorter trips and fewer personal vehicle trips, divided by the VMT reduction associated with transit use alone. Transit Vehicle Miles The full distance a transit vehicle travels, including revenue and non-revenue miles. Transportation Efficiency GHG Savings The GHG emissions saved by passengers riding transit rather than using automobiles (also called “direct effect”). Upstream Emissions The GHG emissions that occurred during fuel production and distribution; also called “well-to-pump” emissions. Van Rubber-tired vehicles operating on roadways and having smaller seating capacity than buses. The NTD describes vans as seating 8 to 18 passengers. For the purposes of this report, the mode type “van” also includes NTD modes “demand response” and “jitney” and may include smaller passenger vehicles.

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An Update on Public Transportation's Impacts on Greenhouse Gas Emissions Get This Book
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 An Update on Public Transportation's Impacts on Greenhouse Gas Emissions
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Transportation is a major source of the greenhouse gas (GHG) emissions that are causing climate change. As communities work to cut emissions and become more resilient, they are including public transportation advances as a significant part of their climate action strategies.

The TRB Transit Cooperative Research Board's TCRP Research Report 226: An Update on Public Transportation's Impacts on Greenhouse Gas Emissions provides updated national analysis of public transportation’s role as a climate solution by documenting its 2018 GHG impacts.

Supplemental materials to the report include three factsheets (Fact Sheet 1, Fact Sheet 2, and Fact Sheet 3); various key findings regarding transit as a climate solution; a PowerPoint presentation summarizing the findings and research and a template for transit agencies to add their own data for climate communications; and a simple spreadsheet tool that provides this study’s 2018 GHG impact findings by transit agency and allows the user to apply several of the future scenarios to see how their transit agency’s GHG impacts change with electrification, clean power, and ridership increases.

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