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Handbook for Estimating Transportation Greenhouse Gases for Integration into the Planning Process

Chapter 8 - Additional Considerations in GHG Analysis: Lifecycle Analysis and GHG Emissions from Transportation Cons

This section discusses two areas of emissions analysis: lifecycle analysis and emissions from transportation infrastructure construction and maintenance. While these may be important considerations for transportation agencies and there are some available methodologies and tools, these approaches are still emerging in practice. Neither lifecycle emissions nor construction and maintenance emissions have comprehensive, agreed-upon methodologies that are widely accepted for use in transportation planning.

8.1 Lifecycle GHG Analysis

Table 30. Selection Criteria for Lifecycle Emissions Analysis Methods

Selection Criteria

Lifecycle Assessments

Alt Fuels, using GREET Model

Electric Transit Emissions

Analysis Type

Inventory or forecast

Inventory or forecast

Geographic Scope

-State
-Regional
-Possible at local level

-State
-Regional
-Possible at local level

Analysis Precision

Incorporation of lifecycle information supplements on-road emissions information

Incorporation of lifecycle information supplements on-road emissions information

Data Needed

Fuel mix, inventory results

Ridership, passenger load

Necessary Analytical Capabilities

Moderate - uses direct emissions inventory results, but requires familiarity with modeling

Limited- relatively simple calculation approach

Level of Resources Required (i.e., staff/budget)

Limited if inventory already prepared

Limited - relatively simple calculation approach

Capable of Addressing Vehicle Technology/Fuels Changes

Yes

Yes

Capable of Addressing Changes in Travel Demand

Accounted for within the direct fuel consumption estimates

Accounted for within the direct fuel consumption estimates

Capable of Addressing Changes in Vehicle Speeds and Operations

Accounted for within the direct fuel consumption estimates

No

Description

A fundamental difference between GHG emissions and criteria pollutant emissions is that the environmental impact of GHG emissions (climate change) does not depend on the location or timing (e.g., diurnal profile) of the emissions. Because of this, it can be important in some circumstances to consider emissions that are caused by transportation plans and projects but do not come directly from the vehicle tailpipe. The field of lifecycle assessment (LCA, also known as lifecycle analysis) is concerned with understanding the full environmental impacts associated with all the stages of a project or product life. In its complete form, LCA can cover raw material extraction through materials processing, manufacture, distribution, use, repair and maintenance, and disposal or recycling. Transportation agencies could potentially use LCA to examine the full lifecycle of GHG emissions associated with all transportation activities. However, its application is typically limited to analyses involving alternative vehicle fuels and electric transit service, since these strategies reduce or eliminate tailpipe emissions but may not yield corresponding reductions in total GHG emissions from a lifecycle perspective.

This section presents two methods: one for analyzing alternative vehicle fuels and one for analyzing electric transit service. Note that these two methods are not substitutes for one another, but rather both examples of types of LCA applied to emissions from different activities. At the present time, LCA is an emerging field of analysis, and analysis methodologies have not been standardized.

Strengths and Limitations

Table 31. Strengths and Limitations of Lifecycle Emissions Analysis Methods

Analysis/Method

Strengths

Limitations

Alternative Fuels, using GREET

  • Use of defaults allows for users to easily estimate reductions associated with each alternative fuel.
  • Incorporates environmental impacts associated with producing and distributing biofuels - known as "upstream" emissions.

  • A lifecycle approach to emissions analysis may be unfamiliar to transportation decision makers and difficult to communicate to stakeholders.
  • Emissions analyses cannot be compared to prior analyses that did not use a lifecycle approach.
  • In some cases, GREET relies on national default values that may differ substantially from local conditions.

Electric Transit Service

  • Methodology is straightforward and easy to apply using accessible data sources.
  • Does not account for emissions associated with electric passenger vehicles.
  • Electricity use by a transit agency may span state or regional boundaries - with varying carbon intensities associated with the electricity sources.

Key Steps and Data Options

Option 1: Alternative Transportation Fuels

For agencies that have conducted LCA analysis, the preferred approach for analyzing lifecycle emissions associated with alternative fuels is Argonne National Laboratory's Greenhouse Gases, Regulated Emissions, and Energy use in Transportation (GREET) model, which simulates the use of fuels in passenger cars and two classes of light duty trucks.

Step 1: Determine the carbon intensity of the fuel pathway. The GREET model, which is available for download for practitioners, provides default estimates for over 100 different fuel pathways. Users can select the vehicle and fuel(s) of interest using the tool and can specify the fuel source if known. A sample table of results from the GREET model appears below.

Table 32. Lifecycle GHG Impacts of Sample Alternative Fuels

Fuel

Feedstock

WTP

PTW

WTW

gCO2e/mi

Gasoline

U.S. Average

93

358

451

Ethanol (E85)

Corn

19

352

371

Switchgrass

-233

352

119

CNG

NA NG: U.S. Average

119

272

391

LNG

NA NG: U.S. Average

118

273

391

Hydrogen

Central NG SMR

238

0

238

Electrolysis, Renewables

3

0

3

Electricity

U.S. Mix

333

0

333

California Mix

172

0

172

Diesel

U.S. Average

79

308

386

FTD

non-NA from NG

170

297

467

Biodiesel (B20)

Soybean

21

308

329

Renewable Diesel

Soybean

-207

298

92

Source: GREET.

Output: Lifecycle impacts of each fuel by grams of CO2 per mile (gCO2e/mi) as:

  • "well to pump (WTP)," - emissions to extract, produce, and transport the fuel
  • "pump to wheel (PTW)," - tailpipe emissions; and
  • "well to wheel (WTW). " - the sum of WTP and PTW.

Common Tool: The GREET Model

State DOT and MPO practitioners can download the GREET results mini-tool (available at: https://greet.es.anl.gov/results%29. The mini-tool is a simple MS Excel™-based tool that users can use to compare the lifecycle emissions attributable to conventional and alternative fuels. Steps to use the mini-tool are as follows:

  1. Select functional unit for comparative purposes. In most cases, State DOT and MPO practitioners would choose per mile ("per mi").
  2. Optional: Select vehicle type. The GREET model has default assumptions for vehicles using gasoline. If the user is interested in comparing the use of alternative fuels to more fuel efficient vehicles, then select HEV (Hybrid Electric Vehicle) or one of the PHEV (Plug-in Hybrid Electric Vehicle) options. Otherwise, all comparisons will be in reference to a typical gasoline vehicle.
  3. Select the alternative fuel to compare against gasoline. Options include Compressed Natural Gas (CNG), Liquefied Natural Gas (LNG), Ethanol, Diesel, Fischer-Tropsch Diesel (FTD), Biodiesel, Renewable Diesel, Pyrolysis Gasoline, Pyrolysis Diesel, Gaseous Hydrogen, and Electricity.
  4. Optional: Select feedstock or source of alternative fuels. Unless the user is confident of the sources of the fuel, the user should select the first option as a feedstock for each alternative fuel. For instance, in the case of CNG, this would be "North America Natural Gas: U.S. Average"; for Ethanol it would be "Corn. "

The results are shown on a results sheet in Excel, with the fuels listed as columns and the breakdown of energy inputs in rows. The total grams of carbon dioxide equivalents per mile (gCO2e/mi) are shown as well-to-pump (WTP), pump-to-wheels (PTW), and well-to-wheels (WTW; sum of WTP and PTW). PTW is effectively the same as tailpipe emissions.

More information about the GREET model can be found here: https://greet.es.anl.gov/main/

Step 2 (if needed): Recalculate Baseline Emissions on WTW Basis. If the existing baseline emissions estimate includes only tailpipe (PTW) emissions, then to properly calculate a lifecycle GHG impact of alternative fuels, the user would need to re-calculate the baseline GHG emissions for WTW, rather than just the tailpipe or PTW emissions.

For example, if the current emissions estimate was calculated as: VMT x PTW_Gasoline, this will need to be re-calculated as: VMT x WTW_Gasoline, which allows for the user to estimate reductions associated with an alternative fuel.

Output: Transportation emissions on a WTW basis.

Reporting Alternative Fuel Benefits.

Unless the DOT or MPO baseline GHG emissions are calculated on a WTW basis, report a percent reduction attributable to alternative fuels on a WTW basis, rather than an absolute (tons) GHG emission reduction. Reporting benefits in this way will help the user avoid the potential of under- or over-estimating the GHG benefits of incorporating alternative fuels based on varying WTP and PTW parameters.

Step 3: Calculate percentage change in emissions per fuel. Using the GREET results, the user can calculate the percentage change in emissions associated with an alternative fuel. That percentage change can be applied to the GHG emissions estimates for the fraction of the VMT that would be using the alternative fuel.

Output: Reduction in CO2e associated with alternative fuels.

Option 2: Electric Transit Service Emissions
Public transit service powered by electricity is considered an indirect source of GHG emissions. Electric transit includes most heavy rail, light rail, and trolley bus systems, as well as some commuter rail systems. The American Public Transportation Association (APTA) has developed recommendations for quantifying GHG emissions from transit for the purposes of a GHG inventory. 1 A similar approach can be used for forecasting emissions.

Note that this approach would not be valid for forecasting lifecycle GHG for new or expanded electric transit infrastructure and vehicles, since that would require LCA analysis for the construction/manufacture of the infrastructure/vehicles, which would likely be significant.

Step 1: Estimate current and/or historic electricity used for transit propulsion. Data for this can generally be obtained from the following source:

Step 2 (for forecasts): Calculate ratio of electricity use per passenger mile or vehicle revenue mile. This can be done by using the known electricity use in kWh per mode from Step 1 and dividing it by passenger miles or vehicle revenue miles associated with electric transit service. Data for this is available through:

Step 3 (for forecasts): Estimate future transit electricity use. Use a forecast of passenger miles or vehicle revenue miles to estimate future electricity use. Using a constant ratio of electricity use per passenger mile assumes no improvement in vehicle load factors. Using a constant ratio of electricity use per vehicle revenue mile assumes no improvement in vehicle fuel efficiency. A more sophisticated approach will account for changes in both of these factors.

Output: Estimate of kWh used by transit service.

Step 4: Estimate GHG emissions. GHG emissions can be estimated using electricity generation emission factors expressed in grams CO2-equivalent per kilowatt hour. Emissions factors for electricity should reflect the source of the electricity and can be obtained from the following sources:

Output: GHG emissions (current or forecast) from electric transit.

Example: Los Angeles County MTA Sustainability Report

An example of an agency that estimates GHG emissions from electricity-based transit service operations is the Los Angeles County Metropolitan Transportation Authority (LACMTA). The agency calculates annual GHG emissions from the agency's heavy rail, light rail, and bus systems in an annual Sustainability Report. Because LACMTA purchases electricity from three different utilities, the electricity generation emission factors are estimated specific for each provider, rather than using a regional average.

8.2 Planning-level Analysis of Emissions from Construction and Maintenance of Transportation Infrastructure

Table 33. Selection Criteria for Construction and Maintenance Emissions Analysis Methods

Selection Criteria

Construction & Maintenance Emissions

Analysis Type

Inventory or forecast

Geographic Scope

-State
-Regional
-Possible at local level

Analysis Precision

Varies based on level of sophistication of analysis and number of factors that are considered.

Data Needed

Type and length of activity; engineering data

Necessary Analytical Capabilities

Varies based on level of sophistication of analysis and number of factors that are considered.

Level of Resources Required (i.e., staff/budget)

Varies based on level of sophistication of analysis and number of factors that are considered.

Capable of Addressing Vehicle Technology/Fuels Changes

N/A - Methods are focused on equipment and materials, not on-road vehicles

Capable of Addressing Changes in Travel Demand

N/A - Methods are focused on equipment and materials, not on-road vehicles

Capable of Addressing Changes in Vehicle Speeds and Operations

N/A- Methods are focused on equipment and materials, not on-road vehicles

Description

Construction and maintenance of transportation infrastructure is a large and often overlooked source of GHG emissions and energy consumption in the transportation sector. Construction of infrastructure consumes significant amounts of energy, mostly in the production of materials needed in the construction process. Once new infrastructure is in place, additional energy must be expended over time to maintain it. Transportation plans and projects that reduce GHG emissions by a marginal amount may actually result in a net increase in GHG emissions if the emissions associated with constructing and maintaining new infrastructure are taken into account. 3

New York State DOT (NYSDOT) has developed a lookup-table procedure for estimating construction and maintenance energy consumption and emissions at the planning level, which is used by all of the New York MPOs to report GHG emissions pursuant to requirements in the state energy plan. Detailed information on specific equipment, technologies, and materials to be used in construction and maintenance typically are not available at a planning stage, so simplified assumptions are made. This analysis provides an estimate of the total magnitude of emissions associated with construction and maintenance and may provide a basis for considering alternative construction and maintenance techniques to reduce these emissions. NYSDOT has also developed a tool known as MOVES-Roadway and Rail Energy and Greenhouse Gas Analysis Extension (MOVES-RREGGAE) that combines construction and maintenance emissions information with operational emissions rates from MOVES. These procedures are available upon request from NYSDOT.

Because the information on construction and maintenance emissions used by New York is somewhat dated (MOVES-RREGGAE also relies on an older version of MOVES), FHWA has a research contract underway to develop up-to-date emissions information and a spreadsheet tool to facilitate estimating these emissions at the planning level. This tool would allow MPO or State DOT users to enter information about the lane miles and roadway/project type of planned construction, and estimate emissions from that level of construction. It will also allow users to estimate maintenance emissions from current and future roadway networks, estimate changes in operational emissions from both work zone delay and improved pavement smoothness, and evaluate the emissions benefits of alternative construction techniques. The tool is expected to be available in 2013.

Strengths and Limitations

Table 34. Strengths and Limitations of Construction and Maintenance Emissions Analysis Methods

Analysis/Method

Strengths

Limitations

Construction and Maintenance of Transportation Infrastructure

  • NYSDOT methodology is straightforward and easy to apply using accessible data sources.
  • Information used in the analysis is somewhat dated (but is in the process of being updated).

Example: Greater Buffalo Niagara Regional Transportation Council (GBNRTC) Energy and GHG Analysis

GBNRTC completed an energy and GHG analysis of its 2030 Long Range Transportation Plan. In addition to estimating the changes in "direct" (motor vehicle) operational energy consumption and GHG emissions associated with the plan, GBNRTC also estimated the "indirect" energy and emissions associated with transportation infrastructure construction. The "indirect" analysis includes energy use and emissions from construction equipment, transportation of materials, and those embodied in materials. Using information on the lane miles and project type associated with the new projects in the plan (track miles for rail transit projects), GBNRTC used NYSDOT procedures to estimate the "indirect" energy, and then convert energy consumption to CO2 emissions. See http://www.gbnrtc.org/index.php/resources/publications/reports/.


1 American Public Transportation Association, Recommended Practice for Quantifying Greenhouse Gas Emissions from Transit, APTA CC-RP-001-09, 2009.

2 See: http://www.epa.gov/cleanenergy/energy-resources/egrid/index.html.

3 This Handbook focuses on methods used for GHG analyses in statewide and metropolitan transportation planning. Detailed information on specific equipment, technologies, and materials to be used in construction and maintenance typically are not available at a planning stage, so simplified assumptions are made. This section does not address project-level analysis tools.

Updated: 07/23/2014
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