1

FRA Locomotive Emissions 

Comparison Tool (LECT):

Emissions Data Documentation
2

Locomotive Emissions Comparison Tool: Emissions Data Documentation

Table of Contents

EMISSION RATES DATA SUMMARY............................................................................................................... 3

EMISSIONS METHODOLOGY ......................................................................................................................... 3

Diesel Locomotive Emission Factors..................................................................................................... 4

Replacement Engine Types................................................................................................................... 5

Greenhouse Gas Emissions................................................................................................................... 7

Energy Consumption............................................................................................................................. 8

Appendix: Emissions Tables & Load Factors................................................................................................. 9
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LOCOMOTIVE EMISSIONS COMPARISON TOOL: EMISSIONS DATA

This document supplements the Locomotive Emissions Comparison Tool (LECT) User Guide. It discusses 

primary data sources and how the emission datasets for the tool were derived. Emission estimates from 

the LECT are not intended to meet specific requirements for State Implementation Plans (SIPs) or 

transportation conformity analyses.

EMISSION RATES DATA SUMMARY

Emission rates and emission reductions for the LECT were acquired from the following sources: 

1. The Environmental Protection Agency’s (EPA) Emission Factors for Locomotives1

2. EPA’s Ports Emissions Inventory Guidance document2

3. EPA’s Emissions & Generation Resource Integrated Database (eGRID)3

4. EPA’s GHG Emissions Factors Hub4

5. The California Air Resources Board’s (CARB) Technology Feasibility Assessment for the Proposed 

In-Use Locomotive Regulation5

EMISSIONS METHODOLOGY

The following sections provide a detailed description of emission rate equations and default input 

parameters used in the LECT. Please see Tables A1 and A2 in the Appendix for relevant emissions factors 

and greenhouse gas (GHG) emission rates associated with upstream electricity generation (electric 

locomotives only). The equations below summarize how the tool calculates emission reductions. The 

change in emissions is the difference between the emissions from the baseline and replacement 

engines. Emission reductions are output in short tons per year for air pollutants and metric tons per year 

for GHGs.

∆EEEEEEEEEEEEEEEEEE = BBBB BBBB BB EEEEEEEEEEEEEEEEEE − RR RR RR RR EEEEEEEEEEEEEEEEEE (1) 

1 U.S. Environmental Protection Agency, Emission Factors for Locomotives, EPA-420-F-09-025 (April 2009). 

Available at: https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P100500B.TXT. 2 U.S. Environmental Protection Agency, Office of Transportation Air Quality, Ports Emissions Inventory Guidance: 

Methodologies for Estimating Port-Related and Goods Movement Mobile Source Emissions, EPA-420-B-22-011

(April 2022). Available at: https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P1014J1S.pdf. 3 U.S. Environmental Protection Agency, Emissions & Generation Resource Integrated Database (eGRID) (web 

page) (November 8, 2023). Available at: https://www.epa.gov/egrid. 

Data Explorer (2021): https://www.epa.gov/egrid/data-explorer. 

Summary Data (2021): https://www.epa.gov/egrid/summary-data. 4 U.S. Environmental Protection Agency, GHG Emission Factors Hub (web page) (April 3, 2023). Available at: 

https://www.epa.gov/climateleadership/ghg-emission-factors-hub. 5 California Air Resources Board, Appendix F: Technology Feasibility Assessment for the Proposed In-Use Locomotive 

Regulation. Available at https://ww2.arb.ca.gov/sites/default/files/barcu/regact/2022/locomotive22/appf.pdf.

Accessed December 2023.
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A positive change in emissions is equivalent to an emissions reduction (benefit), while a negative change 

in emissions can be interpreted as an emissions increase (disbenefit). The tool assumes original 

equipment is powered by diesel fuel, with baseline equipment emissions calculated as:

EEbbbbbbbbbbbbbbbb = EEEEEE ee ee ff ffff ff � gg

bbhpp−h � ∗ CCCC �

bbhpp−h

gg � ∗ FF (gg ) ∗ UU (2)

where Ebaseline is baseline emissions, CF is the EPA-supplied conversion factor for different locomotive 

applications (see below), Fuel is the annual fuel consumption in gallons of diesel for a single 

representative locomotive, and UC is a factor to convert between grams and short tons (air pollutants) 

and metric tons (GHGs).6

 

Diesel Locomotive Emission Factors

The EPA’s locomotive emission factors are given in units of grams of pollutant per brake horsepowerhour (g/bhp-hr). Brake horsepower is a measure of an engine’s horsepower before the loss in power 

caused by the gearbox and drive train. It is measured at the crankshaft, just outside the engine, and is a 

function of engine torque and rotational speed. The two locomotive applications included in this tool 

are line-hauling (Class II/III, including passenger trains) and switching. The following conversion factors7

are applied to calculate the mass of pollutant emitted based on the volume of diesel fuel consumed: 

Small (Class II/III) Line-Haul: 18.2 bhp-hr/gal

Switch locomotives: 15.2 bhp-hr/gal 

The replacement engine emissions are based on the type of replacement locomotive, as described 

under Replacement Engine Types. For replacement diesel engines, emission reductions are expected 

due to newer engines meeting more stringent EPA standards (e.g., replacing a Tier 1 engine with Tier 4). 

For all calculations, PM2.5 emissions are estimated as 97 percent of PM10 emissions.8

THC-to-VOC Conversion

EPA’s hydrocarbon emission factors for locomotive engines are reported in terms of total hydrocarbons 

(THC). THC is converted to volatile organic compounds (VOC) for consistency with air quality standards, 

using the following factor for diesel engines.

9

VVVVVV

TTTT

= 1.053 (3) 

6 1 short ton = 907,185 g and 1 metric ton = 1,000,000 g. 7 These conversion factors were calculated by EPA based on the duty cycles of the different locomotive 

applications (see footnote 2).

8 U.S. Environmental Protection Agency, Office of Transportation Air Quality, Draft Methodologies for Estimating 

Port-Related and Goods Movement Mobile Source Emission Inventories. EPA-420-D-20-001 (February 2020). 

Available at: https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P100YFY8.pdf. 9 U.S. Environmental Protection Agency, Conversion Factors for Hydrocarbon Components, EPA420-R-05-015

(December 2005). Available at: 

https://19january2017snapshot.epa.gov/www3/otaq/models/nonrdmdl/nonrdmdl2005/420r05015.pdf. 
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Replacement Engine Types

The LECT allows users to select from five different engine replacement options: diesel, diesel GenSet 

(switch locomotives only), all-electric or equivalent, diesel-battery hybrid, and other technology. For 

lower-emissions locomotives that exceed the Tier 4 standards, users are required to provide

manufacturer-supplied certification data. Sources of emission rates by engine type are summarized in 

Table 1. 

Table 1. Emissions Source by Engine Type

Engine Type Locomotive Application Emissions Rate Source

Diesel Line-Haul and Switch

EPA10, 11

Manufacturer-supplied if engine 

exceeds Tier 4 standards

Diesel GenSet Switch only California Air Resources Board12

All-Electric or Equivalent Line-Haul and Switch EPA13

Diesel-Battery Hybrid Line-Haul and Switch Manufacturer-supplied

Other Technology Line-Haul and Switch Manufacturer-supplied

The sec�ons that follow describe the engine and fuel types available for modeling with the tool. 

Diesel

Emissions savings from a “Diesel” to “Diesel” engine replacement are primarily due to the replacement 

engine being held to a higher emissions �er (see Table A1). Newer engines may also use fuel more 

efficiently, resul�ng in addi�onal emission reduc�ons. Please see the Fuel Use sec�on of the User Guide

for informa�on on how to es�mate fuel efficiency improvements. 

As more advanced engine technologies are developed, some diesel locomo�ves may exceed the current 

Tier 4 standards. For locomo�ves that exceed Tier 4 standards for any of the air pollutants (i.e., emission 

rates lower than the standards), the tool allows for users to input emissions cer�fica�on data from 

manufacturers in units of g/bhp-hr.

10 U.S. Environmental Protection Agency, Emission Factors for Locomotives, EPA-420-F-09-025 (April 2009). 

Available at: https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P100500B.TXT. 11 U.S. Environmental Protection Agency, Office of Transportation Air Quality, Ports Emissions Inventory Guidance:

Methodologies for Estimating Port-Related and Goods Movement Mobile Source Emissions, EPA-420-B-22-011

(April 2022). Available at: https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P1014J1S.pdf. 12 California Air Resources Board, Locomotive Emission Verifications, Technology Demonstrations, and Incentives 

(web page). Available at: https://ww2.arb.ca.gov/our-work/programs/reducing-rail-emissionscalifornia/locomotive-emission-verifications-technology. Accessed December 2023. 13 U.S. Environmental Protection Agency, Diesel Emissions Quantifier (DEQ) version 9.1. (May 2, 2022). Available at: 

https://cfpub.epa.gov/quantifier/. 
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Diesel GenSet

The “Diesel GenSet” op�on is currently only available for switch locomo�ves.14 While it is technically 

feasible for a diesel GenSet to be used for other applica�ons, they are not commonly used in line-haul 

locomo�ves. Diesel GenSets use a mul�-engine configura�on (typically 2-3 engines) that operate in 

series with each engine powering up as the load increases. These engines are designed for switch 

locomo�ves opera�ng in railyards where locomo�ves can spend the majority of �me idling. During idle, 

two of the engines in a three-engine GenSet can be turned off with only one engine idling. Compared 

with a single diesel engine with the same load capacity as the three-engine GenSet, emissions will be 

lower (mainly due to reduc�ons in fuel use). As the load increases on the GenSet (e.g., the switcher 

begins moving rail cars around the yard), addi�onal engines power up to meet the work demand. 

GenSets are typically built with non-road diesel engines/generators and are cer�fied at EPA’s Tier 4 

emissions standard for switch locomo�ve applica�ons.15 When selected as the replacement equipment 

type, the module calculates emissions based on the EPA Tier 4 standard for switch locomo�ves. 

While fuel savings will vary by switcher use, it is es�mated that railyards can observe 20 to 50 percent 

fuel savings by replacing a diesel switcher with a GenSet.16 It should be noted that these fuel savings are 

assumed only due to the opera�on of the mul�-engine configura�on and not based on assump�ons with 

individual engine characteris�cs, such as age. The LECT does not account for these fuel savings 

automa�cally and the user must account for them in their replacement fuel use input value.

All-Electric or Equivalent

“All-Electric, Battery or Equivalent” replacement equipment is assumed to have zero operational

emissions. This category can be applied to a variety of zero-emission solutions, including, but not limited 

to batteries, hydrogen fuel cells,17 and connection to the grid via overhead lines. 

Diesel-Battery Hybrid

Several railroads and locomotive manufacturers are pursuing hybrid technology as a more cost-effective 

and lower-emissions option to traditional diesel engines. For example, Union Pacific and locomotive 

manufacturer ZTR have partnered on new hybrid-electric locomotives, including “drop-in” technologies 

that can be used to modify existing systems.18,19

14 If new applications and emissions data become available for GenSet locomotives, the tool will be updated 

accordingly. 

15 California Air Resources Board, Locomotive Emission Verifications, Technology Demonstrations, and Incentives 

(web page). Available at: https://ww2.arb.ca.gov/our-work/programs/reducing-rail-emissionscalifornia/locomotive-emission-verifications-technology. Accessed December 2023. 16 Manufacturer claims and demonstrations, including: https://archive.epa.gov/midwestcleandiesel/

web/pdf/il2008.pdf, and https://ww3.arb.ca.gov/railyard/docs/nrele_finalreport_201507.pdf. 17 K. Hess et al. (Fuelcell Propulsion Institute), “Demonstration of a Hydrogen Fuel-Cell Locomotive” (2010). 

Available at: https://pdfs.semanticscholar.org/bc5b/8df3251a993d608295aad4ae795678c046cf.pdf. 18 Union Pacific, “Union Pacific and ZTR Partner on New Hybrid-Electric Locomotives” (October 6, 2022). Available 

at: https://www.up.com/media/releases/hybrid-electric-locomotives-nr-221006.htm. 19 Union Pacific, “Union Pacific Railroad to Assemble World's Largest Carrier-Owned Battery-Electric Locomotive 

Fleet” (January 28, 2022). Available at: https://www.up.com/media/releases/battery-electric-locomotive-nr220128.htm. 
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Hybrid locomotives use a diesel engine and battery power and include different operational and 

charging modes. Modes can include a diesel generator, battery pack, and hybrid drive.20 An on-board 

computer controls which mode or combination of modes receives priority. For example, when the 

locomotive is used in high power, the diesel generator and battery pack may be used together; at low 

power, the battery pack may have priority and the diesel generator is turned off. Three methods may be 

used for charging: diesel generator set to charge the battery pack, regenerative braking that uses

recovered energy to charge the battery, and ground charging equipment (e.g., wayside connection to 

commercial grid). Industry reports indicate that use of hybrid locomotives can result in fuel savings 

between 30 and 50 percent.21

The LECT models diesel-battery hybrid locomotives as diesel engines that conform to EPA’s Tier 3 or Tier 

4 standards or exceed the Tier 4 standards (requires manufacturer-supplied emission rates). The current 

tool version does not model upstream electricity emissions from hybrid locomotives due to a lack of 

data on time spent in different drive and charging modes. 

Greenhouse Gas Emissions

GHG Emission Rates—Operational 

The tool calculates GHG emissions from locomotive engines based on fuel consumption (gallons) and 

emission factors (grams per gallon). CO2 emission benefits in the LECT are reported as both atmospheric 

CO2 and CO2 equivalents (CO2e). 

CO2 emissions are based on the carbon content of the fuel, while CO2e is calculated based on the global 

warming potentials (GWPs) of CO2, CH4, and N2O.22 The carbon content of diesel locomotive engines is 

3,200 grams per gallon and the CH4 and N2O mass emitted by diesel locomotives is estimated to be 0.8

grams and 0.26 grams per gallon, respectively.

23

GHG Emission Rates—Upstream

For electric locomo�ves, the LECT estimates upstream emissions from electricity generation based on 

what eGRID region the project is located in24: 

20 Railway Technology, “Hybrid locomotives will effectively replace traditional diesel locomotives in the future.” 

Available at: https://www.railway-technology.com/sponsored/hybrid-locomotives-replace-diesel-locomotives/.

Accessed December 2023.

21 Ibid. 22 U.S. Environmental Protection Agency. “Understanding Global Warming Potentials” (April 18, 2023). 

https://www.epa.gov/ghgemissions/understanding-global-warming-potentials. 23 T. W. P. Smith et al., Third IMO Greenhouse Gas Study 2014: Executive Summary and Final Report (London: 

International Maritime Organization, April 2015). Available at: 

https://www.imo.org/en/ourwork/environment/pages/greenhouse-gas-studies-2014.aspx; U.S. Environmental 

Protection Agency, Emission Factors for Greenhouse Gas Inventories (2023). Available at: 

https://www.epa.gov/system/files/documents/2023-03/ghg_emission_factors_hub.pdf. 24 U.S. Environmental Protec�on Agency, eGrid Data Explorer 2021 (web page) (September 26, 2023). Available at:

https://www.epa.gov/egrid/data-explorer.
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UU UU

= ee eeee ee ee � ll

MMMMh

� × 1/EEEEEE � MMMMh

gg � × (gg )

where Eff is the fuel efficiency for a switcher locomo�ve (73.7 gal/MWh) or line-haul/passenger 

locomo�ve (64.5 gal/MWh).25

Upstream emissions from diesel equipment are es�mated based on emission factors from GREET26 that 

include contribu�ons from diesel fuel produc�on, transporta�on, and storage (well-to-use): 

Table 1. Emissions factors for diesel well-to-use activities (derived from GREET 2022)

Greenhouse Gas

Well-to-Use Emission

Factor

(grams per gallon)

CO2 1662.1

CH4 14.0581

N2O 0.0285264

CO2 Equivalents (GWP-100) 2096.7

Energy Consumption

The tool also calculates upstream and opera�onal energy use for diesel and electric locomo�ves using 

outputs from GREET 2022. Upstream energy consump�on is based on well-to-use energy factors:

Well-to-use energy for diesel: 44.71 kWh/gallon 

Well-to-use energy for electricity produc�on: 1.07 kWh/kWh used 

Opera�onal energy use for diesel locomo�ves is calculated as:

UU UU = (gg ) ×

1

EE � MMMMhgg � × ee � kk hkk h uu uu

� ×

1000kk h

MMMMh

25 California Air Resources Board. Appendix F: Technology Feasibility Assessment for the Proposed In-Use 

Locomotive Regulation. Available at: 

https://ww2.arb.ca.gov/sites/default/files/barcu/regact/2022/locomotive22/appf.pdf (see Table 8). Accessed 

December 2023.

26 Argonne National Laboratory. The Greenhouse gases, Regulated Emissions, and Energy use in Technologies 

Model (GREET) Tool (2022). Available at: https://greet.anl.gov/net.
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Appendix: Emissions Tables & Load Factors

Table A1. Locomo�ve Emission Factors27

Emission Factors (g/bhp-hr)

Fuel Type Year of Manufacture Tier NOX PM HC28 CO

Diesel (Line-haul)

Pre-1973 Uncontrolled 13.00 0.32 0.48 1.28

1973-1992 Tier 0 8.60 0.32 0.48 1.28

1973-1992 Tier 0+ 7.20 0.20 0.30 1.28

1993-2004 Tier 1 6.70 0.32 0.47 1.28

1993-2004 Tier 1+ 6.70 0.20 0.29 1.28

2005-2011 Tier 2 4.95 0.18 0.26 1.28

2005-2011 Tier 2+ 4.95 0.08 0.13 1.28

2012-2014 Tier 3 4.95 0.08 0.13 1.28

2015+ Tier 4 1.00 0.015 0.04 1.28

Diesel (Switch)

Pre-1973 Uncontrolled 17.40 0.44 1.01 1.83

1973-2001 Tier 0 12.60 0.44 1.01 1.83

1973-2001 Tier 0+ 10.60 0.23 0.57 1.83

2002-2004 Tier 1 9.90 0.43 1.01 1.83

2002-2004 Tier 1+ 9.90 0.23 0.57 1.83

2005-2010 Tier 2 7.30 0.19 0.51 1.83

2005-2010 Tier 2+ 7.30 0.11 0.26 1.83

2011-2014 Tier 3 4.50 0.08 0.26 1.83

2015+ Tier 4 1.00 0.015 0.08 1.83

GenSet* 2015+ Tier 4 1.00 0.015 0.08 1.83

Electric◊

(or equivalent) All N/A 0.0 0.0 0.0 0.0

Tiers with “+” are applicable only to locomotives that were originally manufactured in the 

corresponding Year of Manufacture range and remanufactured in 2008 or later; EPA holds these 

remanufactured locomotives to a higher emissions standard.

* Emission rates are estimated at the Tier 4 switch locomotive emission rates. ◊ Opera�onal emissions only. See Table A2 for emission rates used to quan�fy emissions from 

upstream electricity genera�on. 

27 U.S. Environmental Protection Agency, Emission Factors for Locomotives, EPA-420-F-09-025 (April 

2009).Available at https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P100500B.TXT. 28 Hydrocarbon (HC) emission factors were converted to volatile organic compounds (VOC) emission factors using 

EPA conversion factors.
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Figure A1. eGRID Regions29

29 U.S. Environmental Protection Agency, eGrid Data Explorer 2021 (web page) (September 26, 2023). Available at:

https://www.epa.gov/egrid/data-explorer.
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Table A1. eGRID Subregion Total Output Emission Rates (lb/MWh)30

30 U.S. Environmental Protec�on Agency, Summary Data eGRID with 2021 Data (web page) (January 30, 2023). 

Available at htps://www.epa.gov/egrid/summary-data. 

eGRID 

Subregion CO2 CH4 N2O CO2e 

AKGD 1067.7 0.091 0.012 1073.7

AKMS 485.2 0.025 0.004 487.1

AZNM 819.7 0.052 0.007 823.1

CAMX 531.7 0.031 0.004 533.6

ERCT 813.6 0.054 0.008 817.2

FRCC 832.9 0.053 0.007 836.3

HIMS 1134.4 0.135 0.021 1143.9

HIOA 1633.1 0.176 0.027 1645.5

MROE 1582.1 0.148 0.022 1592.3

MROW 995.8 0.107 0.015 1003.1

NEWE 539.4 0.072 0.009 544

NWPP 634.6 0.058 0.008 638.5

NYCW 816.8 0.019 0.002 817.9

NYLI 1210.9 0.126 0.016 1218.9

NYUP 233.1 0.015 0.002 234

PRMS 1558 0.081 0.013 1563.9

RFCE 672.8 0.049 0.007 676

RFCM 1214.1 0.115 0.016 1221.8

RFCW 1046.1 0.095 0.014 1052.5

RMPA 1158.9 0.109 0.016 1166.2

SPNO 991.7 0.108 0.016 999.1

SPSO 1031.6 0.08 0.012 1037

SRMV 772.7 0.04 0.006 775.4

SRMW 1543 0.171 0.025 1554.7

SRSO 891.9 0.067 0.01 896.4

SRTV 931.6 0.087 0.013 937.5

SRVC 639.7 0.052 0.007 642.9

U.S. 852.3 0.071 0.01 857