January 3, 2012 

ERTAC Rail Emissions Inventory 

Part 1: Class I Line-Haul Locomotives 

Michelle Bergin, GA Environmental Protection Division 

Matthew Harrell, IL Environmental Protection Agency 

Mark Janssen, Lake Michigan Air Directors Consortium 

Acknowledgments: 

 Robert Fronczak, Association of American Railroads

 Raquel Wright, Federal Railroad Administration 

 Julie McDill, Mid-Atlantic Regional Air Management Association 

 Patrick Davis, Mid-Atlantic Regional Air Management Association 

 Laurel Driver, US EPA, Office of Air Quality Planning and Support 

 Byeong Kim, GA Environmental Protection Division 

Introduction 

Air protection agencies from twenty-seven states, coordinated through the Eastern Regional Technical 

Advisory Committee (ERTAC) and headed by the Lake Michigan Air Directors Consortium 

(LADCO), identified a need to better quantify and characterize rail-related emissions inventories. 

Traditional locomotives utilize large diesel engines, resulting in emissions of NOx, diesel PM, 

hydrocarbons, greenhouse gases, and other air pollutants. These emissions are sometimes concentrated 

in areas exceeding National Ambient Air Quality Standards. No cohesive nationwide railroad 

emission estimates based on local operations are known to have been made previously. Inventory 

development methods for locomotive emissions estimates vary from state to state and, in general, lack 

the spatial or temporal resolution needed to support air quality modeling and planning 1-5. 

The ERTAC Rail Subcommittee (ERTAC Rail) was established with active representatives from 

twelve member states, three regional planning offices, and the US EPA. The subcommittee’s goals are 

to (1) standardize agencies’ inventory development methods through a collaborative effort, (2) 

improve the quality of data received and the resulting emission inventories, and (3) reduce the 

administrative burden on railroad companies providing data. 

With support from the Rail industry and assistance from the ERTAC Rail Data Workgroup (Appendix 

A), ERTAC Rail has developed 3 inventories of locomotive emissions (Table 1) for Class I line-haul, 

Shortline and Regional Railroads (Class II and III operations), and Class I railyard switchers. Because 

of the difficulty in obtaining data and differences in states’ needs for inventory years, sources from

both 2007 and 2008 were utilized (Appendix B.) 

The Surface Transportation Board (STB) defines Class I Railroads as having had minimum carrier 

operating revenues of $401.4 million (USD) in 2008. There are 8 Class I Railroads operating in the 

United States (Table 2), about 33 Regional Railroads (Class II), and approximately 540 Class III 

Railroads (Shortlines)6

. While categorized as a Class I Railroad, Amtrak was excluded from these 

inventories because of significant differences in equipment and operational characteristics. Line-haul 

locomotives are usually newer, larger locomotives that travel long distances (e.g. between cities) while 

switcher locomotives are generally older, smaller locomotives that mostly operate within railyards, 
2

splitting and joining rail cars with varying destinations. Shortline railroads often utilize smaller, older 

locomotives than Class I line-haul. Passenger and Commuter Rail (including Amtrak), industrial 

locomotives, and associated non-locomotive equipment are not included in these inventories. 

This paper documents the data sources and methodologies used for calculating the Class I line-haul 

emissions inventory. Class I line-haul activities are the largest source of rail-related emissions, with 

estimates of Class I line-haul fuel consumption totals to be from 74 to 84% of all rail sources 

combined4, 5. For this reason, characterizing Class I line-haul emissions were a focal point of ERTAC 

Rail’s inventory development efforts. This inventory best represents 2007 emissions and can be scaled

for a few years back or forward using annual line-haul fuel use reported to the STB. Information on 

ERTAC Rail, Railroad participation, the Rail industry, and effects of rail on air quality are available 

elsewhere7. 

Table 1. Summary of ERTAC Rail Inventories: U.S. Locomotive Emissions and Fuel Use for 

either 2007 or 2008*. 

 Fuel Use** (gal/yr) Emissions (tons/yr) 

NOx PM2.5 HC SO2 CO NH3 CO2

Class I*** 

line-haul 3,770,914,002 754,443 23,439 37,941 7,836 110,969 347 42,305k

Class I 

switcher 301,046,290 74,431 2,042 4,867 624 9,230 28 3,367k

Class II 

and III 157,800,000 47,035 1,065 1,737 327 4,631 14 1,765k

*See Appendix B for a description of the year and source of data utilized for each inventory. 

**Locomotive grade diesel 

***Excluding Amtrak and including work train fuel use 

Table 2. Class I Railroads, Reported Locomotive Fuel Use, 

 and Railroad Fuel Consumption Index (RFCI) 8. 

Class I Railroads* 

R-1 Reported Locomotive Fuel 

Use (gal/yr) RFCI 

Line-Haul (ton-miles/gal) 

(2007)** 

Switcher 

(2008) 

BNSF 1,393,874,954 52,497,057 883.14 

Canadian National 93,830,751 12,290,022 1190.79 

Canadian Pacific ***50,320,233 4,937,067 1096.28 

CSX 514,687,186 53,717,674 963.81 

Kansas City Southern 69,787,071 1,816,759 785.89 

Norfolk Southern 463,267,278 32,317,375 865.75 

Union Pacific 1,185,146,529 143,470,336 974.64 

Total 3,770,914,002 301,046,290 929.47 

* Excluding Amtrak 

** Includes work trains 

*** CP’s line-haul fuel use values include 2008 data (rather than 2007) for their Delaware and Hudson 

subsidiary. 
3

Method 

Earlier efforts to characterize line-haul railroad emissions relied on highly aggregated activity data and 

generally apportioned annual system-wide fuel use equally across all route miles of track operated by a 

Class I railroad. However, the majority of freight tonnage carried by Class I railroads is concentrated 

on a disproportionately small number of route miles (Figure 1). In addition, emissions calculations 

were previously based on an estimate of annual nationwide-average locomotive fleet mix to create one 

set of emissions factors. 

For this inventory, the Class I Railroads allowed ERTAC Rail access under a confidentiality agreement 

to a link-level (single lengths of track) line-haul GIS layer activity dataset managed by the Federal 

Railroad Administration9

. Each railroad also provided fleet mix information that allowed ERTAC Rail 

to calculate weighted emission factors based on the fraction of their line-haul fleet meeting each Tier 

level category. The use of this data, largely following a line-haul inventory methodology 

recommended by Sierra Research2, 3, resulted in a link-level line-haul locomotive emission inventory 

using railroad-specific emission factors. This segment-level inventory is nationwide, aggregated to 

state and county level files and can be converted to gridded emissions files for use in photochemical 

and dispersion modeling. Link-level emissions may be provided to third parties for special study 

requests pending approval of any Class I railroads operating in the study domain. The calculations are 

described below as a two-part process, first calculating railroad-specific factors and then total 

emissions per rail link. 

Figure 1. US Railroad Traffic Density in 2006.10 MGT is million gross tons. 
4

1. Calculate Railroad-Specific Factors. 

The EPA provides annual default Emission Factors for locomotives based on characteristic operating 

cycles (‘duty cycles’) and the estimated nationwide fleet mixes for both switcher and line-haul 

locomotives. However, fleet mixes vary from railroad to railroad and, as can be seen in Figure 2, Class 

I railroad activity is highly regionalized in nature and subject to issues of local terrain such as 

operation on plains vs. mountainous areas, which can have a significant impact on fuel consumption 

and emissions. 

Figure 2. Class I Railroad Territories in the United States11

. 

As an alternative approach to using a single nationwide set of emission factors, ERTAC Rail requested 

each Class I company to provide a description of their line-haul fleet mix based on Tier rating, which

each company provided under a confidentiality agreement. An engine’s Tier level is based on the year 

the engine was built and determines allowable emission limits (Table 3). 

Table 3. EPA line-haul locomotive Emission Factors by Tier, 1997 standards (grams/gal). Note 

that the new standards released in 2008 did not apply to fleets in the year 2008. 12

PM10 HC NOx CO 

Uncontrolled (pre-1973) 6.656 9.984 270.4 26.624 

Tier 0 (1973-2001) 6.656 9.984 178.88 26.624 
5

Tier 1 (2002-2004) 6.656 9.776 139.36 26.624 

Tier 2 (2005 + ) 3.744 5.408 102.96 26.624 

Based on values in EPA Technical Highlights: Emission Factors for Locomotives, EPA Office of 

Transportation and Air Quality, EPA-420-F-09-025, April 2009. 

Weighted Emission Factors (EF) per pollutant for each gallon of fuel used (gm/gal or lbs/gal) were 

calculated for each Class I railroad fleet based on its fraction of line-haul locomotives at each regulated 

Tier level (Eqn 1; Table 3). 

∑=

=

4

1

( * )

T

iRR iT TRR EF EF f Equation 1 

 EFiRR = Weighted Emission Factor for pollutant i for Class I railroad RR (gm/gal). 

 EFiT = Emission Factor for pollutant i for locomotives in Tier T (gm/gal) (Table 3). 

There were 4 Tiers of locomotives in the 2008 fleets. 

fTRR = Fraction of railroad RR fleet in Tier T. 

While engine emissions are variable within Tier categories, this approach likely provides better 

regional estimates than uniformly applying the nationwide average emission factors. This approach 

likely provides conservative emission estimates as locomotive engines are certified to meet or exceed 

the emissions standard for each Tier, although emission levels may increase after certification and 

actual operations may vary widely from the line-haul duty-cycle estimation. 

Other emission factors are not engine specific. For locomotives, PM2.5 is assumed to be 97% of PM10

12, and emission factors applied for SO2 and NH3 are 1.88 g/gal 12 and 83.3 mg/gal 13 respectively. 

Greenhouse gases are estimated using emission factors shown in Table 4. Note that locomotive and 

marine engines are not subject to general non-road fuel or engine standards. 

Table 4. EPA greenhouse gas emission factors for locomotive diesel fuel (grams/gal). 14

CO2 N2O CH4

Locomotive diesel 1.015E4 0.26 0.80 

A Railroad Fuel Consumption Index (RFCI) was also calculated for each Class I railroad using their 

system-wide line-haul fuel consumption (FC) and gross ton-mile (GTM) data reported in their annual 

R-1 reports submitted to the Surface Transportation Board8

 (Eqn 2). This value represents the average 

number of GTM produced per gallon of diesel fuel used over their system in a year, and varies 

between railroad carriers depending on factors such as fleet mix, system terrain, speeds, loading/weight 

of cargo, train type (e.g., intermodal, unit, and manifest), and operating practices. (Table 2). 

RR

RR

RR FC

GTM RFCI = Equation 2 
6

RFCIRR = Railroad Fuel Consumption Index (gross ton-miles/gal) per Class I railroad (RR).

 GTMRR = Gross Ton-Miles (GTM), annual system-wide gross ton miles of freight 

 transported per RR. (R-1 Report Schedule 755, Line 104) 

 FCRR = Annual system-wide fuel consumption by line-haul and work trains per RR (gal) 

(R-1 Report Schedule 750, Lines 1 and 6). 

2. Calculate Emissions per Link. 

Emissions of pollutant i per link L (EiL) are calculated by multiplying the gallons of diesel fuel 

consumed by each Class I railroad on the link by that railroad’s weighted Emission Factor for the 

pollutant, and then summing emissions for all Class I railroads operating on that link (Eqn 3). This 

approach splits the activity on each link (represented by MGT) evenly between all railroads operating 

on the link. Note that the weighted Emission Factors are converted to tons/gal for these calculations, 

and that variables with units in tons may represent tons of freight hauled (MGT, RFCI) or tons of 

pollutants (EF, E). 

∑=

















=

N

RR

iRR

RR

L

L

iL EF

RFCI

l

N

MGT

E

1

6

*

*

10*

Equation 3 

EiL = Emissions of pollutant i per link L (tons/year). 

N = Number of Class I railroads operating on link L.

MGTL = Millions of Gross Tons hauled per link per year from the FRA database 

(106 tons/yr)9. 

lL = Link length from the FRA database (miles). 

 EFiRR = Weighted Emission Factor for pollutant i per railroad RR (Eqn 1; tons/gal). 

 RFCIRR = Railroad Fuel Consumption Index per railroad RR (Eqn 2; gross ton-miles/gal). 

Note that approximately 36% of Class I route miles in the United States are shared by more than one 

Class I carrier, a fraction that drops to 26% when neglecting track only shared between one Class I 

freight railroad and Amtrak. Accurately apportioning the specific fractions of tonnage (MGT) per 

carrier per link was considered, but after comparing likely worst-case areas, the difficultly of merging 

carrier-specific MGT with the aggregated FRA MGT dataset was considered too great considering the 

potential gain in accuracy. Where warranted, MGT data may be apportioned more accurately in the 

future. 

Limitations, Conclusions, and Future Work 

Rail-related emissions can be important components of emissions inventories used to support effective 

air quality management practices at local, state, regional, and national levels. Previous air quality

studies often have not had the data needed to adequately represent this source sector. This line-haul

inventory, as well as the companion Class I railyard inventory and Class II/III inventory, greatly 

improve our ability to estimate of rail-related emissions. A systematic study of variability and 

uncertainty in line-haul locomotive emissions and activity, by fleets, locations, and through time, 
7

would give additional valuable information for identifying how to best improve this inventory as well 

as provide an indication of how representative the inventory may be. An uncertainty study on the data

used for this inventory, including the R-1 reported fuel use, the confidential link-level tonnage data, 

and the duty-cycle estimate would also help in evaluating the quality of this inventory. Localized 

studies should examine how shared tracks are apportioned between multiple carriers in their domain. 

Early ERTAC Rail discussions concluded that link-level tonnage was the most important data to 

obtain, while other variables such as track grade and track speed could not be addressed at this time. 

ERTAC Rail calculated railroad-specific fleet-averaged emission factors rather than applying the 

estimated national average; however, it is recognized that emissions from individual engines are highly 

variable even within Tier categories depending on variables such as the specific locomotive model, 

operation cycle, and conditions of operation. Future evaluation of emission variability within Tiers and 

between certain types of operation and locations would be valuable. 

Emissions inventory preparation guidance from the U.S. EPA describes locomotive activity as 

relatively constant throughout the year (e.g. no daily, weekly, or seasonal variability); however, actual 

activity levels do vary seasonally and annual averaging may dilute or exaggerate concentrations during

pollution episodes. ERTAC Rail and the Class I railroad community had some discussions addressing 

if incorporating more specific fleet mix or monthly or seasonal variation may be worthwhile, and these

topics should be looked into further. 

Finally, it is important to reiterate that the link-level MGT data maintained by the FRA is proprietary 

and can only be released to agencies/groups outside the FRA with the express permission of each Class 

I railroad. It is possible that one or more Class I railroads could withhold permission for access, but 

data for specialized studies may be provided if requested. This database can also be improved by 

better distinguishing between haulage and trackage rights, and by apportioning tonnage hauled on links

to specific carriers. 

We would like to thank the Class I Railroads and their representatives for their assistance and support 

in the development of this inventory. 

References 

1. Eastern Research Group (ERG) for E.H. Pechan & Associates, Inc., “Documentation for 

Aircraft, Commercial Marine Vessel, Locomotive, and Other Nonroad Components of the 

National Emissions Inventory, Volume I – Methodology”; EPA Contract No.: 68-D-02-063. 

Prepared for the US EPA Emissions, Monitoring and Analysis Division, Sept. 30, 2005. 

ftp://ftp.epa.gov/EmisInventory/2002finalnei/documentation/mobile/2002nei_mobile_nonroad_

methods.pdf. Related documents at 

ftp://ftp.epa.gov/EmisInventory/2002finalnei/documentation/mobile/2002nei_mobile_nonroad_

train.pdf 

2. Sierra Research, Inc., “Revised Inventory Guidance For Locomotive Emissions”; Report No. 

SR2004-06-01. Prepared for Southeastern States Air Resource Managers (SESARM), June 

2004. http://www.metro4-sesarm.org/pubs/railroad/FinalGuidance.pdf 

3. Sierra Research, Inc., “Research Project: Development of Railroad Emission Inventory 

Methodologies”; Report No. SR2004-06-02. Prepared for Southeastern States Air Resource 
8

Managers (SESARM), June 2004. http://www.metro4-

sesarm.org/pubs/railroad/FinalMethodologies.pdf 

4. Environ, “Draft LADCO 2005 Locomotive Emissions”. Prepared for Lake Michigan Air 

Director Consortium, Feb 2007. 

http://www.ladco.org/reports/technical_support_document/references/ladco_2005_locomotive_

emissions.021406.pdf 

5. Southern Research Institute, “NYSERDA Clean Diesel Technology: Non-Road Field 

Demonstration Program, Development of the 2002 Locomotive Survey for New York State”; 

Agreement Number 8958. Prepared for the New York State Energy Research And 

Development Authority (NYSERDA), Feb. 09, 2007. 

http://www.nyserda.org/publications/LocomotiveSurveyReportwithAppendices.pdf

6. American Short Line and Regional Association (ASLRRA) 2008 Fact Book. Available at 

www.alsrra.org. 

7. M. Bergin; M. Harrell; J. McDill; M. Janssen; L. Driver; R. Fronczak; R. Nath,; and D. Seep. 

"ERTAC Rail: A Collaborative Effort in Building a Railroad-Related Emissions Inventory 

Between Eastern States Air Protection Agencies and Participation with the Railroad Industry," 

18th Annual International Emission Inventory Conference. Baltimore, MD. April 14 - 17, 

2009. Paper and presentation available at: 

http://www.epa.gov/ttn/chief/conference/ei18/session6/bergin.pdf

8. Surface Transportation Board R-1 Reports, available at:

http://www.stb.dot.gov/stb/industry/econ_reports.html. 

9. Confidential database was provided with assistance from Raquel Wright of the Federal 

Railroad Administration. Similar public data providing ranges of tonnage hauled rather than 

link-level tonnage is available from the Bureau of Transportation Statistics in the NTAD 2009 

shapefile data (data is representative for the year 2007): 

http://www.bts.gov/publications/national_transportation_atlas_database/2009 . 

10. US DOT Bureau of Transportation Statistics’ 2008 National Transportation Atlas Database. 

11. Freight Railroads in the United States 2008. Association of American Railroads. Available at: 

http://www.aar.org/~/media/AAR/InCongress_RailroadsStates/2008unitedstates.ashx . 

12. EPA Technical Highlights: Emission Factors for Locomotives, EPA Office of Transportation 

and Air Quality, EPA-420-F-09-025, April 2009. 

http://www.epa.gov/otaq/regs/nonroad/locomotv/420f09025.pdf 

13. Estimating Ammonia Emissions From Anthropogenic Nonagricultural Sources - Draft Final 

Report by E.H. Pechan & Assoc. April 2004. Prepared for EPA/STAPPA-ALAPCO Emission 

Inventory Improvement Program. Supported by personal communication (5/6/2010) with Craig 

Harvey, US EPA, OTAQ, and Robert Wooten, NC DENR. 

http://www.epa.gov/ttnchie1/eiip/techreport/volume03/eiip_areasourcesnh3.pdf

14. U.S. Environmental Protection Agency. Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-

2005, EPA 430-R-07-002, Annex 3.2, (April 2007), web site: 

http://www.epa.gov/climatechange/emissions/usinventoryreport.html.
9

Appendix A: ERTAC Rail Data Workgroup

REPRESENTATIVE ORGANIZATION 

Matt Harrell IL EPA 

Michelle Bergin (Co-Chair) and Byeong Kim GA EPD 

Mark Janssen (Co-Chair) LADCO 

Julie McDill and Patrick Davis MARAMA 

Laurel Driver US EPA OAQPS 

Robert Fronczak AAR 

Steven Sullivan ASLRRA 

Rick Nath CSX 

David Seep and Lyle Staley BNSF 

Ken Roberge CPR 

Carl Akins and Peter Conlon KCS 

Erika Akkerman CN 

M. John Germer UP 

Brent Mason and Richard Russell NS 

Joanne Maxwell Amtrak 

Appendix B: Source and Year of Data Utilized for Each Inventory 

Data Year Source 

Class I Line-Haul

Annual Line-Haul Fuel Use 

and Gross Ton-Miles 2007 STB R-1 Reports (CP data for D&H is for 2008.) 

Line-haul fleet mix for 

emission factors 2008 Each Class I railroad 

Link-level tonnage 2007 FRA confidential database 

Class I Railyards (Switcher Locomotives) 

Annual Switcher Fuel Use 2008 R-1 Reports 

Switcher fleet mix for 

emission factors 2008 Each Class I railroad 

Link-level tonnage or 

Density Code (for activity 

estimate) 

2007 FRA confidential database 

Class II and III Locomotives 

Annual Total Fuel Use 2008 ASLRRA Annual Report (2008) 

Track length and railroad 2007 FRA confidential database 

Estimated fleet mix for 

emission factors 

Discussions with ASLRRA and 

Class II and III representatives.