1

DRAFT 

ERTAC Rail Emissions Inventory 

Part 2: Class I Railyard Switcher Locomotives 

Michelle Bergin, GA Environmental Protection Division 

Matthew Harrell, IL Environmental Protection Agency 

Mark Janssen, Lake Michigan Air Directors Consortium 

Acknowledments: Robert Fronczak, Association of American Railroads 

 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 largely utilize diesel engines, resulting in emissions of NOx, diesel PM, hydrocarbons, 

greenhouse gases, and other pollutants. These emissions are sometimes concentrated in areas exceeding

National Ambient Air Quality Standards. No cohesive nationwide railroad emission estimates 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 of 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 for Class I line-haul, Shortline and Regional Railroads, and Class I railyard switchers (Table 

1). 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). 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 travel long distances (e.g. between cities) while switcher locomotives largely operate in 

railyards, splitting and joining rail cars with varying destinations. Passenger and Commuter Rail 

(including Amtrak), industrial locomotives, and associated non-locomotive equipment are not included 

in these inventories. 
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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 and Reported Locomotive Fuel Use6. 

Class I Railroads* 

R-1 Reported Locomotive Fuel 

Use (gal/yr) 

Line-Haul 

(2007)** 

Switcher 

(2008) 

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

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

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

CSX 514,687,186 53,717,674

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

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

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

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

* Excluding Amtrak 

** Includes work trains 

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

subsidiary. 

This paper documents the data sources and methodologies used for calculating the Class I switcher 

(“Railyard”) inventory. Information on ERTAC Rail, Railroad participation, the Rail industry, and 

effects of rail on air quality are available elsewhere

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. 

Method 

Switcher locomotives are expected to be the single largest source of air emissions in railyards. 

Therefore, as a starting point for a comprehensive railyard inventory, a Class I switcher emission 

inventory was developed. It is assumed that estimates for yards of interest, associated equipment and

activity, and smaller railroads could be refined later. 

While ERTAC Rail represents states east of the Mississippi River, the railroad companies specified they 

wanted this effort to result in a consistent nationwide inventory. ERTAC Rail agreed to calculate 

emissions for all states when the data was available and when additional significant effort was not 
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required. Because both the dataset of railyards and switcher fuel use was nationwide in scope, the 

resulting initial railyard inventory is a nationwide, ‘top-down’ derivation. However, railroad companies 

may have different levels and quality of data available, and may have interpreted some data requests 

differently. Also, states are requested to update yards they have detailed information on when possible, 

and a few states (i.e. California) have unique railroad operations and equipment. Therefore, data for

some areas will be more accurate than for others, and locally-derived inventories may be more accurate. 

This documentation describes development of the initial top-down inventory, which consisted of three 

main activities: 

1. Locate Class I Railyards 

2. Select/Calculate Emission Factors 

3. Estimate Locomotive Activity 

4. Improve Estimates 

1. Locate Class I Railyards. 

Identification and correct placement of railyards was an important first step, requiring a comprehensive 

electronic dataset. A confidential database was obtained from the Federal Railroad Administration 

(FRA) with permission from the Class I Railroads (FRA database) 8. A comparable public database 

compiled by the Bureau of Transportation Statistics is also available8. Data from the public source will 

not match the confidential data used for this inventory exactly but will be very similar. The FRA 

database has rail links (track lengths) individually identified as parts of specific railyards. While there 

may be discrepancies in how each railroad defined railyard links, this dataset appears to identify most 

Class I railyards in the U.S., and shows a high density of yards in the eastern states (Figure 1). The 

database gives length, up to 3 owners and 3 operators, and a Federal Density Code (explained below) for 

each railyard link. 

Figure 1. Class I Railyards in the United States and estimates of Annual NOx emissions from 

switcher locomotives (tons/yr in 2008). 
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2. Select/Calculate Emission Factors. 

The EPA provides annual default emission factors based on characteristic operating cycles (‘duty 

cycles’) and an annual estimated nationwide fleet mix for both switcher and line-haul locomotives (i.e. 

percent of locomotives in each Tier level category). However, switcher fleet mix is not uniform from 

company to company and, as can be seen in Figure 2, Class I railroad activity is highly regional. 

As an alternative approach, ERTAC Rail requested each Class I rail company to provide a description of

their switcher fleet mix based on Tier rating, which each company provided under a confidentiality 

agreement. An engine’s Tier level determines allowable emission limits based on the year the engine 

was built and/or re-manufactured (Table 3). While engine emissions are variable within Tier categories, 

this estimate likely provides a better regional estimate than the nationwide average. The companyspecific systemwide fleet mix was used to calculate weighted average emissions factors for switchers 

operated by each Class I railroad, resulting in ranges between fleet emission factors such as from 6.10 to 

6.69 g/gal PM10 and 212.98 to 264.48 g/gal NOx. 

Figure 2. Class I Railroad Territories in the United States9. 

Table 3. EPA switcher locomotive emission factors by Tier, 1997 standards (grams/gal). 

PM10 HC NOx CO 

Uncontrolled (pre-1973) 6.688 15.352 264.48 27.816 

Tier 0 (1973-2001) 6.688 15.352 191.52 27.816 
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Tier 1 (2002-2004) 6.536 15.352 150.48 27.816 

Tier 2 (2005 + ) 2.888 7.752 110.96 27.816 

Listed years apply to the year the engine was built. Table based on values from 8. Note that the new standards released in 

2008 did not apply to existing fleets in the year 2008. 

For locomotives, PM2.5 is assumed to be 97% of PM10

10, and emission factors for SO2 and NH3 are 1.88 

g/gal10 and 83.3 mg/gal11 respectively. VOC emissions are calculated as 1.053 times the HC emissions 

for locomotives12. Note that non-road engine and fuel specific information is sparse for these 

conversions. Greenhouse gases are also estimated using emission factors shown in Table 4. 

Table 4. EPA greenhouse gas emission factors for locomotive diesel fuel (grams/gal).13 

CO2 N2O CH4

Locomotive diesel 1.015E4 0.26 0.80 

These emission factors are based on a characteristic duty cycle for switchers which assumes operation 

over 24-hour per day 365 days per year. An evaluation of the effect of variability in railyards and 

switching duties on emissions would be very useful for future emission estimates. 

3. Estimate Locomotive Activity. 

Class I railroads report total annual switcher locomotive fuel use to the STB, which is reported in 

publicly available ‘R-1’ reports (Table 2). There may be inconsistencies between railroads in how fuel 

use is estimated to be apportioned between line-haul and switcher locomotive use, and possibly even in

the total locomotive fuel use, so these values should be evaluated and may be adjusted in the future. 

However, the use of these values provides a starting point for estimating total U.S. Class I locomotiverelated emissions segregated and spatially allocated by Class I carrier. The R-1 reports were used by

ERTAC for both the line-haul and switcher locomotive emissions inventories to provide consistency. 

The next step for inventory development is to allocate switcher fuel use to each railyard. Two methods

were first applied, one that relies on publicly available line-haul activity (the ‘Dencode’ method), and 

the other using confidential line-haul activity (the ‘MGT’ method.) At this time, Norfolk Southern and 

Kansas City Southern have provided input for use of the MGT method, and the Dencode method is 

applied for the other five railroads. 

The Dencode Method – Publicly available data 

Each link in both the publicly available BTS database and the confidential FRA database has a ‘Federal

Density Code’ (Dencode) ranging from 1 to 7 assigned based on the cumulative annual freight tonnage 

hauled on the link (track). Total Switcher Fuel Use in each railyard Y (SFUY) is estimated as follows: 

First a Switcher Activity Indicator per yard (SAIY) is calculated by multiplying the average dencode of 

the links within a railyard by the sum of the length of the links for that railyard (Eqn 1). 

SAIY = ( * )

nY FDCnY ∑ l Equation 1 

SAIY = Switcher Activity Indicator in Railyard Y 
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nY = number of links identified as part of railyard Y

lnY = length of link n in miles 

FDCn = Federal Density Code (1 to 7) of link n 

Next, this value is then weighted (SAIY’) based on an ownership factor (OF) set between 0 and 1. The 

OF depends on the number of owners listed for each railyard: if there is one owner the OF is set to 1, if 

there are two owners the primary owner is set to 0.8 and the secondary is 0.2, and if there are 3 owners 

the primary is 0.7, the secondary is 0.2, and the tertiary is 0.1. 

SAIY’ = OFY* SAIY Equation 2 

Next, the SAIY’ of all railyards belonging to a Class I railroad (RR) were summed, and the fraction of 

the railroads total SAI associated with each railyard was multiplied by the railroads total annual switcher 

fuel use reported in the R-1 (TFURR), resulting in the total Switcher Fuel Use for each railyard Y (Eqn 

2). 

SFUY = RR

RR

Y

Y TFU

SAI

SAI *

'

'

∑

Equation 3 

SFUY = Switcher Fuel Use at railyard Y 

Finally, the SFUY is multiplied by the emission factors described in the previous section to obtain annual 

switcher emissions at each railyard. 

The MGT Method – Confidential data 

Two railroads, Norfolk Southern and Kansas City Southern (KCS), provided confidential link-level 

tonnage information and weighting factors to correct skewed estimates to improve estimated switcher 

activity at important yards. Other railroads may also allow the use of this technique for their inventories 

in the future. In addition, KCS provided yard-specific activity information. 

The MGT Method also uses the FRA database for railyard identification and link lengths. However, 

rather than using the average dencode per link, confidential annual gross tonnage (MGT) hauled per link 

in the railyard was used to calculate the railyard switcher activity (SAIY). This is calculated by 

replacing FDCn in Equation 2 with link-specific tonnage MGTn (Equation 4). 

SAIY = ) ( *

nY MGTnY ∑ l Equation 4 

SAIY = Switcher Activity Indicator in Railyard Y 

nY = number of links identified as part of railyard Y

lnY = length of link n in miles 

MGTnY = million gross tons on link n 
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This method provides a more refined comparison between railyards than the use of the 7-category 

dencodes; however, is more susceptible to errors for yards where tonnage is not correlated to switching 

activity. For example, a yard with large coal trains pulling through used for crews to change over would 

be assigned an overly high level of emissions for switching activity. To account for this, a discretionary 

Switching Activity Factor (SAF) was introduced to allow railroads to roughly weight yards with clearly

higher or lower levels of switching activity than what results from the mathematical allocation. 

Therefore, SAIY is weighted based on both the ownership factor (OF) as well as the SAF (Equation 5). 

For example, a yard used for crew changes and not switching may have an SAF of 0, while a yard at a 

major interchange between cities may have an SAF of 3. 

SAIY’ = OFY*SAFY* SAIY Equation 5 

Again, the SAIY’ of all railyards belonging to a Class I railroad (RR) are summed, and the fraction of the 

railroads total SAI associated with each railyard was multiplied by the railroads total annual switcher 

fuel use reported in the R-1 (TFURR), resulting in the total Switcher Fuel Use for each railyard Y 

(Equation 6). 

SFUY = RR

RR

Y

Y TFU

SAI

SAI *

'

'

∑

Equation 6 

While the SAF allows estimates of yard-specific emissions to be adjusted, the total level of emissions

for each railroad, which is based on systemwide fuel use and systemwide emission factors, remains 

unchanged. The MGT method SFUY is also later multiplied by the emission factors described in the 

previous section to obtain annual switcher emissions at each railyard. 

4. Improve estimates. 

In addition to the Switching Activity Factor described above, direct input was also used to improve 

emission estimates for important railyards. Each Class I railroad provided an estimate of annual average 

switcher fuel use (generally much lower than the EPA default of 82,490 gal/yr) as well as the name, 

location, and number of operating switchers for railyards with 8 or more switchers operating in ozone or 

PM2.5 nonattainment areas. Some railroads, Kansas City Southern in particular, then provided additional 

railyard specific data. This directly reported data was used to overwrite the dencode or MGT derived 

emissions estimates for those railyards. 

The difference in estimated fuel use for those railyards was re-allocated (added or removed) between the 

remaining railyards belonging to that Class I railroad. It is important to note that there are some 

discrepancies in how this data was reported for the large railyards by each railroad. For example, some 

railroads reported all switchers located at a railyard while others reported ‘full time equivalent’ 

switchers, meaning the number of switchers normalized to a full working cycle (24-hours per day yearround.) This process should be standardized for future inventory versions. Variability is also introduced 

because ‘switcher’ locomotives can also be used for ‘road work’, meaning they occasionally work 

between yards more like a line-haul. 

States also have the option of updating specific railyard emissions estimates. Because this inventory is 

derived ‘top-down’, local studies and familiarity with specific railyards is expected to provide better 
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estimates, which can be used to adjust this inventory. Care must be taken to ensure the other railyard 

estimates are adjusted to account for increases or decreases in estimated fuel use per yard. 

Limitations, Conclusions, and Future Work 

What this ERTAC Rail railyard inventory does well is provide a comprehensive overview of where 

railyards are, who owns them, and gives a geographical allocation of switcher emissions bounded by 

what is reported as nationwide switcher fuel usage by the Class I railroads. These sources can be 

important for air quality management in nonattainment areas, as well as in regional analysis and for 

future transportation and freight planning. This inventory will be useful for regional and some local

modeling, helps identify where railyards need to be better characterized, and provides a strong 

foundation for future development of a meaningful nationwide Class I switcher emissions inventory. 

There are important uncertainties associated with estimates from this method, including, but not limited 

to, the use of tonnage hauled as an indicator of the amount of switching activity, and, for a few of the 

railroads, how the amount of switcher fuel use was determined to be reported in the R-1. The R-1 

reported values are currently under examination. 

There is also likely significant variability in actual switching duty-cycles and, potentially, in the number 

of switchers operating at some railyards at different times of the year. ‘Road-switching’, or the use of 

what are considered switching locomotives to move between nearby yards, should be addressed in either 

this or the ERTAC line-haul inventory. 

It must be noted that freight-related rail activity is not always routine and no annual emissions inventory 

will ever be able to capture the innate variability of the source. However, as other large emission 

sources are reduced, and if rail activity increases as expected, it is important to include our best 

estimates of these sources in air quality and epidemiological analysis. In the future, on-line data loggers 

and other tracking technologies, combined with ambient studies and detailed modeling, will hopefully 

provide more insight to the emissions of locomotives and other railyard sources. 

References 

1. 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_tr

ain.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 
9

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_e

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

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

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

Administration. Similar public data 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 . 

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

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

10. 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 

11. 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

12. “Conversion Factors for Hydrocarbon Emission Components,” EPA420-R-05-015, December 

2005. Docket Document EPA-HQ-OAR-2003-0190-0411. 

http://epa.gov/otaq/models/nonrdmdl/nonrdmdl2005/420r05015.pdf , 

http://www.epa.gov/otaq/regs/nonroad/420r08001a.pdf .

13. 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
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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.