EA~ United States ._.,.,~ Environmental Protection 

"' Agency 

Methodology for Estimating Emission 

Reductions and Cost Savings from 

Missoula Railyard Idle Reduction Policy 

and Auxiliary Power Unit Installation 
ft EA~United States ..... ~ Environmental Protection ,., Agency 

Methodology for Estimating Emission 

Reductions and Cost Savings from 

Missoula Railyard Idle Reduction Policy 

and Auxiliary Power Unit Installation 

Air Program 

U.S. EPA Region 8 

and 

Transportation and Climate Division 

Offce of Transportation and Air Quality 

U.S. Environmental Protection Agency 

EPA-420-F-19-010 

February 2019 
 

 

 

 

 

 

 

Table of Contents 

Project Overview ......................................................................................................................................................2 

Grantee Reported Switcher Locomotive Emissions..................................................................................................2 

Idle Hour Estimates Adjusted for Yard Idling Policy .................................................................................................4 

Estimated APU Project Costs and Emission Benefits................................................................................................7 

Estimated APU Project Fuel Cost Savings .................................................................................................................7 

Acronyms & Abbreviations.....................................................................................................................................11 

Page 1 of 11 
 

 

 

 

 

 

 

 

Project Overview 

An overview of information in this document was published on EPAs Ports Initiative website. The Ports Initiative 

website includes information on other promising practices for ports, railyards, and surrounding communities. 

The railyard project focuses on reducing air pollution and saving money from reduced fuel consumption by 

switcher locomotives at the Montana Rail Link (MRL) Railyard in Missoula, Montana during colder months. Fuel 

savings were realized by installing auxiliary power units (APUs) on eight switcher locomotives, and changing the 

mandatory idling policy to better fit daily temperature conditions. 

The city of Missoula, Montana is located along the Clark Fork River in western Montana and is the second largest 

metropolitan area in the state. Missoula has average low temperatures below 40 degrees Fahrenheit for eight 

months out of the year. 

The APU installation portion of this project was partially funded by a 2009 Diesel Emissions Reduction Act (DERA) 

grant (DE – 97897201) awarded to the Missoula Metropolitan Planning Organization that exercises jurisdictional 

authority over local air quality issues. The grant help fund installation of APUs in eight resident switcher 

locomotives at a mid-sized railyard, located adjacent to downtown Missoula, Montana operated by MRL, a Class II 

regional railroad. 

Grantee Reported Switcher Locomotive Emissions 

Switcher locomotive roster and engine characteristics were provided by the grantee. The grantee reports 8 of the 

16 switcher locomotives presented in Table 1 as being assigned to the Missoula, MT switchyard. 

Table 1 

Switcher Engine Grant Roster and Engine Characteristics 

Engine No. Make Model Engine Year HP Tier Idle Fuel Use (gal/hr) Prolonged Idling (hr/yr) 

1 EMD SW 12 Cyl-567C 1957 1200 Un 3.5 2618 

2 EMD SW 12 Cyl-567C 1957 1200 Un 3.5 2618 

3 EMD SW 12 Cyl-645E 1968 1500 Un 3.5 2618 

4 EMD SW 12 Cyl-645E 1968 1500 Un 3.5 2618 

5 EMD GP9 16 Cyl-567C 1957 1700 Un 3.5 2618 

6 EMD GP9 16 Cyl-567C 1951 1750 Un 3.5 2618 

7 EMD GP9 16 Cyl-567C 1957 1750 Un 3.5 2618 

8 EMD GP9 16 Cyl-567C 1956 1750 Un 3.5 2618 

9 EMD GP9 16 Cyl-567C 1957 1500 Un 3.5 2618 

10 EMD GP9 16 Cyl-567C 1957 1750 Un 3.5 2618 

11 EMD GP35 16 Cyl-567D3A 1964 2500 Un 5 2618 

12 EMD GP35 16 Cyl-567D3A 1964 2500 Un 5 2618 

13 EMD GP35 16 Cyl-567D3A 1965 2500 Un 5 2618 

14 EMD GP35 16 Cyl-567D3A 1965 2500 Un 5 2618 

15 EMD GP35 16 Cyl-567D3A 1965 2500 Un 5 2618 

16 EMD GP35 16 Cyl-567D3A 1979 2500 0+ 5 2618 

Page 2 of 11 
 

 

 

 

 

 

 

 

 

 

Emissions were calculated using EPA-approved switcher locomotive emissions factors in grams per brake 

horsepower hour (g/bhp-hr) with an EPA-provided switcher fuel consumption conversion factor of 15.2 brake 

horsepower hour per gallon (bhp-hr/gal)

1 (Tables 2 and 3; Eq. 1). 

Table 2 

SwitcherEmission Factors (g/bhp-hr) 

PM10 HC NO x CO VOCs PM2.5 

Uncontrolled 0.44 1.01 17.40 1.83 1.06 0.43 

Tier 0 0.44 1.01 12.60 1.83 1.06 0.43 

Tier 0+ 0.23 0.57 10.60 1.83 0.60 0.22 

Tier 1 0.43 1.01 9.90 1.83 1.06 0.42 

Tier 1+ 0.23 0.57 9.90 1.83 0.60 0.22 

Tier 2 0.19 0.51 7.30 1.83 0.54 0.18 

Tier 2+ 0.11 0.26 7.30 1.83 0.27 0.11 

Tier 3 0.08 0.26 4.50 1.83 0.27 0.08 

Tier 4 0.015 0.08 1.00 1.83 0.08 0.01 

"+" Indicates these are revised standards in 40 CFR 1033 

All but one of the switcher engines in the grant were originally manufactured before 1973, the start date for Tier 0 

requirements. Therefore, although the grantee reported Tier 0 engines, emissions reductions for 15 engines have 

been calculated based on the factors for “uncontrolled engines (un)”. 

A locomotive operator trade association reported fuel consumption of 5 gallons per hour (gph) for EMD GP35 

locomotives and 3.5 gph for all other EMD switcher locomotives on the fleet roster.2 The total grant reported 

idling hours is 2618. 

�

15.2 bbhpp hrr 0.44 ggPPMM10,uuuuuuuuuuuuuuuuuuuuuuuu 3.5 gggggg � ∗ �2618 hrr eeiiggeeeegg� ∗ �1.10231×10−6 ttttee Eq 1: � ∗ � � ∗ � � gggggg bbhpp hrr eeeeggeeeeee−hrr yyrr 1gg

= 0.068 ttttttttPPPP10 eetteeeettee−1 yyyy−1

Table 3 provides a summary of the emissions as a result of idling from the 16 switchers in the roster calculated 

using Equation 1 and the emission factors for each pollutant. 

1 Office of Transportation and Air Quality, U.S. Environmental Protection Agency, “Emission Factors for Locomotives,” 

Technical Highlights, EPA-420-F-09-025, April 2009. 2 Source: International Association of Railway Operating Officers 

Page 3 of 11 
 

 

 

 

Total Switcher Preventable Engine Emissions 

PM10 HC NOx co voes PM2.5 

TOTAL (tons/yr) 1.208 2.783 48.120 5.218 2.931 1.172 

Table 3 

Switcher Roster Emissions From Idling 

Annual Emissions (tons/engine-yr) 

Engine No. PM10 HC NOx CO VOCs PM2.5 

1 0.068 0.155 2.671 0.281 0.163 0.066 

2 0.068 0.155 2.671 0.281 0.163 0.066 

3 0.068 0.155 2.671 0.281 0.163 0.066 

4 0.068 0.155 2.671 0.281 0.163 0.066 

5 0.068 0.155 2.671 0.281 0.163 0.066 

6 0.068 0.155 2.671 0.281 0.163 0.066 

7 0.068 0.155 2.671 0.281 0.163 0.066 

8 0.068 0.155 2.671 0.281 0.163 0.066 

9 0.068 0.155 2.671 0.281 0.163 0.066 

10 0.068 0.155 2.671 0.281 0.163 0.066 

11 0.097 0.222 3.816 0.401 0.233 0.094 

12 0.097 0.222 3.816 0.401 0.233 0.094 

13 0.097 0.222 3.816 0.401 0.233 0.094 

14 0.097 0.222 3.816 0.401 0.233 0.094 

15 0.097 0.222 3.816 0.401 0.233 0.094 

16 0.050 0.125 2.325 0.401 0.132 0.049 

Total preventable switcher idling emissions were calculated for the 16 switcher locomotives included in the 

grantee’s reporting (Table 4). 

Table 4 

Idle Hour Estimates Adjusted for Yard Idling Policy 

The updated railyard policy calls for long-term idling of switcher engines or APU usage only during temperatures 

below 40 degrees Fahrenheit. This policy facilitates quick engine start-up and prevents engine damage during 

near-freezing conditions. 

Missoula’s northern continental climate requires 24-hour engine activity for much of the year. National Oceanic 

and Atmospheric Administration (NOAA) data3 can be used to determine the average number of hours which fall 

3 National Oceanic and Atmospheric Administration, “Local Climatological Data for Missoula International Airport, MT US,” 

accessed May 1, 2018, https://www.ncdc.noaa.gov/cdo-web/datasets/LCD/stations/WBAN:24153/detail. 

Page 4 of 11 
 

 

 

 

 

 

 

 

Annual "Must Idle" Condition (<40degrees Fahrenheit) Hours 

Year I 2010 I 2011 I 2012 I 2013 I 2014 I 2015 I 2016 I 2017 

"Must Idle" Hours Count I 3623 1 3746 1 3511 1 3752 1 .1527 I 3376 1 3214 1 3709 

Average Annual "Must Id le" Hours I 3557 1 I I I I 

Annual Overnight (20:00--4:00) "Must Idle" Condition (<40degrees Fahrenheit) Hours 

Year I 2010 I 2011 I 2012 I 2013 I 2014 I 2015 I 2016 I 2017 

Overnight "Must Idle" Hours Count I 1417 1 14041 1318 1 1420 1 1323 1 1281 1 12621 1412 

Avg. Annual Overnight "Must Idle" Hours I 1355 1 I I I I 

below the 40-degree threshold per year. For the years 2010 – 2017, the annual average of hours below 40-

degress was 3,557 (Table 5). 

Table 5 

To clarify, not all 3557 hours are idling hours, as most of them could fall within normal winter usage hours. To 

estimate the number of “must-idle” hours, or time when locomotives are expected to idle solely due to the 

ambient temperature and engine maintenance, the reported annual activity hours per engine (5,736) is converted 

to represent the average daily activity hours- equaling 15.7. This is rounded to the nearest whole number (16) and 

assumed to represent a typical work day. Without detailed yard logs, it’s assumed that the 16 hours represents 

two shifts from early morning to late afternoon (04:00 – 20:00). This would leave an eight-hour window overnight 

in which locomotives, due to yard inactivity, would be required to idle continuously during sub 40-degree 

Fahrenheit conditions. Using the hourly Missoula meteorological data from NOAA for the eight-year period 

(filtered for only the hours 20:00 – 04:00) an average annual “off-shift must-idle” hours number is calculated at 

1,355. This number represents the bulk of the idling hours reduced by APU usage after APU install (Table 6). 

Table 6 

A smaller annual idling-hours number will be added to this bulk-hours total. This smaller number comes from a 

calculation derived from the reported annual use-hours, annual idling-hours and “summer hours,” which together 

is assumed to represent a complete picture of daily use throughout the year. This smaller number of idling hours 

accounts for the grantee’s estimates of locomotive movements during work shifts, annual idling hours and 

summer non-idle hours derived from a strictly defined 275/90-day winter/summer year. Using these reported 

hours, a daily average prolonged idling period of 1.15 hours per day (418 hours annually from Equation 2) is 

assumed during normal usage hours. 

hrriiuuuuiiuuii� − �275 iiggyywwiiuuuuuuuu hrruuoooo−sshiioouu hrriiuuuuiiuuii,uuuu−sshiioouu Eq 2: �2618 ∗ 8 � = 418 

yyrr yyrr iiggyy yyrr

Average annual total hours predicted after yard policy change and APU install: 1,773 (1,355 + 418) 

Average annual total idling hours replaced by APU usage and ambient temperature yard policy: 2618 (grant 

reported) 

Based on the above, engine activity would be reduced by 845 hours annually due to the yard policy change (2618 

hours minus 1773 hours = 845 hours) 

Aggregate APU emissions for the 8 Missoula railyard HotStart DDHSJR-110 APUs with Yanmar 2TNV70-ASA 2008 

EPA Tier 4 engines were based on the APU engine characteristics (Table 7) and EPA emission factors for non-road 

Page 5 of 11 
 

 

 

 

 

 

 

 

APU Engine Characteristics 

Engine Make Model Power kW Tier Number 

Yanmar 2TNV70-ASA 10.2 4 16 

Tier4 Emission Standards 8SkW<19 (g/kW-hr) 

Assumed 

NMHC+NOx PM co NMHC NOx 

7.5 0.4 6.6 0.375 7.125 

APU Aggregate Emissions 

NMHC+NOx PM co NMHC NOx 

Total Operation (hr) : I 1773 

Number Engines: I 8 

TOTAL (tons/yr): 1.196 I 0.064 I 1.053 I 0.060 I 1.136 

Emissions Locomotive (tons) APU Emissions (tons) Net Reduction (tons) 

NOX PM co NOX PM co NOX PM co 

Annual 24.060 0.604 2.609 1.136 0.064 1.053 22.924 0.540 1.556 

8-Year 192.479 4.834 20.871 9.090 0.510 8.420 183.389 4.324 12.450 

lOyear 240.59888 6.0423877 26.08864 11.36286645 0.63791531 10.52560261 229.236018 5.404472354 15.56304 

compression ignition engines4 (Table 8). Aggregate APU emissions were for temperature-defined “must-idle” 

hours tabulated as Local Climatological Data (LCD) hours below 40 degrees Fahrenheit as measured at Missoula 

International Airport, WBAN station ID: 24153. Accessed from NOAA, National Centers for Environmental 

Information’s (NCEI) LCD clearinghouse (www.ncdc.noaa.gov/cdo-web/datatools/lcd). APU usage hours were 

restricted to those hours reported as prolonged idling hours by the grantee (Table 9). 

Table 7 

Table 8 

Table 9 

Annual, 8-year, and 10-year APU lifecycle net emissions reductions were based on a switcher fleet average 

emissions rate applied to the eight switchers assigned to the Missoula railyard. The 16 locomotive roster 

switchers were assumed to periodically be assigned to different yards. The eight switchers represented here are 

composites of the fleet-wide average locomotive (Table 10). 

Table 10 

4 Office of Transportation and Air Quality, U.S. Environmental Protection Agency, Nonroad Compression-Ignition Engines: 

Exhaust Emission Standards, EPA-420-B-16-022, March 2016. 

Page 6 of 11 
 

 

 

 

 

 

 

Estimated APU Project Costs and Emission Benefits 

APU technology and install costs for the 16 switchers were reported by the grantee (Table 11). 

Table 11 

APU Install Costs (USD) 

Locomotive No. Tech Unit Cost Install Cost 

1 27366.93 2566.16 

2 27151.17 3591.69 

3 27755.24 3623.84 

4 27596.37 4119.79 

5 27566.70 3903.97 

6 27994.90 3293.22 

7 27413.28 2995.13 

8 27794.54 3143.81 

9 27808.78 3584.41 

10 27926.00 3429.45 

11 27036.88 2139.07 

12 27037.20 2087.74 

13 27563.35 3018.58 

14 27157.77 2635.90 

15 27464.82 2200.77 

16 27556.94 1461.00 

TOTAL (USD) 440190.87 47794.53 

Total cost of APU installs on 16 locomotives was $487,985. The average cost per locomotive retrofit was applied 

to the eight Missoula yard switchers and used to find cost over a 10-year APU lifecycle per unit reduction of 

pollutant for oxides of nitrogen, particulate matter and carbon monoxide (Table 12). 

Table 12 

Lifecycle Cost per Unit Reduction 

NOx PM CO 

10-year cost (USD/ton) 1064.37 45146.41 15677.69 

10-year cost (USD/lb) 0.53 22.57 7.84 

Estimated APU Project Fuel Cost Savings 

Reduced fuel consumption cost savings were tabulated monthly and summed to find approximate year end cost 

savings. First, temperature dependent APU operation hours were further broken into monthly counts over the 8-

year study period (Table 13). 

Page 7 of 11 
 

 

 

 

 

f f f 

Table 13 

Count of "Off-Shift" Hours Below 40 Between Jan, 2010--Dec, 2017 

2010 2011 2012 2013 2014 2015 2016 2017 

Jan 242 229 236 242 243 247 247 248 

Feb 214 209 231 223 223 195 210 210 

Mar 211 214 188 199 213 138 199 138 

Apr 142 162 79 123 133 134 66 116 

May 61 38 47 23 26 25 7 45 

Jun 0 2 5 3 0 0 6 4 

Jul 0 0 0 0 0 0 0 0 

Aug 0 0 0 0 0 0 0 0 

Sep 1 5 2 8 10 15 9 23 

Oct 102 92 119 158 46 80 67 161 

Nov 202 212 172 203 186 219 205 222 

Dec 242 241 239 238 244 228 246 244 

Yanmar engine specifications list APU fuel consumption rates as either 0.35 grams per hour (gph) (low setting) or 

0.76 gph (high setting). Fuel consumption was calculated for temperature specified operation hours. The high fuel 

consumption rate was used to give a conservative estimate of fuel savings after APU retrofits. Fuel costs over the 

study period were averaged for No. 2 Ultra Low-Sulfur Diesel (ULSD). Averaged monthly fuel prices were 

calculated from weekly ULSD retail prices provided by the U.S. Energy Information Administration at: 

https://www.eia.gov/opendata/qb.php?sdid=PET.EMD_EPD2DXL0_PTE_NUS_DPG.W (Tables 14 and 15). 

Table 14 

Monthly APU Fuel Costs (USD) at High Consumption Rate (0.76 gph) 

2010 2011 2012 2013 2014 2015 2016 2017 

Jan 526.43 592.57 690.76 722.27 722.41 565.26 404.11 488.50 

Feb 456.08 572.41 697.36 700.24 678.61 426.02 320.66 412.10 

Mar 470.42 638.44 593.20 618.76 651.11 306.37 317.92 270.04 

Apr 333.18 503.94 250.66 370.81 404.17 285.78 109.80 229.93 

May 145.13 120.41 145.59 71.03 81.35 57.39 14.34 89.80 

Jun 2.58 9.42 17.57 12.14 3.41 2.51 13.16 9.83 

Jul 2.54 3.41 3.25 3.38 3.39 2.44 2.10 2.18 

Aug 2.59 3.37 3.48 3.41 3.35 2.27 2.05 2.27 

Sep 4.81 17.94 9.86 27.54 32.14 30.75 18.47 51.11 

Oct 239.22 268.85 373.82 469.88 131.89 155.37 127.12 344.34 

Nov 484.80 641.82 526.38 595.60 518.76 412.76 382.05 493.31 

Dec 599.19 710.56 722.90 705.53 635.44 402.21 471.46 541.99 

Page 8 of 11 
 

 

 

 

Table 15 

Monthly APU Fuel Costs (USD) at Low Consumption Rate (0.35 gph) 

2010 2011 2012 2013 2014 2015 2016 2017 

Jan 242.44 272.90 318.12 332.62 332.69 260.32 186.10 224.97 

Feb 210.04 263.61 321.15 322.48 312.52 196.19 147.67 189.78 

Mar 216.64 294.02 273.18 284.96 299.85 141.09 146.41 124.36 

Apr 153.44 232.08 115.44 170.77 186.13 131.61 50.57 105.89 

May 66.84 55.45 67.05 32.71 37.47 26.43 6.60 41.36 

Jun 1.19 4.34 8.09 5.59 1.57 1.16 6.06 4.53 

Jul 1.17 1.57 1.50 1.56 1.56 1.12 0.97 1.00 

Aug 1.19 1.55 1.60 1.57 1.54 1.04 0.95 1.04 

Sep 2.22 8.26 4.54 12.68 14.80 14.16 8.51 23.54 

Oct 110.17 123.81 172.15 216.39 60.74 71.55 58.54 158.58 

Nov 223.26 295.58 242.41 274.29 238.90 190.09 175.94 227.18 

Dec 275.94 327.23 332.92 324.92 292.64 185.23 217.12 249.60 

Locomotive main engine monthly fuel costs due to prolonged idling were based upon the same pricing data, 

reported prolonged idling from the grantee and fuel consumption at idle rates from the International Association 

of Railway Operating Officers. Consumption rate for EMD SW1200, SW1500 and GP9 locomotives was fixed at 3.5 

gph. Fuel consumption rate for EMD GP35 locomotives was set at 5 gph (Tables 16 and 17). 

Table 16 

Monthly Locomotive Fuel Costs (USD/engine) - GP35; 5 gph at idle 

2010 2011 2012 2013 2014 2015 2016 2017 

Jan 4040.24 4804.75 5435.58 5543.23 5521.60 4250.85 3038.96 3658.80 

Feb 3573.03 4591.10 5063.15 5265.55 5102.86 3660.78 2559.69 3289.61 

Mar 4137.89 5537.56 5852.41 5769.09 5673.85 4108.67 2964.14 3621.50 

Apr 4203.28 5578.18 5647.84 5393.93 5440.93 3818.64 2952.93 3544.48 

May 4357.71 5739.37 5642.51 5488.98 5591.81 4095.20 3282.68 3631.29 

Jun 508.79 678.44 648.34 664.00 673.82 495.59 417.88 433.06 

Jul 519.02 696.11 663.27 689.11 692.23 496.92 428.60 444.98 

Aug 527.37 688.01 709.88 695.98 684.12 462.56 418.99 462.56 

Sep 4043.73 5266.63 5654.70 5436.20 5205.07 3438.11 3286.11 3822.07 

Oct 4327.79 5385.95 5806.03 5509.55 5219.87 3572.93 3480.95 3962.87 

Nov 4309.65 5437.85 5490.00 5268.68 5005.85 3385.96 3346.84 3992.26 

Dec 4598.68 5475.86 5617.40 5505.36 4837.08 3275.45 3559.81 4125.69 

Page 9 of 11 
 

 

 

 

 

f f f f 

Table 17 

Monthly Locomotive Fuel Costs (USD/engine) - GP9, SW; 3.5 gph at idle 

2010 2011 2012 2013 2014 2015 2016 2017 

Jan 2828.17 3363.32 3804.91 3880.26 3865.12 2975.59 2127.27 2561.16 

Feb 2501.12 3213.77 3544.21 3685.89 3572.00 2562.54 1791.79 2302.73 

Mar 2896.52 3876.29 4096.69 4038.36 3971.70 2876.07 2074.90 2535.05 

Apr 2942.30 3904.73 3953.49 3775.75 3808.65 2673.05 2067.05 2481.14 

May 3050.40 4017.56 3949.76 3842.29 3914.26 2866.64 2297.88 2541.90 

Jun 356.15 474.91 453.84 464.80 471.67 346.91 292.52 303.14 

Jul 363.31 487.28 464.29 482.38 484.56 347.84 300.02 311.49 

Aug 369.16 481.61 496.92 487.18 478.89 323.79 293.30 323.79 

Sep 2830.61 3686.64 3958.29 3805.34 3643.55 2406.68 2300.28 2675.45 

Oct 3029.45 3770.16 4064.22 3856.68 3653.91 2501.05 2436.67 2774.01 

Nov 3016.76 3806.49 3843.00 3688.08 3504.10 2370.17 2342.79 2794.58 

Dec 3219.07 3833.10 3932.18 3853.75 3385.96 2292.81 2491.87 2887.98 

Fuel cost savings for the Montana Rail Link (MRL) switcher engines were based upon the average fuel savings of 

the 16 retrofitted switcher engines in the Missoula Metropolitan Planning Organization (MPO) DERA grant. Yearend fuel savings were adjusted to 2010 USD to compare total savings over the APU life cycle to the initial 

investment cost for the APU materials and installation labor (Table 18). 

Table 18 

8-year Fuel Cost Savings for the 8-locomotive Missoula Switcher Fleet (2010 USD) 

2010 2011 2012 2013 2014 2015 2016 2018 

228321 282808 292942 280438 271857 191241 159256 180843 

TOTAL: $1,887,707.92 

Note: detailed activity logs of each switcher locomotive, railyard assignment logs, activity data, and engine 

characteristics of the estimated 30 line-haul locomotives that pass through the Missoula yard daily would be 

useful in further ensuring emission benefits and cost savings estimates are accurate. 

Page 10 of 11 
 

 

 

 

 

 

Acronyms & Abbreviations 

APU – Auxiliary Power Unit 

bhp-hr/gal – brake horsepower hour per gallon 

CFR – Code of Federal Regulations 

CO – Carbon Monoxide 

DERA – Diesel Emissions Reduction Act 

EPA – U.S. Environmental Protection Agency 

g/bhp-hr – grams per brake horsepower hour 

GPH – Gallons Per Hour 

HC – Hydrocarbons 

HP – Horsepower 

kW - Kilowatt 

NMHC – Non-methane Hydrocarbon 

MPO – Metropolitan Planning Organization 

MRL – Montana Rail Link 

NOAA - National Oceanic and Atmospheric Administration 

NOx – Nitrogen oxides 

PM10 – Particulate Matter smaller than 10 micrometers in diameter 

PM2.5 – Particulate Matter smaller than 2.5 micrometers in diameter 

ULSD - Ultra Low-Sulfur Diesel 

Un – Uncontrolled Engines 

USD – United States Dollars 

VOC – Volatile Organic Compounds 

Page 11 of 11