1998 Locomotive NOx Fleet Average Emissions Agreement in the South Coast Air Basin

This page last reviewed October 8, 2018

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In 1994, the California Air Resources Board (CARB) adopted Measure M-14 as a federally enforceable measure in California’s State Implementation Plan (SIP).  Measure M-14 provides the South Coast Air Basin (SCAB) with an estimated 65 percent reduction in locomotive NOx emissions (up to 24 tons per day) between 2000 and 2010.

Measure M-14 was achieved through the combination of U.S. EPA regulations for cleaner locomotives and the 1998 Locomotive NOx Fleet Average Agreement (1998 Agreement).  The 1998 Agreement, signed by CARB, Union Pacific Railroad (UP) and BNSF Railway (BNSF), significantly accelerates the introduction of cleaner locomotives into the South Coast Air Basin.  The 1998 Agreement is estimated to provide about half of the total Measure M-14 NOx reductions.

Specifically, under the 1998 Agreement:

  • UP and BNSF agreed to operate locomotive fleets that “on average” meet a Tier 2 NOx emission standard, or 5.5 g/bhphr by 2010 (and through 2030).

  • UP and BNSF are allowed to use ultra-low emitting locomotive (ULEL) credit to meet the fleet average.

  • UP and BNSF must continue to comply with the Tier 2 locomotive fleet average from 2010 to 2030.

Additionally, U.S. EPA agreed to enforce the 1998 Agreement with “backstop” or “contingency” emission reductions, if necessary.  (Source: Federal Register / Vol. 63, No. 73 / Thursday, April 16, 1998 / Rules and Regulations – p. 18979).

Agreement Documents

  • 1998 Locomotive NOx Fleet Average Agreement (PDF - 361 KB)

  • Statement of Principles - 1998 Locomotive NOx Fleet Average Agreement (PDF - 589 KB)

Determining Locomotive Fleet Average Emissions for Compliance

The UP and BNSF fleet average is measured by the work that an individual locomotive performs in the South Coast Air Basin.  Locomotive work is measured in megawatt-hours (MWhrs) - the electricity that a diesel-electric locomotive produces to operate.  MWhrs are measured by a watt-meter located on a locomotive.  The watt-meter measures the electricity used by the locomotive, and transmits that information by radio signal to UP and BNSF.  The percent of work performed by each locomotive is multiplied by that locomotive’s emission level to determine the weighted emission level.  The weighted emission levels are summed for all locomotives to determine the total fleet average emission level.

Ultra-Low Emitting Locomotive (ULEL) Credit

The 1998 Agreement allows UP and BNSF to help meet the NOx fleet average of 5.5 g/bhp-hr through credits generated by operating advanced technology or ultra-low emitting locomotives (ULELs).  A ULEL is defined as meeting either a 4.0 g/bhp-hr NOx level or better through 2011, or a 3.0 g/bhp-hr NOx level or better through 2014.  Some examples of ULELs include genset locomotives and battery electric hybrid locomotives.  

ULEL credit provides an incentive for UP and BNSF to invest in and promote the development of advanced locomotive technologies while maintaining operational flexibility of their respective locomotive fleets.  Both companies have elected to generate ULEL credit.  UP has generated ULEL credit by operating switch locomotives with NOx levels below 3.0 g/bhp-hr.  BNSF has generated ULEL credit by operating line haul locomotives with NOx levels below 4.0 g/bhp-hr.  Together, these strategies have resulted in significant emission reductions and public health benefits.  These benefits have occurred both locally, in and around railyards, and regionally throughout the South Coast Air Basin.  

Moreover, these locomotive technologies have been obtained and operated by other railroads across the state, providing California with additional and early locomotive emission reductions.  The ULEL credit can be used annually (2010-2030) by each railroad to help achieve the required 5.5 g/bhp-hr NOx fleet average.

Fleet Average Credit (FAC)

The 1998 Agreement has another option for UP and BNSF to generate NOx emissions credit (other than ULEL credit).  This type of NOx emissions credit is referred to as the Fleet Average Credit (FAC).

FAC from 2005-2009:

From 2005-2009, the Fleet Average Target is designed to decline from 11.1 g/bhp-hr (2005) to 8.0 g/bhp-hr (2009).  UP and BNSF can obtain FAC for locomotive fleet average NOx emissions levels below the Fleet Average Target for a given year.

FAC from 2010-2030:

From 2010-2030, the 1998 Agreement requires both UP and BNSF locomotive fleets in the South Coast Air Basin to achieve a NOx emissions level of 5.5 g/bhp-hr.  To obtain FAC during this timeframe, UP and BNSF must have a locomotive NOx fleet average emissions level below 5.5 g/bhp-hr.

The figure below shows the Fleet Average Target that a participating railroad’s Fleet Average Emission level must be below, to obtain FAC.

Fleet Average Targets

As an example, in 2007 the 1998 Agreement Fleet Average Target for NOx was 9.6 g/bhp-hr.  If a railroad had a fleet average NOx emissions level of 9.0 g/bhp-hr, that railroad would receive the NOx emissions difference in FAC.  In this example (9.6 Fleet Average Target – 9.0 NOx Fleet Average Emissions Level), the railroad would receive 0.6 g/bhp-hr NOx of FAC.

FAC can be used to offset locomotive Fleet Average (FA) emissions above the Fleet Average Target. For example, if UP had an FA of 6.1 g/bhp-hr, the 0.6 g/bhp-hr of FAC could be used to meet the Final FA of 5.5 g/bhp-hr. 

Finally, if a railroad submits a Fleet Average prior to 2010, including the requisite locomotive activity information, to ARB staff for FAC, that submittal is reviewed in the same manner as discussed below.

CARB Review of Fleet Average Information

The 1998 Agreement requires UP and BNSF to submit this locomotive information to CARB staff through 2030.  Beginning April 1, 2011, each railroad is required to annually demonstrate its final fleet average for the preceding year by providing operational information, such as MWhrs, for all locomotives operating within the South Coast Air Basin along with a demonstration of ULEL credits.  CARB does an initial review and ensures that all necessary information was provided before issuing a Letter of Completion. CARB evaluates the submitted ULEL credit data, including individual locomotive emission and activity levels, and provides an Approval Letter for ULEL Credit for any acceptable credits.  Finally, CARB analyzes the locomotive work data and the fleet average calculations and provides an Approval Letter if the information demonstrates compliance with the 1998 Agreement. 

CARB validates the levels of UP and BNSF locomotive activity and locomotive fleet composition (i.e. tier levels) reported for the South Coast Air Basin through the use of data from semi-annual railyard inspections, quarterly field surveys, and extensive photographic tracking of UP and BNSF locomotives operating in California.

Summary for 2017 Calendar Year

The tables below summarize each railroad’s compliance data for the 2017 calendar year.  For clarity, the information is categorized by tier or ULEL levels.  However, many locomotives are certified to emission levels cleaner than the locomotive emission standards.  For the purposes of determining compliance, actual certification or ULEL levels were used.  

Note that this data is a “snap shot” for calendar year 2017 operations, and those locomotives may or may not be operating in the South Coast Air Basin at this point in time.  Additionally, certified emission levels are subject to change as locomotives are remanufactured to lower emission levels.  The tables below provide the aggregated number of locomotives, MWhrs by each tier levela, and the average and weighted NOx emission levels.

1998 Agreement Locomotive Compliance Summary Information

Union Pacific Railroad
Tier1 Number of Locomotives2 Megawatt-Hours
%MWhrs by
Tier Level
Weighted Average NOx Emission Level3
Tier Contribution
to Fleet Average4
Pre-Tier 0 55 323 0.2% 11.0 0.02
Tier 0 1,726 40,951 22.6% 7.8 1.77
Tier 1 1,891 40,549 22.4% 6.5 1.46
Tier 2 1,479 53,247 29.4% 4.9 1.45
Tier 3 81738,38621.2%4.91.03
Tier 41005,4303.0%1.10.03
Total 6,107 181,094 100% 5.8
ULEL Credit Used 0.3
Fleet Average 5.5

BNSF Railway
Tier1 Number of
%MWhrs by Tier Level Weighted Average NOx Emission Level3
Tier Contribution
to Fleet Average4
Pre-Tier 0 196 1,826 0.6 13.0 0.08
Tier 0 152 6,880 2.4 7.7 0.19
Tier 1 1,403 109,907 38.7 6.1 2.36
Tier 2 1,392 89,654 31.5 4.9 1.53
Tier 31,16863,66622.44.71.04
Tier 425512,3914.41.00.05
Total 4,566 284,327 100% 5.3

1.  For more information on the U.S. EPA locomotive emission standards please visit. http://www.epa.gov/oms/locomotives.htm. 
2.  Number of locomotives is the sum of all individual locomotives that visited or operated within the South Coast Air Basin at any time during  2017.  
3.  Many locomotives are certified to emission levels cleaner than the U.S. EPA emission standards or tiers.  For the purposes of this table, a locomotive’s actual certified emission level is grouped with the required tier level.  Within each tier, the Weighted Average NOx Emission Level is calculated by multiplying each indivual locomotive's actual certification level by its megawatt-hours of operation. 
4.  The Tier Contribution is calculated by multiplying the %MWhrs by Tier Level by the Weighted Average NOx Emission Level.

For 2017, both UP and BNSF have demonstrated compliance with the Tier 2 (5.5 g/bhp-hr) locomotive NOx fleet average required by the 1998 Agreement.  The links below provide formal correspondence for 2017 compliance between the ARB and UP or BNSF. 

Fleet Average Archives

To view or download a previous year Fleet Average Compliance Report and Approval letter please click on the link above. 

a.  BNSF and UP requested that CARB treat the activity (MWhrs) of the individual locomotives as business confidential information.  Upon review, CARB staff determined that the information meets the criteria for Trade Secrets as defined in California Government Code 6254.7, therefore, aggregate information is presented.