SmartWay SIP and Transportation 

Conformity Guidance: 

Accounting for NOx Reductions 

from Trailer Aerodynamic Kits and 

Low Rolling Resistance Tires 

Guidance for State and Local 

Air and Transportation Agencies 
SmartWay SIP and Transportation


Conformity Guidance:


Accounting for NOx Reductions 


from Trailer Aerodynamic Kits and 


Low Rolling Resistance Tires


Guidance for State and Local 


Air and Transportation Agencies


Transportation and Regional Programs Division 

Office of Transportation and Air Quality 

U.S. Environmental Protection Agency 

EPA420-B-07-004 

June 2007 
TABLE OF CONTENTS 

CHAPTER 1 Introduction.............................................................................................................. 5

1.1 What is the purpose of this guidance? ....................................................................... 5 

1.2 Which SmartWay technologies are addressed by this guidance?.............................. 6 

1.3 What trucks can be part of a SmartWay project? ...................................................... 7

1.4 How can NOx emission reductions from SmartWay projects be used to 

meet SIP and conformity needs?................................................................................ 8 

1.5 How does this guidance relate to the Voluntary Mobile Source Emission 

Reduction Program SIP guidance? ............................................................................ 9 

1.6 How does this guidance relate to existing Clean Air Act requirements? .................. 9 

1.7 Who should I contact for additional information?.....................................................10

CHAPTER 2 Quantifying Retrofit Emission Reductions............................................................13

2.1 How do I quantify emission reductions from SmartWay projects?...........................13 

2.2 What is NMIM and why does EPA recommend its use to quantify 

emission reductions from SmartWay projects? .........................................................13 

2.3 What are the uses and limitations of NMIM?............................................................15 

2.4 Can I use NMIM to quantify emission reductions from SmartWay projects 

even if I am not using it to generate the local inventory?..........................................16 

2.5 Can I use NMIM to estimate emission reductions from SmartWay projects 

for uses other than SIPs or conformity determinations?............................................16 

2.6 Where would I get estimates of specific SmartWay project information 

needed to quantify emissions reductions from a SmartWay project?........................17 

2.7 How do I use NMIM to quantify emission reductions from SmartWay 

projects? .....................................................................................................................17 

CHAPTER 3 Using Emission Reductions in SIPs........................................................................25

3.1 What are the basic requirements for using emission reductions in SIPs?..................25 

3.2 How can the estimated NOx emission reductions be used for SIP 

purposes?....................................................................................................................29

3.3 What would a state submit to EPA to meet the requirements for 

incorporating a SmartWay project in a SIP?..............................................................29 

3.4 What monitoring and record keeping should occur to document NOx 

emission reductions from SmartWay projects? .........................................................30

3.5 What validation and reconciliation should occur for emission reductions in 

SIPs approved under the VMEP guidance? ...............................................................31

3.6 What penalties can EPA impose for not complying with Clean Air Act 

requirements?.............................................................................................................31 

3 
CHAPTER 4 Using Emission Reductions in Transportation Conformity 

Determinations ........................................................................................................................33

4.1 What is transportation conformity? ...........................................................................33

4.2 How can NOx emission reductions from SmartWay projects be included 

in transportation conformity determinations?............................................................34 

4 
CHAPTER 1

INTRODUCTION 

(Note: As used in this document, the terms “we,” “us,” and “our” refer to the 

Environmental Protection Agency (EPA). The terms “you” and “your” refer to a state or 

local air pollution control agency or state or local transportation agency or other federal 

agency, as appropriate.) 

1.1 What is the purpose of this guidance?

Economic prosperity in the United States is inextricably tied to the commercial 

movement of goods by truck. Trucks carry three-fourths of the value of freight shipped 

in the United States and two-thirds of the weight, according to the U.S. Department of 

Transportation’s Bureau of Transportation Statistics.1 While essential to business and 

consumers, transporting goods by truck also consumes energy and produces pollution. 

Recognizing the importance of trucking to both the economy and to the environment, 

EPA has developed the SmartWay Transport program to reduce greenhouse gas 

emissions and air pollution from the ground freight transport industry, including longhaul diesel trucks. 

The purpose of this guidance is to describe how to quantify and use reductions in 

nitrogen oxides (NOx) that result when trucks are outfitted with two specific SmartWay 

fuel efficient technologies: low rolling resistance tires and trailer aerodynamic kits. This 

guidance describes how to apply these NOx reductions in state implementation plans 

(SIPs) and in transportation conformity determinations. Therefore, this guidance could 

be of interest primarily to ozone and particulate matter (PM2.5 and PM10) nonattainment 

and maintenance areas that are considering additional ways to reduce NOx for reasonable 

further progress (RFP) SIPs, attainment demonstrations, or maintenance plans, or in 

transportation conformity determinations. EPA’s intent in producing this guidance is to 

facilitate the adoption of SmartWay projects as a cost-effective way to achieve needed 

NOx emission reductions while ensuring that these projects meet SIP and conformity 

requirements. 

The SIP and conformity policy elements of this guidance in Chapters 1, 3, and 4 

are applicable to all states that have nonattainment or maintenance areas. However, the 

methodology that is described in Chapter 2 specifically applies to states that use EPA’s 

MOBILE and NONROAD models. State and local agencies developing SIPs and 

conformity analyses for California should consult EPA Region 9 for information on the 

1

 http://www.bts.gov/press_releases/2005/bts003_05/html/bts003_05.html

5 
2

 Please refer to EPA’s SmartWay website for more information, including a fact sheet on aerodynamics: 

http://www.epa.gov/otaq/smartway/smartway_fleets_strategies.htm#aero. 3

 EPA will include on its SmartWay website a list of low rolling resistance tires that could be used to meet 

the terms of this guidance. 4

 The SmartWay Technology Package Savings Calculator can be found at:

http://www.epa.gov/otaq/smartway/calculator/loancalc.htm

current version of EMFAC approved for use in California and for information on how to 

quantify NOx reductions from the SmartWay technologies addressed by this guidance. 

This guidance is focused on quantifying NOx reductions for SIP and conformity 

purposes and therefore has an intended audience of air quality and transportation 

planners. Other audiences may wish to use this guidance for quantifying NOx reductions 

for non-SIP or conformity purposes by reading Chapter 1 for background and referring to 

Chapter 2’s Questions 2.4 through 2.7 of the guidance for quantifying emission 

reductions. 

1.2 Which SmartWay technologies are addressed by this guidance? 

This guidance pertains to a truck or truck fleet that is outfitted with both of the 

following two technologies: 

A. Trailer aerodynamic kits,2

 which would include the following: 

• air deflecting fairings on the bottom of each trailer side (“side skirts”), and 

• an air deflecting fairing on the front of the trailer (“gap reducer”); and 

B. Low rolling resistance tires,3 e.g., single-wide tires with aluminum or low-weight 

steel wheels on: 

• all trailer axles, and 

• all tractor drive axles. It is optional to also install low rolling resistance tires on 

the tractor steer axle. 

These technologies would typically be applied to long-haul trucks that are used to move 

freight long distances, rather than trucks used for freight movement within a single 

nonattainment or maintenance area. 

For the purposes of this guidance only, a project that includes these two 

technologies together will be referred to as a “SmartWay project.” A SmartWay project 

is defined as the purchase and installation of both the trailer aerodynamic kits and low 

rolling resistance tires on a truck or fleet of trucks, as described above. According to 

EPA’s SmartWay Technology Package Savings Calculator, the cost of adding the 

aerodynamic kits and low rolling resistance tires to a truck would be recuperated in fuel 

savings in about two years.4

6 
5

 For more information regarding the testing program used to establish that the SmartWay aerodynamic 

fairings and low rolling resistance tires reduce NOx, please see Bachman, L. Joseph, Anthony Erb, and 

Cheryl L. Bynum, “Effect of Single Wide Tires and Trailer Aerodynamics on Fuel Economy and NOx 

Emissions of Class 8 Line-Haul Tractor-Trailers,” SAE Paper Number 05CV-45, 2005, found at the

website: http://www.epa.gov/smartway/documents/sae-05cv045-110105.pdf

6

 These two guidance documents, “Guidance for Quantifying Long Duration Truck Idling Emission 

Reductions in State Implementation Plans and Transportation Conformity” (EPA420-B-04-001, January

2004), and “Diesel Retrofits: Quantifying and Using Their Benefits in SIPs and Conformity - Guidance for 

State and Local Air and Transportation Agencies” (EPA420-B-06-005, June 2006), can both be found at

EPA’s website: http://www.epa.gov/otaq/stateresources/transconf/policy.htm#sips . 

This combination of aerodynamic kits and low rolling resistance tires is the only 

package of SmartWay fuel efficient technologies that has been evaluated for NOx 

reductions thus far.5 SmartWay projects could be undertaken by a truck or truck fleet 

owner, or by state or local governments who are seeking to reduce NOx for SIP or 

transportation conformity purposes. 

EPA notes that a SmartWay project may be part of a larger Agency effort to 

provide incentives for private and public agencies or truck owners to apply “SmartWay 

Upgrade Kits” to a truck or fleet of trucks. A SmartWay Upgrade Kit can include idle

reduction devices, retrofits for particulate matter, low rolling resistance tires, and trailer 

aerodynamic kits. EPA has issued previous SIP and conformity guidance for quantifying 

and using the benefits of idle reduction devices and retrofit projects.6 This document 

provides the remaining guidance needed for agencies to quantify and use the NOx 

reductions from SmartWay Upgrade Kits in SIPs and conformity. Additional general 

information about the SmartWay Transport program can be found at: 

http://www.epa.gov/smartway/swresources.htm

This guidance document is based on the most current scientific information 

available on NOx emission reductions from fuel efficient technologies on long-haul 

trucks. EPA’s Office of Transportation and Air Quality (OTAQ) intends to make 

available in the future a formal list of EPA-approved technologies that achieve fuel 

efficiency and produce NOx emission reductions, including the technologies addressed 

by today’s guidance. It is possible that additional fuel efficient technologies which may 

evolve in the future could provide additional NOx reductions. Please contact OTAQ if

you have further technical information regarding fuel efficient technologies that may 

demonstrate additional NOx reductions. EPA will review such information on a case-bycase basis. See Question 1.7 of this guidance document for OTAQ contact information. 

1.3 What trucks can be part of a SmartWay project?

New emission standards will affect all 2007 and future model year on-road heavyduty highway vehicles and engines. In general, this guidance applies to trucks 

manufactured before those standards take effect and that will not have to comply with 

EPA’s regulations for heavy duty trucks (i.e., pre-2007 model years). EPA does not 

believe that the SmartWay technologies described in Section 1.2 will result in significant 

7 
7

 In this guidance, the term “SIP” could mean an initial SIP developed to show RFP, attainment, or

maintenance, or a revision to such a SIP. 

8 Note that if a SmartWay project is included in a SIP, it would not be considered a transportation control 

measure (TCM) for the purposes of demonstrating timely implementation for transportation conformity, 

because the definition of TCM in the transportation conformity regulation at 40 CFR 93.101 specifically

excludes it: “Notwithstanding the first sentence of this definition, vehicle technology-based, fuel based,

and maintenance-based measures which control the emissions from vehicles under fixed traffic conditions

are not TCMs for the purposes of this subpart.” Therefore, the regulations at 40 CFR 93.113 do not apply 

to SmartWay projects, and SmartWay projects are not covered by Clean Air Act 176(c)(8) which allows 

TCMs to be added or replaced in an approved SIP. 

additional NOx reductions for 2007 and later vehicles because of the NOx control 

strategies that will apply to them. However, you might be able to apply this guidance to 

some trucks with model years for 2007-2009, because the 2007 standard will be phased 

in and therefore not every truck manufactured in 2007, 2008, or 2009 will be required to 

meet the 2007 standard initially. Please check with EPA before including any trucks with 

model years for 2007-2009 in a project. 

1.4 How can NOx emission reductions from SmartWay projects be used to meet 

SIP and conformity needs?

This document describes two options for using NOx emission reductions from

these projects to meet both near term and longer term SIP and conformity needs. 

1.4.1 SIPs

One option is to use NOx reductions from SmartWay projects to help demonstrate 

RFP, attainment, or maintenance in upcoming SIP submissions. To be included in a SIP, 

NOx reductions from SmartWay projects must meet the same SIP requirements as any 

other control measures. This guidance document provides the necessary information to 

include NOx reductions from SmartWay projects in a SIP7, including a calculation 

method that ensures that emission reductions calculated for the SmartWay project are 

consistent with the rest of the SIP. 

State and local agencies can consider including NOx reductions from SmartWay 

projects especially in SIPs being developed to meet current ozone and PM2.5 air quality 

standards. General SIP requirements are described in Chapter 3 of this document.8

1.4.2 Transportation conformity

Alternatively, state and local agencies could use NOx reductions from SmartWay 

projects to meet transportation conformity requirements now or in the future, with little 

additional effort beyond what is required to properly implement the project and quantify 

the emission reductions. These reductions could be incorporated into a transportation 

8 
9

This guidance is found at: http://www.epa.gov/otaq/stateresources/policy/pag_guidance.htm. EPA notes 

that the VMEP guidance pertains to SIP measures, rather than transportation or general conformity

determinations. Control measures for conformity determinations must meet the relevant criteria in the 

transportation conformity regulation (40 CFR Parts 51 and 93).

conformity determination without making any change in the SIP. Chapter 4 of this 

document explains transportation conformity requirements. 

1.5 How does this guidance relate to the Voluntary Mobile Source Emission 

Reduction Program SIP guidance?

In October 1997, EPA issued its “Guidance on Incorporating Voluntary Mobile 

Source Emission Reduction Programs in State Implementation Plans (SIPs)” (the VMEP 

guidance).9 The purpose of the 1997 VMEP guidance is to support innovative methods 

in achieving emission reductions for SIPs. The VMEP guidance applies to SIP emission 

reduction measures that rely on voluntary actions of individuals and other parties, 

including non-governmental parties. EPA anticipates that many SmartWay projects will 

fall into the voluntary category, e.g., projects undertaken by fleet owners or operators. 

However, a state-funded SmartWay project included in a SIP may not fall under the 

VMEP guidance if it has well-defined requirements to ensure its full implementation as a 

SIP program. For example, a state program to adopt a SmartWay project for state owned 

trucks would not be subject to the VMEP guidance. Please consult your EPA Region 

early in the development of a SmartWay project to determine the appropriate use of the 

VMEP guidance. 

Under the VMEP guidance, the amount of emission reductions allowed for 

voluntary mobile measures in a SIP is presumptively capped at three percent of the total 

projected future year emission reductions required to attain the applicable air quality 

standards. EPA acknowledges that some areas may be able to demonstrate that voluntary 

measures may achieve credible reductions higher than the three percent cap. In that case, 

EPA will re-evaluate that cap on a case-by-case basis and allow the cap to be exceeded if

the cap hinders the implementation of effective voluntary control measures, subject to 

notice and comment during SIP approval. Today’s guidance relies on EPA’s 1997 

VMEP guidance for voluntary SmartWay projects. Interested parties should refer to that 

guidance at the time a specific SmartWay project is under development. 

1.6 How does this guidance relate to existing Clean Air Act requirements?

This document provides guidance to state and local air pollution control agencies, 

transportation agencies, metropolitan planning organizations (MPOs), and the general 

public on quantifying and using SmartWay projects to reduce NOx emissions in SIPs and 

transportation conformity determinations. SIP requirements can be found in Clean Air 

Act sections 110(a)(2) and 172(c). Transportation conformity requirements can be found 

in Clean Air Act section 176(c) and 40 CFR Parts 51 and 93. This guidance document 

9 
does not substitute for those provisions, nor is it a regulation itself. It does not by itself

impose binding, enforceable requirements on any party. Further, it does not assure that 

EPA will approve all instances of its application, and thus the guidance may not apply to 

a particular situation based upon the circumstances. The EPA and state decision makers 

retain the discretion to adopt approaches on a case-by-case basis that differ from this 

guidance where appropriate and consistent with the statute and applicable regulations. 

Any decisions by EPA regarding a particular SIP demonstration will only be made based 

on the statute and applicable regulations, and following notice and opportunity for public 

review and comment. 

Where specific recommendations are provided, you should consider whether or 

not such recommendations are appropriate for your particular project or situation. This 

guidance may be revised periodically without public notice. EPA welcomes public 

comments on this document at any time and will consider those comments in any future 

revisions of this guidance document. 

Readers of this document are cautioned not to regard statements recommending 

the use of certain procedures as either precluding other procedures or information or 

providing guarantees that using these procedures will result in actions that are fully 

approvable. As noted above, EPA cannot assure that actions based upon this guidance 

will be fully approvable in all instances, and all final SIP actions may only be taken 

following notice and opportunity for public comment. 

1.7 Who should I contact for additional information?

If this guidance document does not answer a specific question, please contact the 

appropriate EPA Regional Office with responsibility for air quality planning and/or 

transportation conformity in the area where the SmartWay project is located. A contact 

list of the EPA Regions is available at the following web address: 

http://www.epa.gov/epahome/locate2.htm. In addition, contact information for EPA 

regional transportation conformity staff can be found at the following website: 

http://www.epa.gov/otaq/stateresources/transconf/contacts.htm. 

For additional information about the SmartWay Transport program, please contact 

Cheryl Bynum of EPA’s Office of Transportation and Air Quality at (734) 214-4844, 

bynum.cheryl@epa.gov. 

For technical questions regarding the use of the National Mobile Inventory Model 

(NMIM) for calculating emission reductions from SmartWay projects, please contact 

EPA’s Office of Transportation and Air Quality at mobile@epa.gov. 

For general questions concerning the use of NOx reductions from SmartWay 

projects in SIPs or in transportation conformity, please contact Laura Berry of EPA’s 

Office of Transportation and Air Quality at (734) 214-4858, berry.laura@epa.gov; or 

10 
Gary Dolce also at EPA’s Office of Transportation and Air Quality at (734) 214-4414, 

dolce.gary@epa.gov. 

11 
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12 
10 The intended audience for this chapter is state and local air quality and transportation planners who are 

already familiar with how SIP inventories and transportation conformity determinations are developed. For 

readers less familiar with this subject matter, please note that Section 1.7 contains contact information if 

you have additional questions. 

CHAPTER 2 

QUANTIFYING EMISSION REDUCTIONS FROM SMARTWAY PROJECTS 

2.1 How do I10 quantify emission reductions from SmartWay projects?

For states other than California, EPA recommends the use of the National Mobile 

Inventory Model (NMIM) to estimate emission reductions from SmartWay projects for 

SIPs and for transportation conformity analyses. NMIM is the recommended method 

because it estimates the impact of a SmartWay project for the particular model years that 

it applies to under local conditions. Due to the nature of the aerodynamic kits and low 

rolling resistance tires, emission reductions from SmartWay projects will vary based on 

the average speed of the vehicles. The method described here accounts for the variable 

impacts of the SmartWay equipment described in Section 1.2 based on average speeds of 

vehicles on different roadway types. 

The NOx reductions by speed provided in the table in Section 2.7.1.6 of this 

Chapter should be applied to class 8 tractor-trailer (combination) trucks with the 

SmartWay aerodynamic fairings and low rolling resistance tires described in Section 1.2 

of the model years specified in Section 1.3 in any state, including California. However, 

NMIM may not be appropriate to derive emission factors for fleets of trucks in 

California. State and local agencies developing SIPs and conformity analyses for 

California should consult with EPA Region 9 for information on the current version of 

EMFAC approved for use in California and for information on how to apply the emission 

reductions given in Section 2.7.1.6 to EMFAC emission factors. 

2.2 What is NMIM and why does EPA recommend its use to quantify emission 

reductions from SmartWay projects?

NMIM is a graphical user interface that contains the MOBILE6.2 and 

NONROAD2005 models and a database of county-level input information, the National 

County Database (NCD) (note cautions about the use of the NCD in Question 2.3). 

NMIM2005 is capable of producing monthly inventories by source classification code 

(SCC) and county for every state, but should not be used for California, which has its 

own modeling tools. NMIM was created to simplify the process of developing countyby-county emissions inventories for multi-county areas, states, or the entire nation. 

When using NMIM, users can simply select the year, months, and county or counties 

they wish to evaluate. Since NMIM includes county-level information, it will 

automatically create MOBILE6.2 input files, run MOBILE6.2, and multiply the emission 

13 
11 “EPA’s National Mobile Inventory Model (NMIM), a Consolidated Emissions Modeling

System for MOBILE6 and NONROAD,” H. Michaels, et al. U.S. EPA, 

http://www.epa.gov/otaq/models/nmim/420r05024.pdf. 

factors by vehicle miles traveled (VMT) to produce highway vehicle emissions 

inventories for each county for each month.11 NMIM will also automatically create 

NONROAD2005 input files, run NONROAD2005, and produce nonroad equipment 

emissions inventories for each county for each month. NMIM also provides a postprocessing module that will aggregate the months into an annual inventory and produce 

tab-delineated output that can be read into database or spreadsheet software applications. 

Because NMIM provides a graphical user interface for MOBILE6.2 and 

NONROAD2005, new and past users of these models may find that NMIM is an easier 

way to use MOBILE6.2 and NONROAD2005. Input options and output results from 

NMIM will be familiar to air quality and transportation agency professionals who have

used MOBILE6.2 and/or NONROAD2005 in the past to create emissions inventories for 

use in SIPs or transportation conformity determinations. 

NMIM2005 includes the capability to model retrofit projects, a capability that 

does not exist in MOBILE6.2. The post-processors in NMIM include retrofit modules 

that allow you to specify the details of a retrofit project. These retrofit modules take 

emission factors generated by MOBILE6.2 and apply adjustments to those emission 

factors or inventories to reflect the specifics of the retrofit project as described in a usergenerated input file. The resulting emission factors are used to generate emissions 

estimates for the project.

While SmartWay projects are not retrofit projects, the retrofit modules in NMIM 

can be adapted to easily calculate emission reductions from SmartWay projects. For 

example, if the input file indicates that the SmartWay equipment described in Section 1.2 

was installed in 2005 on 1998 model year class 8 trucks and you want to estimate the 

emissions of these trucks in 2010, NMIM will apply the appropriate adjustments to only 

the emissions of model year 1998 class 8 trucks in 2010 when generating an emission 

estimate. Because NMIM can be run using the same local inputs as used in the SIP, 

NMIM can calculate emission reductions from a SmartWay project based on the same 

conditions used to generate the rest of the inventory used in the SIP or conformity 

analysis. 

EPA recommends NMIM for assessing the emission reductions from SmartWay 

projects for SIP and conformity purposes. However, EPA acknowledges that alternative 

methods to NMIM are available and others may be developed. Alternative approaches 

will be reviewed by EPA on a case-by-case basis. Please provide EPA with all relevant 

technical support documentation, including the assumptions and other relevant 

information used to calculate emission reductions so EPA has the information necessary 

to make a decision. Also, any alternative approach must use the latest information as 

required by applicable SIP and conformity requirements. 

14 
2.3 What are the uses and limitations of NMIM?

EPA’s current approved model for estimating emissions from highway vehicles 

for SIP and conformity purposes in states other than California is MOBILE6.2. NMIM 

incorporates MOBILE6.2 along with pre- and post-processors, similar to those that many 

states have developed on their own, that simplify the process of inventory preparation. 

NMIM is not considered a new emissions model and does not start a new transportation 

conformity grace period pursuant to 40 CFR 93.111. Because NMIM incorporates 

MOBILE6.2 and NONROAD2005, it may be used to generate emissions inventories for 

SIPs and conformity analyses or it may just be used to estimate emission reductions from

retrofit or SmartWay projects, as discussed in Section 2.4. For general SIP and 

conformity inventory preparation, the pre- and post-processors in NMIM may have 

advantages or disadvantages in various areas or applications compared to pre-existing 

methods. Therefore, before using NMIM for general SIP and conformity inventory 

preparation, state and local air quality and transportation agencies should work together 

with EPA and DOT to determine whether NMIM is appropriate given local conditions 

and modeling methods, and to determine what modifications are needed to the NMIM 

database to accurately model local conditions. 

The use of NMIM is not required for general inventory preparation for SIPs or 

regional conformity analyses. Some areas may choose not to use NMIM simply because 

it does not provide a significant resource advantage compared to pre- and post-processing 

methods already being used. In addition, the use of NMIM may not be appropriate to 

generate emissions inventories in all areas. For example, some areas may already be

using more sophisticated methods for pre- and post-processing input and emissions data 

than NMIM can accommodate. In that case, state and local agencies should not use 

NMIM for inventory development, but should continue to use the more appropriate 

modeling already being conducted in the area. Those agencies should still use NMIM for 

estimating emission reductions from retrofit or SmartWay projects. 

States have provided information for the National County Database (NCD) as part 

of the National Emissions Inventory (NEI) development process. However, given the 

NEI cycle, this may not be the most recent or best available information at the time a 

state initiates modeling. For SIPs and regional conformity analyses, state and local 

agencies should review the information in the NCD to evaluate whether it includes the 

latest and best information currently available including latest planning assumptions 

where applicable. Where more current information is available, you must modify the 

database to incorporate that information in your analysis to meet regulatory requirements 

for the use of latest planning assumptions in SIPs and conformity determinations. (In 

addition to updating the NCD for your project, EPA also encourages states to separately 

submit updates to the NCD to EPA so that the most accurate database is available for 

both national and local inventory development.) The NCD works at the county level and 

will need to be modified to account for areas containing partial counties, if necessary. 

The NCD also does not contain VMT estimates for future years, so any use of NMIM for 

a future evaluation year will have to include a projection of future VMT. The 

interagency consultation process should be used to evaluate whether the use of NMIM is 

15 
appropriate in a given area, and to evaluate what changes are needed in the NMIM 

database for the area. 

If you are using NMIM to develop inventories for SIPs or conformity, and have 

made certain that the appropriate local conditions have been entered in the NMIM 

database, entering the appropriate SmartWay project inputs as described below will 

ensure that SmartWay project reductions are incorporated in the inventory. In order to 

calculate the emission reductions from SmartWay projects, you will have to run NMIM 

twice - a base case without the SmartWay project and a control case with the SmartWay 

project and with all other NMIM inputs unchanged. You would then calculate the 

difference between these two inventories to determine the emission reductions from the 

SmartWay project. 

2.4 Can I use NMIM to quantify emission reductions from SmartWay projects 

even if I am not using it to generate the local inventory?

Yes, even if NMIM is not being used for inventory development, EPA 

recommends that you use it for the calculation of emission reductions for SmartWay 

projects. Because NMIM uses MOBILE6.2 to develop estimates of reductions from

SmartWay projects, emission reductions calculated using NMIM should be consistent 

with the rest of the local inventory. When using NMIM solely to calculate emission 

reductions from SmartWay projects, you should first make sure that all NMIM inputs in 

the base case (i.e., the case without the SmartWay project in place) are as consistent as 

possible with the MOBILE6.2 inputs being used to generate the inventory used in the SIP 

or conformity analysis. You should use those same inputs, along with those needed to 

describe the SmartWay project, for the control case. Given that some differences in 

inputs and effects of pre- and post-processors may result in differences between 

emissions calculated using NMIM compared to other inventory methods, NMIM 

SmartWay project reductions should be calculated as a percentage reduction to the 

affected fleet, which can then be converted to mass reduction by multiplying by the total 

emissions for the affected fleet derived from the local inventory. 

2.5 Can I use NMIM to estimate emission reductions from SmartWay projects 

for uses other than SIPs or conformity determinations?

Yes. NMIM could also be used to evaluate SmartWay projects for other 

purposes, such as the development of proposals for SmartWay projects. For these 

purposes, NMIM users could rely more on default data in NMIM or other more 

simplified methods for using NMIM than would otherwise be necessary for SIP or 

conformity purposes. Other, more simplified approaches that do not rely on NMIM may 

also be appropriate for non-SIP or conformity uses. You should be aware that these 

simplified methods may result in emission reduction estimates that are not completely 

consistent with emission reductions calculated for SIP or conformity purposes using more 

rigorous methods. Consultation between organizations developing project proposals and 

16 
12 The transportation conformity regulations at 40 CFR 93.105 establish general procedures for interagency

consultation on the development of SIPs, transportation plans and TIPs, and transportation conformity 

determinations. Many states have adopted conformity SIPs which further tailor these procedures. Consult

your EPA Regional Office if you are unsure whether your state has a conformity SIP. 

state and local air quality and transportation agencies about appropriate methods and 

interpretation of results is important to ensure that SmartWay projects are properly 

evaluated. 

2.6 Where would I get estimates of specific SmartWay project information 

needed to quantify emissions reductions from a SmartWay project?

As described in the following sections, in order to quantify emission reductions 

from a SmartWay project, you will need specific information about the trucks in the 

project and their activity in the nonattainment area. Details of the implementation of the 

SmartWay project, such as the first and last years of implementation, the percentage of 

the fleet receiving the SmartWay equipment described in Section 1.2 each year, and the 

model years of the trucks getting this equipment should be readily available in the project 

documentation. 

Estimates of VMT needed for quantifying the NOx reductions from SmartWay 

projects could come from a variety of sources, including global positioning systems 

(GPS) on the trucks themselves, trucker logs, maintenance records, or fuel records. In the 

absence of this kind of information, the interagency consultation process12 should be used 

to determine the best available information to account for activity in the calculation of

emission reductions from a SmartWay project. In the absence of better information, 

agencies could agree to use local average estimates of vehicle VMT for the class and 

model year of vehicles included in the SmartWay project. 

Estimates of average vehicle speeds needed to determine the appropriate 

emissions reduction can be based on average speeds by roadway type for class 8 trucks in 

the nonattainment area as used to develop the SIP inventory. If specific speed 

information for the SmartWay project trucks operating in the nonattainment area is 

available (i.e., through the use of GPS or other similar technology), this information 

could be used in place of average speeds for determining the appropriate emission 

reduction by roadway type. The interagency consultation process should be used to 

determine the best available information to account for activity in the calculation of

emission reductions from a SmartWay project.

2.7 How do I use NMIM to quantify emission reductions from SmartWay 

projects?

The NMIM User Guide (available at http://www.epa.gov/otaq/nmim.htm) 

provides details of how to use the retrofit modules within NMIM. Note that throughout 

the NMIM User guide, the term “retrofit” is used to describe the input files and 

17 
13 Only NOx should be input here because NOx is the only pollutant for which SmartWay projects have 

been evaluated for SIP and conformity purposes. 

parameters used by the retrofit modules. Since this quantification method for SmartWay 

projects relies on the use of the retrofit module in NMIM, the terminology used in this 

guidance document will be consistent with the terminology used in the NMIM User 

Guide. SmartWay projects should be modeled as “fleet specific” projects, and the rest of 

this section indicates what information is necessary. 

As discussed in detail in the NMIM User Guide, the specifics of a highway 

retrofit project are described in an input file called the “Onroad Retrofit Parameters File.” 

In addition, you will need a second input file called the “Onroad Fleet Information 

Parameters File” to describe in detail the specific fleets affected by the SmartWay 

project. 

2.7.1 The Onroad Retrofit Parameters File 

The Onroad Retrofit Parameters File is used to describe the details of the 

SmartWay project. These include inputs that specify: 

• the pollutant affected by the SmartWay project, 

• the vehicle types affected, 

• the calendar years during which the SmartWay equipment described in Section 

1.2 is installed, 

• the model years of the vehicles that will be part of the SmartWay project, 

• the percentage of the fleet that will be part of the SmartWay project per year, and 

• the percentage effectiveness of the SmartWay equipment described in Section 1.2. 

Details on the use of these inputs are described in the NMIM User Guide. Specific 

guidance on these inputs, where applicable, is given below. 

2.7.1.1 Pollutants affected by the retrofit project

While NMIM allows you to enter the entire range of pollutants for which 

MOBILE6.2 and NONROAD2005 provide emissions estimates, the only pollutant 

affected by SmartWay projects in SIPs and conformity analyses is NOx. Therefore, users 

should enter only NOx for this input at this time.

13

2.7.1.2 Vehicle types affected

The SmartWay equipment described in Section 1.2 can only be installed on class 

8 diesel trucks and their trailers and therefore, this is the only category of vehicles for 

which reductions can be taken in a SIP or conformity analysis. Users should enter 

HDDV8a and HDDV8b to calculate reductions for these vehicles. 

18 
 2.7.1.3 Initial and final calendar years of retrofit implementation

These inputs are used to describe the first and last year of implementation of the 

SmartWay project. For example, if the SmartWay equipment described in Section 1.2 

was installed on trucks in a fleet over a multi-year period, enter the first and last year the 

equipment is installed. 

2.7.1.4 Initial and final model years retrofitted

These inputs are used to describe the first and last model years of the trucks in the 

SmartWay project. Because the effects of the SmartWay equipment described in Section 

1.2 on the emissions of trucks with significant after-treatment controls installed is not yet 

known, for SIPs and conformity determinations, reductions would typically not be 

applied to trucks with model years later than 2006. 

2.7.1.5 Percentage of the fleet retrofit per year

This input is used together with the inputs described in section 2.7.2.3 to describe 

the implementation of the SmartWay project. If the SmartWay project is implemented 

over a multi-year period, use this input to specify the percentage of the fleet that will get 

the SmartWay equipment described in Section 1.2 each year. For example, if the initial 

and final calendar years of implementation are 2007 and 2009 and the percentage of the 

fleet getting the SmartWay equipment described in Section 1.2 each year is 20%, NMIM 

will calculate emissions for a fleet in which 20% of the fleet gets the SmartWay 

equipment described in Section 1.2 in 2007, 20% in 2008, and 20% in 2009. 

2.7.1.6 Percentage effectiveness of the retrofit

This input is used to specify the percentage emission reduction associated with the 

SmartWay project. However, unlike retrofit projects, the emission reductions associated 

with SmartWay projects vary by vehicle speed. Based on vehicle testing, EPA has 

determined the following relationship between average vehicle speed and NOx reductions 

from SmartWay projects. This table should be used to determine the appropriate 

emission reduction associated with a particular average speed. NOx reductions for 

intermediate average speeds can be rounded to the nearest value in the table or 

interpolated.

19 
NOx Reductions Associated with Average Speeds: 

Speed (mph) 

%NOx 

reduction 

5 2.0 

10 2.3 

15 2.6 

20 3.0 

25 3.5 

30 4.0 

35 4.6 

40 5.2 

45 6.0 

50 6.8 

55 7.8 

60 9.0 

65 10.3 

NMIM produces output for vehicles on each of twelve roadway types. For SIPs 

and conformity determinations, the NOx reductions used should be based on the average 

speeds used in the SIP or conformity analysis for class 8 trucks on each of the twelve

roadway types specified by NMIM. For example, if the average speed used in the SIP for 

class 8 trucks on rural interstates is 65 mph, the NOx reduction for trucks that are part of 

a SmartWay project on rural interstates is 10.3%. Because NMIM only allows a single 

percentage effectiveness to be applied in any one run, it may take multiple NMIM runs to 

get the appropriate reductions on all roadway types. There are two possible approaches 

to doing the NMIM runs: 

1. Do separate NMIM runs for each roadway type. For the first run, enter the 

appropriate percentage reduction in the retrofit parameter file based on the 

average speed of class 8 trucks on rural interstates. In the NMIM output, use 

only the total emissions for class 8 trucks on rural interstates. Repeat for rural 

principal arterials, using the appropriate percentage reduction based on the 

average speed of class 8 trucks on rural principal arterials and taking the 

output only for that roadway type. Continue for each of the other roadway 

types. 

Under this approach, it would take as many as twelve NMIM runs to develop 

a new inventory with the SmartWay project in place. It could take fewer if

some of the roadway types have the same average speed. 

2. Do two NMIM runs – one base case run with no SmartWay project in place 

and a second run with the retrofit parameter file that describes the SmartWay 

project and with the percentage effectiveness set to 100%. Take the output 

from the two runs for class 8 trucks by roadway type and calculate the 

difference for each roadway type (i.e., subtract the class 8 rural interstate 

20 
emissions with 100% effectiveness from the base case class 8 rural interstate 

emissions). The result is the total emissions for trucks in the SmartWay 

project on rural interstates. Multiply that result by the appropriate percentage 

reduction from the table above based on the average speed of class 8 trucks on 

rural interstates in the nonattainment area. Repeat for each of the other 

roadway types. 

Under this approach, only two NMIM runs are required, but additional time

and effort are required to post-process the results.

Properly done, either approach is acceptable for SIPs and conformity analyses. 

Regardless of the approach used, speeds used in the analysis should be consistent with 

average speeds for class 8 trucks for each roadway type used in the SIP. Within a 

nonattainment area, each roadway type might actually have multiple average speeds 

based on time of day or location (i.e., some urban interstate links may have different 

average speeds than others). For purposes of this analysis, a single average speed for 

each roadway type is acceptable as long as it is calculated on a VMT-weighted basis from

the speeds used in the SIP. 

Note that under either approach, it is not necessary to know the actual average 

speeds of the specific trucks that are in the SmartWay project. The general method 

outlined here is based on the assumption that trucks in a SmartWay project have similar 

activity to all other class 8 trucks in the nonattainment area, i.e., they travel at the same

average speed on a particular roadway type and their VMT is distributed across the 

different roadway types proportionally to the total distribution of class 8 VMT. If you 

believe that the trucks in the SmartWay project have different average speeds or VMT 

distribution than other class 8 trucks in the nonattainment area and you want to account 

for that in a SIP or conformity analysis, you would need to document the methods and 

information used to develop alternative speeds and VMT distributions. The interagency 

consultation process should be used to determine the best approach for your local area. 

2.7.2 The Fleet Information Parameters File

The file for on-road fleet information is used to provide details of specific fleets 

of vehicles that are part of a SmartWay project. This file should be used, along with the 

retrofit parameter file described above, when quantifying the emission reductions from

SmartWay projects. This file includes inputs for: 

• vehicle class, 

• model year, 

• number of vehicles, and 

• annual VMT per vehicle. 

Details on the use of these inputs are described in the NMIM User Guide. 

Specific guidance on these inputs where applicable is given below. For any SmartWay 

project, you should be able to enter detailed information for all of these inputs. Note that 

21 
these files only describe characteristics of a fleet of vehicles; they do not describe any 

details of a SmartWay project. When quantifying the reductions for a SmartWay project, 

the fleet information parameter files are used to describe the specific fleet, while the 

retrofit parameter files are used to describe the SmartWay project applied to that fleet. 

When used without retrofit parameter files, the fleet information files can be used to 

simply quantify the emissions for any specific fleet of vehicles or engines. 

 2.7.2.1 Vehicle class parameters

Users should enter HDDV8a and HDDV8b because SmartWay projects only 

apply to class 8 diesel trucks. 

 2.7.2.2 Model year

The fleet information file will have one input line for each model year in the 

SmartWay project. Typically, the 2006 model year will be the last model year that can be 

part of a SmartWay project. 

 2.7.2.3 Number of vehicles

The number of vehicles entered for the specific fleet should be based on the 

calendar year for which emission estimates are being calculated. When estimating 

emissions for a specific fleet of trucks that are part of a SmartWay project in the current 

year, this is the current size of the fleet of trucks with the SmartWay equipment described 

in Section 1.2. However, in future years the fleet of affected vehicles may become

smaller as some vehicles in the fleet are scrapped while other newer vehicles that are not 

part of the SmartWay project may be added to the fleet. MOBILE6.2 includes the effects 

of normal attrition when projecting future emissions for the entire fleet (e.g., the model 

assumes that the number of 1998 model year vehicles decreases in each future year). 

However, these effects are not applied to the number of vehicles entered in the fleet 

information file for a specific fleet (e.g., if your input file indicates that you have twenty 

1998 model year vehicles in your SmartWay project fleet in 2005, NMIM will assume

twenty 1998 model year vehicles in any future year that you model). 

Unless you have reason to believe that all the trucks that are part of the SmartWay 

project would still be in the fleet by the calendar year that is being evaluated, reduce the 

input for number of vehicles appropriately. 

Example: Trucking Company A will install SmartWay aerodynamic fairings and 

low rolling resistance tires as described in Section 1.2 on 100 trucks in the year 

2007. Trucking Company A intends to sell half of these trucks to other trucking 

firms in 2010, and replace them with brand new model year 2010 trucks. 

Suppose the emissions estimates are needed for 2009 and 2015. For this 

SmartWay project, you would enter the following information in the Fleet 

Information Parameters File input file for Number of Vehicles: 

22 
Number of vehicles in 2009: 100 

Number of vehicles in 2015: 50 

2.7.2.4 Average annual mileage

The VMT entered for the specific fleet should be based on the activity that 

actually occurs within the nonattainment or maintenance area to which the SIP or 

conformity analysis applies. For a SmartWay project applied to a fleet of long-haul 

trucks, you must not include VMT that occurs outside the nonattainment or maintenance 

area. 

The activity level (VMT or hours of use) entered for the specific fleet should be 

based on the calendar year for which emission estimates are being calculated. When 

estimating emissions for a specific fleet in a current year, this is the current activity level 

of the fleet. However, in future years, the activity level of the affected vehicles in the 

fleet may change as older vehicles are often used less than newer ones. MOBILE6.2 

includes the effects of decreased activity with age when projecting future emissions for 

the entire fleet (e.g., MOBILE6.2 assumes that the activity of 1998 model year vehicles 

decreases in each future year). However, these effects are not applied to the activity 

levels entered in the fleet information file for a specific fleet (e.g., if your input file 

indicates that 1998 model year vehicles are driven 100,000 miles in 2005, NMIM will 

assume that 1998 model year vehicles are driven 100,000 miles in any future year that 

you model). Unless you have reason to believe that activity levels of vehicles currently 

in the specific fleet would not have changed by the calendar year that is being evaluated, 

you should account for this lowered activity by reducing the input for VMT or hours of 

use appropriately. 

Specific information on the VMT or hours of use of vehicles that are part of a 

SmartWay project may be available from maintenance records, user logs, or fuel records. 

In the absence of this kind of information, the interagency consultation process should be 

used to determine the best available information to account for activity in the calculation 

of emission reductions from a SmartWay project. In the absence of better information, 

agencies could agree to use local average estimates of vehicle VMT for the class and 

model year of vehicles included in the SmartWay project. 

23 
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24 
CHAPTER 3 

USING EMISSION REDUCTIONS IN SIPS

3.1 What are the basic requirements for using emission reductions in SIPs?

In order to be approved as a control measure that provides NOx emission 

reductions in a SIP, a SmartWay project would need to be consistent with SIP RFP, 

attainment, or maintenance requirements and other requirements of the Clean Air Act, as 

appropriate. The SmartWay project must provide emission reductions that meet the basic 

SIP requirements: 

• quantifiable,

• surplus, 

• federally enforceable, 

• permanent, and 

• adequately supported. 

These requirements are described below. You will notice information under both “SIP

Requirement” and “Specific Recommendations” headings. The “SIP Requirement” 

heading refers to requirements under Clean Air Act section 110 concerning SIPs that are 

mandatory. The “Specific Recommendations” headings include our recommendations 

for implementing a SmartWay project. While these recommendations are not binding, 

they may provide appropriate safeguards and considerations for a successful SmartWay 

project. 

3.1.1. Quantifiable - 

 SIP Requirement: The NOx emission reductions from a SmartWay project are 

quantifiable if they are measured in a reliable manner and can be replicated (e.g., the 

assumptions, methods, and results used to quantify emission reductions can be 

understood). NOx reductions must be calculated for the time period during which the 

reductions will occur and will be used for SIP purposes. 

Specific Recommendations: 

• In general, quantifying the NOx reductions from installing the SmartWay 

equipment described in Section 1.2 on trucks is fairly straightforward. You will 

need to document the NOx reductions by providing all relevant data to EPA for 

review. 

• Chapter 2 of this document provides you with EPA’s recommended method for 

quantifying NOx reductions from SmartWay projects. You can use this 

methodology or you can submit your own methodology. If you submit your own 

methodology, we will review it and make a decision as to its appropriateness on a 

25 
 case-by-case basis. If you choose to use an alternative method, we encourage 

you to engage the applicable EPA Region early. 

3.1.2 Surplus - 

SIP Requirement: Emission reductions are considered “surplus” if they are not 

otherwise relied on to meet other applicable air quality attainment or maintenance 

requirements for that particular NAAQS pollutant (i.e., there can be no double-counting 

of emission reductions). In the event that the SmartWay project is used to meet such air 

quality related program requirements, its NOx reductions are no longer surplus and may 

not be used as additional emission reductions. Emissions from the trucks that will be part 

of a SmartWay project must be in the applicable mobile source emissions inventory 

before the NOx reductions from that SmartWay project can be used for RFP, attainment 

or maintenance in a SIP. 

3.1.3 Federally Enforceable - 

SIP Requirement: A SIP SmartWay project must be enforceable, regardless of 

whether it is in the SIP as a voluntary measure or a mandatory one. However, the 

requirements for enforceability differ depending on whether the project is voluntary or

mandatory. 

Voluntary SmartWay projects. A voluntary SmartWay project is one that relies 

on voluntary actions of individuals or other parties for achieving emission reductions, 

rather than a required response to a state or local regulation. If your SmartWay project is 

a voluntary measure, it would be approved into the SIP under EPA’s VMEP guidance, 

and the state is responsible for assuring that the reductions quantified in the SIP occur. 

The state would need to make an enforceable SIP commitment to monitor, assess, and 

report on the emission reductions resulting from the voluntary measure and to remedy 

any shortfalls from forecasted emission reductions in a timely manner. Under the current 

VMEP guidance, the total of all voluntary mobile source measures (including SmartWay 

projects) may not exceed three percent of the total reductions needed to meet any 

requirements for RFP, attainment, or maintenance. EPA acknowledges that some areas 

may be able to demonstrate that voluntary measures may achieve credible reductions 

higher than the three percent cap provided by the VMEP guidance. In that case, EPA will 

re-evaluate that cap on a case-by-case basis and allow the cap to be exceeded if the cap

hinders the implementation of effective voluntary control measures, subject to notice and 

comment during SIP approval. If you wish to have a SmartWay project approved as a 

voluntary measure, consult the 1997 VMEP guidance for further information. 

Mandatory SmartWay projects. Where a control measure, such as a SmartWay 

project, is implemented as part of a rule or regulation for SIP purposes, it would be a 

mandatory measure. In this case, the SmartWay project would be considered federally 

enforceable only if it meets all of the following criteria: 

26 
• The emission reductions from the SmartWay project are independently verifiable. 

• Violations are defined, as appropriate. 

• You and EPA have the ability to enforce the measure if violations occur. 

• Those liable for violations can be identified. 

• Citizens have access to all the emissions-related information obtained from the 

responsible party. 

• Citizens can file lawsuits against the responsible party for violations. 

• Violations are practicably enforceable in accordance with EPA guidance on 

practicable enforceability. 

• A complete schedule to implement and enforce the project has been adopted by the 

implementing agency or agencies. 

If your SmartWay project is mandatory, then there is no cap on the amount of 

NOx emission reductions that can be claimed as long as such reductions are supported 

and meet standard SIP enforceability requirements for mandatory measures and the 

baseline emissions are in the inventory. 

3.1.4 Permanent - 

SIP Requirement: The NOx emission reductions produced by the SmartWay 

project must be permanent throughout the time period that the reductions are used in the 

applicable SIP. 

• For a voluntary SmartWay project, the state would need to commit to monitor, 

assess, and report on the emission reductions resulting from a truck owner’s 

voluntary application of SmartWay equipment. The emission reductions that 

result from a voluntary project are available only for the time covered by this 

commitment. For example, a state includes a voluntary SmartWay project in its 

SIP based on Trucking Firm A’s commitment to install SmartWay equipment 

described in Section 1.2 on 100 trucks in its fleet. Trucking Firm A is expected to 

own these trucks for five years. Precluding any other stipulations or 

commitments, the state can only include the emission reductions from this 

voluntary SmartWay project for the five years that Trucking Firm A is expected 

to have the trucks. The state commits to monitor these 100 trucks while they are 

owned by Trucking Firm A. Once Trucking Firm A sells these trucks to Trucking 

Firm B, their emission reductions can no longer be included in the SIP, unless 

additional commitments can be obtained. 

• For a mandatory SmartWay project, the time period that the emission reductions 

are used in the SIP can be no longer than the useful life of the trucks that are part 

of the SmartWay project, and may be less if the SmartWay equipment described 

in Section 1.2 is removed or not maintained over time. 

27 
Specific Recommendations: 

• As stated in Chapter 1, SmartWay projects will typically involve truck fleets 

operating over long distances and thus only part of their travel occurs in the 

nonattainment or maintenance area. NOx emission reductions claimed from

such SmartWay projects should be limited to the fleets’ activity (and the 

associated NOx emission reductions) expected to occur within the nonattainment 

or maintenance area, as well as those accounted for in the inventory. Refer to 

Sections 2.6 and 2.7.2.4 for more information. 

• If trucks that are part of a SmartWay project operate exclusively within the 

nonattainment or maintenance area, NOx reductions from these trucks may be 

entirely applied to that area. Trucks that typically operate within a captive area 

may include State/local government owned trucks. 

• For voluntary or mandatory SmartWay projects, you should demonstrate that the 

trucks outfitted with the SmartWay equipment described in Section 1.2 remain in 

use within the nonattainment or maintenance area for their useful life to the 

extent emission reductions are claimed. 

3.1.5 Adequately Supported - 

SIP Requirement: The state must demonstrate that it has adequate funding, 

personnel, implementation authority, and other resources to implement the SmartWay 

project on schedule. 

Specific Recommendations: 

• The state should ensure it has identified appropriate funds from a reliable funding 

source (e.g., a private trucking company submitting a letter to the state committing 

to install the SmartWay equipment described in Section 1.2 on a certain number of 

trucks). 

• The state should ensure that the truck fleet operators correctly install and maintain 

the SmartWay equipment described in Section 1.2 according to the kit and tire 

manufacturers’ recommendations. 

o Example: A private company has installed the SmartWay equipment 

described in Section 1.2 on 50 long-haul trucks. The state should ensure 

that such a company has staff that are properly trained to operate, 

maintain, and detect problems with the SmartWay equipment as 

appropriate. 

• The state should assess and verify the status of the implementation of SmartWay 

projects and the associated emission reductions, as applicable for the duration of 

the NOx reduction claimed. 

28 
3.2 How can the estimated NOx emission reductions be used for SIP purposes?

For your RFP, attainment, or maintenance SIP strategy, you can use NOx 

emission reductions that are expected to be generated from the SmartWay project by 

applying the following criteria: 

• NOx emission reductions would be calculated as required in the SIP process for a 

given pollutant and standard. 

o For example, NOx reductions from SmartWay projects would be 

calculated in an 8-hour ozone SIP for tons reduced per day for a typical 

summer day within the ozone season. 

o In contrast, NOx reductions would be calculated on a tons per year basis 

for SIP inventories for the annual PM2.5 standard; state and local agencies 

should consult on what typical day is appropriate for SIP inventories for 

the daily PM2.5 standard. 

• Any calculations would consider factors that may affect emission reductions and 

their surplus status over time, including changing patterns of operations or use, 

vehicle deterioration factors, SmartWay equipment useful life (i.e, useful life of 

the SmartWay aerodynamic fairings and low rolling resistance tires described in 

Section 1.2), and government emission standards. Note that if you use NMIM to 

quantify the NOx reduced from the project, government emission standards are 

automatically taken into account. Furthermore, NMIM gives you the opportunity 

to enter information to correctly account for other factors such as changes in the 

number and activity of the trucks in the affected fleet in the user input files. See 

Chapter 2 for more information about NMIM. 

• Emission reductions would be commensurate with the level of activity from

SmartWay project trucks within a given nonattainment or maintenance area as 

described in Question 3.1.4. For example, if SmartWay project trucks are operated 

partially within the nonattainment or maintenance area, the associated reductions 

from the SmartWay project would be limited to the activity that is expected to 

occur from such trucks within the nonattainment or maintenance area, as well as 

those accounted for in the inventory. 

3.3 What would a state submit to EPA to meet the requirements for 

incorporating a SmartWay project in a SIP?

You would submit to EPA a written document that: 

• Identifies and describes the SmartWay project, i.e., the number and type of trucks 

that will receive the SmartWay equipment described in Section 1.2, and the 

schedule on which the project will be implemented; 

29 
• Contains estimates of emission reductions attributable to the project, including the 

methodology and other technical support documentation used for your estimates. 

EPA recommends NMIM for assessing the emission reductions from SmartWay 

projects for SIP purposes. Please refer to Chapter 2 for detailed information about 

using NMIM for SmartWay projects. However, EPA acknowledges that 

alternative methods to NMIM are available and others may be developed. 

Alternative approaches will be reviewed by EPA on a case-by-case basis. Please 

provide EPA with all relevant technical support documentation, including the 

assumptions and other relevant information used to calculate emission reductions 

so EPA has the information necessary to make a decision. Also, any alternative 

approach must use the latest information as required by applicable SIP 

requirements; 

• Contains either: 

o an enforceable commitment for the state to monitor, assess and report the 

resulting emission reductions if the project is developed under the VMEP 

guidance; or 

o federally enforceable requirements for the state to implement, track, and 

monitor the project. 

• If the project is developed under the VMEP guidance, includes an enforceable 

commitment to remedy any SIP emission shortfall in a timely manner in the event 

that the project does not achieve the estimated emission reductions; and 

• Meets all other requirements for SIPs under Clean Air Act sections 110 and 172. 

3.4 What monitoring and record keeping should occur to document NOx 

emission reductions from SmartWay projects?

3.4.1 What should the state air agency monitor and record? 

Clean Air Act section 110(a)(2)(C) requires that submitted SIPs “include a 

program to provide for the enforcement of the measures” that the state adopts to reduce 

emissions. A state's decision about whether a measure needs to be enforced will depend 

on the state's knowledge of the emission reductions achieved by the measure. Therefore, 

this Clean Air Act requirement for a program that provides for enforcement makes it 

necessary for states to monitor measures that they include in their SIPs, including 

SmartWay projects. 

EPA recommends that for each truck outfitted with the SmartWay equipment 

described in Section 1.2 , the state air agency or another responsible party should monitor 

and record the following information, where applicable, for each time period for which 

an emission reduction is generated: 

30 
14 This guidance is found at: http://www.epa.gov/otaq/stateresources/policy/pag_guidance.htm. EPA notes 

that the VMEP guidance pertains to SIP measures, rather than transportation or general conformity

determinations. Control measures for conformity determinations must meet the relevant criteria in the 

transportation conformity regulation (40 CFR Parts 51 and 93).

• Actual use and operation of the truck; 

• Proper installation of the aerodynamic kit and low rolling resistance tires at project 

initiation; and 

• Proper training of truck operators and technicians at project initiation. 

Monitoring and recording these data is one way to ensure that the statute is met. A state 

can propose other methods of monitoring and recording data in its SIP submission, and 

EPA would consider whether or not it would be sufficient to meet Clean Air Act 

requirements. 

3.4.2 How long should the state air agency maintain records? 

Under 28 U.S.C. 2462, the government has five years to bring an enforcement 

action or suit for the failure to implement a measure in a SIP. Based on this statute of 

limitations, all information to be monitored and recorded in accordance with this 

guidance for existing SIP requirements should be maintained by the state air agency or 

another responsible party for a period of no less than five years, or longer where 

appropriate. 

3.5 What validation and reconciliation should occur for emission reductions in 

SIPs approved under the VMEP guidance?

The SIP submission for a voluntary measure should contain a description of the 

evaluation procedures and time frame(s) in which the evaluation of SIP reductions will 

take place. Once the voluntary control measure is in place, emission reductions should be 

evaluated by you as required to validate the actual emission reductions. You should 

submit the results of your evaluation to EPA in accordance with the schedule contained in 

the SIP. If the review indicates that the actual emission reductions are not consistent with 

the estimated emission reductions in the SIP, then the amount of emission reductions in 

the SIP should be adjusted appropriately or applicable remedial measures should be taken 

under the VMEP guidance. See EPA’s VMEP guidance for further information 

regarding validation and reconciliation requirements for such measures.

14

3.6 What penalties can EPA impose for not complying with Clean Air Act 

requirements?

Use of this guidance does not relieve you of any obligation to comply with all 

otherwise applicable Clean Air Act requirements, including those obligations pertaining 

to the use of emission reductions in your SIP, such as emission reductions for your 

31 
attainment demonstration or maintenance plan. Violations of Clean Air Act requirements 

are subject to administrative, civil, and/or criminal enforcement under Clean Air Act 

section 113, as well as to citizen suits under Clean Air Act section 304. The full range of 

penalty and injunctive relief options would be available to the federal or state government 

(or citizens) bringing the enforcement action. 

32 
15 Note that in a PM2.5 area, transportation conformity applies with respect to NOx unless both

EPA and the state find it is not a significant contributor and the SIP does not include a NOx motor vehicle 

emissions budget. In a PM10 nonattainment or maintenance area, transportation conformity applies with

respect to NOx only if either the EPA or the state air agency has made a finding that this precursor is a

significant contributor to the PM10 nonattainment problem or if the SIP includes a NOx budget. See 40

CFR 93.102(b)(2) for details. 16 In areas without SIP budgets, an interim emissions test(s) must be met. These tests are the 

“baseline year test” and the “build/no-build test.” See 40 CFR 93.109, 93.118, and 93.119 for specific 

requirements in various types of nonattainment and maintenance areas. 

CHAPTER 4

USING EMISSION REDUCTIONS IN 

TRANSPORTATION CONFORMITY DETERMINATIONS

4.1 What is transportation conformity?

Transportation conformity is required under Clean Air Act section 176(c) (42 

U.S.C. 7506(c)) to ensure that federally supported highway and transit project activities 

are consistent with (“conform to”) the purpose of the SIP. Conformity to the purpose of 

the SIP means that transportation activities will not cause new air quality violations, 

worsen existing violations, or delay timely attainment of the relevant national ambient air 

quality standards (NAAQS or “standards”). EPA’s transportation conformity rule (40 

CFR Parts 51 and 93) establishes the criteria and procedures for determining whether 

transportation plans, transportation improvement programs (TIPs) and projects conform

to the SIP. Transportation conformity applies to areas that are designated nonattainment, 

and those redesignated to attainment after 1990 (“maintenance areas” with SIPs 

developed under Clean Air Act section 175A) for transportation-related criteria 

pollutants. Some areas that are currently subject to transportation conformity could 

benefit from NOx reductions that result from SmartWay projects, including 8-hour 

ozone, PM2.5, and PM10 nonattainment and maintenance areas.15

In urban areas, transportation planning and conformity determinations are the 

responsibility of the metropolitan planning organization (MPO). MPOs are responsible 

for updating and revising the transportation plan and TIP on a periodic basis, as well as 

making transportation plan and TIP conformity determinations. Such a determination 

includes a regional emissions analysis that shows that the emissions expected from the 

area’s planned transportation system do not exceed the motor vehicle emissions target 

(“budgets”) set by the SIP for meeting RFP, attainment, or maintenance requirements. In 

cases where an area does not yet have a SIP in place, a different type of emissions test

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is used for conformity. After an MPO’s conformity determination, the U.S. Department 

of Transportation (DOT) must also determine conformity of the transportation plan 

and/or TIP. The interagency consultation process is required to be used when developing 

transportation plans, TIPs, conformity determinations, and SIPs, and the process includes 

MPOs, state departments of transportation, public transit agencies, other transportation 

agencies, state and local air quality agencies, EPA, and DOT (40 CFR 93.105). 

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17 See 40 CFR 93.122(a) for the requirements regarding what must be included when estimating 

regional emissions in a conformity determination. 

18 40 CFR 93.118 describes the process and criteria that EPA considers when determining whether

submitted SIP budgets are appropriate for transportation conformity purposes prior to EPA’s SIP approval 

action. 

4.2 How can NOx emission reductions from SmartWay projects be included in 

transportation conformity determinations?

The transportation conformity rule describes the specific requirements for 

including emission reductions from projects in a transportation conformity determination. 

If the emission reductions from the SmartWay project have been accounted for in the 

SIP’s budget, the MPO would also include the reductions from the SmartWay project, to 

the extent it is being implemented, when estimating regional emissions for a conformity 

determination. Including the emission reductions in both the SIP’s budget and in a 

conformity determination in this way is not “double-counting,” but rather correctly 

accounting for all the control measures that are in place in both the SIP and transportation 

conformity processes.17

To include NOx emission reductions from SmartWay projects in a regional 

emissions analysis, the appropriate jurisdictions must be committed to the measure. The 

appropriate level of commitment varies according to the requirements outlined in 40 CFR 

93.122(a), which are described as follows: 

• If the SmartWay project does not require a regulatory action to be implemented 

and it is included in the transportation plan and TIP with sufficient funding and 

other resources for its full implementation, it can be included in a transportation 

conformity determination. 

• If the SmartWay project requires a regulatory action to be implemented, it can be 

included in a conformity determination if one of the following has occurred: 

o The regulatory action for the SmartWay project is already adopted by the 

enforcing jurisdiction (e.g., a state has adopted a rule to require such a 

project); 

o The SmartWay project has been included in an approved SIP; or 

o There is a written commitment to implement the SmartWay project in a 

submitted SIP with a motor vehicle emissions budget that EPA has found 

adequate.18

• If the SmartWay project is not included in the transportation plan and TIP or the 

SIP, and it does not require a regulatory action to be implemented, then it can be 

included in the transportation conformity determination’s regional emissions 

analysis if the determination contains a written commitment from the appropriate 

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entities to implement the project. An example of a SmartWay project that would 

not be included in the transportation plan and TIP would be a state-sponsored loan 

or grant program to install SmartWay equipment described in Section 1.2 on local 

truck fleets. 

Whatever the case, any NOx emission reductions can only be applied in a 

transportation conformity determination for the time period or years in which the 

SmartWay project will be implemented. Written commitments must come from the 

agency with the authority to implement the SmartWay project (as required by 40 CFR 

93.122(a)(4) and 93.101). 

For example, an MPO includes a SmartWay project in its emissions estimates 

done for a transportation conformity determination based on Trucking Firm A’s 

written commitment to install SmartWay equipment described in Section 1.2 on 

100 trucks in its fleet in the year 2008. Trucking Company A’s written 

commitment indicates that these 100 trucks will be sold and replaced with brand 

new trucks during the years 2011 - 2015. 

Suppose the MPO determines conformity in the year 2008, and it determines that 

it needs to analyze emissions for the attainment year of 2010, the last year of the 

transportation plan of 2030, and 2020 (an intermediate year). Based on the 

written commitment from Trucking Firm A, the MPO would enter the following 

information in the Fleet Information Parameters File input file for Number of

Vehicles: 

Number of vehicles in 2010: 100 

Number of vehicles in 2020: 0 

Number of vehicles in 2030: 0 

Note that in future conformity determinations, the MPO could include the 

emission reductions from these trucks after they are sold if it can obtain similar 

written commitments from the new owners of the SmartWay trucks. 

The latest emissions model and planning assumptions must also be used when calculating 

emission reductions, according to 40 CFR 93.110 and 93.111. 

You would utilize the interagency consultation process required by 40 CFR 

93.105 to discuss the methods and assumptions used to quantify the NOx reductions from

the SmartWay project. Chapter 2 of this document describes how to quantify emission 

reductions. 

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