Performance Standard Modeling for 

New and Existing Vehicle Inspection 

and Maintenance (I/M) Programs Using 

the MOVES Mobile Source Emissions 

Model 
Transportation and Climate Division

Office of Transportation and Air Quality

U.S. Environmental Protection Agency

Performance Standard Modeling for 

New and Existing Vehicle Inspection 

and Maintenance (I/M) Programs Using 

the MOVES Mobile Source Emissions 

Model 

EPA-420-B-13-059

November 2013
Page 1

Performance Standard Modeling for New and Existing Vehicle Inspection and 

Maintenance (I/M) Programs Using the MOVES Mobile Source Emissions Model 

1.0 Does this guidance create any new requirements?

This guidance does not create any new requirements, but was instead developed by the 

U.S. Environmental Protection Agency’s (US EPA) Office of Transportation and Air Quality 

(OTAQ) for use by EPA’s Regional Offices, state and local air agencies, and other stakeholders 

in the vehicle inspection and maintenance (I/M) community interested in modeling the impacts 

of I/M program design on the mobile source inventory for the development of I/M State 

Implementation Plans (SIPs) and/or other purposes. The legally binding requirements for 

vehicle I/M programs can be found in Clean Air Act (CAA) sections 182 (a-c), 184(b), and 187 

(a-b) and in the I/M rule (40 CFR Part 51, subpart S). This policy document does not substitute 

for those provisions or regulations, nor is it a regulation itself. Thus, it does not impose binding, 

enforceable requirements on any party, and may not be applicable in all situations. EPA and 

State decision makers retain the discretion to adopt approaches for approval of State 

Implementation Plan (SIP) measures like I/M that differ from this guidance where appropriate 

and consistent with applicable law and regulations. Any final decisions by EPA regarding a 

particular SIP measure will only be made based on the statute and regulations in the context of 

EPA notice and comment rulemaking on a submitted SIP revision. This guidance may be 

revised periodically without public notice. 

2.0 A Brief History Of The I/M Performance Standards

Since the early 1980’s, vehicle I/M programs have been used as an air quality control 

strategy in certain areas1 of the United States found to be violating the National Ambient Air 

Quality Standards (NAAQS) for either ozone, carbon monoxide (CO), or both. I/M programs 

help improve air quality by identifying high emitting vehicles in the in-use fleet and causing 

them to be repaired. A high emitting vehicle is one which is emitting at some increment above 

the standard to which it was certified, either 2-3 times the standard for vehicles being tailpipe 

tested, or 1.5 times the standard for vehicles equipped with onboard diagnostic (OBD) systems 

and subject to the OBD test. 

Early I/M programs varied widely based upon the tests performed, the design of the 

testing network, the level of enforcement against motorists and test stations, and overall program 

effectiveness. As a result, in 1990, the CAA was amended to – among other things – formalize 

the minimum program requirements for mandatory I/M programs. As part of this effort, the 

1990 CAA established two types of I/M programs: basic I/M for certain moderate ozone and/or 

CO nonattainment areas and enhanced I/M for certain serious or worse nonattainment areas, as 

well as certain areas located within the North East Ozone Transport Region (OTR) regardless of 

attainment status. Among its I/M provisions, the CAA required the US EPA to establish 

 

1 See Appendix E of this guidance document for a complete discussion of the criteria for determining whether a 

given area is required to adopt an I/M program.
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performance standards that mandatory I/M programs had to either meet or exceed in terms of the 

emission reductions they achieved. 

EPA first promulgated performance standards for basic and enhanced I/M programs in 

November 1992 as part of the original I/M rule. The I/M performance standards have been 

revised several times since to provide areas greater flexibility to design I/M programs that meet 

local needs and also to address the change from the original 1-hour ozone standard to an 8-hour 

ozone standard. The last time the I/M performance standards were revised was in April 2006 to 

address I/M programs newly required under the original and subsequent 8-hour ozone standards. 

Until recently, I/M performance standard modeling was performed using the MOBILE 

series of emission factor models. With the exception of California (which uses the EMFAC 

model developed specifically for that state), all other I/M programs currently in operation in the 

United States were developed using one of the versions of the MOBILE model to determine 

whether they met the applicable performance standard as part of developing their I/M SIPs. 

To meet its own regulatory needs and the needs of states for greater analytical capability 

in SIP and transportation planning development, in December 2009, EPA released its next 

generation of mobile source emission factor model – known as the MOtor Vehicle Emission 

Simulator or MOVES model – to replace the MOBILE model. Any new or existing I/M 

program needing to do I/M performance standard modeling or needing to assess the SIP impacts 

of revisions to an I/M program now or in the foreseeable future will be required to use a version 

of the MOVES model, with the possible exception of California for the reason stated above. 

Readers interested in more information on the history, uses, and development of the MOVES 

model can find it online at the following web address: 

http://www.epa.gov/otaq/models/moves/index.htm 

3.0 How Were the I/M Performance Standards Established?

States new to I/M must demonstrate their program’s ability to meet the relevant 

performance standard when the program is first proposed as part of the I/M SIP. Existing I/M 

program areas which have not been redesignated to attainment must also do performance 

standard modeling whenever they revise their I/M SIP in a way that is likely to change the level 

of emission reductions achieved by the program. 

Historically, EPA’s approach to establishing minimum performance standards for basic 

and enhanced I/M has involved publishing a list of program parameters for each performance 

standard in the Federal Register as part of the larger I/M rule. These program parameters tend to 

be those that impact the amount of reductions a program is projected to achieve and include: test 

frequency, test type, test standards, vehicle model year and vehicle type coverage, compliance 

rate, waiver rate, etc. To determine whether a state’s proposed program is projected to meet or 

exceed the relevant performance standard, the state needs to perform three modeling scenarios: a 

no-I/M case, the proposed program, and the applicable I/M performance standard. These 

modeling scenarios are to be performed using the most recently required mobile source emission 
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factor model along with other locally variable parameters, such as the age distribution of the 

local in-use fleet, average ambient temperature, the distribution of vehicle miles travelled 

(VMT), average speed, etc. The proposed program and performance standard scenarios are 

compared to the no-I/M case to determine the percent reduction produced by the proposed 

program and the applicable performance standard, respectively. If the proposed program is 

projected to achieve the same or greater percent reductions in hydrocarbons (HC), oxides of 

nitrogen (NOx), and/or carbon monoxide (CO) as would be achieved by the performance 

standard, then the proposed program is considered to have met the performance standard and is 

one step closer to being deemed approvable. 

4.0 Can an I/M Program be Changed Without Doing Performance Standard Modeling?

States can change their I/M programs without doing performance standard modeling if 

the I/M program area in question has been redesignated to attainment for the pollutant(s) that 

originally triggered the I/M requirement and the I/M program is being continued as part of the 

area’s maintenance plan. In this case, the state must simply demonstrate that the revisions to the 

I/M program will not interfere with the area’s ability to attain or maintain any NAAQS, or with 

any other applicable CAA requirement. One means of making this demonstration is by 

quantifying the difference in emission reductions between the original program and the proposed 

program and offsetting any shortfall through new, previously unclaimed and contemporaneous 

emission reductions. The shortfall can be quantified in much the same way that the program 

demonstrates that it meets the performance standard: by modeling the original and proposed 

programs using the most recently approved mobile source emission factor model, which is 

currently the MOVES model2. 

It should be noted that areas seeking to drop tailpipe testing in favor of OBD-only testing 

without strengthening the program in some other way (for example, by changing the test 

frequency from biennial to annual, or covering more of the newer model years) will necessarily 

create a shortfall that will either have to be filled with reductions from non-I/M control measures 

for the SIP to remain whole, or the program will need to make a demonstration (for example, by 

using photochemical grid modeling) showing that the shortfall does not prevent the area from 

maintaining the NAAQS for which the program was required. The program will also need to 

demonstrate that the shortfall will not interfere with the area’s ability to meet any other relevant 

NAAQS.

5.0 Why is EPA Issuing this Guidance Now?

As noted above, in December 2009, EPA released its next generation of mobile source 

emission factor model, MOVES, to replace the MOBILE model. Like MOBILE, MOVES is 

intended to be used for several different purposes, from the development of federal regulations 

 

2 In addition to using the most recently approved mobile source emission model, areas seeking approval for I/M 

program revisions also need to update program inputs that may have changed since the last time the program was 

modeled, including replacing projected rates for compliance, waivers, etc., with numbers based upon actual 

operating program data.
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related to mobile sources to the development by states of their individual mobile source SIPs. 

Although the two models were originally designed with similar purposes in mind, nevertheless 

there are significant differences between the two. This is especially true when it comes to how 

various elements of the I/M performance standards are addressed. Because of these differences – 

and because the use of the MOBILE model is no longer accepted for performance standard 

modeling – EPA believes this guidance is needed, especially by users familiar with the previous 

MOBILE model who may be confused by the change in approach to performance standard 

modeling taken by MOVES versus MOBILE. 

While all areas required to implement an I/M program under the CAA are currently doing 

so, this guidance is nevertheless timely for at least two reasons: 

1) As the majority of the in-use fleet turns over to vehicles equipped with onboard 

diagnostic (OBD) technology, many existing I/M program areas may seek to 

revise their programs to achieve greater efficiencies at lower costs; and 

2) As the current ozone standard is revised (as it was in 2008) areas previously 

exempt from the I/M requirement may be required to adopt such programs for the 

first time. 

In either of the above events, the I/M areas – whether new or existing – will be required to 

demonstrate that their new or revised programs will meet the applicable CAA requirements. 

This demonstration will require modeling to demonstrate the program meets the relevant I/M 

performance standard or to quantify how proposed program changes will impact the emission 

reductions achieved by the existing program. This guidance will discuss how I/M programs are 

to be modeled using MOVES, including how to perform the relevant performance standard 

modeling. The guidance will also address which type of modeling demonstration is required 

under various scenarios. 

6.0 The Fundamentals of Performance Standard Modeling

When modeling any of the I/M performance standards, it is necessary to perform a 

minimum of three modeling runs. These include: 

1) A no-I/M run which includes all the required local area parameters and control

measures with the exception of an I/M program; 

2) The proposed program run which includes all the local area parameters and 

control measures as well as the sequence of inputs required to define the proposed 

program; and 

3) The performance standard run which includes all the local area parameters and 

control measures and an I/M program including all the program elements of the 

required I/M performance standard. 

By comparing both the proposed program results and the performance standard results to the no 

I/M case, the state can estimate the emission reductions projected to be achieved by the two 

different cases as a percent reduction relative to no I/M. For a basic I/M program, if the 
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proposed program achieves the same or greater emission reductions as does the performance 

standard program, then the proposed program is considered to have “met” the performance 

standard and that portion of the state’s I/M SIP is therefore approvable3

. In the case of an 

enhanced I/M program, if the proposed program’s net reductions are within 0.02 grams-per-mile

(gpm) of the reductions achieved by the relevant performance standard for hydrocarbons (HC) 

and/or oxides of nitrogen (NOx), it is considered to have met the applicable performance 

standard4

. 

7.0 Which Performance Standard Should be Used?

As stated above, outside of maintenance areas, all new I/M programs and existing I/M 

programs undergoing revision must include I/M performance standard modeling as part of their 

I/M SIP or I/M SIP revision. Sections 51.351 and 51.352 of the I/M rule include numerous 

iterations of the I/M performance standards for basic and enhanced I/M programs. The reason 

for this variety is twofold: 1) to provide I/M program areas greater flexibility in designing their 

I/M programs as warranted by the relative severity of the air quality issue being addressed; and 

2) to address revisions to the ozone NAAQS. The modeling requirements vary depending on 

whether the non-attainment area in question has an existing I/M program or, if it does not, 

whether it meets the other triggering requirements for a mandatory I/M program, such as being 

classified as moderate or worse nonattainment for ozone, or being located within the Ozone 

Transport Region (OTR), regardless of attainment status5

. Below, we discuss the I/M modeling 

requirements for new and existing non-attainment areas.

7.1 I/M Modeling Requirements for New Non-attainment Areas

Certain areas of the country that do not currently have an I/M program may be required to 

adopt such a program in the future if the area is found to meet certain criteria. The first of these 

is that the area must be designated non-attainment for the most recent 8-hour ozone standard, and 

must also be classified as moderate non-attainment or worse. If the area is classified as moderate 

non-attainment for the 8-hour standard (and is not part of a multi-state non-attainment area) then 

the area must also have an urbanized population of at least 200,000 or more based upon the 1990 

U.S. Census. If the new ozone non-attainment area is classified as serious or worse nonattainment for the 8-hour ozone standard (and is not part of a multi-state non-attainment area) 

 

3 Meeting the relevant performance standard is not the only hurdle to be cleared when revising an existing I/M 

program. Areas will also need to consider the section 110(l) anti-backsliding provisions of the Clean Air Act 

although any shortfall resulting from revising the I/M program does not need to be made up by the program. Such 

shortfalls can be made up by new, previously uncredited emission reductions from other control measures. 4 The 0.02 gpm enhanced performance standard buffer applies to pollutants separately, not cumulatively. Therefore, 

a program that came within 0.02 gpm for HC and 0.02 gpm for NOx would be considered to meet the performance 

standard while one which met or exceeded the performance standard reductions for HC while falling short of the 

NOx reductions by 0.03 gpm or more would not. 

5 Classification as moderate non-attainment for ozone and/or an area’s location within the OTR do not, in and of 

themselves, automatically trigger the I/M requirement. Such areas also need to meet minimum population 

thresholds before I/M is required. These population levels vary, depending upon whether the area in question is 

subject to basic, enhanced, or OTR enhanced I/M, as discussed elsewhere in this guidance.
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then the area must also have an urbanized population of at least 200,000 or more based upon the 

1980 U.S. Census6. 

As part of designing an approvable I/M program, the State must demonstrate that the 

proposed program will meet or exceed the applicable I/M performance standard. 

For areas classified as moderate non-attainment for an 8-hour ozone standard, the 

applicable I/M performance standard consists of the following elements under 40 CFR 

51.352(e): 

(1) Network type. Centralized testing.

(2) Start date. 4 years after the effective date of designation and classification under the 

8-hour ozone standard. 

(3) Test frequency. Annual testing.

(4) Model year coverage. Testing of model year 1968 and newer vehicles. 

(5) Vehicle type coverage. Light duty vehicles. 

(6) Emission test type. Idle testing for model year 1968–2000 vehicles; onboard 

diagnostic checks on model year 2001 and newer vehicles.

(7) Emission standards. Those specified in 40 CFR part 85, subpart W. 

(8) Emission control device inspections. None. 

(9) Evaporative system function checks. None, with the exception of those performed by 

the OBD system on vehicles so-equipped and only for model year 2001 and newer 

vehicles.

(10) Stringency. A 20% emission test failure rate among pre-1981 model year vehicles. 

(11) Waiver rate. A 0% waiver rate, as a percentage of failed vehicles.

(12) Compliance rate. A 100% compliance rate.

(13) Evaluation date. Newly required basic I/M programs shall be shown to obtain the 

same or lower emission levels as the model program described above by an evaluation 

 

6 The CAA also includes I/M requirements for metropolitan statistical areas (MSAs) within the OTR with 

populations of 100,000 or more, regardless of attainment status for ozone. It is not likely that any area in the OTR 

would be newly required to adopt an I/M program based upon classification under a new or subsequent ozone 

standard because the enhanced I/M requirement for the OTR is tied to population threshold only, and not to 

attainment status. It is possible, however, that an existing OTR I/M program might need to be upgraded if its status 

changed from attainment to serious or worse nonattainment for ozone.
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date set 6 years after the effective date of designation and classification under the 8-hour 

ozone standard for the applicable ozone precursor(s). 

For 8-hour non-attainment areas classified as serious or above, the applicable 

performance standard consists of the following elements under 40 CFR 51.351(i): 

(1) Network type. Centralized testing.

(2) Start date. 4 years after the effective date of designation and classification under the 

8-hour ozone standard. 

(3) Test frequency. Annual testing.

(4) Model year coverage. Testing of model year 1968 and newer vehicles. 

(5) Vehicle type coverage. Light duty vehicles, and light duty trucks, rated up to 8,500 

pounds GVWR. 

(6) Emission test type. Idle testing for model year 1968–2000 vehicles; onboard 

diagnostic checks on model year 2001 and newer vehicles.

(7) Emission standards. Those specified in 40 CFR part 85, subpart W. 

(8) Emission control device inspections. Visual inspection of the positive crankcase 

ventilation valve on all 1968 through 1971 model year vehicles, inclusive, and of the 

exhaust gas recirculation valve on all 1972 and newer model year vehicles.

(9) Evaporative system function checks. None, with the exception of those performed by 

the OBD system on vehicles so-equipped and only for model year 2001 and newer 

vehicles.

(10) Stringency. A 20% emission test failure rate among pre-1981 model year vehicles. 

(11) Waiver rate. A 3% waiver rate, as a percentage of failed vehicles.

(12) Compliance rate. A 96% compliance rate.

(13) Evaluation date. Newly required enhanced I/M programs shall be shown to obtain 

the same or lower emission levels for HC and NOX as the model program described 

above assuming an evaluation date set 6 years after the effective date of designation and 

classification under the 8-hour ozone standard to within 0.020 grams-per-mile (gpm) of 

the performance standard expressed as a gpm benefit relative to no I/M. Subject programs 

shall demonstrate through modeling the ability to maintain this percent level of emission 

reduction (or better) through their applicable attainment date for the 8-hour ozone 

standard. 
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7.2 I/M Modeling Requirements for Existing Non-attainment Areas

All existing I/M program areas are either: 1) located in the OTR, regardless of attainment 

status; 2) maintenance for carbon monoxide and/or ozone; or 3) they are non-attainment for one 

or more 8-hour ozone standards. As discussed previously, I/M programs in maintenance areas 

do not need to perform performance standard modeling as part of revising their I/M SIP. Instead, 

the program must demonstrate that any potential shortfall created by the change does not 

adversely affect an area’s ability to attain or maintain any applicable NAAQS or to meet any 

other relevant CAA requirement. To revise an existing I/M program in a current nonattainment 

area, the program must make the same non-interference demonstration as required of an I/M 

program in a maintenance area undergoing similar changes, but must also demonstrate that the 

revised program will continue to meet the applicable 8-hour ozone I/M performance standard(s). 

For areas classified as moderate non-attainment for an 8-hour ozone standard, the I/M 

performance standard consists of the program elements identified under 40 CFR 51.352(e) (see 

section 6.1 above for the complete list). For 8-hour non-attainment areas classified as serious or 

above, the applicable performance standard consists of the program elements identified under 40 

CFR 51.351(i), which are also listed above, in section 6.1. 

8.0 How do the I/M Input Parameters for MOVES Compare to Those for MOBILE?

While the performance standards for existing and newly required I/M programs have not 

changed since areas were designated and classified under the 1997 8-hour ozone standard, the 

model used for performing those performance standard demonstrations has changed 

significantly. In particular, the way that I/M programs are modeled has been simplified with the 

elimination of some and the consolidation of other program parameters previously used with 

earlier versions of EPA’s mobile source emission factor model. State modelers familiar with the 

MOBILE series of emission factor models as well as first-time modelers trying to follow the text 

of the performance standards described above may notice that some modeling parameters called 

for in the performance standards are no longer needed to model an I/M program or its associated 

performance standard. These input parameters have been eliminated as part of EPA’s effort to 

streamline and simplify the I/M modeling process and the reasons for doing so are discussed in 

detail below. 

In addition to streamlining the input parameters required to model an I/M program, 

another difference between the MOBILE model and MOVES that modelers may notice is the 

way in which the model’s outputs are expressed. While the MOBILE model’s outputs were 

generally expressed as an average gram-per-mile emission factor, MOVES has the option of 

producing outputs as either the total mass of emissions over a particular time period (known in 

MOVES as the “inventory “calculation type) or as an emission rate in grams per mile for running 

emissions, but in grams per vehicle for start and evaporative emissions (known in MOVES as the 

“emission rates” calculation type). Neither of these output options is exactly equivalent to the 

gram-per-mile emission factors produced by MOBILE. 

While this difference between the two models doesn’t matter when it comes to comparing 

a program to the basic performance standard it is an issue when it comes to comparing a 
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proposed program to the enhanced performance standard. This is because the enhanced 

performance standard includes an optional buffer, so that an area that comes within 0.020 gramsper-mile of the performance standard is considered to have met that standard. Areas that fall 

slightly short of meeting the enhanced I/M performance standard under MOVES may still take 

advantage of this buffer by converting MOVES’ mass-over-time inventory output to the 

equivalent in grams per mile by using the script EPA has provided with MOVES that 

automatically converts MOVES inventory output to the equivalent in grams per mile7. The 

script needed to do this is called “EmissionRates.sql” and can be run using the “Run MySQL 

Script on Output Database” option in the Post Processing menu in MOVES. Once the outputs 

for the no I/M case, the performance standard, and the proposed program have been converted to 

gram-per-mile emission factors, the gram-per-mile reduction from the I/M runs can be derived 

by subtracting the I/M emission factor from the no-I/M emission factor. After that, the 0.020 

gpm buffer can be applied as was done under the MOBILE model. 

To aid potential new and existing I/M program areas in developing their I/M performance 

standard runs, EPA is providing default templates for both the basic and enhanced I/M 

performance standards for use by the states with the MOVES emission factor model. These 

templates can be found as tables in Appendix A, and are also available as Excel spreadsheets, 

which are included with the electronic version of this guidance and are also available online at: 

http://www.epa.gov/otaq/epg/techguid.htm. 

In the sections that follow, we will discuss the current status of each I/M performance 

standard input parameter, including whether or not it is still required to model I/M under the 

MOVES model, and if not, why. 

8.1 Network Type

Network type is no longer part of modeling an I/M program because the difference 

between centralized and decentralized programs has become insignificant. This is because 

centralized test information databases allow programs to monitor all test stations at once – 

effectively centralizing program oversight. Also, the introduction of onboard diagnostic (OBD) 

testing technology – which is currently replacing traditional tailpipe testing in many areas – has 

allowed for several sophisticated enforcement methods that have helped investigators to identify 

and protect against vulnerabilities that previously distinguished centralized versus decentralized 

programs. 

8.2 Start Date

Given that the attainment dates for all I/M programs assume that programs will be fully 

implemented at least one full inspection cycle prior to the attainment date, the need for inputting 

the start date is effectively moot. As a result, the input parameter for start date previously 

 

7 MOVES emission rates output cannot be used for this purpose because there is no simple way to convert gramsper-vehicle output for starts and evaporative emissions to grams per mile.
Page 10

available in the MOBILE model was removed as part of the general effort to streamline the 

number of required I/M inputs needed to run MOVES. 

8.3 Test Frequency

MOVES allows users to enter either annual (1) or biennial (2) test frequency under the 

template column named “inspectFreq,” which is short for “inspection frequency.” 

8.4 Model Year Coverage

The MOVES I/M performance standard templates address model year coverage with 

columns for the first and last model years covered relative to the evaluation year. MOVES uses 

these two columns (i.e., “begModelYearID” and “endModelYearID”) to specify the beginning 

and ending model years affected by a particular portion of the I/M program. 

8.5 Compliance Rates, Waiver Rates, and Vehicle Types

MOVES uses the compliance factor input (“complianceFactor”) to account for I/M 

program compliance rates, waiver rates, and adjustments needed to account for the fraction of 

vehicles within a source type that are covered by the I/M program. The last will be referred to 

here as the “regulatory class coverage adjustment.” The compliance factor is entered as a 

number from 0 to 100 and represents the percentage of vehicles within a source type that actually 

receive the benefits of the program. Since all three components of the compliance factor are 

calculated as multiplicative factors, the total compliance factor entered in MOVES2010 is 

calculated as:

Compliance Factor = percent compliance rate x (100 - percent waiver rate) x regulatory class 

coverage adjustment 

Appendix C provides a sample adjustment calculation using compliance rate, waiver rate, 

and regulatory class coverage to arrive at a single percent compliance factor (see template 

column heading, “complianceFactor”). The terms “compliance rate,” “waiver rate,” and “vehicle 

type adjustment” are discussed in more detail below.

8.5.1 Compliance Rate

The compliance rate is the percentage of vehicles in the fleet covered by the I/M program 

that complete the I/M program and receive either a certificate of compliance or a waiver. 

Historical compliance should be determined by sticker surveys, license plate surveys, or a 

comparison of the number of final tests to the number of vehicles subject to the I/M requirement. 

Planners should not assume a compliance rate of 100%. An area planning to implement an I/M 

program using a registration denial system that automatically generates compliance documents 
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that uniquely identify the complying vehicle and that are serially numbered, accounted for, and 

subject to centralized processing by government clerks with management oversight may assume 

a 96% compliance rate for modeling purposes prior to program implementation. Once the 

program begins implementation, however, the compliance rate should be based on operating 

program data. 

8.5.2 Waiver Rate

The waiver rate is the percentage of vehicles that fail an initial I/M test and do not pass a 

retest, but instead receive a certificate of compliance via a waiver. Actual historical waiver rates 

should be used as the basis for estimating future waiver rates. Because the Compliance Factor in 

MOVES is a measure of the percentage of vehicles registered in the modeling domain that 

actually receive an I/M benefit, the percentage of vehicles that are not waived (i.e., 100 - percent 

waiver rate) is used as one input when calculating the compliance factor.

8.5.3 Vehicle Type Adjustment

I/M programs entered in MOVES can only be applied to across entire source types. It 

should be noted, however, that MOVES’s source types are composed of several vehicle weight 

classes, some of which may be subject to I/M in a given area while others are exempt. Therefore 

applying I/M benefits to the entire MOVES source type may not always be appropriate. To 

account for this, a table of adjustment factors has been included in Appendix B which can be 

used to adjust the compliance factor to account for the portion of a given source type that is 

subject to I/M. The adjustments in Appendix B are percentages of Vehicle Miles Traveled 

(VMT) by the various regulatory weight classes within the various source types. After reviewing 

the table, users should sum the adjustments for weight classes within a source type that are 

covered by an I/M program. This sum provides users with a multiplicative factor that can be 

applied along with the compliance rate and waiver rate discussed above. Users who believe 

regional regulatory class coverage adjustments are more appropriate than the defaults provided in 

Appendix B should provide documentation in the SIP or regional conformity analysis of the local 

data and methods used to derive those adjustments. 

8.6 Emission Test Type and Emission Standards

In the MOBILE model, the need to input a series of emission standards or cutpoints for 

the various I/M test types was gradually reduced until only the IM240 required a separate input 

for emissions standards. For the other test types, like the idle or the Acceleration Simulation 

Mode (ASM) tests, the cutpoints were essentially hardwired into the model. With MOVES, this 

process of phasing out the cutpoint input has been completed. Users need only select the 

appropriate test type and the model will automatically apply the relevant standard. 

MOVES allows users to choose among 13 exhaust emissions tests and 7 evaporative 

emissions tests. The MOVES inputs for these tests can be found in Appendix D. In the I/M 
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performance standard template, emission test type is entered under the column headed 

“testStandardsID.” These test types include the MOBILE I/M input parameter for evaporative 

system functional checks but do not include emission control device inspections, which are 

discussed below. 

8.7 Emission Control Device Inspections

While the last version of the MOBILE model included a modest amount of credit for 

some of the eight potential emission control device inspections (also known as anti-tampering or 

ATP checks) that programs have used historically, most such checks received little if any credit. 

As a general matter, the trend over the course of the MOBILE model’s existence was for 

tampering checks to get progressively less credit, either because the checks were too difficult to 

perform correctly in the field or because the kind of tampering gradually became irrelevant. For 

example, testing for misfueling is no longer necessary as a result of the phase-out of leaded fuel. 

Tampering checks were finally removed from MOVES as a logical progression of the 

downgrading of tampering credits that had been going on in the MOBILE model through 

MOBILE6.2. Also, as a practical matter, tampering inspections are becoming increasingly 

redundant as OBD-equipped vehicles come to dominate the in-use fleet. This is because the 

most common forms of tampering – like catalyst removal – are easily detected by the OBD 

system, which will cause the “Check Engine” light to illuminate, which in turn will result in the 

vehicle in question failing its I/M test.

8.8 I/M Stringency

The “I/M stringency” input parameter was used to allow users of earlier iterations of the 

MOBILE model to input the failure rate among pre-1981 model year vehicles. As the model 

evolved (and fleets turned over to the point where pre-1981 model year vehicles became an 

insignificant fraction of the in-use fleet) this input was retained as a place keeper to avoid having 

to redesign the structure of existing input files. As a place keeper, the number that was input did 

not affect the results, but was required for the model to run properly. As long as users input a 

number within the acceptable range, the model would run, but the choice of number did not 

impact the results of a given run. Because MOVES was programmed as a brand new kind of 

mobile source emission factor model from the ground up, it was no longer necessary to retain 

I/M stringency for the model to run properly. Therefore, it was removed as part of a larger effort 

to streamline and simplify the I/M modeling process.

8.9 Evaluation Date

The date for which the I/M program is being evaluated – also known as the evaluation 

date – is entered as a four-digit year under the template column headed “yearID.”
Page 13

9.0 Modeling Non-Performance Standard Vehicle Exemptions

In addition to the I/M-related inputs required to model an I/M performance standard, the 

MOBILE model also allowed users to model exemptions of the newest and/or oldest model 

years. In MOBILE, for new vehicles, this allowance was known as a “grace period,” and for 

older vehicles, this allowance was called an “exemption age.” These last two program 

parameters can be modeled in MOVES by adjusting the first and last covered model years 

relative to the evaluation year. MOVES uses these two columns (i.e., “begModelYearID” and 

“endModelYearID”) to specify the beginning and ending model years affected by a particular 

part of the I/M program. For I/M programs without a grace period for new vehicles or an 

exemption period for older vehicles, this is simply the first and last model year affected by the 

program. 

For I/M programs with a grace period for new vehicles or an exemption period for older 

vehicles, this entry should reflect the actual model years covered by the program in the calendar 

year of evaluation. As a result, the beginning and ending model years for an I/M program may 

vary depending on the calendar year of analysis. For example, a typical OBD I/M program 

might apply to all model years beginning with 1996. However, if that program also includes a 

grace period during which newer vehicles are exempt from the program, the ending model year 

of the program should reflect the most recent model year included in the program based on the 

calendar year of analysis. For example, if in calendar year 2005, the most recent model year 

being tested in a program with a three-year grace period is the 2002 model year, a MOVES run 

for calendar year 2005 would have an ending model year of 2002. An analysis of the same 

program for calendar year 2010 would have an ending model year of 2007. 

Similar adjustments to the beginning model year should be made to account for 

exemptions of older model years. In that case, the beginning model year of the program should 

reflect the oldest model year still being tested. For example, if a program stops testing vehicles 

after they reach 20 years old, then in 2005, the oldest model year still being tested in a program 

would be the 1985 model year. Therefore, a MOVES run for calendar year 2005 for such a 

program would have a beginning model year of 1985. An analysis of the same program for 

calendar year 2010 would have a beginning model year of 1990. 

Note that because of this treatment of beginning and end years, a unique set of I/M inputs 

would be needed for each calendar year modeled. This is different than what was possible under 

MOBILE, where one set of I/M inputs could be used for any calendar year. 

10.0 Other I/M-Related MOVES Input Parameters

In addition to the MOVES inputs described above there are other inputs that are unique to 

the MOVES model and are required for the model to run properly. These include the state, 

county and year IDs as well as pollutant process ID, source type ID, fuel type ID, and I/M 

program ID. These program descriptors are explained in greater detail below.
Page 14

10.1 Pollutant process ID (polProcessID)

MOVES estimates emission reductions from I/M programs for hydrocarbons, NOx, and 

CO. For exhaust emissions, I/M programs can affect both running and start emissions. For 

evaporative emissions, I/M programs affect hydrocarbon emissions from fuel vapor venting and 

fuel leaks.

10.2 Source Type ID (sourceTypeID) and Fuel Type ID (fuelTypeID)

These entries are used to describe the source (vehicle) types and fuel types included in 

the I/M program. Users should check to make sure that the vehicle and fuel types match the I/M 

program parameters for the vehicles included in the local program. MOVES currently calculates 

I/M program benefits only for gasoline vehicles. 

I/M programs have historically applied to vehicles by regulatory weight class; however, 

MOVES applies I/M benefits by source type. This can lead to discrepancies between the number 

of vehicles covered in the actual I/M program and the number of vehicles that MOVES assumes 

are covered. For example, an I/M program that targets trucks less than 8,501 pounds Gross 

Vehicle Weight Rating (GVWR) (i.e. regulatory classes LDT1, LDT2, LDT3, and LDT4) would 

include parts of two MOVES source types: passenger trucks (sourcetypeID 31) and light 

commercial trucks (32). However, these source types also include vehicles with GVWR greater 

than 8,501 lbs. When an I/M program is applied to source types 31 and 32 in MOVES, all of the 

vehicles in these source types get I/M benefits. Users can adjust the compliance factor to 

account for the fraction of vehicles within a source type that are actually covered by the I/M 

program. How this calculation is performed is illustrated in Appendix C. 

10.3 I/M Program ID (IMProgramID)

In MOVES, I/M programs that have both exhaust and evaporative inspection 

components, including OBD programs, are modeled as two separate, simultaneous programs 

identified using different I/M program ID numbers in the I/M program ID column. Users should 

be careful to include both the exhaust and evaporative components to ensure proper credit for the 

program. Likewise, an I/M program that applies different tests to different vehicles (e.g., an 

IM240 program that applies to older model years and an OBD program that applies to newer 

model years) is also modeled as two separate, simultaneous programs identified using different 

I/M program ID numbers in the I/M program ID column and using the beginning and ending 

model year columns to differentiate what model years are covered by each program. 

10.4 Use I/M? (useIMyn)

Lastly, the MOVES I/M input parameters include a column labeled “useIMyn” which 

allows the user to turn off (“N”) or on (“Y”) the portion of the I/M program described in that row 

of the table. 
Page 15

11.0 Local Input Parameters

Depending upon the modeling exercise being done, users may need to include local data 

for locally variable input parameters such as vehicle type and age distribution, average speed, 

temperature, and vehicle-miles-travelled (VMT). For areas needing to demonstrate whether a 

proposed I/M program meets the performance standard only (i.e., without quantifying the actual 

mass emission reductions of the program for a shortfall calculation or other SIP purposes, such 

as an attainment demonstration), such areas will have the option of using MOVES’ national 

defaults for these local variables in place of locally derived data. If an area has reason to believe 

that using national defaults may reduce the flexibility it has in designing its I/M program (by, for 

example, requiring that more model years be included than might otherwise be the case), such 

areas may be better served by using the same locally-derived inputs it previously used for 

developing emissions inventories for a SIP. State and local agencies should consult EPA’s 

Technical Guidance on the use of MOVES for SIPs and transportation conformity guidance 

(available at www.epa.gov/otaq/models/moves/420b10023.pdf) for more details on choosing 

MOVES RunSpec parameters and appropriate local inputs when developing emission inventories 

for a SIP. For areas that are modeling a proposed I/M program or program revision for other 

purposes, such as for a shortfall calculation or attainment demonstration, the local inputs used 

should be consistent with those used to develop the emissions inventory. 

12.0 Additional Questions?

 The guidance in this document should cover the majority of day-to-day I/M modeling 

questions that may arise when running the most recent version of the MOVES mobile source 

emission factor model. Should users run into issues not addressed in this guidance, please 

contact your Regional I/M contact with a detail description of the issue. OTAQ will work with 

its Regional partners to resolve any issues that may arise on a case-by-case basis. Any unique 

interpretation or supplemental guidance that results from these individual consultations will be 

made available through updates to this guidance, or through separate communication to the 

States and Regions, as circumstances warrant.
Page 16

APPENDIX A: I/M Performance Standard Templates for MOVES2010 

The table below contains the inputs a user needs to enter into the MOVES County Data Manager 

to model the basic I/M performance standard with the following exceptions: the user needs to 

supply a county ID in the third column and may need to change the year ID in the fourth column, 

depending upon the evaluation year desired. If the year ID is changed, please note that the End 

Model Year ID in column 11 will also need to be adjusted, relative to the evaluation year 

selected. For more information on how to enter inputs into the County Data Manager, please 

refer to the MOVES Technical Guidance released with the latest version of MOVES. 

Basic I/M Performance Standard Default MOVES2010 Input

polProc

essID

stat

eID

cou

ntyI

D 

yearI

D 

sour

ceTy

peID

fuel

Typ

eID

IMProg

ramID

insp

ectFr

eq

testSta

ndardsI

D 

begModel

YearID

endMo

delYea

rID

useIM

yn

complianceFacto

r 

101 2019 21 1 111 1 11 1968 2000 y 100

102 2019 21 1 111 1 11 1968 2000 y 100

301 2019 21 1 111 1 11 1968 2000 y 100

302 2019 21 1 111 1 11 1968 2000 y 100

101 2019 21 1 151 1 51 2001 2018 y 100

102 2019 21 1 151 1 51 2001 2018 y 100

301 2019 21 1 151 1 51 2001 2018 y 100

302 2019 21 1 151 1 51 2001 2018 y 100

101 2019 21 1 143 1 43 2001 2018 y 100

102 2019 21 1 143 1 43 2001 2018 y 100
Page 17

Enhanced I/M Performance Standard Default MOVES2010 Input

The table below contains the inputs a user needs to enter into the MOVES County Data Manager 

to model the basic I/M performance standard with the following exceptions: the user needs to 

supply a county ID in the third column and may need to change the year ID in the fourth column, 

depending upon the evaluation year desired. If the year ID is changed, please note that the End 

Model Year ID in column 11 will also need to be adjusted, relative to the evaluation year 

selected. For more information on how to enter inputs into the County Data Manager, please 

refer to the MOVES Technical Guidance released with the latest version of MOVES. 

polProce

ssID

stat

eID

count

yID yearID

sourc

eType

ID

fuelTy

peID

IMProgr

amID

inspect

Freq

testStanda

rdsID

begModelY

earID

endModelY

earID

useI

Myn

compliance

Factor

101 2019 21 1 111 1 11 1968 2000 y 93.12

101 2019 31 1 111 1 11 1968 2000 y 87.53

101 2019 32 1 111 1 11 1968 2000 y 81.95

102 2019 21 1 111 1 11 1968 2000 y 93.12

102 2019 31 1 111 1 11 1968 2000 y 87.53

102 2019 32 1 111 1 11 1968 2000 y 81.95

301 2019 21 1 111 1 11 1968 2000 y 93.12

301 2019 31 1 111 1 11 1968 2000 y 87.53

301 2019 32 1 111 1 11 1968 2000 y 81.95

302 2019 21 1 111 1 11 1968 2000 y 93.12

302 2019 31 1 111 1 11 1968 2000 y 87.53

302 2019 32 1 111 1 11 1968 2000 y 81.95

101 2019 21 1 151 1 51 2001 2018 y 93.12

101 2019 31 1 151 1 51 2001 2018 y 87.53

101 2019 32 1 151 1 51 2001 2018 y 81.95

102 2019 21 1 151 1 51 2001 2018 y 93.12

102 2019 31 1 151 1 51 2001 2018 y 87.53

102 2019 32 1 151 1 51 2001 2018 y 81.95

301 2019 21 1 151 1 51 2001 2018 y 93.12

301 2019 31 1 151 1 51 2001 2018 y 87.53

301 2019 32 1 151 1 51 2001 2018 y 81.95

302 2019 21 1 151 1 51 2001 2018 y 93.12

302 2019 31 1 151 1 51 2001 2018 y 87.53

302 2019 32 1 151 1 51 2001 2018 y 81.95

101 2019 21 1 143 1 43 2001 2018 y 93.12

101 2019 31 1 143 1 43 2001 2018 y 87.53

101 2019 32 1 143 1 43 2001 2018 y 81.95

102 2019 21 1 143 1 43 2001 2018 y 93.12

102 2019 31 1 143 1 43 2001 2018 y 87.53

102 2019 32 1 143 1 43 2001 2018 y 81.95
Page 18

APPENDIX B: Gasoline I/M Regulatory Coverage Adjustments 

Source Type 

Description SourceTypeID MOBILE6 Vehicle Class 

Description M6VClassID

Regulatory Class 

Coverage Adjustment 

(%)

Motorcycle 11 Motorcycles (Gasoline) 24 100%

Passenger 

Car 21 LD Gas Vehicles 

(Passenger Cars) 1 100%

Passenger 

Truck 31

LD Gas Trucks 1 

(0 - 6,000 lbs. GVWR, 

0 - 3,750 lbs. LVW)

2 31%

LD Gas Trucks 2 

(0 - 6,000 lbs. GVWR, 

3,751 - 5,750 lbs. LVW)

3 31%

LD Gas Trucks 3 

(6,001 - 8,500 lbs. GVWR, 

0 - 5,750 lbs. ALVW)

4 16%

LD Gas Trucks 4 

(6,001 - 8,500 lbs. GVWR, 

> 5,751 lbs. ALVW)

5 16%

Class 2b HD Gas Vehicles 

(8,501 - 10,000 lbs. GVWR) 6 3%

Class 3 HD Gas Vehicles 

(10,001 - 14,000 lbs. GVWR) 7 3%

Light 

Commercial 

Truck

32

LD Gas Trucks 1 

(0 - 6,000 lbs. GVWR, 

0 - 3,750 lbs. LVW)

2 29%

LD Gas Trucks 2 

(0 - 6,000 lbs. GVWR, 

3,751 - 5,750 lbs. LVW)

3 29%

LD Gas Trucks 3 

(6,001 - 8,500 lbs. GVWR,

0 - 5,750 lbs. ALVW)

4 15%

LD Gas Trucks 4 

(6,001 - 8,500 lbs. GVWR, 

> 5,751 lbs. ALVW)

5 15%

Class 2b HD Gas Vehicles 

(8,501 - 10,000 lbs. GVWR) 6 5%

Class 3 HD Gas Vehicles 

(10,001 - 14,000 lbs. GVWR) 7 5%

Class 4 HD Gas Vehicles 

(14,001 - 16,000 lbs. GVWR) 8 1%

Class 5 HD Gas Vehicles 

(16,001 - 19,500 lbs. GVWR) 9 1%
Page 19

Gasoline I/M Regulatory Coverage Adjustments (cont.) 

Source Type 

Description SourceTypeID MOBILE6 Vehicle Class 

Description M6VClassID

Regulatory Class 

Coverage Adjustment 

(%)

Transit Bus 42

Class 6 HD Gas Vehicles 

(19,501 - 26,000 lbs. GVWR) 10 50%

Class 7 HD Gas Vehicles 

(26,001 - 33,000 lbs. GVWR) 11 50%

School Bus 43

Class 6 HD Gas Vehicles 

(19,501 - 26,000 lbs. GVWR) 10 50%

Class 7 HD Gas Vehicles 

(26,001 - 33,000 lbs. GVWR) 11 50%

Refuse Truck 51

Class 6 HD Gas Vehicles 

(19,501 - 26,000 lbs. GVWR) 10 50%

Class 7 HD Gas Vehicles 

(26,001 - 33,000 lbs. GVWR) 11 50%

Single Unit 

Short-haul 

Truck

52

Class 6 HD Gas Vehicles 

(19,501 - 26,000 lbs. GVWR) 10 49%

Class 7 HD Gas Vehicles 

(26,001 - 33,000 lbs. GVWR) 11 49%

Class 8a HD Gas Vehicles 

(33,001 - 60,000 lbs. GVWR) 12 1%

Class 8b HD Gas Vehicles 

(> 60,000 lbs. GVWR) 13 1%

Single Unit 

Long-haul 

Truck

53

Class 6 HD Gas Vehicles 

(19,501 - 26,000 lbs. GVWR) 10 48%

Class 7 HD Gas Vehicles 

(26,001 - 33,000 lbs. GVWR) 11 48%

Class 8a HD Gas Vehicles 

(33,001 - 60,000 lbs. GVWR) 12 2%

Class 8b HD Gas Vehicles 

(> 60,000 lbs. GVWR) 13 2%

Motor Home 54

Class 6 HD Gas Vehicles 

(19,501 - 26,000 lbs. GVWR) 10 50%

Class 7 HD Gas Vehicles 

(26,001 - 33,000 lbs. GVWR) 11 50%

Combination 

Short-haul 

Truck

61

Class 6 HD Gas Vehicles 

(19,501 - 26,000 lbs. GVWR) 10 48%

Class 7 HD Gas Vehicles 

(26,001 - 33,000 lbs. GVWR) 11 48%

Class 8a HD Gas Vehicles 

(33,001 - 60,000 lbs. GVWR) 12 2%

Class 8b HD Gas Vehicles 

(> 60,000 lbs. GVWR) 13 2%
Page 20

APPENDIX C: Sample Adjustment using Compliance Rate, Waiver Rate, and Regulatory Class 

Coverage 

Using an I/M program that targets trucks less than 8501 lbs. Gross Vehicle Weight Rating 

(GVWR) (regulatory classes LDT1, LDT2, LDT3, and LDT4) would include parts of two 

MOVES2010 source types: passenger trucks (sourcetypeID 31) and light commercial trucks 

(32). Users should first determine the compliance rate and waiver rate for the trucks covered by 

that program. For this example, we will assume that the compliance rate is 96% and the waiver 

rate is 8%. 

The user would then determine the regulatory class coverage adjustment by summing the 

percentages of those regulatory classes less than 8501 lbs. GVRW separately for source types 31 

and 32 using the information in Table A in this Appendix. For source type 31, the regulatory 

class coverage adjustment is 94% (31% + 31% + 16% + 16%). For source type 32, the 

regulatory class coverage adjustment is 88% (29% + 29% + 15% + 15%). 

Using these results, the compliance factor for source type 31 is: 

Compliance factor = compliance rate x (100 - waiver rate) x regulatory class coverage

83% = 96% x (100-8)% x 94% 

 

The compliance factor for source type 32 is:

Compliance factor = compliance rate x (100 - waiver rate) x regulatory class coverage

78% = 96% x (100-8)% x 88% 

 

These values would be entered as compliance factors of 83 for source type 31 and 78 for source 

type 32. 
Page 21

APPENDIX D: MOVES2010 I/M Emission Test Types 

Test 

Standards 

ID

Test Standards 

Description

Description

11 Unloaded Idle Test Test performed while vehicle idles in Park or Neutral

12 Two-mode, 2500 

RPM/Idle Test

Test performed while vehicle idles and at 2500 rpm

13 Loaded / Idle Test Test performed while vehicle operates on a chassis dynamometer at

constant load

21 ASM 2525 Phase-in

Cutpoints

Test performed on a dynamometer, under load, through a defined “steady 

state” driving cycle at 25 mph and 25% load, at phase-in cutpoints.

22 ASM 5015 Phase-in 

Cutpoints

Test performed on a dynamometer, under load, through two defined

“steady state” driving cycles at 25 mph and 25% load, and 15 mph and

50% load, at phase-in cutpoints.

23 ASM 2525/5015 Phase-in 

Cutpoints

Test performed on a dynamometer, under load, through two defined

“steady state” driving cycles at 25 mph and 25% load, and 15 mph and

50% load, at phase-in cutpoints.

24 ASM 2525 Final 

Cutpoints

Test performed on a dynamometer, under load, through a defined “steady 

state” driving cycle at 25 mph and 25% load, at final cutpoints.

25 ASM 5015 Final 

Cutpoints

Test performed on a dynamometer, under load, through a defined “steady 

state” driving cycle at 15 mph and 50% load, at final cutpoints.

26 ASM 2525/5015 Final 

Cutpoints

Test performed on an inertia-weighted dynamometer through two defined 

“steady state” driving cycles at 25 mph and 25% load, and 15 mph and 

50% load, at final cutpoints.

31 IM240 Phase-in Cutpoints Test performed on a dynamometer, under load, through a pre-defined

“transient” driving cycle of up to 240 seconds at phase-in cutpoints.

33 IM240 Final Cutpoints Test performed on a dynamometer, under load, through a pre-defined

“transient” driving cycle of up to 240 seconds.

41 Evaporative Gas Cap 

Check

A test conducted by pressurizing the gas cap for the purpose of

identifying leaks in the gas cap.

42 Evaporative System 

Pressure Check

A test conducted by pressuring the evaporative system by way of the fuel 

tank’s fill neck and sometimes referred to as the fill neck pressure (FP) 

test.

43 Evaporative System OBD 

Check

Test of the evaporative emission related systems and components

performed by visual check of the MIL and scan of the OBD computer

system for readiness, MIL status, and stored trouble codes, on 1996 and 

newer, OBD-equipped vehicles.

44 Evaporative Gas Cap and 

Pressure Check

A pair of tests to identify leaks in the gas cap (GC) and the rest of the

vehicle’s evaporative system. The latter test is conducted by pressuring 

the evaporative system by way of the fuel tank’s fill neck and is referred 

to as the fill neck pressure (FP) test.

45 Evaporative Gas Cap and 

OBD Check

The evaporative OBD test performed in conjunction with a separate 

check of the gas cap (GC) for the purpose of identifying leaks in the gas 

cap not otherwise identified by the evaporative OBD check. This 

combination of tests can only be conducted on 1996 and newer, OBDequipped vehicles. 

46 Evaporative Pressure and 

OBD Check

The evaporative OBD test performed in conjunction with a separate fill 

neck pressure test.

47 Evaporative Gas Cap, 

Pressure and OBD Check

The evaporative OBD test performed in conjunction with a separate fill 

neck pressure test and gas cap test.

51 Exhaust OBD Check Test of exhaust-related systems and components performed by visual

check of Malfunction Indicator Light (MIL) and scan of on-board (OBD) 

computer for system readiness, MIL status and stored trouble codes, on 

1996 and newer OBD-equipped vehicles only
Page 22

APPENDIX E: Determining Whether an Area is Required to Do I/M Under the Ozone Standard 

Under the Clean Air Act there are several factors to consider when determining whether an area 

is required to implement an I/M program under the ozone standard. 

• The first of these is the area’s classification for the ozone standard:

o If the area is classified as marginal and is not already running an I/M program 

due to some other standard or requirement, then I/M is not required. 

o If the area is classified as moderate and is not already running an I/M program 

due to some other standard or requirement, then a basic I/M program may be 

required depending on whether the area meets certain other criteria related to 

population. [CAA §182(b)(4)] 

o If the area is classified as serious or worse and is not already running an I/M 

program due to some other standard or requirement, then an enhanced I/M 

program may be required depending on whether the area meets certain other 

criteria related to population. [CAA §182(c)(3)] 

• Once an area’s classification has been set, the next factor to consider is whether the area 

is contained completely within the boundaries of a single state, or is part of a multi-state 

nonattainment area.

• If the nonattainment area is wholly contained within a single state, then the next thing to 

consider is the area’s population: 

o If the area is moderate and had a 19908 Census-defined urbanized area with a 

population of 200,000 or more, it must implement a basic I/M program in the 

1990 Census-defined urbanized area. [40 CFR 51.350(a)(4)] 

o If the area is serious or worse and had a 1980 Bureau of Census-defined 

urbanized area population of 200,000 or more, then it must implement an 

enhanced I/M program in the 1990 Census-defined urbanized area. [CAA 

§182(c)(3); 40 CFR 51.350(a)(2)] 

• If the nonattainment area covers a multi-state area, then the next thing to consider is how 

much of the nonattainment area’s urbanized population is contained within the state in 

question: 

 

8 The use of these older census figures is driven by the fact that the 1990 Clean Air Act was explicit with regard to 

the census that was to be used to determine the applicability of enhanced I/M. The Act specifies both the 200,000 

urbanized population threshold and use of the 1980 Census. EPA has taken the position that since we cannot change 

these statutory requirements for enhanced I/M, it does not make sense to change the regulatory population 

requirements for basic I/M.
Page 23

o If the overall nonattainment area had a total urbanized area population of 200,000

or more based upon the applicable census (1990 for moderate areas; 1980 for 

serious and above), and the state in question included a 1990 Census-defined 

urbanized population of at least 50,000, then the state in question must implement 

either a basic or enhanced I/M program in the 1990 Census-defined urbanized 

area, depending upon the nonattainment area’s classification. 

• Lastly, we need to determine how current Census Bureau metropolitan area boundaries 

compare to the Census Bureau definitions and boundaries in place at the time the Clean 

Air Act was enacted in 1990. The boundaries in place in 1990 are the key to determining 

whether such an area will be required to implement an I/M program.

• The reason for doing this is because in many cases areas currently being grouped together 

were not so grouped under the boundaries and definitions being used in 1990, when the 

Act was enacted. 

o For example, the current combined statistical area (CBSA) known as BeaumontPort Arthur, Texas (which consists of Jefferson, Orange, and Hardin counties) 

was not treated as a single area back in 1990. 

o Instead, the counties were treated separately.

o Individually, the counties’ urbanized populations fell well below the minimum 

200,000 threshold for triggering either the basic or enhanced I/M requirement. 

o As a result, the areas of Beaumont and Port Arthur – which were treated as 

separate urbanized areas back in 1990 – are not subject to either the basic or 

enhanced I/M requirement, regardless of their designation and/or classification 

under the current ozone standard.