Commuter Programs: 

Quantifying and Using Their 

Emission Benefits in SIPs and 

Conformity 

Guidance for State and Local Air and 

Transportation Agencies
Transportation and Climate Division

Office of Transportation and Air Quality

U.S. Environmental Protection Agency

Commuter Programs: 

Quantifying and Using Their 

Emission Benefits in SIPs and 

Conformity

Guidance for State and Local Air and 

Transportation Agencies

NOTICE

This technical report does not necessarily represent final EPA decisions or 

positions. It is intended to present technical analysis of issues using data 

that are currently available. The purpose in the release of such reports is to 

facilitate the exchange of technical information and to inform the public of 

technical developments.

EPA-420-B-14-004, February 2014

Supersedes EPA-420-B-07-015
3

Contents

Section 1: Background Information .................................................................................... 4

1.1 What is the purpose of this guidance? .................................................................. 4

1.2 What are commuter programs, and how do they work? ...................................... 5

1.3 Does this guidance create any new requirements? ............................................... 6

1.4 Who should I contact if I have questions on this guidance? ................................ 6

Section 2: Basic Requirements for Using Emissions Reductions from Commuter 

Programs ............................................................................................................................. 7

2.1 What are the basic requirements for using emission reductions in SIPs? ............ 7

2.2 What must a state submit to EPA to meet the requirements for incorporating a 

commuter program as a control measure in a SIP? ........................................ 8

2.3 How can the estimated emission reductions be used for SIP purposes? .............. 9

2.4 How can the emission reductions be used for transportation conformity 

purposes? ........................................................................................................ 9

2.5 What quantification methodologies are available to estimate emission reductions 

of commuter programs for SIPs and transportation conformity 

determinations? ............................................................................................ 11

2.6 What types of penalties can be assessed for not complying with CAA 

requirements? ............................................................................................... 13
4

Section 1: Background Information

1.1 What is the purpose of this guidance? 

The purpose of this guidance is to help states or agencies1 estimate the emission benefits 

of commuter programs and, under appropriate circumstances, take credit for them in SIPs 

and conformity determinations. “Commuter programs” are programs that provide 

incentives or support to employees to reduce the frequency that they drive alone to work, 

and are offered by private- and public-sector employers throughout the country. Through 

these commuter programs, the numbers of vehicle trips and miles, and hence, emissions 

of criteria pollutants, as well as greenhouse gases, are reduced in many communities. 

This has led to an interest on the part of planners in some areas to incorporate the criteria 

pollutant benefits into their state implementation plans (SIPs) or transportation 

conformity determinations. 

Commuter programs can be incorporated into the SIP as mandatory measures, an 

Economic Incentive Program (EIP) or as a voluntary mobile source measure.2 For each 

of these options, a different entity may administer and evaluate the commuter program’s 

measures. For example, a voluntary measure program may be entirely administered by 

individual employers. EPA has issued comprehensive guidance documents for each of 

these types of SIP measures, and you should consult the guidance for the type of SIP 

submission in which you are interested as this guidance does not reiterate all the 

requirements for each. 

Quantifying the emissions benefits from commuter programs is covered in Section 2, 

which has information regarding the basic submission and quantification requirements for 

commuter programs in SIPs and conformity. 

This guidance supersedes the 2007 document, “Guidance for Quantifying and Using 

Emission Reductions from Best Workplaces for Commuter Programs in State 

Implementation Plans and Transportation Conformity” (EPA420-B-07-015). In addition, 

with the release of EPA’s MOtor Vehicle Emissions Simulator (MOVES) model, the 

COMMUTER model described in the 2007 guidance can no longer be used, as it was 

based on MOBILE, the model that preceded MOVES. The 2007 guidance and the 

COMMUTER model have been removed from EPA’s website. 

 

1 This document uses “state or agency” to refer to those entities that have authority to submit a SIP or 

conformity determination, such as a local or state government, regional transit authority, local or regional 

transportation planning agency or state or regional air quality agency. 

2 EPA’s Economic Incentive Program guidance and Mobile Source Voluntary Measures Policy can be 

found on EPA’s web site at: http://www.epa.gov/otaq/stateresources/policy/pag_guidance.htm and also at: 

http://www.epa.gov/ttn/ecas/incentiv.html . 
5

1.2 What are commuter programs, and how do they work?

Commuter programs are those programs that reduce the frequency that employees drive 

alone to work. These programs are usually offered to employees by their employer, but 

other organizations, such as a business park, 

downtown district, developer, or property 

owner may provide them. These programs 

can consist of any of the following 

components: 

• Free or reduced cost fares for public 

transportation (such as subway cards, 

bus tokens, or train tickets), 

• Transit and vanpool vouchers and 

subsidies, 

• Services to facilitate vanpools and 

carpools (such as providing vans, ridematching, and guaranteed ride home 

services),

• Park and Ride subsidies, 

• Telecommuting options (so employees 

can work at home more often), 

• Proximate Commuting: a program that matches employees of multi-site 

employers (such as banks or chain stores) to the branch office nearest their home,

• Incentives to bike and walk, and 

• Parking Cash Out: employees can trade employer-paid parking space for cash or 

other benefits. 

With more options, commuters can be expected to use single-occupant vehicles less 

often. Reducing the frequency that commuters drive alone generates air quality benefits. 

Air quality improvements are due to the reduction of emissions associated with a 

reduction in vehicle miles traveled. The Clean Air Act acknowledges these types of 

programs at Section 108(f), which includes a list of categories of “transportation control 

measures.” Several of the categories on the Section 108(f) list could describe commuter 

programs, or the components of one, such as, 

• “(iii) employer-based transportation management plans, including incentives;” 

• “(viii) programs for the provision of all forms of high-occupancy, shared-ride 

services;” and 

• “(x) programs for secure bicycle storage facilities and other facilities...”, 

among others. 

Commuter Choice program means an 

organized program to encourage employers to 

offer flexible commuter benefit options to 

employees.

 

Best Workplaces for CommutersSM is a 

innovative membership program that provides 

qualified employers with national recognition for 

offering outstanding commuter benefits. BWC 

assists participating employers by offering public 

recognition and promotion, technical assistance, 

training, web-based tools, and forums for 

information exchange.

 

Commuter benefit options are any of a number 

of flexible commute benefits offered by 

employers. Basic Commuter Choice alternatives 

include transit benefits, vanpool benefits, cash, 

or parking.
6

1.3 Does this guidance create any new requirements?

This guidance does not create any new requirements, but explains to state and local air 

agencies, transportation agencies, MPOs, and the general public how the air quality 

benefits of commuter programs could be included in a SIP or in a transportation 

conformity determination. The Clean Air Act (CAA) and implementing regulations 

contain legally binding requirements. 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 applicable regulations (40 CFR Parts 51 and 93). This 

guidance 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 SIP measures 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. 

1.4 Who should I contact if I have questions on this guidance? 

If you are interested in including the emission benefits of a commuter program into a SIP 

or transportation conformity determination, please contact the EPA Regional Office with 

responsibility for air quality planning in the relevant area. A contact list of EPA Regional 

Offices is available at the following web address: 

http://www.epa.gov/otaq/transp/conform/contacts.htm

For general questions regarding this document, please contact Laura Berry at (734) 214-

4858 or berry.laura@epa.gov. 
7

Section 2: Basic Requirements for Using Emissions Reductions 

from Commuter Programs

2.1 What are the basic requirements for using emission reductions in

SIPs? 

In order to be approved as a measure which provides additional emission reductions in a 

SIP, a control measure – in this case, a commuter program – cannot interfere with other 

requirements of the CAA, and would need to be consistent with SIP reasonable further 

progress, attainment, or maintenance requirements, as applicable. In addition, the control 

measure must provide emission reductions that meet the requirements described below. 

(A) Quantifiable - The emission reductions from a control measure are quantifiable if 

they can be reliably measured or modeled, and the quantification can be replicated. 

Emission reductions must be calculated for the time period for which the reductions will 

be used in the SIP. See Section 2.5 for more information on quantifying emission 

reductions from commuter programs. 

(B) Surplus - Emission reductions are generally surplus if they are not otherwise relied 

on to meet other applicable air quality attainment and maintenance requirements (i.e., no 

double-counting of emission reductions). In the event that the measure is used to meet 

such air quality-related program requirements, the measure is no longer surplus and may 

not be used for additional credit. 

(C) Federally Enforceable - Depending on how the emission reductions are to be used, 

control measures must be enforceable through a SIP. Where the emission reductions are 

part of a rule or regulation for SIP purposes, they are considered federally enforceable if 

they meet all of the following requirements: 

• They are independently verifiable. 

• Violations are defined, as appropriate. 

• The state or agency 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 suits 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 measure has been 

adopted by the implementing agency or agencies. 

Because commuter programs may rely on voluntary actions of individuals and other 

parties, these programs may be considered under EPA’s “Guidance on Incorporating 
8

Voluntary Mobile Source Emission Reduction Programs in State Implementation Plans 

(SIPs)” (the VMEP guidance).3 The purpose of the VMEP guidance is to support 

innovative methods in achieving emission reductions for SIPs. If a SIP revision that 

relies on the VMEP guidance is approved, the state is responsible for assuring that the 

reductions credited 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 VMEP guidance, the amount of emission reductions allowed for voluntary 

mobile source measures, including commuter programs, in a SIP is not expected to 

exceed three percent of the total reductions needed to meet any requirements for 

reasonable further progress, attainment or maintenance, as applicable. 4

(D) Permanent - The emission reduction must be permanent throughout the time period 

that the reduction is used in the applicable SIP. 

(E) Adequately Supported – The state must demonstrate that it has adequate funding, 

personnel, and other resources to implement the control measure on schedule. 

2.2 What must a state submit to EPA to meet the requirements for 

incorporating a commuter program as a control measure in a 

SIP? 

The state must submit to EPA a document which: 

• Identifies and describes the commuter program and its implementation schedule 

to reduce emissions within a specific time period;

• Contains estimates of emission reductions attributable to the commuter program, 

including the methodology and all other relevant technical support documentation 

for your estimates (you must rely on the most recent information available at the 

time the SIP is developed);

• Either contains federally enforceable requirements for the state to implement, 

track, and monitor the commuter program; or if the measure is developed under 

the VMEP guidance, the state includes an enforceable commitment to monitor, 

assess and report the resulting emission reductions of the commuter program; 

 

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

4 EPA acknowledges that it may be possible 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. Interested parties should refer to the VMEP 

guidance for more information when a specific commuter program is under development. 
9

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

commitment to remedy any SIP emissions shortfall in a timely manner in the 

event that the commuter program does not achieve the estimated emission 

reductions; and 

• Meets all other requirements for SIP revisions under sections 110 and 172 of the 

CAA.

2.3 How can the estimated emission reductions be used for SIP 

purposes? 

For a reasonable further progress, attainment or maintenance SIP, you can use the 

emission reductions produced from the commuter program by applying the following 

criteria: 

 

(A) Where required, emission reductions must account for seasonality. For 

example, if your SIP credits only those reductions which take place during the 

summer ozone season, then only reductions which take place during that season 

may be credited.

(B) An appropriate baseline must be chosen, so that the reductions are estimated 

only from measures that are not already accounted for in the baseline estimates. 

For example, if commuter programs were already in effect when the SIP was 

developed and were accounted for in the SIP’s baseline, the emission reductions 

associated with implementation or continuation of those same programs cannot be 

included as surplus emission reductions for the SIP. 

(C) As required by Clean Air Act section 172(c)(3) and EPA’s regulation at 40 

CFR 51.112(a), states must use the latest planning assumptions available at the 

time that the SIP is developed. In addition, the latest emissions model approved 

by EPA must be used in quantifying reductions from SIP control measures that 

are under development. State, local, and other interested agencies should consult 

with their EPA Regional Office on the latest approved MOVES model for use in 

quantifying motor vehicle emissions in most states and the latest approved 

EMission FACtor (EMFAC) model for use in California. 

2.4 How can the emission reductions be used for transportation 

conformity purposes? 

The transportation conformity regulation (40 CFR Part 93) describes the requirements for 

including emission reductions from on-road mobile control measures in a conformity 

determination for a transportation plan, transportation improvement program (TIP), or 

transportation project. The conformity rule requires a regional emissions analysis be 
10

conducted for the transportation plan and TIP. In the regional emissions analysis, the 

emissions from the planned transportation system are estimated or modeled, just as they 

are when creating or revising a SIP’s motor vehicle emissions budget. If credit is 

obtained for a commuter program in the SIP’s motor vehicle emissions budget, 

transportation agencies should also include the credit in the regional emissions analysis of 

the transportation conformity determination to the extent the program is being or will be 

implemented and appropriate commitments have been made, as described below. 

To include emission reductions from a commuter program in a regional emissions 

analysis, the appropriate jurisdictions must be committed to implementing the measure. 

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

CFR 93.122(a), which are described as follows: 

(A) If the measure does not require a regulatory action to be implemented, it can 

be included in an emissions analysis if it is included in the transportation plan and 

TIP with sufficient funding and other resources for its full implementation. 

 

(B) If the measure requires a regulatory action to be implemented, it can be 

included in an emissions analysis if one of the following has occurred:

(1) The regulatory action for the measure is already adopted by the 

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

measure); 

 (2) The measure has been included in an approved SIP; or 

(3) There is a written commitment to implement the measure in a 

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

adequate.

(C) If an on-road mobile measure 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 regional emissions analysis if the conformity 

determination contains a written commitment from the appropriate entities to 

implement the measures. Section 93.101 of the conformity rule defines what is 

intended by a “written commitment.”

Whatever the case, the emission reductions from a commuter program can only be 

applied in a conformity determination for the time period or years in which the measure

will be implemented and in effect. Written commitments must come from the agency 

with the authority to implement the measure. The latest emissions model and planning 

assumptions that are available must be used when calculating emission reductions from 

the measure, according to 40 CFR 93.110 and 93.111. 

Areas should utilize the conformity interagency consultation process to discuss the 

methods and assumptions used to quantify the reductions from the measure. The 

conformity determination should include documentation of the methodology, 

assumptions, and models that were used to calculate emission reductions from the 

commuter program as well any commitments that are necessary for implementation, as 
11

described above. 

2.5 What quantification methodologies are available to estimate 

emission reductions of commuter programs for SIPs and 

transportation conformity determinations? 

If a commuter program is considered to be regionally significant, then the travel impacts 

of the program should be considered in the context of a nonattainment or maintenance 

area’s regional travel demand forecasting.5

 (See 40 CFR 93.122 for applicable 

procedures for determining regional transportation-related emissions.) The interagency 

consultation process should be used to determined which projects are considered 

regionally significant (see 40 CFR 93.105(c)(1)(ii)). An example of the regionally 

significant project may be a campaign to implement commuter programs for all 

employers of a certain size or number of employees throughout a metropolitan area. 

However, EPA expects that the majority of commuter programs would not be regionally 

significant, and therefore the emission reductions could be quantified using modeling 

techniques other than regional travel models (i.e., “off-model” techniques or 

methodologies). State, local, and federal air quality and transportation agencies should 

consult on what methods and data are appropriate for quantifying the impacts of 

commuter programs for SIPs and conformity determinations. 

To estimate the emission reductions due to commuter programs, the recommended 

approach is to estimate the number of commuters who would change their mode of travel 

(i.e., single-occupant vehicle (SOV), carpool, vanpool, transit, bicycle, etc.) or tripmaking behavior (e.g., telecommuters will no longer be making regular worktrips) in 

response to incentives, assistance, or support offered through a commuter program. From 

this, the resultant change in vehicle activity could be calculated. The next step would be 

to use this information with the latest emissions model approved by EPA (i.e., the latest 

version of MOVES or EMFAC in California) to estimate the emissions that the 

commuter program would reduce.6

 

Forecasting travel behavior impacts is typically the most challenging aspect of 

quantifying a commuter program. Commuter programs can have a wide range of 

effectiveness, based on the details of the particular programs and their implementation 

context. The following paragraphs describe currently available tools for quantifying the 

 

5

Section 93.101 of the transportation conformity rule defines a “regionally significant project” as applying 

to a project that is on a facility that serves regional transportation needs (such as access to and from the area 

outside of the region, major activity centers in the region, major planned developments such as new retail 

malls, sports complexes, etc. or transportation terminals as well as most terminals themselves) and would 

normally be included in the modeling of a metropolitan area’s transportation network, including at a 

minimum all principal arterial highways and all fixed guideway transit facilities that offer an alternative to 

regional highway travel. 

6 The latest version of EPA’s Motor Vehicle Emission Simulator (MOVES) model, as well as model 

guidance, the user guide, and other documentation can be found on EPA’s website at: 

http://www.epa.gov/otaq/models/moves/index.htm. The latest version of California’s EMFAC model and 

model documentation can be found on the California Air Resources Board website at: 

http://www.arb.ca.gov/msei/modeling.htm. 
12

travel impacts of non-regionally significant commuter programs. 

Available Tools for Non-regionally Significant Measures 

For commuter programs that are not regionally significant, EPA may accept the use of 

other methodologies and analytic tools, in combination with the latest emissions model 

approved by EPA, to estimate the emission reductions of commuter programs for SIPs 

and conformity purposes. As mentioned above, EPA expects that the majority of 

commuter programs would not be regionally significant. 

For example, the Center for Urban Transportation Research TRIMMS (Trip Reduction 

Impacts of Mobility Management Strategies) is one such tool that can estimate the 

change in vehicle activity from a commuter program, and others are also available. 

Considerations for Data for Quantification of All Commuter Programs

When quantifying the impacts of commuter programs, a state or agency should 

carefully consider the underlying data utilized to estimate travel behavior, especially if 

using off-model and sketch planning techniques. The interagency consultation process 

should be used when deciding the appropriate inputs and methods for quantifying the 

emissions reductions associated with commuter programs. The following items should 

be considered when quantifying the travel impacts of any commuter program.

(A)Reasonable assumptions for employee participation. A state or agency should 

assume a reasonable level of participation from eligible employees, since not every 

eligible employee may be expected to take advantage of a commuter program. 

Survey methods can be used to capture the level of employee participation, both 

before and after a measure has been implemented. For example, a survey of 

employees at an employment site may be performed to determine how many people 

expect to use or have actually used employer-subsidized transit passes. Pre- and postimplementation surveys of actual travel behavior are often both feasible and 

necessary if the effectiveness of a commuter program is to be evaluated 

retrospectively. 

(B) Experience from other areas. In some cases, a state or agency may be able to use 

input information from other nonattainment or maintenance areas when an area does 

not have such local information. For example, a study may have found in another 

area that five percent of office workers will telecommute one day a week if provided 

the opportunity. It is important to consider whether information from another area is 

appropriate to apply to your area. 

(C) Elasticities. Finally, a state or agency should use the most appropriate elasticity 

assumptions for travel decisions when quantifying commuter programs. An elasticity 

says that an X percent change of an input variable (e.g., the cost of parking) produces 

a Y percent change of an output variable (e.g., drive-alone mode share). Elasticities 

may be developed from direct observation or from coefficients of a model such as a 
13

mode choice model. While such elasticities can account for different levels of the 

input variable, they are not necessarily valid outside the range for which they were 

developed. For example, an increase in the cost of parking from $0.00 to $1.00 is an 

infinite percentage change, producing meaningless results. Also, elasticities 

developed in one setting cannot necessarily be assumed accurate in another setting. 

For example, the elasticity describing how driving alone varies with the percentage 

change in the cost of parking developed from a dense urban area with extensive 

transit alternatives would be different from that same elasticity developed in a 

suburban area with limited transit. 

Another important consideration is interaction among strategies. Some strategies may 

complement each other (e.g., parking management and ridesharing incentives), leading to 

cumulative effects greater than the sum of the effects of the strategies if applied 

individually. Conversely, in some cases the effects of multiple programs may be smaller 

than the sum of their individual effects. 

2.6 What types of penalties can be assessed for not complying with 

CAA requirements?

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

applicable CAA requirements, including those pertaining to the crediting of emission 

reductions for your SIP, such as for your attainment demonstration or maintenance plan. 

Violations of CAA requirements are subject to administrative, civil, and/or criminal 

enforcement under Section 113 of the CAA, as well as to citizen suits under Section 304 

of the CAA. The full range of penalty and injunctive relief options would be available to 

the federal or state government (or citizens) bringing the enforcement action.