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Transportation Conformity: A Basic Guide for State & Local Officials

Executive Summary

This document has been prepared for State and local officials who are involved in decision making on transportation investments.

State’s air quality implementation plan (SIP)

The concept of transportation conformity was introduced in the Clean Air Act (CAA) of 1977, which included a provision to ensure that transportation investments conform to a State implementation plan (SIP) for meeting the Federal air quality standards. Conformity requirements were made substantially more rigorous in the CAA Amendments of 1990. The transportation conformity regulations1 that detail implementation of the CAA requirements were first issued in November 1993, and have been amended several times. The regulations establish the criteria and procedures for transportation agencies to demonstrate that air pollutant emissions from metropolitan transportation plans, transportation improvement programs and projects are consistent with (“conform to”) the State’s air quality goals in the SIP. This document has been prepared for State and local officials who are involved in decision making on transportation investments.

What is Transportation Conformity?

Transportation conformity is required under CAA Section 176(c) to ensure that Federally-supported transportation activities are consistent with (“conform to”) the purpose of a State’s SIP. Transportation conformity establishes the framework for improving air quality to protect public health and the environment. Conformity to the purpose of the SIP means Federal Highway Administration (FHWA) and Federal Transit Administration (FTA) funding and approvals are given to highway and transit activities that will not cause new air quality violations, worsen existing air quality violations, or delay timely attainment of the relevant air quality standard, or any interim milestone.

Where Does Transportation Conformity Apply?

Conformity requirements apply in areas that either do not meet or previously have not met national ambient air quality standards (NAAQS) for ozone (O3), carbon monoxide (CO), particulate matter (PM10 and PM2.5), or nitrogen dioxide (NO2). These areas are known as “nonattainment areas” and “maintenance areas,” respectively.

What Actions Are Subject to Conformity?

In areas that are nonattainment or maintenance for one or more of the pollutants mentioned above, conformity applies to long-range metropolitan transportation plans, shorter-term metropolitan transportation improvement programs (TIPs), and transportation projects funded or approved by FHWA or FTA.

The projected emissions must meet the requirements of the budget test and/or interim emissions test depending on the area.

What is a Conformity Determination?

A conformity determination demonstrates that implementation of the metropolitan transportation plan, TIP, or project will not cause any new violations of the air quality standard, increase the frequency or severity of violations of the standard, or delay timely attainment of the standard or any interim milestone. For metropolitan transportation plan and TIP conformity, the determination shows that the total emissions from on-road travel on an area’s transportation system are consistent with goals for air quality found in the SIP. Before a SIP is available, other tests of conformity are used. For project-level conformity, the determination shows that the project is consistent with the regional conformity determination and that potential localized emissions impacts are addressed.

Who is Responsible for Making a Conformity Determination?

Conformity determinations are made by FHWA/FTA. Metropolitan planning organization (MPO) policy boards make initial conformity determinations for metropolitan transportation plans and TIPs in metropolitan areas, while State Departments of Transportation (DOTs) usually do so in areas without MPOs and typically conduct the analyses associated with project-level conformity. A formal interagency consultation process is required for developing SIPs, metropolitan transportation plans, TIPs, and making conformity determinations, and includes the Environmental Protection Agency (EPA), FHWA, FTA, and State and local transportation and air quality agencies.

How Frequently are Conformity Determinations Required?

Conformity determinations must be made at least every four years, but may occur more often if metropolitan transportation plans or TIPs are updated more frequently or amended with non-exempt projects. Also, conformity determinations must be made within 24 months after SIP motor vehicle emissions budgets (MVEB) are found adequate or approved, whichever is first. Project-level conformity must be determined prior to the first time a non-exempt Federal project is adopted, accepted, approved, or funded. In addition, conformity determinations must be made within 12 months of an area being designated by EPA as nonattainment for ozone, carbon monoxide, particulate matter, or nitrogen dioxide.

How is the Public Involved?

A conformity analysis is made available to the public as part of the MPO metropolitan transportation planning process. MPOs are required to make metropolitan transportation plans, TIPs, and conformity determinations available to the public, to accept and respond to public comment, and to provide adequate notice of relevant public meetings. Project sponsors must also provide an opportunity for public involvement during the project development process where otherwise required by law.

How is Metropolitan Transportation Plan/TIP Conformity Determined?

Regional emissions are estimated based on projected travel on existing and planned highway and public transportation facilities consistent with an area’s metropolitan transportation plan and TIP. Projected emissions must be based on the latest available information and the latest EPA-approved emissions estimation model. The projected emissions must meet the requirements of the budget test and/or interim emissions test depending on the area. Also, the MPO is required to demonstrate that Transportation Control Measures (TCMs) in approved SIPs are implemented in a timely fashion. In addition, interagency consultation is required on the conformity determination.

What is a State Implementation Plan (SIP)?

A SIP is the State air quality plan for meeting the National Ambient Air Quality Standards (“NAAQS” or “air quality standards”.) It is a compilation of legally enforceable rules and regulations prepared by a State or local air quality agency and submitted by the State’s governor to EPA for approval. A SIP is designed to achieve better air quality by attaining, making progress toward attaining, or maintaining the NAAQS.

The SIP assigns emissions reductions for each pollutant or precursor for each source type (on-road motor vehicles, non-road equipment and vehicles, stationary, and area sources).

What are Motor Vehicle Emissions Budgets?

A motor vehicle emissions budget (MVEB) is that portion of the total allowable emissions in the SIP that is allocated to on-road mobile sources, such as cars, trucks, and buses. It is the level of on-road emissions that the area can have and still meet the SIP’s goals. Budgets are established in the applicable SIP as part of the air quality planning process by State air quality or environmental agencies, and approved by EPA.

All Federally- funded or approved highway and public transportation projects subject to conformity are required to meet project-level conformity requirements.

Photo of a divided highway with heavy traffic near a city

Transportation agencies participate in this process in accordance with required interagency consultation procedures.

For transportation conformity, projected emissions from highway and public transportation use must be less than or equal to the budgets. In other words, the budget acts as a ceiling on emissions from the on-road transportation sector.

What are Transportation Control Measures (TCMs)?

TCMs are specific projects or programs designed to reduce emissions from transportation sources that are included in the approved SIP. Examples include programs for improving public transportation, developing high occupancy vehicle (HOV) lanes, and ordinances to promote non-motorized vehicle travel.

What is Project-Level Conformity?

All Federally-funded or approved highway and public transportation projects subject to conformity are required to meet project-level conformity requirements. To demonstrate project-level conformity, a project must come from a conforming metropolitan transportation plan and TIP; its design concept and scope must not have changed significantly from that in the metropolitan transportation plan and TIP; the analysis must have used the latest planning assumptions and latest emissions model; and in PM areas, there must be a demonstration of compliance with any control measures in the SIP. In carbon monoxide and particulate matter nonattainment and maintenance areas, additional analysis may be necessary to determine if a project has localized air quality impacts. This localized air analysis is referred to as a “hot-spot” analysis.

What Happens if an MPO Cannot Make a Conformity Determination?

When a conformity determination is not made according to schedule, areas have a one-year grace period to make the determination before there is a conformity lapse. During a lapse, only certain types of projects can proceed: (1) projects that are exempt from conformity; (2) TCMs in approved SIPs; and (3) projects or project phases that are already authorized. Also, during a lapse no new non-exempt projects can be amended into the metropolitan transportation plan/TIP and the use of Federal-aid funds is restricted. The one-year conformity lapse grace period does not apply to new nonattainment areas that must make a determination on their metropolitan transportation plans and TIPs within 12 months of final designation.

What Options Do States and MPOs Have to Reduce Emissions?

A variety of projects and programs can be implemented to reduce emissions. Options include traditional investments like public transportation, HOV lanes, and signal timing, as well as technology-based measures such as retrofitting, repowering, replacing heavy-duty diesel trucks or implementing idling reduction programs.

1Title 40 CFR Parts 51 and 93.

Updated: 5/16/2017
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