California Air Resources Board

What is transportation conformity?

State and federal law require regional planning officials to prepare both a transportation plan to benefit public mobility and an air quality plan to benefit public health. Under the federal Clean Air Act, transportation activities that receive federal funding or approval must be found to be fully consistent with (or ‘conform’ to) the plan developed to meet federal clean air standards, known as the State Implementation Plan, or SIP. The requirement that federal activities--especially transportation plans and projects--be shown to help communities attain federal air quality standards is known as conformity.

Where does conformity apply?

Conformity applies to federal transportation decisions in all areas that are designated "nonattainment" for specific pollutants (ozone, carbon monoxide, particulate matter) by the U.S. Environmental Protection Agency (U.S. EPA). These are areas that have recorded violations of the National Ambient Air Quality Standards. "Attainment" areas that have adopted air quality maintenance plans are also subject to conformity. Areas that have exceeded the more stringent State of California air quality standards but are within national standards are not subject to conformity. The California Environmental Quality Act applies to plans and projects in these areas, however.

What actions are subject to conformity assessment?

Adoption by a metropolitan planning organization (MPO) of a 20-year regional transportation plan (RTP), or a short-term federal transportation improvement program (TIP), must include a conformity analysis prepared by the MPO. In addition, sponsors of transportation projects that require a federal approval are responsible for assessing project-level conformity. Final determinations of conformity for RTPs, TIPs and projects are made by the Federal Highway Administration and the Federal Transit Administration. Conformity assessments are part of a broader regional transportation planning process carried out by the MPO, or by another transportation agency in less urbanized areas. Because joint transportation and air quality planning assists both conformity assessments and air pollution reduction efforts, local air districts and transportation planning agencies regularly consult with each other and with involved state and federal agencies. Local transportation and air quality planning processes are also open to interested organizations and members of the public.

What are the primary tests of conformity for a region?

For RTPs and TIPs, conformity first involves an emissions test. The air quality plan (SIP) forecasts levels of pollutant emissions that will enable steady progress toward attainment of air quality standards by Clean Air Act deadlines, backed up by control strategies that will enable these levels to be reached. Such forecasts are divided by emissions source. The on-road mobile source portion of the forecast is known as a motor vehicle emissions budget. To be found in conformity with the SIP, a region's transportation plan and program must be found to result in emissions that fall below the applicable emissions budget. Other emissions tests may apply during the period before emissions budgets are submitted and found adequate for conformity by U.S. EPA. Emissions from implementation of the RTP or TIP may need to be shown to be below the levels that would result if the RTP or TIP was not implemented (known as the "build/no-build" test), or below levels for the SIP's base year, or both.

Are there other tests of conformity?

Though California's air quality is steadily improving due to stricter motor vehicle emissions control standards and vehicle fleet turnover, some areas need to adopt additional measures to reduce emissions from mobile sources in order to attain and maintain air quality standards. These areas may rely on transportation control measures (TCMs) to reduce emissions due to traffic congestion and high growth in vehicle trips and miles of travel. Examples of TCMs include public transit improvements, high occupancy vehicle lane systems, bicycle lane networks and pedestrian facilities. Where TCMs have been included in regions' air quality plans, RTPs and TIPs must implement them according to the schedule in the air quality plan in order to be found to conform. There are several additional qualitative tests associated with conformity findings. These include requirements for public and interagency consultation, and inclusion of adequate funding for RTP and TIP implementation. The federal conformity regulation details the full set of conformity tests. A copy of this rule is available through the U.S. EPA conformity website.

How is conformity determined for transportation projects?

Project conformity is primarily linked to regional conformity. Generally the project must be part of the metropolitan planning organization's conforming RTP and TIP. Outside of metropolitan planning areas, projects need to be included in a regional emissions analysis performed by a neighboring MPO or the California Department of Transportation (Caltrans). All "regionally significant" projects, regardless of funding source, should be accounted for in the regional emissions analysis. City and county public works agencies have responsibility for assuring that significant arterial projects are included in the analysis. In carbon monoxide (CO) and particulate matter (both PM10 and PM2.5) nonattainment and maintenance areas, project sponsors also must demonstrate that their projects will not result in a localized violation of CO or PM standards, or increase the frequency or severity of existing violations. ARB’s mobile source emissions inventory website includes links to the protocols for making these assessments. Caltrans has responsibility for assessing the conformity of state highway projects, and the actual conformity determination is made by the Federal Highway Administration. Transit project conformity findings are made by the Federal Transit Administration. Finally, some safety and rehabilitation projects, as well as certain projects with neutral or beneficial effects on air quality, are exempt from conformity. These project types are listed in the federal conformity regulation.

What happens when a transportation activity cannot be found to conform?

Federal funds cannot be spent for transportation plans, programs and projects that do not conform to the SIP. Federal funds for transit and highway improvements can be delayed, diverted, or even lost, as only SIP TCMs and a limited set of exempt projects and programs can be funded. Because conformity failures have serious implications for both mobility and air quality improvement, involved agencies work hard to correct them.

What is the key to conformity?

Consultation. Successful conformity findings benefit from a dynamic, interactive regional planning process that considers both air pollution reduction and transportation needs. For this reason, affected regions are required to develop and include in the SIP specific procedures for consultation on conformity findings and transportation-air quality planning. With ongoing input from each other and from concerned members of the public, decision-makers can make informed choices that improve air quality and mobility at the same time.