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9.0 Conformity

The Clean Air Act prohibits federally-funded projects from interfering with the ability of a state to come into compliance with an NAAQS through its SIP. SIPs establish baseline emissions and also project emission changes through the period of future years covered by the SIP. The projected emission levels throughout this period are considered to be a part of the state's budget for emissions of the pollutant(s) covered by the SIP.

Under conformity requirements, emissions from federally-funded or approved projects are not allowed to cause these emission budgets to be exceeded. These budgets appear in Section 9.3.4 of this document.

There are two general types of conformity: transportation and general. EPA promulgated the Transportation Conformity Regulations (58 FR 62188) (applicable to highways and mass transit) on November 24, 1993. On November 30, 1993, EPA promulgated the General Conformity Regulations (58 FR 63214) (applicable to everything else).

9.1 Transportation Conformity

Under the CAA, federally funded transportation projects must not cause or contribute to new air quality violations, worsen existing violations, or delay timely attainment of national ambient air quality standards (NAAQS). In other words, these projects, and any emissions changes resulting from them, must "conform" to implementation plans developed by states for the criteria pollutants. Conformity generally applies to projects funded or approved by the Federal Highway Administration (FHWA) or the Federal Transit Administration (FTA) in areas that do not meet or previously have not met national ambient air quality standards for a criteria pollutant (i.e., nonattainment or maintenance areas). A one year grace period is allowed for newly-designated nonattainment or maintenance areas.

Conformity does not apply in attainment or unclassifiable areas. Conformity determinations are also not required for certain exempt projects, such as safety projects (lighting, guardrails, etc.), vehicle rehabilitation, shelters, and maintenance building construction, and other projects such as sign removal, noise reduction and planning.

Generally, the metropolitan planning organizations (MPOs) involved in transportation planning for each area are responsible for determining if projects and their overall transportation implementation plan (TIP) conform to the state's SIP. The MPOs develop the necessary conformity determinations allowing for public input and hearings in the process demonstrating that their transportation projects meet conformity requirements. State transportation departments and air agencies, and the Federal Highway Administration, Federal Department of Transportation (DOT), and EPA are all involved in reviewing conformity determinations and TIPs developed by the MPOs.

State air quality plans contain emission reductions for each pollutant or precursor for each source sector (on-road motor vehicles, nonroad equipment and vehicles, stationary and area sources). The level of emissions for on-road motor vehicles, such as cars, trucks, and buses, is referred to as the "motor vehicle emissions budget." Budgets are developed as part of the air quality planning process by State air quality or environmental agencies, and approved by EPA. For transportation conformity, projected emission changes resulting from construction projects involving highway and transit use must not cause this budget to be exceeded. Both long and short term emissions must be considered, including the direct emissions of PM2.5 from exhaust, brake and tire wear, road and construction dust, along with indirect PM2.5 precursor emissions.

To maintain conformity, emissions from new projects can be mitigated or offset. This can be done through planning strategies or Transportation Control Measures (TCMs), which are specific projects or programs designed to reduce emissions from transportation sources by reducing vehicle use, changing traffic flow or congestion conditions. Examples include programs for improving public transit, developing high occupancy vehicle (HOV) facilities, and ordinances to promote non-motorized vehicle travel.

9.2 General Conformity

Section 176(c) of the Clean Air Act prohibits Federal agencies from conducting activities in nonattainment or maintenance areas that do not conform to a state's SIP. General conformity requirements are in place to ensure federal activities not related to transportation or highway projects do not interfere with the SIP budgets, do not cause or contribute to new violations, and ensure the timely attainment and maintenance of the NAAQS as the schedule exists in the SIP. Examples of these sorts of activities are harbor dredging or beach rehabilitation by the Army Corps of Engineers, where heavy diesel equipment is used both on land and on off-shore vessels, increasing the emissions of particulate matter and oxides of nitrogen.

General conformity differs from transportation conformity in that it applies to projects that were not considered in the TIP as the TIP applies to highways and mass transit. All federal actions not covered under transportation conformity are covered under general conformity requirements unless the actions do not exceed de minimus levels. General conformity requirements can be met by: (1) showing emission increases are already covered in the SIP; (2) the state agrees to modify the SIP to include the emissions; (3) offsets are found for the increased emissions; (4) or the emissions are mitigated. Conformity restrictions may also be avoided through construction strategies or planning, such as conducting construction operations outside of the ozone season when specific NOx emission restrictions do not apply.

9.3 Conformity Budget

9.3.1 Motor Vehicle Emission Budgets (MVEBs)

For the purposes of transportation conformity, the emission budget is essentially a cap on the total emissions allocated to onroad vehicles. The projected regional emissions calculated based on a transportation plan, transportation improvement program, or project, may not exceed the motor vehicle emissions budget or cap contained in the appropriate SIP. Emissions in years for which no motor vehicle emissions budgets are specifically established must be less than or equal to the motor vehicle emissions budget established for the most recent prior year.

9.3.2 PM2.5 Precursors

For transportation conformity, four PM2.5 precursors - oxides of nitrogen (NOx), volatile organic compounds (VOCs), oxides of sulfur (SOx), and ammonia (NH3) - must be considered in the conformity process in PM2.5 nonattainment areas.1 The USEPA requirements for the consideration of PM2.5 precursors are:

  • Regional emissions analysis must include NOx as a PM2.5 precursor in all PM2.5 nonattainment areas, unless the head of the state air agency and the USEPA Regional Administrator make a finding that NOx is not a significant contributor to the PM2.5 air quality problem in a given area.
  • Regional emissions analyses are not required for VOC, SOx or NH3 before an approved SIP budget for such precursors is established, unless the head of the state air agency or the USEPA Regional Administrator makes a finding that onroad emissions of any of these precursors is a significant contributor.
  • The following criteria are considered in making significance or insignificance findings for PM2.5 precursors:
    • The contribution of onroad emissions of the precursor to the total 2002 baseline SIP inventory;
    • The current state of air quality for the area;
    • The results of speciation monitoring for the area;
    • The likelihood that future motor vehicle control measures will be implemented for a given precursor; and,
    • Projections of future onroad emissions of the precursor.

After reviewing the USEPA requirements and the criteria regarding significance, the transportation conformity budgets for PM2.5 precursors will only include the establishment of an annual NOx budget for the PM2.5 nonattainment area addressed by this attainment demonstration SIP revision.

9.3.3 Road Dust and Construction Related Fugitive Dust

The Federal Transportation Conformity Rule specifies that re-entrained road dust is to be included as a component of direct PM2.5 for transportation conformity regional emissions analysis only if the USEPA Regional Administrator or the director of the State air agency has made a finding that emissions from re-entrained road dust within the area are a significant contributor to the PM2.5 nonattainment problem and has so notified the MPO and the Department.2 Also, for PM2.5 areas in which the implementation plan does not identify construction-related fugitive PM2.5 as a significant contributor to the nonattainment problem, the fugitive PM2.5 emissions associated with highway and transit project construction are not required to be considered in the regional emissions analysis.3

The USEPA has indicated that a finding of significance for re-entrained road dust would be based on a case-by-case review of the following factors: the contribution of road dust to current and future PM2.5 nonattainment; an area's current design value for the PM2.5 standard; whether control of road dust appears necessary to reach attainment; and whether increases in re-entrained dust emissions may interfere with attainment. Such a review would include consideration of local air quality data and/or air quality or emissions modeling results.4

Findings of significance have not been made for either re-entrained road dust or construction-related fugitive dust for the NYMA nonattainment area. Previous review of speciated data by the Department indicates between 3 to 6 percent of fine particulate mass is attributable to all sources of geologic material. Therefore, neither re-entrained road dust emissions or fugitive dust emissions from highway and transit project construction have been included in the PM2.5 transportation conformity budgets. A more detailed discussion of re-entrained road dust is included in section 5.3.

9.3.4 Budgets for Attainment of the Annual PM2.5 NAAQS

The existing and proposed attainment transportation conformity emission budgets for directly emitted fine particulate matter (direct PM2.5) and annual NOx (PM2.5 precursor) are provided in Table 9-1. The proposed attainment budgets are based on the latest planning assumptions.

Table 9-1 Transportation Conformity Emission Budgets for PM2.5 Attainment (Tons/Year)
Type of Budget PM2.5 (a) NOx
NYMA nonattainment area 2009 MVEB 1,750 77,571
NYMA nonattainment area 2011 MVEB 1,580 65,339

Notes: (a) Direct PM2.5 consists of the sum of: organic carbon, elemental carbon, particulate matter from gasoline vehicles, brake particles and tire particles.


1 Transportation Conformity Rule Amendments for the New PM2.5 National Ambient Air Quality Standard: PM2.5 Precursors, Final Rule, 70 Fed. Reg. 24280-92 (May 6, 2005).
2 40 C.F.R. § 93.119(f)(8).
3 40 C.F.R. § 93.122(f)(1).
4 69 Fed. Reg. 40033 (July 1, 2004).

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