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Air Quality Planning for Transportation Officials

State Implementation Plans (SIPs)

State air, environmental or health agencies are responsible for the development of state implementation plans (SIPs). The SIP is an air quality plan that explains how the nonattainment area will meet the requirements of the Clean Air Act. A SIP is required for each pollutant for which the nonattainment area violates the National Ambient Air Quality Standards (NAAQS). A SIP includes the regulations and any other measures a State will use to bring nonattainment areas into attainment. States must involve the public, through hearings and opportunities to comment, in the development of each SIP. EPA must approve each SIP, and if a SIP isn't acceptable or the State fails to submit one, EPA must impose sanctions and ultimately assume responsibility for enforcing the Clean Air Act in that State through a Federal Implementation Plan (FIP) if the State does not correct its SIP deficiency.

Although the Clean Air Act (CAA) is a Federal law covering the entire country, each State air quality agency is tasked with determining how best to achieve the Act's goals for the people of their State and in specific nonattainment and maintenance areas. In some States, local air quality agencies also play a major role in air quality planning.

There are three basic types of SIPs that are relevant to transportation conformity:

SIP requirements vary according to pollutant type and classification (severity of pollution). The Clean Air Act uses a classification system to tailor air quality planning requirements to the severity of the pollution and sets deadlines for attaining the air quality standards. The Clean Air Act established a tiered system of requirements that are based on the classification of the nonattainment area. For example, ozone nonattainment areas may be classified as marginal, moderate, serious, severe or extreme. Each nonattainment area has an attainment deadline based on its classification. For most classifications, if the area fails to reach attainment by its established attainment date, EPA is required to "bump up" the area to the next higher classification, and the area must meet additional CAA requirements within the prescribed timeframe. Not only must nonattainment areas meet these deadlines, but those with certain classifications must also demonstrate that they are making measurable progress in reducing emissions within specific timeframes prior to the deadline for attainment.

States usually do most of the planning for reducing emissions. They typically rely on emission-limiting regulations and permit systems for stationary source emissions reductions and a program of State and locally selected supplemental measures to reduce emissions from all sectors (e.g. stationary, area, transportation, etc.). Transportation planning can be affected by the choice of these supplemental measures.

Transportation measures are a key component of SIP development. Depending on the severity of nonattainment, the CAA requires various transportation-related activities, programs and strategies. States also have the option of choosing among a variety of additional voluntary transportation measures that will best serve their needs. If these voluntary measures are included in a SIP, they then become enforceable under Federal law. As State and local transportation agencies will be required to implement these measures, it is vital that they take an active role in SIP development.

The following depict transportation-related SIP requirements for mobile source criteria pollutants:

Transportation Related SIP Requirements for Ozone Nonattainment Areas by Classification

Marginal:

  • Inventory of emissions sources every three years
  • Implement current SIP commitments and correct deficiencies
  • Basic inspection and maintenance program (only if existing prior to 1990 in marginal areas)

Moderate:

  • All of the requirements for marginal areas
  • Control strategies that will reduce emissions to obtain reasonable further progress (RFP) in meeting the air quality standards
  • Vapor recovery program for gas stations
  • Contingency measures to implement if area fails to meet emissions targets

Serious:

  • All of the requirements for moderate areas
  • Demonstrate an emissions reduction of 3% on average each year
  • Confirm vehicle mileage, emissions, and congestion levels every three years
  • Enhanced inspection and maintenance program
  • Clean-fuel vehicle program for centrally fueled fleets

Severe:

  • All of the requirements for serious areas
  • Measures to offset growth in emissions due to growth in vehicle miles traveled (VMT)
  • Reformulated gasoline

Extreme

  • All of the requirements for severe areas
  • Measures during heavy traffic hours to reduce the use of high-polluting or heavy-duty vehicles

 

Transportation Related SIP Requirements for Carbon Monoxide Nonattainment Areas by Classification

Moderate <12.7 ppm:

  • Inventory of emissions sources every three years
  • Oxygenate gasoline in areas with a design value of 9.5 ppm or above
  • Basic inspection and maintenance program (if existing prior to 1990)

Moderate >12.7 ppm:

  • All of the requirements for moderate <12.7 ppm areas
  • Annual emissions reductions
  • Enhanced inspection and maintenance program
  • Vehicle miles traveled (VMT) forecasts and estimates for years prior to attainment year
  • Contingency measures to implement if area fails to attain or exceeds VMT forecasts
  • Clean-fuel vehicle program for centrally fueled fleets

Serious:

  • All of the requirements for moderate >12.7 ppm areas
  • Measures to offset growth in emissions due to growth in vehicle miles traveled (VMT)

 

Transportation Related SIP Requirements for PM10 Nonattainment Areas by Classification

Moderate:

  • Meet quantitative milestones every 3 years

Serious:

  • Meet quantitative milestones every 3 years
Updated: 07/06/2011
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