Sunday, 28 October 2012


Although the transportation planning process is concerned primarily with the issues facing a particular metropolitan area or state, there are many issues common to all parts of the country. This section addresses these common transportation topics, and provides details on several important issues facing MPOs and states engaged in transportation planning.
Each section provides a basic understanding of the topic, discusses the role of the MPO and state DOT as appropriate, answers questions about how the topic is addressed in the transportation planning process, and provides resources for additional information.

What is the relationship between transportation and air quality?
Usage of the transportation system is an influential factor in a region’s air quality. Therefore, the estimated emission of pollutants from motor vehicles is a key consideration in transportation planning. Regions that have nonattainment or maintenance air quality status are required to ensure that emissions from transportation investments are consistent, or in conformity with, levels set forth in state air quality plans. Therefore, state DOTs and MPOs need to have a clear understanding of the air quality-related transportation planning requirements.
What are the major sources of pollution?
The air quality of an area is affected by the emission of pollutants and their interaction with sunlight, topography, and weather patterns. Pollutants are emitted by motor vehicle operation and a variety of other activities, including manufacturing, use of petroleum-based products like gasoline, and even small business activities such as dry cleaning.
Sources of air pollutant emissions can be classified as stationary, area, or mobile sources, as shown in Figure 3.
Stationary sources include relatively large, fixed facilities such as power plants, chemical process industries, and petroleum refineries.
Area sources are small, stationary, non-transportation sources that collectively contribute to air pollution such as dry cleaners, gas stations, landfills, wastewater treatment plants, and others.
Mobile sources include on-road vehicles such as cars, trucks, and buses; and off-road sources such as trains, ships, airplanes, boats, lawnmowers, and construction equipment.
Figure 3: All sources of pollution can be looked at for ways to reduce emissions and improve air quality.  Click for text version.D
Figure 3: All sources of pollution can be looked at for ways to reduce emissions and improve air quality
The key transportation-related pollutants are ozone and its precursors hydrocarbons (HC) and nitrogen oxides (NOx), carbon monoxides (CO), and particulates (PM-10 or PM-2.5, particles that are smaller than 10 micros or 2.5 micron, respectively). These pollutants emanate in part from on-road mobile sources and cannot exceed certain specified levels in a given region.
The Clean Air Act (CAA), Title 23 and Title 49 U.S.C. requires that transportation and air quality planning be integrated in areas designated by the U.S. Environmental Protection Agency (EPA) as air quality nonattainment or maintenance areas. In fact, in nonattainment and maintenance areas, federal funding and approval for transportation projects is only available if transportation activities are consistent with air quality goals through the transportation conformity process. The transportation conformity process includes a number of requirements that MPOs must meet (see section below on transportation conformity).
The CAA requires that each state environmental agency develop a plan called a State Implementation Plan (SIP). The SIP shows how the state will implement measures designed to improve air quality enough to meet National Ambient Air Quality Standards (NAAQS) for each type of air pollutant, according to the schedules included in the CAA. Pollutants are usually measured in parts per million (PPM) of ambient air, and standards vary by type of pollutant.
For each source category (stationary, area, or mobile), the SIP assigns emission reduction targets of the pollutant. For on-road mobile sources, the emission reduction target is further refined into a motor vehicle emissions "budget"—emissions limits for motor vehicle emissions sources.
Vehicle emissions reductions programs (e.g., the use of reformulated gasoline or implementation of Inspection and Maintenance [I/M] programs), changing how we travel (e.g., ride sharing or use of transit), or transportation projects that reduce congestion (e.g., signal synchronization programs) can all help areas meet emission reduction targets for on-road mobile sources. MPOs should be actively involved with the state in setting the motor vehicle emissions budgets. Transportation officials need to educate themselves about the options and trade-offs available to them, so they can balance the need for transportation investment with the need to achieve healthful air.
Motor vehicle emissions budgets can be revised. However, doing so requires revising the SIP, which can be a complicated and lengthy process. MPOs should participate in the SIP revision process if it is undertaken.


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