Transportation Conformity: Basic Guide

APPENDIX A: Health Effects of Pollutants

EPA has established standards⁸ for four transportation-related pollutants:

ground level ozone formed by volatile organic compounds [VOCs] and oxides of nitrogen [NOx], the primary ingredients of smog;
carbon monoxide [CO];
particulate matter (less than 10 microns [PM10] and less than 2.5 microns [PM2.5]; and,
nitrogen dioxide.

The standards are based upon EPA's assessment of the health risks associated with each of the pollutants on at-risk populations. These assessments are based upon short and long-term scientific studies by noted health professionals and medical research institutions. At-risk groups include children, the elderly, persons with respiratory illnesses, and even healthy people who exercise outdoors. The 8-hour ozone standard and PM-2.5 standard were established in 1997 based upon an assessment of the health-risks associated with exposure to these pollutants. The effective date of the 8-hour ozone standard also coincides with the revocation of the 1-hour ozone standard such that only one ground-level ozone standard is in effect at a given time.

Air pollution often involves a complex set of chemical reactions including combinations of pollutants and other factors such as weather and geography. Each pollutant plays a different role in the overall air quality in any given geographic area. Below is a brief overview of the key transportation-related pollutants.

Ozone: Ozone often irritates the eyes, impairs the lungs, and aggravates respiratory problems. Ozone can cause chest pain, coughing, nausea, pulmonary congestion, and possible long-term lung damage. Nitrogen oxides (NOx) and volatile organic compounds (VOCs) are precursors to ozone formation.

Volatile Organic Compounds (VOCs): VOCs come from vehicle exhaust, paint thinners, solvents and other petroleum-based products. VOCs and nitrogen oxides react in the presence of sunlight to form ozone. A number of exhaust VOCs are also toxic, with the potential to cause cancer.
Nitrogen Oxides (NOx): Under the high pressure and temperature conditions in an engine, nitrogen and oxygen atoms in the air react to form various nitrogen oxides, collectively known as NOx. NOx, like hydrocarbons, is a precursor to the formation of ozone and also contributes to the formation of acid rain. NOx impacts the respiratory system, causing a high incidence of acute respiratory diseases. Pre-school children are especially at risk. NOx also degrades visibility due to its brownish color and the conversion to nitrate particles.

Carbon Monoxide (CO): Carbon monoxide is a product of incomplete combustion and occurs when carbon in the fuel is partially oxidized rather than fully oxidized to carbon dioxide (CO2). Carbon monoxide reduces the flow of oxygen in the bloodstream and is particularly dangerous to persons with heart disease. Exposure to carbon monoxide can impair visual perception, manual dexterity, learning ability, and performance of complex tasks.

Particulates (PM): These are tiny particles that can cause irritation and damage to the respiratory system which can result in difficulty breathing, induce bronchitis and aggravate existing respiratory disease. Exposure to particles may more dramatically impact individuals with chronic pulmonary or cardiovascular disease, people with influenza or asthma, and children and elderly persons. Particles may aggravate breathing difficulties, damage lung tissue, alter the body's defense against foreign materials, and can lead to premature mortality. There are two PM standards: PM-10 and PM-2.5. PM-10 refers to particles with a diameter of 10 microns (µm) or less, and PM-2.5 refers to particles with a diameter of 2.5 microns or less. As a comparison, an average grain of table salt is 100 µm in diameter.

APPENDIX B: Options to Reduce Emissions from On-Road Motor Vehicles

The CAA identifies actions that may be taken to reduce emissions from mobile sources. While some of the measures are not the responsibility of State and local transportation officials, it is beneficial for officials to be familiar with on-road motor vehicle control programs implemented by other public agencies (e.g., motor vehicle departments, environmental agencies), automobile manufacturers and fuel suppliers. It is also important to understand the trade-offs between those measures others implement and the transportation strategies and TCMs that MPOs might include in their transportation plans and TIPs. Having an understanding of the costs and benefits of all available options to achieve emission reductions is also useful to officials in advance of being asked to make decisions on specific strategies for implementation.

Vehicle controls and fuel-based standards

Emission reductions resulting from the implementation of nationwide vehicle emission control strategies and fuel standards have been the most substantial to date in efforts to reduce mobile source emissions. Nevertheless, due to expected growth in vehicular travel, tailpipe emission standards for cars and light-duty trucks were tightened in the CAA and, as of 1996, applied to all new vehicles sold nationwide. In addition, heavy-duty trucks had to meet new NOx emission standards after 1998. Urban transit buses also have to meet tighter emissions standards under the CAA.

EPA adopted the Tier II Vehicle & Gasoline Sulfur program that took effect in January 2004. This rule affects every new passenger vehicle and every gallon of gasoline in the U.S. For the first time SUVs, pickups, vans, and even the largest passenger vehicles are subject to the same, more stringent, national emission standards as cars. New emission standards apply to all passenger vehicles, regardless of fuel type (gasoline, diesel or alternative fuels). Vehicles meeting the Tier II standards are 77 to 95 percent cleaner, depending on the size of the vehicle, compared to model year 2003 and earlier vehicles. The new standards reduce the sulfur content of gasoline by up to 90 percent. Heavy-duty gasoline engines are also required to meet new, more stringent standards starting with model year 2005.

In July 2000, EPA finalized a two-phased rule for heavy-duty diesel trucks and buses. In the first phase, new diesel engine standards apply beginning in 2004 for all diesel vehicles over 8,500 pounds. Additional diesel standards and test procedures will begin in 2007. The new standards require diesel trucks to be more than 40 percent cleaner than in 2000. The second phase of the program requires cleaner diesel fuels and even cleaner engines starting with model year 2007 trucks, and will reduce air pollution from diesel trucks and buses by another 90 percent. Starting in June 2006, the sulfur content of highway diesel fuel will be reduced from its current level of 500 parts per million to 15 parts per million, a 97 percent reduction in sulfur content.

The CAA included a clean fuel fleet program for serious ozone nonattainment areas with a population of more than 250,000. These areas were required to adopt a clean-fuel vehicle program for centrally fueled fleets of 10 or more vehicles by May 15, 1994. By requiring fleet owners (public and private) to convert to clean-fueled vehicles, it was hoped that the market for such vehicles will increase and broad-based public acceptance of clean-fueled vehicles will increase. However, it should be noted that existing nonattainment and maintenance areas can opt out of this program and no new 8-hour ozone areas meet the criteria for this program.

In addition to vehicle-related measures, stricter fuel volatility requirements (the rate at which fuel evaporates) may be required in some areas and can be useful in others. The use of reformulated gasoline (or RFG; fuel containing a different mix of ingredients than conventional gasoline) is mandated in the Nation's most serious ozone areas. EPA now allows areas that voluntarily opted into the RFG program to "opt out" of the requirements under certain conditions. In addition, no new 8-hour ozone areas are required to implement RFG. However, this is a measure that officials may want to consider because it is possible that all light-duty vehicles operating in the nonattainment or maintenance area could be using cleaner fuels, whereas certain other strategies such as TCMs apply only to limited numbers of vehicles and trips (e.g., commute trips). Oxygenated gasoline is also required during the winter months in areas with serious carbon monoxide pollution, and where low-sulfur content diesel fuel was required beginning in 1993.

An intermediate measure between mobile source controls and stationary source controls is to reduce VOC emissions by mechanical means, rather than by reducing the volatility of the fuel. In many areas, emissions from tanker truck delivery of fuel to gasoline stations are already controlled by what is known as "Stage 1" vapor recovery. This can be taken a step farther with "Stage II" vapor recovery nozzles, which reduce VOC emissions from fueling individual vehicles by capturing them at the pump. Automobile manufacturers will soon begin incorporating onboard vapor recovery controls into new vehicles, but the Stage II controls could provide benefits until these on-board controls are fully integrated into the vehicle fleet, which will be in about 25 years.

Inspection and Maintenance Programs

The CAA requires inspection and maintenance programs to be adopted in certain ozone (O3) and carbon monoxide (CO) nonattainment areas. The requirements of the program vary depending upon the severity of pollution in the nonattainment areas in each State. The emission reduction potential of inspection and maintenance programs is substantial and is critical to many areas achieving the short-term emission reductions required from mobile sources.

Transportation Control Measures (TCMs)

Another set of options to control and reduce emissions from motor vehicles comes under the category of TCMs. Implementation of these measures is typically within the purview of transportation agencies, and TCMs are usually funded with FHWA/FTA or State and local transportation funds. The emission reduction potential of conventional TCMs, such as ridesharing and bicycling programs, is not likely to be as substantial as the technology-based transportation measures discussed above. Nevertheless, TCMs can be useful in reducing congestion and may be needed in some areas in order to demonstrate attainment of the NAAQS. TCMs such as expanded transit services can also provide and enhance travel options and increase travel choices.

The CAA requires that in ozone nonattainment areas classified as severe or extreme, the State must identify and adopt specific transportation control strategies and TCMs to offset any projected growth in emissions from growth in vehicle miles traveled. States and MPOs should consider the CAA list of TCMs (Section 108(f)(1)(A) for strategies they might include in the SIP. These 16 TCMs (with the exception of programs to encourage the removal of pre-1980 vehicles) are eligible for Congestion Mitigation and Air Quality Improvement Program (CMAQ) funding. Below is the list of TCMs included in the CAA. There is overlap between some of the measures and the descriptions listed illustrate types of projects that might be considered in nonattainment areas to reduce mobile source emissions or to increase overall vehicle occupancy.

CAA Section 108(f)(1)(A) Transportation Control Measures

programs for improved public transit;
restriction of certain roads or lanes to, or construction of such roads or lanes for use by, passenger buses or high-occupancy vehicles (HOV);
employer-based transportation management plans, including incentives;
trip-reduction ordinances;
traffic flow improvement programs that achieve emissions reductions;
fringe and transportation corridor parking facilities serving multiple-occupancy vehicle programs or transit service;
programs to limit or restrict vehicle use in downtown areas or other areas of emission concentration particularly during periods of peak use;
programs for the provision of all forms of high-occupancy, shared-ride services;
programs to limit portions of road surfaces or certain sections of the metropolitan area to the use of non-motorized vehicles or pedestrian use, both as to time and place;
programs for secure bicycle storage facilities and other facilities, including bicycle lanes, for the convenience and protection of bicyclists, in both public and private areas;
programs to control extended idling of vehicles;
reducing emissions from extreme cold-start conditions;
employer-sponsored programs to permit flexible work schedules;
programs and ordinances to facilitate nonautomobile travel, provision and utilization of mass transit, and to generally reduce the need for need for single-occupant vehicle travel, as part of transportation planning and development efforts of a locality, including programs and ordinances applicable to new shopping centers, special events, and other centers of vehicle activity;
programs for new construction and major reconstruction of paths, tracks, or areas solely for use by pedestrian or other nonmotorized means of transportation when economically feasible and in the public interest. For purposes of this clause, the Administrator shall also consult with the Secretary of the Interior;
programs to encourage removal of pre-1980 vehicles.

Market-Based Transportation Control Measures

In addition to conventional TCMs, work is underway in nonattainment areas to explore options to reduce mobile source emissions using market-based TCMs such as road pricing, congestion pricing, vehicle miles of travel (VMT) fees, and parking pricing. These mechanisms can be relatively cost-effective and can be designed to impact vehicles at either certain times of the day (e.g., peak-period pricing), or at all times. In addition, these measures in combination with traditional TCMs have the potential to address other public policy objectives such as congestion reduction and energy conservation.

In many areas public acceptance of market-based TCMs has been slow due to practical and political considerations. For example, implementation of market-based measures may require State legislation (e.g., congestion pricing) or a voter referendum. Therefore, regardless of the potential merits and cost-effectiveness of these measures, the implementation of market-based TCMs is likely to occur gradually. While it is too soon to predict whether widespread use of market-based measures will occur in the future, experts generally agree that this is one option available to make substantial reductions in emissions from onroad mobile sources.