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Strategic Workplan for Air Toxics Research

4: Control Strategies/Measures

A. Introduction

1. Background

Control options for on-road and off-road vehicles are normally of one of four types: engine standards, fuel standards, in-use emission/compliance programs, and travel management. This organization is useful for enumerating the control possibilities for air toxics as well as criteria air pollutants.

For engines, the technologies differ for gasoline (spark ignition) and diesel (compression ignition). Emission control technologies on today's SI engine-powered vehicles include electronic control systems, three-way catalysts, evaporative emissions control, and onboard vapor recovery systems. New gasoline-powered vehicle requirements include Tier 2 emission standards, lower sulfur content gasoline [30 parts per million (ppm)], and a change in the HC emission standard to 0.075 grams per mile non-methane organic gas from the current 0.25 grams per mile non-methane hydrocarbon. Future replacements for gasoline-powered vehicle technologies could include hybrid electric, battery electric, and fuel cells.

HDDV emission control technology has included injection timing retard, low sac volume and valve covering nozzle, turbo-charging, charge cooling, and improved fuel injection. New HDDV requirements in EPA's HDDV rule include fuel sulfur limits for motor vehicle diesel fuel, and PM certification levels that are 90 percent lower than those applied to truck engines being sold today. Transit and school buses have traditionally been diesel-powered, but alternative technologies include natural gas and battery electric.

For gasoline fuels, most areas in the United States currently have either regular unleaded gasoline, Federal reformulated gasoline (RFG), or California RFG. The primary change to gasoline characteristics in the next few years is a lowering of the sulfur content to 30 ppm. Light-duty vehicle alternative fuels that have been evaluated in some form have included methanol, ethanol, oxygenated fuel, natural gas, and liquefied petroleum gas (LPG).

Motor vehicle diesel fuel regulations as part of the EPA heavy-duty vehicle rulemaking will require that the sulfur in diesel fuel be lowered to a maximum of 15 ppm in 2007 from a current sulfur level of 500 ppm with the phase-in to low sulfur diesel beginning in mid-2006. The next tier of diesel emission standards begins with the 2007 model year. Heavy-duty diesel alternative fuels include bio-diesel, fuel additives, as well as alternative engine lubricants.

In-use compliance programs include vehicle emission inspections, remote sensing to flag high emitters, and vehicle replacement and retrofit programs. For gasoline-powered vehicles, emission inspections programs have taken a variety of forms including inspection and maintenance IM-240-based, Accelerated Simulation Mode tests, 2 speed idle tests, on-board diagnostic system checks, gas cap checks, and general anti-tampering programs. In-use compliance testing of diesel trucks is limited to random smoke emissions evaluations.

Travel management programs, which have been investigated or adopted with at least one of the purposes being reducing motor vehicle emissions in urban areas, fall into the categories of: intelligent transportation systems, market-based pricing mechanisms, land use and growth management policies, alternative work or trip schedules, and use of information technology as travel substitutes.

There has also been recent interest in studying HDDV operating practices with an interest in reducing excess idling emissions. Diesel engines operate at truck stops to provide power, heat and air conditioning to cabins. There are alternative technologies that can meet these power demands at lower emission rates. Truck stop electrification has been identified as a cost-effective technology. Truck stop electrification can take one of two forms. One option is to install electrical outlets at each parking space. This requires trucks to be equipped with power conversion systems. The second option provides climate control at the truck parking area without requiring modification, or added equipment, on each truck. Transit and school bus operating practices may also include excess idling emissions that could be mitigated as well.

2. Recent Information Summary

As noted in the companion literature review report, control strategies for mobile source air toxics have primarily focused on technological changes, such as tailpipe controls and changes to fuels for both diesel and gasoline engines. Development and evaluation of new and improved fuels includes fuel reformulation, fuel additives, fuel blends, alternative fuels, and alternatively fueled vehicles. Advances in this area have typically focused on fuel efficiency and reduction of ozone precursors. However, fuel changes can have a significant effect on toxic emissions, both positively (e.g., compressed natural gas [CNG]) and negatively (e.g., MTBE).

The primary tool available to transportation practitioners for estimating emission factor changes of mobile source strategies is MOBILE6.2. This EPA model allows users to estimate emission factors for six air toxics directly, and many more with modifications to input files. Therefore, any area can use MOBILE6.2 to estimate the air toxic emission reductions associated with control options such as reformulated gasoline and vehicle emission inspection programs in the same way that criteria pollutant emission reductions are estimated. The current practice for estimating the air pollution benefits of transportation control measures is explained in the National Cooperative Highway Research Program Report 462 "Quantifying Air-Quality and Other Benefits and Costs of Transportation Control Measures" (Cambridge, 2001). This report also addresses potential improvements to analytical frameworks for assessing transportation control strategies. While the report's focus is on criteria pollutants, the same principles apply for air toxic analyses.

B. Workshop Discussion Summary

1. Introduction

Part of the discussion in the control measures sessions was identifying the appropriate/needed metrics for evaluating measures. Such metrics would be included in any control measure evaluation regardless of whether it affects engine technology, fuel characteristics, in-use vehicle programs, or travel management. Suggested metrics included the following:

There need to be surrogates established as markers for the air toxics of interest because direct measurement of all air toxic compounds for all strategy evaluations will not be possible. Where appropriate, key toxic compounds should be delineated and control strategy research should focus on providing information for these compounds.

The crossover between this session topic and emissions characterization is the need to establish a link between emission measurements and control strategies. This means that there would be a discernable link between control strategies with an understanding of emissions and a focus on the biggest sources.

There needs to be more research on the full effects of control strategy options across air pollution issues (PM and toxics) and media (air, water, soil). The potential consequences of implementing a strategy need to be identified. State and local agencies are concerned with creating further situations like using MTBE in gasoline and later learning that a consequence of this action is finding MTBE in water bodies.

There needs to be more research on market-based incentive programs, and how behavior is likely to change under these stimuli. Likely responses to education programs are needed as well. Study incentives for fleet upgrades and other actions that might reduce air toxic emissions. This would include voluntary programs with rewards. Research which incentives work best. An example might be a tax incentive that would get fleet owners to replace older engines with new ones earlier than they might otherwise make this change.

Research needs to define toxics emissions reduction benefits that result from criteria pollutant controls. The next set of control strategy decisions that individual areas will face is for attainment of 8-hour ozone standards and PM2.5 standards. Before these decisions/selections are made, it would be informative to have estimated air toxic emission changes available, so that strategies can be selected with full knowledge of the likely air toxic emission changes. This air toxic information does not have to be quantitative, it can be directional changes in situations where quantitative information is not available.

Research atmospheric chemistry so that we can identify the air concentration benefits of measures as well as the tailpipe emission changes. This would include evaluating how particle size distributions might be changing with PM control applications. Also include assessments of greenhouse gases, toxics, criteria air pollutants, energy use, congestion measures, etc. Focus on identifying and adopting measures with positive results for all of these metrics. One example of what is needed here involves public transit agency bus purchases. Criteria pollutant analyses would probably show that a CNG-powered bus would be favored over a diesel-powered bus. However, CNG buses have a greenhouse gas disbenefit relative to diesel, depending on whether both direct and indirect greenhouse gas emissions are counted, and this may not be known by transit agencies, or incorporated in their decision-making process. The other issue related to atmospheric chemistry is that with respect to ozone, some areas of the country are VOC limited and others are NOx limited. Strategy selection in these areas will be strongly influenced by this, therefore the need to distinguish atmospheric changes in the strategy selection process.

For air toxics, workshop participants thought that it would be valuable to make drivers aware of what they emit, and what they breathe as they drive. One example would be to have portable signs that displayed the emission readings to drivers after they passed a sensor. This would have to be combined with studies of what real-time feedback does to driver/vehicle owner behavior. It was noted that the UC-Davis studies of in-vehicle dashboard lights that show when a vehicle is in enrichment mode are usually ignored after about 16 hours of driving.

Research is needed into the effectiveness of control strategies on toxics. This initiative specifically focuses on identifying the most cost effective control strategies available for reducing air toxic emissions. What would provide the best and most cost-effective results in situations where the most cost-effective air toxics control strategies could differ from the most cost-effective criteria pollutant options?

2. Fuels

There needs to be information available that compares alternative fuels and fuel blends, both technically (emission differences) and economically (cost). A recent analysis that was published in Environmental Science and Technology provided a cost-effectiveness analysis for various urban transit bus fuel types (Cohen et al., 2003). This was noted as an example of the type of analysis that is needed for air toxics. As with most analyses in the literature, this paper addresses criteria pollutant and CO2 emission differences (not air toxics).

Identify the potential emission benefits of clean contracting for construction projects to encourage emission reductions from non-road diesel equipment. Can contracts include requirements for cleaner than Federally mandated equipment, or is providing bonus evaluation points a better approach? Can FHWA evaluate how approaches to such contracting have been applied in practice thus far, and whether these have been successful? Are there instances where the additional costs to use clean (low sulfur) diesel or to retrofit engines have been paid, or subsidized by, FHWA, or other agencies?

3. Off-Road Engines/Vehicles

Non-road construction equipment control measure assessments (and those for any other non-road equipment of interest) need to provide more information about the different applications of such equipment, and how the effectiveness of controls might differ according to those applications. With the many applications of non-road equipment, they are more challenging to understand. It appears that there are many examples of non-road technology installations, such as using ultra low sulfur fuel, retrofits, and early adoption of filter technology, but cost-benefit information about these installations is not readily available. Identify the potential emission benefits of clean contracting for construction projects to encourage emission reductions from non-road diesel equipment. Can contracts include requirements for cleaner than Federally mandated equipment, or is providing bonus evaluation points a better approach? Can FHWA evaluate how approaches to such contracting have been applied in practice thus far, and whether these have been successful? Are there instances where the additional costs to use clean (low sulfur) diesel or to retrofit engines have been paid, or subsidized by, FHWA, or other agencies?

4. In-Use Compliance Programs

What is the need for and effectiveness of diesel vehicle emissions inspection programs? What is the effectiveness of these programs in reducing air toxics? What kind of a diesel inspection and maintenance (I/M) program might actually work? Part of such a research study would involve identifying whether there are excess diesel truck emissions that are not captured by MOBILE6, or the equivalent models, and what the relationship was between vehicle age or accumulated mileage and emissions. Then, different methods for estimating vehicle emissions in-use could be studied, as well as techniques for reducing the excess emissions when they are found.

5. Retrofits

Near-term research should be practical and focus on what we are already doing and have some information for. One focus should be on the effectiveness of retrofits. This is important because they are occurring. The information needed for retrofits includes in-use emissions performance and durability. In-use is important because we need to be sure that the analyses capture all of the duty cycles associated with real world operation.

There needs to be more research on PM filter effectiveness in reducing emissions (retrofits for diesels). Since the workshop was held, there has been much experience gained with school bus retrofits, though.

C. Priority Research Recommendations

Sound strategies to manage air toxics risks will require an improved understanding of relationships among air toxic sources, the atmospheric processes that transport and transform them, and the ambient concentrations to which people are exposed. Technical materials or computer models based on such understanding will provide State and local agencies with the tools necessary to determine how best to control emissions in ways that (1) focus on the pollutants and geographic areas with the highest risks and (2) identify cost-effective strategies for reducing population exposure to those pollutants.

Proposed Programmatic Initiatives

Programmatic Initiative P11: Performing studies of potential control measures and their cost effectiveness is predicated on there being observed harmful levels which can be ameliorated by reducing motor vehicle emissions. Therefore, any programmatic initiatives to reduce air toxic emissions need to be informed by research on existing ambient air toxic concentrations, estimated associated risks, and the mobile source contributions to them.

This research then focuses the control strategy evaluations on area-wide versus localized occurrences of high air toxic concentrations, specific air toxic compounds, and certain vehicle types.

While there are significant uncertainties in what is known about current air toxic concentrations, their variability, associated risks, and mobile source contributions, there are existing and ongoing urban scale studies that can be used to develop initial assessments of key factors. This includes EPA's Mobile Source Air Toxics Study, recently completed or ongoing EPA-sponsored efforts to evaluate air toxics concentrations in Houston, Texas, Portland, Oregon, and Philadelphia, Pennsylvania, as well as an FHWA-sponsored effort to examine EPA Supersite measurements along with nearby traffic data to examine relationships between traffic volumes and air toxic concentrations, as well as the Multiple Air Toxic Exposure Study-II, and recently initiated Multiple Air Toxic Exposure Study-III studies.

Priority program areas for research to provide more information to the transportation community about air toxic control strategies/measures are described below. These include a near-term need for adding information about potential air toxic emission benefits or disbenefits to the control measure studies being performed to support 8-hour ozone or PM2.5 SIPs, the need for more information about how to reduce emissions from the non-road construction equipment used in highway projects, and a longer-term need to research highly cost effective measures for reducing transportation-related air toxic emissions.

Sub-Area 1: Research the expected multi-media MSAT benefits or dis-benefits of the control measures that are expected to be the leading candidates for adoption in upcoming 8-hour ozone and PM2.5 nonattainment plans.

The next set of control strategy decisions that individual areas will face is for attainment of 8-hour ozone standards and PM<sub>2.5</sub> standards. Before these decisions/selections are made, it would be informative to have estimated air toxic emission changes, so that strategies can be selected with full knowledge of likely air toxic emission benefits or disbenefits. This air toxic information does not have to be quantitative, it can be directional changes in situations where quantitative information is not available.

The schedule for when the control strategy information will be needed is probably most directly related to the State Implementation Plan (SIP) submittal schedule for the 8-hour ozone NAAQS. Designations for attainment and nonattainment areas were made by April 15, 2004. On May 28, 2003, EPA issued the proposed rule that outlines the steps areas would have to take to meet the new standard. In this proposal, EPA is seeking comment on options for how States should apply ozone control requirements when developing their SIPs.

Part of the scope of work for this project would be to enumerate the appropriate/needed metrics for evaluating measures. Such metrics would be included in any control measure evaluation regardless of whether it affects engine technology, fuel characteristics, in-use vehicle programs, or travel management. Some suggested metrics are listed earlier in this chapter.

Estimated Cost: $150,000
Duration: 1 year

Sub-Area 2: Determine the emissions and potential emission reductions for measures that could be applied to mitigate the emissions from non-road construction equipment that is typically used in constructing/widening highways.

Non-road construction equipment control measure assessments (and those for any other non-road equipment of interest) need to provide more information about the different applications of such equipment, and how the effectiveness of controls might differ according to those applications. With the many applications of non-road equipment, they are more challenging to understand.

A project might include observations/measurements of activity at existing highway construction sites to develop population estimates and activity patterns by equipment type. PEMS are one option for measuring activity information, although the technology for measuring on-board emissions/activity may not yet be commercial for non-road CI engines. Evaluations should include studies of different-sized projects to allow transportation agencies to develop likely emissions and mitigation options by project size.

This program area study should address the potential emission benefits of clean contracting for construction projects to encourage emission reductions from non-road diesel equipment. Can contracts include requirements for cleaner than Federally mandated equipment, or is providing bonus evaluation points a better approach? Evaluate how approaches to such contracting have been applied in practice thus far, and whether these have been successful. Are there instances where the additional costs to use clean (low sulfur) diesel, or to retrofit engines, have been paid, or subsidized by FHWA or other agencies? Are there significant limitations on what can be required of construction contractors due to public contracting or other laws?

Estimated Cost: $100,000
Duration: 9 months

Sub-Area 3: Research the effectiveness of control strategies on toxics. This initiative specifically focuses on identifying the most cost effective control strategies available for reducing air toxic emissions. What would provide the best and most cost effective results where the most cost effective air toxics control strategies could differ from the most cost effective criteria pollutant options?

There are a number of potential needs for information about the effectiveness and cost of control strategies for reducing MSATs. One might be to mitigate a situation in an urban area where estimated risks resulting from air toxics exposure in some parts of the city were unacceptably high. Transportation and air pollution agencies would need information about the control strategies likely to provide the most cost effective reductions of the MSATs of concern. A second need would be for a project-level situation (a practical example is adding one or more new lanes to an existing freeway) where there might be a need to reduce near roadway exposures to specific MSATs. The types of air toxic mitigation measures for project-level situations could be considerably different from those to be applied in an urban-scale mitigation effort.

Emission reduction strategies should differentiate vehicle model year/technology groups and PM characteristics whenever possible. This will be especially important when EPA's heavy-duty vehicle and diesel fuel sulfur limits are implemented. In situations where diesel PM emission reduction strategies are being evaluated, these results need to define the expected emission reductions by model year/technology group and fuel characteristics. Another potential area for research is whether roadway design elements hold any promise for air toxics mitigation. Roadway design elements could include noise walls, depressed/elevated sections, landscaping, etc.

Estimated Cost: $150,000
Duration: 1 year

Updated: 07/06/2011
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