D.C. TO RICHMOND SOUTHEAST HIGH SPEED RAIL

MOBILE SOURCE AIR TOXICS TINFORMATION
D.C. to Richmond Southeast High Speed Rail T-1 Mobile Source Air Toxics Information

MOBILE SOURCE AIR TOXICS INFORMATION

Currently, the Federal Railroad Administration (FRA) does not have any guidelines related to 

Mobile Source Air Toxics (MSAT) analysis. In the absence of FRA MSAT guidelines, regional 

MSAT effects associated with the Project are discussed qualitatively. The qualitative assessment 

presented in Chapter 4 of the Draft EIS is based on the Federal Highway Administration’s 

(FHWA) Interim Guidance Update on Air Toxic Analysis in NEPA Documents, released December 6, 

2012, and in part from a study conducted by FHWA entitled A Methodology for Evaluating Mobile 

Source Air Toxic Emissions among Transportation Project Alternatives (FHWA, 2010). The FHWA 

guidance recommends that the information provided below be included in the NEPA document 

to accompany the qualitative assessment provided. 

Council on Environmental Quality (CEQ) Provisions Covering Incomplete or 

Unavailable Information (40 CFR 1502.22)

Sec. 1502.22 Incomplete or Unavailable Information

When an agency is evaluating reasonably foreseeable significant adverse effects on the human 

environment in an environmental impact statement and there is incomplete or unavailable 

information, the agency shall always make clear that such information is lacking. 

If the incomplete information relevant to reasonably foreseeable significant adverse impacts is 

essential to a reasoned choice among alternatives and the overall costs of obtaining it are not 

exorbitant, the agency shall include the information in the environmental impact statement. 

If the information relevant to reasonably foreseeable significant adverse impacts cannot be 

obtained because the overall costs of obtaining it are exorbitant or the means to obtain it are not 

known, the agency shall include within the environmental impact statement:

 a statement that such information is incomplete or unavailable;

 a statement of the relevance of the incomplete or unavailable information to evaluating

reasonably foreseeable significant adverse impacts on the human environment;

 a summary of existing credible scientific evidence which is relevant to evaluating the

reasonably foreseeable significant adverse impacts on the human environment; and

 the agency's evaluation of such impacts based upon theoretical approaches or research

methods generally accepted in the scientific community. For the purposes of this section,

"reasonably foreseeable" includes impacts that have catastrophic consequences, even if

their probability of occurrence is low, provided that the analysis of the impacts is

supported by credible scientific evidence, is not based on pure conjecture, and is within

the rule of reason.

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APPENDIX T

D.C. to Richmond Southeast High Speed Rail T-2 Mobile Source Air Toxics Information

The amended regulation will be applicable to all environmental impact statements for which a 

Notice to Intent (40 CFR 1508.22) is published in the Federal Register on or after May 27, 1986. 

For environmental impact statements in progress, agencies may choose to comply with the 

requirements of either the original or amended regulation.

Incomplete or Unavailable Information for Project-Specific MSAT Health Impacts 

Analysis

In FHWA’s view, information is incomplete or unavailable to credibly predict the project-specific 

health impacts due to changes in mobile source air toxic (MSAT) emissions associated with a 

proposed set of highway alternatives. The outcome of such an assessment, adverse or not, would 

be influenced more by the uncertainty introduced into the process through assumption and 

speculation rather than any genuine insight into the actual health impacts directly attributable to 

MSAT exposure associated with a proposed action.

The Environmental Protection Agency (EPA) is responsible for protecting the public health and 

welfare from any known or anticipated effect of an air pollutant. They are the lead authority for 

administering the Clean Air Act and its amendments and have specific statutory obligations with 

respect to hazardous air pollutants and MSAT. The EPA is in the continual process of assessing 

human health effects, exposures, and risks posed by air pollutants. They maintain the Integrated 

Risk Information System (IRIS), which is “a compilation of electronic reports on specific 

substances found in the environment and their potential to cause human health effects” (EPA, 

https://www.epa.gov/iris). Each report contains assessments of non-cancerous and cancerous 

effects for individual compounds and quantitative estimates of risk levels from lifetime oral and 

inhalation exposures with uncertainty spanning perhaps an order of magnitude.

Other organizations are also active in the research and analyses of the human health effects of 

MSAT, including the Health Effects Institute (HEI). A number of HEI studies are summarized in 

Appendix D of FHWA’s Updated Interim Guidance on Mobile Source Air Toxic Analysis in 

NEPA Documents. Among the adverse health effects linked to MSAT compounds at high 

exposures are: cancer in humans in occupational settings; cancer in animals; and irritation to the 

respiratory tract, including the exacerbation of asthma. Less obvious is the adverse human health 

effects of MSAT compounds at current environmental concentrations (HEI Special Report 16, 

https://www.healtheffects.org/publication/mobile-source-air-toxics-critical-review-literatureexposure-and-health-effects) or in the future as vehicle emissions substantially decrease.

The methodologies for forecasting health impacts include emissions modeling; dispersion 

modeling; exposure modeling; and then final determination of health impacts – each step in the 

process building on the model predictions obtained in the previous step. All are encumbered by 

technical shortcomings or uncertain science that prevents a more complete differentiation of the 

MSAT health impacts among a set of project alternatives. These difficulties are magnified for 

lifetime (i.e., 70 year) assessments, particularly because unsupportable assumptions would have 

to be made regarding changes in travel patterns and vehicle technology (which affects emissions 

rates) over that time frame, since such information is unavailable.

It is particularly difficult to reliably forecast 70-year lifetime MSAT concentrations and exposure 

near roadways; to determine the portion of time that people are actually exposed at a specific 

location; and to establish the extent attributable to a proposed action, especially given that some 

of the information needed is unavailable.
APPENDIX T

D.C. to Richmond Southeast High Speed Rail T-3 Mobile Source Air Toxics Information

There are considerable uncertainties associated with the existing estimates of toxicity of the various MSAT, 

because of factors such as low-dose extrapolation and translation of occupational exposure data to the 

general population, a concern expressed by HEI (Special Report 16, https://www.healtheffects.org/

publication/mobile-source-air-toxics-critical-review-literature-exposure-and-health-effects). As a result, 

there is no national consensus on air dose-response values assumed to protect the public health and 

welfare for MSAT compounds, and in particular for diesel PM. The EPA states that with respect to diesel 

engine exhaust, “[t]he absence of adequate data to develop a sufficiently confident dose-response 

relationship from the epidemiologic studies has prevented the estimation of inhalation carcinogenic risk 

(EPA IRIS database, Diesel Engine Exhaust, Section II.C. https://cfpub.epa.gov/ncea/iris/

iris_documents/documents/subst/0642.htm#quainhal).”

There is also the lack of a national consensus on an acceptable level of risk. The current context is 

the process used by the EPA as provided by the Clean Air Act to determine whether more 

stringent controls are required in order to provide an ample margin of safety to protect public 

health or to prevent an adverse environmental effect for industrial sources subject to the 

maximum achievable control technology standards, such as benzene emissions from refineries. 

The decision framework is a two-step process. The first step requires EPA to determine an 

“acceptable” level of risk due to emissions from a source, which is generally no greater than 

approximately 100 in a million. Additional factors are considered in the second step, the goal of 

which is to maximize the number of people with risks less than 1 in a million due to emissions 

from a source. The results of this statutory two-step process do not guarantee that cancer risks 

from exposure to air toxics are less than 1 in a million; in some cases, the residual risk 

determination could result in maximum individual cancer risks that are as high as approximately 

100 in a million. In a June 2008 decision, the U.S. Court of Appeals for the District of Columbia 

Circuit upheld EPA’s approach to addressing risk in its two step decision framework. 

Information is incomplete or unavailable to establish that even the largest of highway projects 

would result in levels of risk greater than deemed acceptable 

(https://www.cadc.uscourts.gov/internet/opinions.nsf/284E23FFE079CD59852578000050C9D

A/$file/07-1053-1120274.pdf ).

Because of the limitations in the methodologies for forecasting health impacts described, any 

predicted difference in health impacts between alternatives is likely to be much smaller than the 

uncertainties associated with predicting the impacts. Consequently, the results of such 

assessments would not be useful to decision makers, who would need to weigh this information 

against project benefits, such as reducing traffic congestion, accident rates, and fatalities plus 

improved access for emergency response, that are better suited for quantitative analysis.