The recent concurrent introduction of models (MOVES2010, CAL3QHCR and AERMOD) and associated guidance new to federally-required project-level “hot-spot” analyses poses significant challenges for state DOTs and other agencies with responsibilities in project implementation. The burden associated with the extensive new modeling requirements may be significantly reduced however through the development and implementation of standard programmatic agreements (PAs) and categorical determinations (CDs) that, once customized by state DOTs for application in their respective jurisdictions and executed with the US DOT, may be applied to appropriately categorize projects for carbon monoxide (CO) and particulate matter (PM) modeling. As resources permit, software may also be developed to facilitate the project assessment and categorization process.  

In general, projects would fall into one of two categories: 1) projects of a type and/or scope for which the potential air quality impacts are very limited and the project may therefore be assessed categorically consistent with federal regulations and guidance, or 2) projects with greater potential air quality impacts that would require detailed project-specific modeling. For projects that fall into the first category, the NEPA/conformity documentation for the project would reference the applicable PA/CD and provide project-specific data as needed to show that the applicable criteria from that PA/CD were met for that project. Project-specific modeling analyses would then not be required for that project for the pollutant(s) addressed in the PA/CD for which the criteria were met.

The technical criteria specified in the PA/CD would be developed based on the results of detailed modeling exercises conducted for several typical project types or categories, which would focus initially on highway projects but could be extended to intermodal and transit projects as resources permit. The modeling approach and results would be documented in detail in a technical support document (TSD) to be developed for the PA/CD as part of this study, and would meet or be consistent with as appropriate all applicable regulatory requirements and guidance. The criteria would generally be limited to reasonably-available project information such as forecast traffic (e.g., peak period/average daily traffic, and truck and bus percentages, or, preferably, increments thereto) and description or detail (e.g., project type, facility type and intersection skew angle) as well as relevant air quality information such as background concentrations.

Project deliverables, at least for the initial phase of the study, would include not only generic PAs/CDs but also technical support documents (TSDs) and associated modeling files. The PAs/CDs would be designed to meet US DOT approval once customized by state DOTs. A combined PA/CD format is needed for use in nonattainment and maintenance areas. The TSD, associated modeling files, and PAs/CDs would need to be designed to be readily-customizable by state DOTs for implementation in their respective jurisdictions. Software to facilitate project assessment and categorization in a manner consistent with the PAs/CDs would also be addressed as resources permit.

PAs/CDs would differ for CO and PM in a number of ways, including modeling approach,
level of detail, criteria to be recommended, and area of applicability (attainment/“not classified” areas versus nonattainment/maintenance areas). Regarding the latter, while documentation for CO would be needed for all areas, documentation for PM would generally be needed for nonattainment and maintenance areas only.

The modeling, identification of acceptable criteria, and preparation of PAs/CDs for CO is generally expected to be straightforward, in part because many states have previously developed PAs and CDs for this pollutant (based on the MOBILE series of models), giving this study a wealth of experience from which to draw, and in part because typical background concentrations are well under the NAAQS.

The opposite holds for PM: the modeling, identification of acceptable criteria, and preparation of PAs/CDs for this pollutant is not expected to be straightforward, given that the models and requirements are new, there appears to be little to no experience to draw upon in terms of PAs or CDs for this pollutant, and background concentrations in many areas approach or exceed the NAAQS. Innovative approaches for addressing PM in PAs and CDs would therefore need to be considered. Related research such as that underway at ICT would be reviewed to inform this effort.

A survey of state DOTs is recommended to support the development of both the PAs/CDs and the software. Regarding the former, state DOTs would be surveyed for examples of PAs and CDs (and associated modeling approaches and documentation) already in place relating to project-level air quality analyses and to identify any issues with their development and implementation. Work in
progress by state DOTs (including the ICT study referenced above) relating to the development of PAs, CDs, or criteria would be included in the survey. The survey results would be summarized and used to inform the modeling approach and development of PAs and CDs in this study.

Regarding the latter, State DOTs, the US DOT, and others as appropriate would be surveyed
for software in use or in development that would be feasible to employ or modify to meet with the objectives of this study[5]. The software to be developed for this study would need to be consistent with the final approach taken in or recommended for the PAs/CDs. A unified approach that
addresses the multiple pollutants considered in hot-spot analyses in one software package is desirable but not required. The survey would also identify interest and funding opportunities among state DOTs, the US DOT and others for development of software. Therefore, depending on resource availability and the results of the survey, a software development task could be initiated either as part of this NCHRP study or as a separate effort initiated following the completion of this study. The software development task could be conducted with NCHRP funding or as a joint effort depending on funding opportunities identified in the survey.

The study may be conducted in phases, with a focus for example on CO for highway projects for the initial phase, since this task may be expected to be relatively straightforward compared to PM. The initial phase for CO would include developing PAs and CDs, supporting technical analyses and documentation, and, as resources permit, software. PM (including other project types) could be addressed in a subsequent phase, following the completion of related research in progress. An alternative approach for the initial phase would be to develop PAs and CDs with supporting technical analyses and documentation for both CO and PM, leaving all software development to a future phase. Mobile source air toxics (MSATs) may also be addressed depending on resource
availability and interest among agency partners.