The National Academies

NCHRP Synthesis 20-05/Topic 51-18 [Active (Synthesis)]

Practices for Project-Level Analyses for Air Quality
[ NCHRP 20-05 (Synthesis of Information Related to Highway Practices) ]

  Project Data
Funds: $45,000
Authorization to Begin Work: 5/1/2019 -- estimated
Staff Responsibility: Tanya Zwahlen
Research Agency: Zamurs and Associates, LLC
Principal Investigator: John Zamurs
Effective Date: 9/19/2019
Fiscal Year: 2019

Final Scope

Air quality project-level analyses that state departments of transportation (DOTs) are required to prepare for purposes of the National Environmental Policy Act (NEPA) and the Environmental Protection Agency (EPA) transportation conformity rules are complicated, time-consuming and costly to prepare. Changes in the air quality requirements and associated guidance by federal and state agencies make transportation project-level analyses more challenging. As a result, state DOTs are conducting these project-level analyses in different ways.


The objective of this synthesis is to summarize existing practices related to project-level analysis for air quality by State DOTs.


Information to be gathered will include, but not be limited to:

·         Scoping practices and appropriately budgeting time and cost for consultant analyses by project type, pollutant and level of public interest

·         Which pollutants DOTs include in project-level analyses

·         Whether and when qualitative analyses are used where applicable, including indirect effects and cumulative impacts (IECI) and greenhouse gases (GHGs)

·         How DOTs approach screening, modeling and analysis for all regulatory pollutants, mitigation, quality assurance and control (QA/QC), agency and public consultation, risk management, time and cost constraints, and documentation

·         Modeling and data sources used for the analysis including traffic, emission (including construction), dispersion modeling (e.g. AERMOD, CALINE, Cal3QHC/R), and the determination of background concentrations

·         How DOTs may use streamlining tools, such as programmatic agreements, pre-vetted modeling inputs, templates and documentation


Information will be collected through literature review, survey of DOTs, and follow-up interviews with selected agencies for the development of case examples. A minimum of five representative case examples will be developed to describe assumptions, methodology and lessons learned for relevant pollutants identified by DOTs. The case examples will represent different regions of the country, levels of project analyses, facility types, and pollutants. Information gaps and suggestions for research to address those gaps will be identified.


Information Sources:

·         NCHRP 25-25 Task 78, “Programmatic Agreements for Project-Level Air Quality Analyses”, 2015. http://apps.trb.org/cmsfeed/TRBNetProjectDisplay.asp?ProjectID=3311 This study developed templates for clearing projects (typically ones of smaller scope or expected impacts) for one pollutant (CO). An update is in progress under Task 104.

·         NCHRP 25-25 Task 96, “Quick Reference Guide for Traffic Modelers for Generating Traffic and Activity Data for Project-Level Air Quality Analyses”, 2018 http://apps.trb.org/cmsfeed/TRBNetProjectDisplay.asp?ProjectID=3971 This recent report was designed as a supplement to NCHRP 765, which is the standard reference for traffic for project-level design purposes and may serve as a good example of the level of detail and coverage proposed for the air quality BPs.

·         NCHRP 08-101, “Enhanced Truck Data Collection and Analysis for Emissions Modeling”, in progress (expected publication early 2019) http://apps.trb.org/cmsfeed/TRBNetProjectDisplay.asp?ProjectID=3860

·         NCHRP 25-38, “Input Guidelines for Motor Vehicle Emissions Simulator Model”, 2014. http://apps.trb.org/cmsfeed/TRBNetProjectDisplay.asp?ProjectID=3191

·         NCHRP 25-25 Task 89, “Establishing Representative Background Concentrations for Quantitative Hot-spot Analyses for Particulate Matter”, 2014http://apps.trb.org/cmsfeed/TRBNetProjectDisplay.asp?ProjectID=3514

·         CalTrans, “Quantitative Particulate Matter Hot-Spot Analysis Best Practices Guidebook”, Version 2.0, CTAQ-RT-17-317.02.6, 2017. See: http://www.dot.ca.gov/env/air/docs/pm-hot-spot-best-practices- guidebook.pdf

·         CalTrans, “Streamlining Air Quality Dispersion Modeling to Support Quantitative Particulate Matter Hot-Spot Analysis”, CTAQ-RT-17-317.12.29, 2017. See: http://www.dot.ca.gov/env/air/docs/dispersion-modeling-support- pm-hot-spot-analysis.pdf

·         AASHTO, “Addressing Air Quality Issues in the NEPA Process for Highway Projects,” 2017, 22 pages. See: https://environment.transportation.org/center/products_programs/practitioners_handbooks. aspx#17

·         NCHRP 25-55 https://apps.trb.org/cmsfeed/TRBNetProjectDisplay.asp?ProjectID=4383

·         NCHRP 25-48 http://www.trb.org/Main/Blurbs/178003.aspx

·         National Assessment of Near-Road Air Quality in 2016: Multi-Year Pollutant Trends and Estimation of Near-Road PM2.5 Increment https://journals.sagepub.com/doi/full/10.1177/0361198119825538


Topic Panel

Beverly T. Chenausky, Arizona DOT

Thomas F. Hanf, Michigan DOT

Miles Kemp, Georgia DOT

Kathryn McKelvey, Pennsylvania DOT

Kathryn "Jenny" Narvaez, North Central Texas Council of Governments

Suriya Vallamsundar, Texas A&M Transportation Institute

Victoria Martinez, Federal Highway Administration

Christine Gerencher, Transportation Research Board


TRB Staff
Tanya M. Zwahlen


First meeting: September 19, 2019, Washington, DC 
Teleconference: TBD
Second meeting: June 15, 2020



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