Air Quality and Planning and Environmental Linkages

Greenhouse Gas (GHG) & Climate Change

Climate Change can be felt through increasing severity and longer duration of major heat wave, drought, wildfire, high wind, heavy rainfall, and higher storm surge as a result of sea level rise. Potential impacts to the State Highway System include flood, washout, landslide, pavement deterioration, slope instability, bridge scour, and increased wildfires. As California faces these extreme weather events, the transportation infrastructures must be prepared to withstand such forces of nature in order to maintain the lifelines of the State. Efforts are currently underway to plan and implement a resilient transportation system to reduce the impacts of Climate Change. State and regional transportation agencies are incorporating resiliency needs into the transportation planning processes while minimizing transportation-related fuel consumption and air pollution.

The predominant driver of Climate Change is greenhouse gas (GHG). The transportation sector is a major contributor of greenhouse gas (GHG) emissions. Mobile source GHG includes carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), black carbon (BC), and fluorinated gases including hydrofluorocarbons (HFCs). While GHG regulations can differ in some aspects than the other air pollutants, mitigation measures to reduce GHG have been noted to also reduce air pollutants. Energy and fuel consumptions are major factors of a GHG analysis. The same fuel combustions that produce air pollutants also generate GHG. As such, many of the tools available to estimate GHG emissions are the same as air quality analysis.

On-Road GHG Emissions

The analysis approaches for on-road GHG emission differ depending on the context of the discussion. Caltrans prefers to conduct project analysis using a travel activity-based approach that relies on speed-distributed travel activity data and gram-per-mile (g/mi) emission factors from EMFAC. Regional analyses and the annual statewide GHG inventory prefer to use a fuel-based approach that relies on fuel sales data and the carbon content of the fuel mixtures. For project-level application, the fuel-based approach has limitations in developing project-specific fleet fuel economy and reflecting variations in project travel activities (e.g., speed changes during peak and off-peak time periods).

  • EMFAC The ARB EMFAC model includes CO2 and CH4 emissions. Typically, the EMFAC-PL module would be used to conduct a project-level analysis.
  • CT-EMFAC Caltrans developed the CT-EMFAC to combine the emission factors from EMFAC with project-specific vehicle activity data (e.g. traffic volume, speed, and fleet mix) to calculate emissions for multiple project scenarios (e.g. no-build and build alternatives), roadway links, and time period.

Construction GHG Emissions

GHG analysis may entail a full life-cycle assessment of a project, from the initial construction to long-term operation and maintenance of the facility. Construction GHG emissions may include material processing and delivery, on-site construction equipment, and traffic delays due to construction. To estimate construction GHG emissions, the following tools are available for consideration.
  • Caltrans Construction Emissions Tool (CAL-CET) v1.1, November 2018 CAL-CET Technical Support Document (PDF)  Caltrans developed the CAL-CET to analyze construction emissions for various types of highway improvement projects that Caltrans administers annually statewide. The methodology and assumptions are based on Caltrans-specific data and construction practices, knowledge, and experiences. For non-Caltrans projects, consideration should be given to account for differences between Caltrans equipment rental rates and construction fleets and the lead agency’s construction practices. 
  • Road Construction Emission Model (RCEM) The RCEM was developed by the Sacramento Metropolitan Air Quality Management District (Sac Metro) as a part of their CEQA Guidance & Tools to analyze construction emissions for roadway projects within the Sacramento region. For projects outside of the Sac Metro jurisdiction, please be aware that RCEM utilizes emission factors specific to the Sacramento region.
  • FHWA Infrastructure Carbon Estimator (ICE) The ICE was developed by the FHWA to estimate the lifecycle energy and GHG emission from construction and maintenance of transportation facilities. It is based on national average data.
  • California Emissions Estimator Model (CalEEMod) The CalEEMod was developed for the California Air Pollution Officers Association in collaboration with several local air districts. This is a statewide land-use emission model that include a construction emission module. CalEEMod's primary focus is on land development projects more so than roadway projects. It is more viable for projects that involve building structures or parking lots facilities, such as offices, safety roadside rest areas, park and rides, or transit hubs.
  • ARB Off-road Diesel Analysis & Inventory Construction equipment is classified as off-road. The predominant fuel type for construction equipment is diesel. ARB OFFROAD model provides emission factors for analysis of off-road equipment.

Additional References

Project-Level Air Quality Analysis

Air quality analysis is a complex process that must follow established regulatory procedures and requirements. The information and tools described below comprise of materials developed by Caltrans, as well as materials developed by external agencies including the U.S. Environmental Protection Agency (EPA), the Air Resources Board (ARB), and local air districts.

The graphic below presents a simplified visual aid of the necessary information and the tools available to complete an air quality analysis.

Travel Activity Data

Travel Forecast In general, the basis of transportation project air quality analysis is directly attributed to how a transportation project affects travel activity and traffic flow. Assembling travel activity data is one of the first step of an air quality analysis.
  • DataBridge DataBridge is a spreadsheet tool that process travel activity data into a compatible input format for CT-EMFAC and EM4AQ.

Emission Modeling

Criteria Pollutants

The EPA sets National Ambient Air Quality Standards (NAAQS) for six common air pollutants, also known as criteria pollutants. These pollutants are particulate matters (PM10 and PM2.5), ozone, carbon monoxide, sulfur oxides, nitrogen oxides, and lead. In addition to the NAAQS, there is also the California Ambient Air Quality Standards.

  • EMFAC The EMFAC is the mobile source emission inventory that ARB developed to assess emissions from on-road vehicles in California. The latest version, EMFAC2014, was approved for use in transportation conformity analyses by the EPA on 12/14/15, under the federal register docket number EPA-R09-OAR-2015-0779.
  • CT-EMFAC Caltrans developed the CT-EMFAC to combine the emission factors from EMFAC with project-specific vehicle activity data (e.g. traffic volume, speed, and fleet mix) to calculate emissions for multiple project scenarios (e.g. no-build and build alternatives), roadway links, and time period. CT-EMFAC can also estimates Mobile Source Air Toxics.

Mobile Source Air Toxics (MSAT)

In addition to the criteria pollutants, the EPA identified nine air toxic compounds with mobile sources as the considerable contributors. These are 1,3-butadiene, acetaldehyde, acrolein, benzene, diesel particulate matter (diesel PM), ethylbenzene, formaldehyde, naphthalene, and polycyclic organic matter.

FHWA considers these as priority mobile source air toxics to be considered in NEPA documents. The FHWA issued an Updated Interim Guidance on Mobile Source Air Toxic Analysis in NEPA Documents on 10/18/2016. The guidance describes three categories for analyzing MSAT in NEPA documents, depending on specific project circumstances:

    1. No analysis for projects with no potential for meaningful MSAT effects;
    2. Qualitative analysis for projects with low potential MSAT effects; or
    3. Quantitative analysis to differentiate alternatives for projects with higher potential MSAT effects.

Construction Emission Analysis

Construction can result in fugitive dust emissions and engine exhaust emissions from various types of activities. While construction emissions are typically considered as temporary impacts, in areas that are non-attainment or attainment (maintenance) for CO or PM, construction emissions must be included in the conformity hot-spot analysis if construction will last more than five years at any individual site (40 CFR 93.123(c)(5)).

Analysis for shorter construction periods may be considered for NEPA and CEQA if sensitive receptors, such as schools, hospitals, elderly-care facilities, or child-care facilities, are nearby, or if construction emissions are anticipated to be high. Consult with the project's Caltrans Headquarters Environmental Coordinator if a construction emission analysis is being considered for the project.

  • Caltrans Construction Emissions Tool (CAL-CET) v1.1, November 2018 CAL-CET Technical Support Document (PDF)  Caltrans developed the CAL-CET to analyze construction emissions for various types of highway improvement projects that Caltrans administers annually statewide. The methodology and assumptions are based on Caltrans-specific data and construction practices, knowledge, and experiences. For non-Caltrans projects, consideration should be given to account for differences between Caltrans equipment rental rates and construction fleets and the lead agency’s construction practices.
  • Road Construction Emission Model (RCEM)  The RCEM was developed by the Sacramento Metropolitan Air Quality Management District (Sac Metro) as a part of their CEQA Guidance & Tools to analyze construction emissions for roadway projects within the Sacramento region. For projects outside of the Sac Metro jurisdiction, please be aware that RCEM utilizes emission factors specific to the Sacramento region.
  • California Emissions Estimator Model (CalEEMod) The CalEEMod was developed for the California Air Pollution Officers Association in collaboration with several local air districts. This is a statewide land-use emission model that include a construction emission module. CalEEMod's primary focus is on land development projects more so than roadway projects. It is more viable for projects that involve building structures or parking lots facilities, such as offices, safety roadside rest areas, park and rides, or transit hubs.
  • ARB Off-road Diesel Analysis & Inventory Construction equipment is classified as off-road. The predominant fuel type for construction equipment is diesel. ARB OFFROAD model provides emission factors for analysis of off-road equipment.

Dispersion Modeling

Carbon Monoxide Dispersion Modeling

  • CO Protocol The CO Protocol provides procedures and guidelines to conduct a project-level CO analysis. *Do Not use Appendix A of the CO Protocol. Appendix A is no longer applicable. Where the CO Protocol mentions EMFAC or CT-EMFAC, refer to the criteria pollutants estimate guidance above for the latest required model.
  • CALINE4 CALINE4 manual and background information about the development of the model. The CALINE4 dispersion model is currently only applicable for CO hot-spot analysis, as referenced in the CO Protocol. *DO NOT use CALINE4 to analyze any other pollutant.

Particulate Matter Dispersion Modeling

  • EPA Guidance on PM Hot-Spot Analysis The EPA "Transportation Conformity Guidance for Quantitative Hot-spot Analyses in PM2.5 and PM10 Nonattainment and Maintenance Areas" provides procedures and guidelines to conduct a project-level PM hot-spot analysis. Where the guidance mentions EMFAC or CT-EMFAC, refer to the criteria pollutants estimate guidance above for the latest required model.
  • AERMOD Dispersion Model AERMOD is codified in 40 CFR Part 51 Appendix W as the EPA's preferred/recommended model to conduct project-level PM hot-spot analysis.
  • Paved Road Dust
  • EM4AQ This spreadsheet processes CT-EMFAC PM emissions data and the project-level travel activity data into AERMOD-ready hourly emission rates inputs for PM hot-spot modeling. *Note, the DataBridge can assist with preparing the project-level travel activity data for EM4AQ.
  • DVTOOL The DVTOOL assists with calculating "Design Value" for a project-level PM hot-spot analysis.

Other References

Project-Level Air Quality Overview

The Federal Clean Air Act (e.g. Transportation Conformity), the California Clean Air Act, the National Environmental Policy Act (NEPA), and the California Environmental Quality Act (CEQA) require transportation planning and project development to consider air quality as a part of the environment review process. Caltrans coordinates with Federal, State, and regional transportation planning agencies and local air districts to address transportation-related air quality issues. The Department develops policies, guidance, and tools to conduct air quality analyses in compliance with Federal and State regulations. Caltrans also initiates and participates in air quality researches and studies to advance its scientific knowledge and state-of-practice on the subject.

For more information on Transportation Conformity, NEPA, and CEQA, as well as other air quality policies, guidance, forms, and templates, refer to the Caltrans Standard Environmental Reference, Chapter 11 – Air Quality.

Research and Studies

Caltrans has carried out air quality research since the 1970s. Some of the first mobile-source dispersion models were developed here; Caltrans worked with the Air Resource Board (ARB) developing early versions of EMFAC; key mobile source emission data were collected by Caltrans in collaboration with ARB and others, and Caltrans has worked with various university partners including the University of California, Davis and Riverside.

From the late 1990s until about 2008, Caltrans had an ongoing relationship with the University of California, Davis (UCD) that we called the "Caltrans/UCD Air Quality Project" (UCD usually reversed that: UCD/Caltrans). Since about 2008, air quality research has continued under the auspices of the Caltrans Divisions of Research and Innovation, Environmental Analysis, and Transportation Planning. Caltrans staff members also frequently participate in working groups and research project panels with the American Association of State Highway and Transportation Officials (AASHTO) and the Transportation Research Board (TRB)/National Cooperative Highway Research Program (NCHRP).

This site attempts to make available a central directory of Caltrans-sponsored and partnered air quality research project results. It's organized partially by time period, and also by performing entity or project. It's not by any means exhaustive, but an effort has been made to be reasonably complete. In most cases, products are listed as links to another web site, whether within Caltrans or external; there is no guarantee that such links will remain active.

Please note that most of these documents and data files are historical in nature and may not be directly related to current policies. In addition, by their nature (scanned images of paper documents or raw data files in many cases) they may not fully comply with Section 508 of the U.S. Rehabilitation Act.

Links

 

Statewide Conformity Working Group

Transportation Conformity

"Conformity" is a requirement of the Federal Clean Air Act (Section 176(c), at 42 U.S.C. 7506 (PDF) (c)), to ensure that federal actions are consistent with the State Implementation Plan ("SIP") to achieve and maintain Federal air quality standards. "Transportation Conformity" requirements for highway and transit projects are defined by U.S. Environmental Protection Agency (EPA) regulations in 40 CFR 93 Subpart AUS EPA and US DOT (FHWA) guidance, and local consultation procedures set up by Metropolitan Planning Organizations and Air Pollution Control Districts. The map and table below illustrate the areas that are subject to Transportation Conformity requirements in California in 2014. For other types of federal actions, not related directly to highways and transit, the conformity process is governed by 40 CFR 93 Subpart B (General Conformity).

Conformity requirements apply only in areas that are designated nonattainment, or attainment with a "Maintenance SIP" as defined in 42 U.S.C. 7505a (PDF) , by the US EPA. It applies only for the pollutants that trigger those designations, and analysis requirements only apply to those pollutants. It is therefore possible for some conformity procedures (for instance, project-level hot spot requirements) to be inapplicable if the area is attainment/unclassifiable for the pollutants triggering them, even though the area is subject to conformity requirements in general. Conformity requirements do not apply at all if an area is attainment/unclassifiable for all federal air quality standards.

 

Or view a Table of Areas Subject to Transportation Conformity Requirements (PDF) (645 KB)

How to Participate

The Statewide Conformity Working Group is a coordinating group for discussion and interagency agreement about transportation-related air quality and Federal Clean Air Act conformity issues in California. The public is welcome to participate, and there is a time on the agenda for public comment regarding issues not otherwise on the agenda. Actions taken by the group are not regulations; rather, they are informational in nature, or are agreements regarding procedures and interpretation of the transportation conformity regulations to be used by transportation agencies and project proponents.

Statewide Conformity Working Group meetings are generally held twice a year by teleconference. Teleconference access to the meeting is provided through regional call centers, usually located at offices of regional transportation planning agencies, air pollution control or air quality management districts, or Caltrans. Individual call-in access to the teleconference may also be provided; please contact the Working Group chair to arrange it.

The meeting and call center locations, with site contact information, are noted on the printable copy of the agenda for each meeting. Contact information for the call centers is also provided on the agenda.

Caltrans maintains an electronic mail list to forward announcements and other information to the working group. For network security reasons, the list archives are only available to list members. Go to the mailing list page to sign up.

Interagency Consultation in General

The Federal Clean Air Act "conformity" process includes an Interagency Consultation process that involves Federal Agencies (US EPA, Federal Highway Administration, and Federal Transit Administration), the State transportation agency (Caltrans), the State air quality management agency (California Air Resources Board), and regional transportation planning and air quality agencies (Metropolitan Planning Organizations, Air Pollution Control/Air Quality Management districts, and in some California cases Regional Transportation Planning Agencies). Transit and other transportation service providers are also involved.

Most Interagency Consultation occurs at the regional level. An Interagency Consultation group for the conformity process exists in all Federal nonattainment areas. In most cases, the Transportation Planning Agency (Metropolitan Planning Organization - MPO) is the lead agency for the consultation process.

The Statewide Conformity Working Group coordinates and considers issues of a statewide nature. The Group normally meets twice a year: usually in March and September or October. Meetings are held by teleconference using regional call-in meeting centers to minimize travel.

Statewide Conformity Working Group meetings, as with regional Interagency Consultation meetings in the Transportation Conformity process, are open to the public. Members of the public who wish to attend should either call in to the teleconference using the number announced here or arrange with regional teleconference coordinators for attendance. Regional teleconference centers and the agenda are usually posted at this site 1-2 weeks before the meeting.

The Statewide Conformity working group has been meeting since the mid-1990's. Formal Interagency Consultation requirements for conformity purposes came from the 1990 Federal Clean Air Act Amendments and the EPA Conformity Regulations at 40 CFR Part 93. The group was chaired initially by Caltrans, then by the California Air Resources Board until 2003. The Federal Highway Administration, California Division chaired the group in 2003, and US EPA, Region IX chaired the group in 2004. The group is currently chaired by the California Department of Transportation (Caltrans), Transportation Planning Division, and suggestions or requests for agenda items should be sent to a Caltrans conformity staff member.

2018 Meetings

2017 Meetings

Hot Topics

 

Guidelines and Procedures

  • Under development