• Air Toxics
• CMAQ
• Conformity
• It All Adds Up

• Laws and Regulations
• Maps
• Policy and Guidance
• Research
• Resources
• Models & Methodologies
  • MOBILE
  • EMFAC
  • AP–42 Methods for Re-entrained Dust
  • MOVES
  • NMIM
  • Dispersion Models
  • Off-Model Analysis
  • Others
• Training

Off-Model Analysis

Air Quality analysis methodologies have become more refined over the years to fill the need in the transportation community to satisfy various requirements including Transportation Conformity and Congestion Mitigation and Air Quality Program project justification. Off-Model methods have been developed and refined to allow for analysis of innovative, as well as some common, projects to account for reductions in vehicular emissions. The most typical analysis is associated with Vehicle Miles of Travel (VMT) reductions, but reductions in emissions also can occur due to decreases in vehicular delay.

COMMUTER Model

Software

• COMMUTER Programs - EPA website for its COMMUTER Software, as well as related files

Training

• COMMUTER Model Workshop - FHWA Resource Center course that provides a comprehensive overview and analysis on EPA's COMMUTER Model, which estimates the travel and emissions impacts of transportation air quality programs focused on commuting

Transportation Control Measures / CMAQ Analysis

Under the transportation conformity regulation, Transportation Control Measures (TCMs) are strategies that

1. are specifically identified and committed to in State Implementation Plans (SIPs); and
2. are either listed in Section 108 of the Clean Air Act (CAA) or will reduce transportation-related emissions by reducing vehicle use or improving traffic flow such as improved public transit, traffic flow improvements and high-occupancy vehicle lanes, shared ride services, pedestrian/bicycle facilities, and flexible work.

Timely implementation of TCMs criterion must be satisfied before conformity determinations can be made. Consequently, TCMs receive the highest priority for funding under the Congestion Mitigation and Air Quality Improvement (CMAQ) Program. Off-Model methods have been developed to allow for emissions reduction analysis of these projects.

Policy & Guidance

• Diesel Retrofits: Quantifying and Using Their Emission Benefits in SIPs and Conformity - Guidance for State and Local Air and Transportation Agencies (EPA, February 2014) - Guidance on quantifying and using emission reductions from on-road and nonroad diesel vehicles, engines, and equipment that have been retrofitted with emission reduction technology. This guidance supersedes EPA's June 2006 guidance under the same name.

Research

• Off-Model Air Quality Analysis: A Compendium of Practice - FHWA Resource Center paper about Off-Model methods (analyses performed without the specific use of a Travel Demand Model) being successfuly used in the South

Training

• Air Quality Benefit Estimation Methodologies for TCM Projects - FHWA Resource Center course that covers available methods for virtually all eight major CMAQ project categories

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