Integration of Air Quality Models Used in Highway Air Quality Analysis

Focus Area

Air Quality


Air Quality






1-2 years

Research Idea Scope

There are several types of models used in analyzing highway emission impacts to air quality for both regional analysis and project or hotspot analysis. These models include traffic operations, transportation demand, emission factor, and dispersion models for most applications. Another type of model, although not typically used in the transportation analysis process are exposure models. Generally, the output of one model is used as input to another model, and thus the linkage of these models. Traffic operation and transportation demand models generate the volume of traffic and characteristics of that traffic such as speed. Emission factor models generate the emission rates in mass/distance or mass/time. Traffic characteristic and emission factors from these two types of models can be used together to develop emission inventories or can serve as inputs to dispersion models to yield concentrations in the ambient air. Concentrations outputs from dispersion models can then be used for exposure models to potentially provide some indication of the health effects and may provide risk assessment related to those emissions.

The study would examine the commonly used transportation demand and traffic models used when initiating air quality analyses. Since there is a variety of these models used, and since some models can be quite specific to a location, evaluation of all these models is not possible, but the inputs, outputs and assumptions that were used are relevant to all models. The emission factor models should generally focus on MOVES and EMFAC. An examination of these models would include the assumptions made in the traffic and transportation model output used with the emission factor models to yield inventories for regional analysis or as inputs themselves to dispersion models. Dispersion models discussions would evaluate the two commonly used dispersion models, AERMOD and CAL3QHCR, and possibly other dispersion models that may be considered useful in the discussion. Examination of exposure models and risk assessment could be optional as this topic isn’t generally dealt with in highway air quality impact assessment.

Each model (NETSIM, CORSIM, MOVES, EMFAC, AERMOD, CAL3QHCR..) and each model type (traffic, transportation demand, emission factor, dispersion) has certain assumptions built into its design and those assumptions need to be explored especially as it relates to the output they generate and how that output is then used in other models that it serves as input to. With the release of the MOVES model and the AERMOD model for transportation applications, and the requirements surrounding the use of these and other models, a study of this topic area would be timely and informative. The attached outline serves as a very fundamental format of the topics to cover to examine the linkages and interrelations between these models.

Urgency and Payoff

The benefits of such a study would be:

  1. Clarification of the proper use of the several types of air quality models used for regional and project level conformity as well as NEPA requirements
  2. Assessment of the accuracies and limitations of such models
  3. Increase the validity in using the models and confidence in the results obtained from the models
  4. Further the goal of the linking of the project planning and environmental review process ( Planning and Environmental Linkage – PEL) which may help “streamline” the environmental assessment process

Suggested By

Kevin Black, Federal Highway Administration

[email protected]