UC Davis Institute of Transportation Studies

In general, the limitations of the current California vehicle emissions inventory models can be summarized as:

- There is no direct connection between the regional emissions inventory model and the gridded emissions model. Separate model runs must be processed to develop regional emissions inventories and gridded emissions.

- The emission estimates from the regional emissions inventory model and the gridded emissions model are not in agreement.

- The regional emissions inventory model is not directly connected to the transportation forecasting models.

- The gridded emissions model has an inappropriate interface between the transportation data and the emissions rates.

The purpose of this study is to develop a new transportation and emission interface model. This requires advancing the knowledge with respect to gridded emissions calculations, as well as improving current spatial computations of emissions. Oriented at the grid cell level, the new model will establish a direct connection between regional emissions inventories for conformity and gridded emissions for airshed dispersion modeling.

The new model will be able to use transportation data from the standard four-step travel demand models, and emissions rates from EMFAC2000 or a set of newly developed link-based facility-specific CAMP running exhaust emissions rates. EMFAC2000 represents the latest understanding of mobile emissions development. Its algorithm and methodologies on basic emission rates development, driving cycle adjustment, speed adjustment factors, vehicle fleet age distribution, and traffic activity data significantly improve the emissions inventory estimates. Alternatively, the link-based CAMP emissions rates disaggregate travel activities by facility type, so that emissions rates will more closely represent link-level emissions than previously available. When developing emissions inventories, both transportation data and emissions rates will sit at the link level. This will ensure that transportation data and emissions rates in the new model sit at the same level of interface, and the model will be methodologically sound.

The implementation of the new model will be flexible with the ability to model areas ranging from county level to individual project level. The spatial and temporal emissions evaluation can be conducted at any level of the model's implementation.

The proposal is organized into five chapters. Chapter 2 provides a broad overview of related research in transportation and emissions modeling. A summary of the available transportation, emissions rates, and emissions inventory models is presented, and their strengths and weaknesses are discussed. Model development trends are discussed at the end of the chapter.

Chapter 3 provides an in-depth evaluation of the two emissions inventory models widely used in California (BURDEN7G and DTIM3). The strengths and weaknesses of each model are discussed. The chapter concludes with a summary of the challenges and motivations behind the proposed new interface model.

Chapter 4 presents the design of the new transportation and emission interface model. The model structure, required transportation data, emissions rates, and the interface of transportation data and emissions rates are discussed. Finally, Chapter 5 discusses the strengths and weaknesses of the new model.