The development and application of a load-based modal emissions model

In order to develop and evaluate transportation policy in the United States, agencies at the local, state, and federal levels currently rely on the mobile source emission-factor models that predict vehicle emissions based primarily on average trip speeds. These models are not well suited for evaluating transportation improvements at the microscopic level. Modal emission models, on the other hand, can be appropriately applied. A modal emission model considers at a more fundamental level the detailed operation of a vehicle, i.e. emissions that are directly related to vehicle operating modes such as idle, steady-state cruise, various levels of acceleration/deceleration, etc. Researchers at the University of California Riverside are currently carrying out a four-year project developing a comprehensive modal emissions model for light duty vehicles. This project involves a substantial amount of vehicle emissions testing of over 300 vehicles from a variety of vehicle/technology categories. A number of sub-models were created representing the different vehicle/technologies, including modeling of high-emitting vehicles. The overall model output has been compared with independent emission measurements with promising results. This paper briefly describes research to date on the development of the model long with its associated vehicle testing program. The overall concept of the model is then described, followed by a discussion of how the modal emissions model can be integrated into various transportation modeling frameworks. Numerous integration issues are discussed, including vehicle fleet distribution, vehicle operating parameters, temporal level-of-detail, and vehicle aggregation.