University of California Transportation Center

The failures of models used in the analysis of travel and vehicle emissions effects of transportation plans and policies have been enumerated by many in the transportation profession over a period of almost three decades. Models can be insensitive to policy effects, and predictions are typically inaccurate. Despite these shortcomings, travel and emission modeling continues to be widely employed in transportation and environmental policy analysis. Within the last decade, travel and emission modeling has been made necessary by the Clean Air Act Amendments of 1990 (CAAA), the Intermodal Surface Transportation Efficiency Act of 1991 (ISTEA), and its successor the Transportation Equity Act for the 21st Century (TEA-21). Moreover, the legislation and resulting regulation demand a high degree of accuracy and precision from these models.