New Approached to Urban-Scale Transporation Emissions Modeling Under a New Clean Air Act

In 1990, America renewed its commitment to clean air. While the detrimental effects of air pollution could be observed in the countryside as well as the cities, the most influential stimulus to re-attack the problem with vigor arose during the drought summer of 1988, when record numbers of urban areas experienced violations of the ambient ozone standard and the U.S. population exposed to "bad air" exceeded 120 million. Thus, urban pollution was once again the catalyst to action, and became the primary focus of the nation’s fight for better air. The sources of urban air pollution were well known and documented, but standard practice in estimating the specific contribution of these sources (hence their appropriate respective roles in scaling back emissions) has been found in many instances to be no more precise now than in the late 1970s, as development of the last major round of State Implementation Plans (SIPs) was underway around the nation. In particular, techniques of estimating (and forecasting) emissions from transportation sources in specific urban areas, with the possible exception of those in California, have not progressed significantly in ten years. Reasons for this are numerous, many of which have been beyond the control of the responsible state and regional agencies, but the fact remains that significant imprecision in urban-scale transportation emissions modeling persists at the very time that greater precision is most needed, driven by the relatively stringent control requirements for chronic and severe air quality non-attainment areas. The objective of this paper is to identify possible ways for state and regional planners to improve estimation of mobile source emissions without the need for substantially more resources than would have to be allocated in any case to compliance with requirements of the 1990 Clean Air Act Amendments (CAAA), and by using tools and data sources that are already "on the shelf."