Passage of the clean air act amendments of 1990 has initiated a new round of state implementation plans, and their associated current- and future-year mobile source baseline emission inventories. Existing highway vehicle emission inventory practices are assessed in 15 urban areas throughout the country, and these existing capabilities are compared with recommended epa guidance. Network-based travel demand model approaches are most frequently used and come closest to meeting urban area needs. However, existing approaches often are deficient in their estimation of highway vehicle speeds and also are inconsistent with methodological approaches used for national-level emissions inventories. A variety of institutional problems, though, may present more significant obstacles to the preparation of satisfactory mobile source inventories than any technical limitations. These problems include funding limitations, institutional fragmentation, lack of available technical expertise, and an unfortunately high level of staff turnover. This paper appears in transportation research record no. 1312, Energy and environmental issues 1991.
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