Abstract
Off-model tools are introduced, the role of off-model tools in supplementing regional network model-based conformity analysis is discussed, and the impact that these tools have had on recent conformity determinations in three nonattainment areas is assessed. The impact of off-model tools is examined through case studies from Chicago, Illinois; Richmond and Hampton Roads, Virginia; and statewide in Pennsylvania. In Chicago, Richmond, and Hampton Roads, the transportation improvement program or long-range plan conformity documentation was reviewed to determine what role off-model tools had in conformity analysis and what impact they had in conformity determinations. In Pennsylvania, projects were reviewed to assess the transportation and air quality impacts of a range of individual projects. Three primary conclusions can be drawn from the analysis: (a) off-model tools have had a significant impact in conformity analyses—often enabling a region to demonstrate conformity, (b) the data requirements are extensive and data collection may prove to be more time consuming than anticipated, and (c) off-model tools generally do not provide a framework for assessing the synergistic or systemic effects of projects. Further developments in off-model tools should focus on integrating off-model analysis with regional travel demand modeling processes and project data bases in an effort to develop a truly comprehensive modeling framework.
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