USE OF TOPAZ FOR TRANSPORTATION-LAND USE PLANNING IN A SUBURBAN COUNTY

Abstract

Techniques used to create and assess a variety of year 2000 joint land use and highway network patterns for Prince William county, Virginia, are described. The assessment has been done mainly in terms of travel and related impacts. The related impacts include the overall cost of travel, congestion levels, fuel consumption, and air pollution emissions. Volume capacity ratios on each highway link in the county were also estimated. A sketch-planning procedure called Technique for the Optimum Placement of Activities in Zones (TOPAZ) was used to allocate expected future land use activities to 11 districts in the county so as to minimize overall travel cost. Travel impacts were then analyzed in more depth through separate and more detailed models included in a model called Transportation Integrated Modeling Systems (TRIMS) used by the Metropolitan Washington Council of Governments. The results of these efforts led to several preliminary conclusions concerning not only the techniques themselves but also their place in the comprehensive planning process: (a) residents of the county will be faced with an increase in overall travel costs and congestion no matter which reasonable alternatives are implemented; (b) the most ambitious highway improvement program will reduce costs by about 9 percent, and the proper organization of land use will reduce this by an additional 6 percent; (c) future changes in external factors, such as population and fuel price levels, can have impacts on travel as substantial as those created through new highway construction and proper land use organization in the county; and (d) although TOPAZ supported the Prince William County comprehensive planning effort, it had relatively little direct impact on county decision makers, probably because it was not used at a time when citizens and local elected and appointed officials began to examine the draft comprehensive plan.

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