In 2002, Pierce County developed its first ever Traffic Impact Fee program system based on provisions of the Washington State Growth Management Act. Both Geographic Information Systems (GIS) and a travel demand model (EMME/2) were heavily utilized in developing and calculating "fair-share" contributions that developers will pay toward County roadway improvements. Twelve Transportation Service Areas (TSAs) were created in the unincorporated area. A daily service threshold (capacity) was established. Existing roadway deficiencies and future improvement needs were determined by using observed traffic counts and the model forecasts. The analytical powers of GIS and EMME/2 enabled creation of a system that has several features that are uncommon among most impact fee systems in the country. First, the system requires that developers in every TSA pay for a portion of road improvements throughout the County based on their expected traffic impacts on each improvement. Secondly, impacts will be assessed based on each TSA's projected percentage of new Vehicle Miles Traveled (VMT) on each project segment, instead of the traditional approach of using traffic volumes. This requires longer trips to pay more based on their travel distance. Thirdly, a procedure was developed to separate out truly "new" trips from "redistributed" background trips that are inherent in any future trip table. For each existing Transportation Analysis Zones (TAZ), a "mirror" TAZ was created to represent only the "new development" trips. The "new" trips determine the impacts of future traffic, rather than the common method of including redistributed trips in the calculation.
Abstract