Forecasting Traffic Impacts on a Citywide Street Network in the Absence of a Travel Demand Model

Abstract

A process is described for predicting traffic volumes along the transportation network of a small city in western Oregon, for which a travel demand model is not available. A cumulative analysis method which considered traffic generated by expected development as well as external traffic traveling through the study area, was used. A buildable lands inventory based on tax assessor records and a geographic information system (GIS) was updated and queried to identify vacant and underdeveloped parcels inside the city limits. The city's comprehensive plan was used to identify expected growth by land use category. GIS tools were used to allocate growth on the basis of the location and attractiveness of available land, its access to urban services, and current plan designations. Peak hour trip generation was calculated with the Institute of Transport Engineers's Trip Generation report. Trips were distributed to the network, following general principles of the gravity model and by using historical traffic counts as a guide. Through trips were identified by using a number of factors including road classification, existing traffic volumes, and historical growth rates. Trips were assigned and used to identify deficiencies on the future transportation network. This process is valuable to cities developing long-range transportation plans in the absence of a travel demand model. The tools needed for this analysis—comprehensive plan, tax assessor data, trip generation rates—are available to cities of all sizes. Innovations in the geospatial analysis arena facilitate this analysis without requiring large investments of time or money.