This report documents the technical results of a WSDOT-sponsored research effort to determine the nature and cause of congestion on Seattle-area freeways based on an analysis of available databases of traffic incidents and freeway performance. The focus of this effort was to develop a methodology for estimating freeway congestion as a function of its estimated cause (principally, its recurring or nonrecurring nature) by using readily available data, as well as to develop, implement, and use a prototype tool set that would apply that methodology.
The resulting methodology and tool set produce estimates of congestion (delay) associated with recurring and non-recurring conditions as a function of various user-specified parameters and assumptions. The method is able to analyze Seattle area corridors using data from existing databases. The process makes extensive use of the TRAC-FLOW analysis process, as well as supplementary prototype tools.