Traffic congestion is a major freeway operational problem in Washington State due to significant increases in traffic demand in Washington's metropolitan areas over the past decades. Recent studies showed that about 50% of freeway congestion in the United States results from traffic incidents. Therefore, a better understanding of incident-induced delay can help the Washington State Department of Transportation (WSDOT) identify countermeasures against freeway traffic congestion.

The WSDOT has invested in several research projects for improving its understanding of freeway traffic congestion. Most of these research efforts rely on inductance loop data to identify freeway bottlenecks and calculate cost of congestion. However, the credibility of these studies is discounted by errors in loop detector data. Inductance loop detectors are subject to various malfunctions that significantly compromise the quality of loop data. Identifying loop detector malfunctions and improving loop data accuracy are extremely important for both traffic research and operations.

Therefore, the first objective of this study is to develop a new method for improving inductance loop data quality. Such a new method takes advantage of high-resolution loop event data to conduct in-depth investigations of loop detector health. Malfunctioning loops must be identified and fixed to ensure good quality loop data.

Considering that capacity-reducing incidents are a major cause of freeway congestion, the second objective of this study is to develop an innovative method for quantifying incident-induced delay based on incident log data and quality loop data. The method combines theories of deterministic queuing, shock-wave propagation, and travel time estimation for quantifying incident-induced delay. Precisely calculated delay data can help transportation agencies estimate congestion cost and compile appropriate policies to mitigate freeway congestion.

Each proposed new method will be implemented in a computer application to automate the computational process. These computer applications have the potential to serve as standard tools for loop data quality control and freeway delay analysis.