The Highway Congestion Monitoring Program (HICOMP) of the California Department of Transportation (Caltrans) is a legislatively mandated program. On an annual basis, Caltrans provides highway congestion information to the legislature for highway performance monitoring and improvement purposes. In this paper, the state of the practice of highway congestion monitoring in California is presented. This includes the congestion definition, congestion data collection and estimation methodologies, and congestion reporting formats. Both floating car and loop detector-based methods of highway congestion data collection are discussed in detail, with an explicit evaluation of their accuracies and compatibilities as a special feature. Applications of global positioning system and freeway performance measurement system in improving the highway performance monitoring program are also presented. (a).
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