EXAMINATION OF INDICATORS OF CONGESTION LEVEL

This research report examines the relationships between many possible indicators of congestion and estimated congestion level in an attempt to identify and validate indicators for areawide congestion measurement purposes. The study estimates the congestion level for 50 large and medium-sized U.S. urban areas with 3 congestion measures. The estimated congestion level for each urban area is then graphically and statistically compared to indicators composed of travel, facility supply, and demographic characteristics to determine close relationships. Two of the congestion measures used in this study, the roadway congestion index and the congestion severity index, produced results with a high correlation to each other. An index-incorporating congestion duration on freeway segments (lane-mile duration index) suffered from unobtainable data for several urban areas and was consequently less comparable between the other two measures. It was determined that two indicators related to travel intensity--daily vehicle miles of travel per lane-mile and daily vehicle miles of travel per square mile--had the closest correlation to estimated congestion levels. Average annual daily freeway traffic per hourly capacity, previously used as a facility measure, was identified also as having a close relationship to areawide congestion level.