Prioritization of Freeway Segments Based on Travel Time Reliability and Congestion Severity

Abstract

Improving road geometry to mitigate congestion within a given budget is a constant challenge for state agencies. It is important to prioritize among different projects to serve the need in the best possible way. Bottlenecks on freeways affect travel time reliability and congestion. Many prioritization methods have been developed to rank bottlenecks based on congestion. No existing research has tried to combine both travel time reliability and congestion to capture the effects of bottlenecks on freeways. A new index, vulnerability index, is developed combining buffer index and 95th percentile travel rate. This index reflects the effects of travel time reliability and congestion severity. Buffer index indicates the variability of travel time and 95th percentile travel rate indicates the congestion of the freeway. Interrelationships between buffer index and 95th percentile travel rate have also been analyzed. Two approaches (i.e. yearly data analysis, daily data analysis) have been used in estimating travel time reliability and congestion indices. Three prioritization methods have been proposed. One approach uses the yearly data, while the other approaches use the daily data to rank the freeway segments. US 169 NB and SB corridor has been used as the study corridors. Each corridor is segmented into three segments each, and the travel time reliability and congestion severity measures were estimated for each segment. The new prioritization methods are then applied to these segments, whose priorities were determined with the value of vulnerability index.