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Identification of Locations and Causes of Unreliable Travel Times on Virginia Freeways
Chien-Lun Lan, Ph.D., and Ramkumar Venkatanarayana, Ph.D., P.E
Chien-Lun Lan
Chien-Lun Lan
Year: 2019
VTRC No.: 22-R17

Travel time unreliability on roadway networks and its mitigation continue to be increasingly strong focus areas for many transportation agencies.  Although the transportation agencies and motorists are often interested in improving corridor and network travel time reliability, the predominant state-of-the-art methods available to practitioners focus on individual “hotspots.” 

This study first developed a systemic approach to calculate travel time reliability measures to analyze limited access facility links along with their detour routes or in conjunction with their upstream/downstream links.  A novel network screening methodology for travel time reliability called the “Top20-20” method was then developed that considered the hotspots (relatively smaller links) in conjunction with their spatiotemporal contexts.  Methods for performing corridor causal event analyses in conjunction with the causal events at the link hotspots were also developed.  These methods were applied to a large 2,800-mile limited access facility network in Virginia.  A qualitative validation of these methods and their results was conducted using an expert panel, and the concepts were found to be sound.  The validation expert panel identified several use cases for these planning-level methods and results, including travel time reliability needs identification for long-range planning and development and implementation of operational strategies for improving travel time reliability on corridors and in networks. 

The study recommends that the Virginia Department of Transportation (1) consider applying systemic analyses wherever corridor travel time reliability is the main focus; (2) conduct additional research to further the developed methods; and (3) pursue computational resources needed to carry out the systemic analyses.