Travel time reliability in transportation networks: A review of methodological developments

•Review the methodological developments on modeling travel time reliability (TTR).•Provide an integrated framework from the network perspective to review the TTR.•Present methods for modeling uncertainty propagation from the sources to the TTR.•Discuss future research directions in the era of new environments and technologies. The unavoidable travel time variability in transportation networks, resulted from the widespread supply-side and demand-side uncertainties, makes travel time reliability (TTR) be a common and core interest of all of the stakeholders in transportation systems, including planners, travelers, service providers, and managers. This common and core interest stimulates extensive studies on modeling travel time reliability. Researchers have developed a range of theories and models of TTR, many of which have been incorporated into transportation models, transport policies, and project appraisals. Adopting the network perspective, this paper aims to provide an integrated framework for summarizing the methodological developments of modeling TTR in transportation networks, including its characterization, evaluation and valuation, and traffic assignment. Specifically, the TTR characterization provides a whole picture of travel time distribution in transportation networks; TTR evaluation and TTR valuation (known as the value of reliability, VOR) interpret abstract characterized TTR in a simple and intuitive way in order to be well understood by different stakeholders of transportation systems; and lastly TTR-based traffic assignment investigates the effects of TTR on the individual users’ travel behavior and consequently the collective network flow pattern. As the above three topics are mainly separately studied in different disciplines and research areas, the integrated framework allows to better understand their relationships and may contribute to developing more possible combinations of TTR modeling philosophy. Also, the network perspective enables to pay more attention to some common challenges of modeling TTR in transportation networks, especially the uncertainty propagation from the uncertainty sources to the TTR at various spatial levels including link, route, and the entire network. Some potential directions for future research are discussed in the era of new data environment, applications, and emerging technologies.