DEVELOPMENT OF A DECISION/DEPLOYMENT SUPPORT TOOL FOR VARIABLE SPEED LIMITS IN RECURRENT CONGESTION

Traffic demand increases are pushing aging ground transportation infrastructures to their theoretical capacity. The result of this demand is traffic bottlenecks that are a major cause of delay on urban freeways. In addition, the queues associated with those bottlenecks increase the probability of a crash while adversely affecting environmental measures such as emissions and fuel consumption. With limited resources available for network expansion, traffic professionals have developed active traffic management systems (ATMS) in an attempt to mitigate the negative consequences of traffic bottlenecks. Among these ATMS strategies, variable speed limits (VSL) and ramp metering (RM) have been gaining international interests for their potential to improve safety, mobility, and environmental measures at freeway bottlenecks. Though previous studies have shown the tremendous potential of variable speed limit (VSL) and VSL paired with ramp metering (VSLRM) control, little guidance has been developed to assist decision makers in the planning phase of a congestion mitigation project that is considering VSL or VSLRM control. To address this need, this study has developed a comprehensive decision/deployment support tool for the application of VSL and VSLRM control in recurrently congested environments. The decision tool will assist practitioners in deciding the most appropriate control strategy at a candidate site, which candidate sites have the most potential to benefit from the suggested control strategy, and how to most effectively design the field deployment of the suggested control strategy at each implementation site. To do so, the tool is comprised of three key modules, (1) Decision Module, (2) Benefits Module, and (3) Deployment Guidelines Module. Each module uses commonly known traffic flow and geometric parameters as inputs to statistical models and empirically based procedures to provide guidance on the application of VSL and VSLRM at each candidate site. These models and procedures were developed from the outputs of simulated experiments, calibrated with field data. To demonstrate the application of the tool, a list of real-world candidate sites were selected from the Maryland State Highway Administration Mobility Report. Here, field data from each candidate site was input into the tool to illustrate the step-by-step process required for efficient planning of VSL or VSLRM control. The output of the tool includes the suggested control system at each site, a ranking of the sites based on the expected benefit-to-cost ratio, and guidelines on how to deploy the VSL signs, ramp meters, and detectors at the deployment site(s). This research has the potential to assist traffic engineers in the planning of VSL and VSLRM control, thus enhancing the procedure for allocating limited resources for mobility and safety improvements on highways plagued by recurrent congestion.

Credible Commitments and Post-Conflict Refugee Return: A Statistical and Network Analysis

I examine determinants of refugee return after conflicts. I argue that institutional constraints placed on the executive provide a credible commitment that signals to refugees that the conditions required for durable return will be created. This results in increased return flows for refugees. Further, when credible commitments are stronger in the country of origin than in the country of asylum, the level of return increases. Finally, I find that specific commitments made to refugees in the peace agreement do not lead to increased return because they are not credible without institutional constraints. Using data on returnees that has only recently been made available, along with network analysis and an original coding of the provisions in refugee agreements, statistical results are found to support this theory. An examination of cases in Djibouti, Sierra Leone, and Liberia provides additional support for this argument.

INTERGENERATIONAL SUPPORT AND WELL-BEING OF OLDER ADULTS IN CHANGING FAMILY CONTEXTS

This dissertation consists of three papers that examine the complexities in upward intergenerational support and adult children’s influence on older adults’ health in changing family contexts of America and China. The prevalence of “gray divorce/repartnering ” in later life after age 55 is on the rise in the United States, yet little is known about its effect on intergenerational support. The first paper uses the life course perspective to examine whether gray divorce and repartnering affect support from biological and stepchildren differently than early divorce and repartnering, and how patterns differ by parents’ gender. Massive internal migration in China has led to increased geographic distance between adult children and aging parents, which may have consequences for old age support received by parents. This topic has yet to be thoroughly explored in China, as most studies of intergenerational support to older parents have focused on the role of coresident children or have not considered the interdependence of multiple parent-child dyads in the family. The second paper adopts the within-family differences approach to assess the influence of non-coresident children’s relative living proximity to parents compared to that of their siblings on their provision of support to parents in rural and urban Chinese families. The study also examines how patterns of the impact are moderated by parents’ living arrangement, non-coresident children’s gender, and parents’ provision of support to children. Taking a multigenerational network perspective, the third paper questions if and how adult children’s socioeconomic status (SES) influences older parents’ health in China. It further examines whether health benefits brought by adult children’s socioeconomic attainment are larger for older adults with lower SES and whether one of the mechanisms through which adult children’s SES affects older parents’ health is by changing their health behaviors. These questions are highly relevant in contemporary China, where adult children have experienced substantial gains in SES and play a central role in old age support for parents. In sum, these three papers take the life course, the within-family differences, and the multigenerational network perspective to address the complexities in intergenerational support and older adults’ health in diverse family contexts.