A. James Clark School of Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/1654
The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item Evasive Flow Capture(2013) Markovic, Nikola; Schonfeld, Paul; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The flow-capturing location-allocation problem (FCLAP) consists of locating facilities in order to maximize the number of flow-based customers that encounter at least one of these facilities along their predetermined travel paths. In FCLAP, it is assumed that if a facility is located along (or "close enough"' to) a predetermined path of a flow, the flow of customers is considered captured. However, existing models for FCLAP do not consider the likelihood that targeted users may exhibit non-cooperative behavior by changing their travel paths to avoid fixed facilities. Examples of facilities that targeted subjects may have an incentive to avoid include weigh-in-motion stations used to detect and fine overweight trucks, tollbooths, and security and safety checkpoints. The location of these facilities cannot be adequately determined with the existing flow-capturing models. This dissertation contributes to the literature on facility location by introducing a new type of flow capturing framework, called the "Evasive Flow Capturing Problem" (EFCP), in which targeted flows exhibit non-cooperative behavior by trying to avoid the facilities. The EFCP proposed herein generalizes the FCLAP and has relevant applications in transportation, revenue management, and security and safety management. This work formulates several variants of EFCP. In particular, three optimization models, deterministic, two-stage stochastic, and multi-stage stochastic, are developed to allocate facilities given different availability of information and planning policies. Several properties are proved and exploited to make the models computationally tractable. These results are crucial for solving optimally the instances of EFCP that include real-world road networks, which is demonstrated on case studies of Nevada and Vermont.Item Scheduling under uncertainty for a Single-Hub Intermodal Freight System(2010) Markovic, Nikola; Schonfeld, Paul; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis addresses the optimization of an intermodal system with freight transfers at a single hub. It investigates the transportation processes and constraints that arise in a system's recovery after a major disruption during which backlogs have accumulated along the routes. When dealing with the backlogs, the system operator must coordinate the transportation processes and control the inflow of freight to the terminal in order to avoid overloading its storage facilities, which might reduce the throughput of the system. The coordination of transportation processes during the system's recovery can further improve the overall system performance by reducing the dwell time, increasing vehicle utilization and reducing late delivery penalties. This work focuses on the scheduling problem and develops an approach that would help the system operator reduce the overall system cost while taking into account the constraints arising in actual intermodal and intra-modal systems. Assuming that the schedule on some routes is exogenously determined and inflexible, we seek to optimize the schedules of vehicles on remaining routes. Models are developed that minimize the total cost of operating an intermodal system with freight transfers at one hub by optimizing the departure times of vehicles on the routes with flexible schedules. This model can be solved numerically without the approximations of alternative methods such as simulation. Moreover, it can be successfully applied to situations when statistical or queuing analyses are not applicable due to the small number of events (vehicle arrivals). We specifically analyze an intermodal system consisting of multiple feeder truck routes and multiple main airline routes. The specific example of two transportation modes was used to make the development and application of the model easier to understand. However, the mathematical model developed in this thesis is applicable to any other combination of transportation modes using discrete vehicles.