Transportation Problems with Safety and Security Considerations

Safety and security are of primary concern for any transportation system, which include safety of passengers, shipments, transporters and environment. Internal and external resources are being used to enhance the safety of a transportation system. In this dissertation three optimization problems of transportation units with external resources for safety and security considerations have been studied in three areas of routing, assignment and scheduling. The first two problems relate to routing and formation of convoys and the third problem addresses the assignment and scheduling of tugboats as external resources for container vessels.;The first study relates to "convoy movement problem: a civilian perspective" in peacetime by seeking to minimize civilian traffic disruptions. The Convoy Movement Problem is a special case of the vehicle routing and scheduling problem in which vehicle length cannot be neglected and in which there are special rules regarding convoy encounters on the network. We develop a hybrid algorithm that combines the k-shortest path algorithm along with a branch and bound method for finding a minimum weighted k-clique in a k-partite graph. Through this coupling scheme, we are able to solve large instances of the convoy movement problem without relaxing any of its complicating constraints. An experimental study is performed based on pseudo transportation networks to illustrate the computational viability of the method as well as policy implications.;In the second study, "Exploration of Strategies to Form Convoys to Facilitate Effective Movement of Items", we introduce and analyze the convoy formation problem for multiple origins and destinations. The goal of this problem is to define feasible vehicle configurations for convoys, i.e. convoy formations, that lead to superior route choices for the convoy movement problem. We start by using hypothetical staircase paths for each pair of origin and destination and then sequentially solve the demand satisfaction and vehicle assignment problem to find an initial feasible solution. To improve the quality of the initial feasible solution, a column generation based algorithm is presented. The efficiency of the proposed method is tested and experimental results are provided.;The third problem is "Maritime Escort Transportation: Tugboat Scheduling Problem" with an existing berthing plan aiming to minimize the maximum flow time of vessels. A general mathematical formulation for tugboat scheduling problem is proposed and garnished with some detailed constraints. We first prove the optimal characteristic of Berth scheduling model and propose a greedy algorithm to find this optimal solution. We use this solution as the lower-bound for our problem. Later we develop this greedy algorithm to include the tugboat assignment. Then we embody this greedy algorithm in the branch and bound tree to improve its performance.