Showing papers in "Transportation Science in 1991"
TL;DR: Methods of shortest paths, a zero-one mathematical program for siting, and the weighting method of multiobjective programming are blended to show how to derive optimal solutions to the development of a model which simultaneously sites the storage facilities, assigns reactors to those facilities and chooses routes for the shipment of the spent fuel.
Abstract: The development of a system of storage facilities for spent fuel rods from commercial nuclear reactors requires solution of a model which simultaneously sites the storage facilities, assigns reactors to those facilities and chooses routes for the shipment of the spent fuel. The problem is multiobjective in its transportation component because shipment is made under two criteria: minimum transportation burden and minimum perceived risk. We blend methods of shortest paths, a zero-one mathematical program for siting, and the weighting method of multiobjective programming to show how to derive optimal solutions to this problem. Applications of the methodology demonstrate how transportation burden and risk influence location decisions and the dual role of siting/routing models in transportation policy analysis. The model is a prototype for the shipment and storage of any hazardous waste whose characteristics make the process of shipment itself an activity with risk.
265 citations
TL;DR: The review traces the evolution of models from single-criterion optimizations to multiobjective analyses, and highlights the emerging direction of dealing explicitly with distributions of outcomes, rather than simply optimizing expected values.
Abstract: We survey research on hazardous materials transportation in the areas of risk analysis, routing/scheduling and facility location. Our focus is primarily on work done since 1980, and on research which is methodological rather than empirical. We also limit our focus to transport by land-based vehicles (truck and rail), excluding pipeline, air and maritime movements. The review traces the evolution of models from single-criterion optimizations to multiobjective analyses, and highlights the emerging direction of dealing explicitly with distributions of outcomes, rather than simply optimizing expected values. We also indicate examples of work which integrate risk analysis with routing, and routing with facility location. We conclude with a discussion of several aspects of hazardous materials transportation which offer important challenges for further research.
244 citations
TL;DR: This initial version of the Schedule Analysis (SCAN) system is based upon notions from both simulation and combinatorial optimization, and is designed to provide decision makers with a tool for scheduling which provides a truly interactive system.
Abstract: This paper presents an overview of a decision-support model for the tactical scheduling of freight railroad traffic which is designed to support the weekly or monthly scheduling of rail operations. This initial version of the Schedule Analysis (SCAN) system is based upon notions from both simulation and combinatorial optimization, and is designed to provide decision makers with a tool for scheduling which provides a truly interactive system. After describing the conceptual underpinnings of the SCAN system and its associated algorithms, examples taken from a major railroad are used to illustrate the capabilities and limitations of the current system. Future research directions aimed at removing SCAN I's limitations are then discussed in light of recent advances in railroad management philosophies and technological advancements in this industry.
195 citations
TL;DR: A model is formulated to optimize both sets of decisions simultaneously under dynamic and uncertain conditions and it is concluded that this model is useful in identifying good strategies for the sizing of vehicle fleets and for the allocation of empty vehicles.
Abstract: There are important interactions between decisions on sizing a vehicle fleet and decisions on utilizing that fleet. A model is formulated to optimize both sets of decisions simultaneously under dynamic and uncertain conditions. A network approximation to this model is presented and a solution procedure proposed. The convergence behavior of the solution procedure and the potential consequences of using simpler models to solve the fleet sizing and vehicle allocation problem are illustrated using several hypothetical problems. We conclude that this model is useful in identifying good strategies for the sizing of vehicle fleets and for the allocation of empty vehicles.
165 citations
TL;DR: This paper presents a model useful in making routing decision, for either material or waste shipments, and siting decisions for waste treatment facilities, and government agencies will find it helpful in determining how regulations should be set to obtain publicly desirable routing and sitting patterns.
Abstract: Dealing with hazardous materials and wastes has become a problem of major concern for countries throughout the world. This paper presents a model useful in making routing decision, for either material or waste shipments, and siting decisions for waste treatment facilities. Risk, cost, and risk equity are considered jointly in a multiobjective framework. Costs are treated as link attributes while risks, from both transport and treatment, are zonal attributes, pertaining to nonoverlapping geographic areas spread out over the plane. Risks accrue within these zones, due to shipments crossing nearby links or wastes being processed, stored or disposed of at nearby treatment facilities. Total risk is the sum of the zonal risks. Equity is measured as the maximum zonal risk per unit population. Shippers will find the model useful in optimizing their logistics plans. Government agencies will find it helpful in determining how regulations should be set to obtain publicly desirable routing and siting patterns. The mo...
159 citations
TL;DR: A mathematical programming model is formulated that maximizes total profit for multiple ships and determines the optimal sequence of ports of call for each ship and the number of trips each ship makes in a planning horizon.
Abstract: International shipping is a multibillon dollar business and shipping companies may expect large benefits from improving the routing and scheduling processes of their ships. In this paper, we describe a container-ship routing scenario in which a shipping company provides services to a network of ports. We formulate a mathematical programming model that maximizes total profit (i.e., revenue minus operating costs) for multiple ships and determines: (a) the optimal sequence of ports of call for each ship, (b) the number of trips each ship makes in a planning horizon, and (c) the amount of cargo transported between any two ports by each ship. The model contains discrete, 0–1 and continuous variables, and nonlinear complicating constraints. The multiple container ship model is quite different from those of vehicle routing and traveling salesman problems. We use a decomposition method for the model as well as for the network in order to solve the problem. Several problems on 10- to 20-port networks are solved an...
137 citations
TL;DR: A branch and bound algorithm for solving network design problems (NDP), based on a stochastic incremental traffic assignment approach, is presented for solving the NDP.
Abstract: In this paper, a branch and bound algorithm is presented for solving network design problems (NDP). Route selection for the NDP is based on a stochastic incremental traffic assignment approach. Experiments are performed to compare the behaviors of three assignment methods. Numerical examples are presented to illustrate the algorithm for solving the NDP.
128 citations
TL;DR: Analytic models developed and used in comparing fixed route conventional bus and flexible route subscription bus systems for providing feeder services to a single point and the relative advantage of subscription bus services generally increases with smaller service areas, higher speeds, lower fixed bus cost, lower incremental costs of vehicle size, higher values of access and wait time, and lower values of in-vehicle time.
Abstract: Analytic models are developed and used in comparing fixed route conventional bus and flexible route subscription bus systems for providing feeder services to a single point (such as a transportation terminal). In the mathematical models for these two systems, vehicle size and service zone size are the optimizable decision variables, and total system cost, including operator and user costs, is the objective function to be minimized. Average cost per trip is the criterion used to determine which system is preferable and how it should be optimized in various circumstances. With an approximation for subscription services, closed form solutions for optimal vehicle size and service zone area are obtained for both alternatives. The analytic results for optimized conventional services indicate that constant ratios should be maintained at all demand densities between vehicle size and route spacing and between fleet size and user wait time. Analytic solutions are extended to conditions where (1) demand and costs ar...
100 citations
TL;DR: An optimization model is formulated that extends previous work by allowing stochastic travel times, unequal vehicle utilizations, various call types, and service times that depend on call location to be allowed.
Abstract: This paper deals with the problem of locating emergency vehicles in an urban area. We formulate an optimization model that extends previous work by allowing stochastic travel times, unequal vehicle utilizations, various call types, and service times that depend on call location. The basis of the model is a procedure for approximating the performance of spatially distributed queueing systems. In previous work the model has been validated using data from the Tucson Emergency Medical Services (EMS). We test the computational effectiveness of pairwise interchange heuristics on 192 test problems. Demand and service time components of the test data are generated using characteristics of the Tucson data set. For these test problems, simple pairwise interchange techniques yield reasonable solutions with little computational effort. Also, solutions obtained from the model differ from those generated using methods previously presented in the literature.
95 citations
TL;DR: The problem of equitably sequencing a given set of hazardous materials shipments is considered as an integer programming problem and as a dynamic programming problem, and several heuristic solution strategies are proposed to obtain the upper bounds needed for dynamic programming fathoming and for obtaining reasonable solutions to large-sized problems.
Abstract: In a recent paper, R. Gopalan, K. Kolluri, R. Batta and M. Karwan (1990) consider a model to route a set of hazardous materials shipments from an origin to a destination, so as to minimize the global risk to the community while simultaneously maintaining a desired level of equity between zones within the community. If one follows the routes produced via their solution methodology, the overall risk is small and equity between zones is achieved after all the shipments are over. However, equity may be severely violated at an intermediate stage of the shipment process. Since an accident can occur at any stage, this is not a desirable situation. Motivated by this, in this paper we consider the problem of equitably sequencing a given set of hazardous materials shipments. We presume, of course, that the set of routes are such that they engender low overall risk to the community as a whole, and once they are all traversed the risk is equitably distributed among the zones of the community—Gopalan, Kolluri, Batta, ...
58 citations
TL;DR: A network decomposition algorithm is developed for the all-pairs shortest path problem on a SIMD fine-grained, massively parallel computer, the Connection Machine, and the sensitivity of the execution time of the algorithm to different decomposition strategies is examined.
Abstract: The shortest path problem is a classical and important combinatorial problem with many applications. We examine the solution of the all-pairs shortest path problem on a SIMD fine-grained, massively parallel computer, the Connection Machine. We develop a network decomposition algorithm for the problem and implement it on the Connection Machine. The algorithm consists of the following phases: (1) Decompose the network into subnetworks and identify the set of cutset nodes associated with each subnetwork. (2) For every cutset node determine the shortest path to all other nodes in the network. (3) For each subnetwork solve the all-pairs shortest path problem. (4) Combine results from the two preceeding phases to obtain the final shortest path distances.
We discuss mapping strategies of the network to the processors and examine the sensitivity of the execution time of the algorithm to different decomposition strategies. We compare running times on different architectures and draw conclusions on appropriate network decomposition strategies. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.)
TL;DR: This paper provides numerical examples to show that the assumption that total cost decreases with the reduction of noncooperative players on the network does not hold in general.
Abstract: Paradoxes may occur when different traffic equilibrium models are applied starting from the same data. When in the traffic system “players” of different size are present, a Mixed Behavior Equilibrium can be stated. One should expect, by intuition, that total cost decreases with the reduction of noncooperative players on the network. This assumption does not hold in general. This paper provides numerical examples to show it. The problem of investigating the relationship between different equilibrium models arises when one considers a strategy for rerouting vehicles in road networks, in order to reduce congestion (Route Guidance Systems, for example). The importance of identifying paradoxical situations in such problems is briefly discussed.
TL;DR: A branch and bound algorithm to identify the optimal solution for the 5% of the test problems for which the new heuristic for the hierarchical network design problem failed to do so is developed.
Abstract: In this paper we develop a new heuristic for the hierarchical network design problem. The heuristic is based upon Lagrangian relaxation of a reformulation of the problem. In addition, we develop a branch and bound algorithm to identify the optimal solution for the 5% of the test problems for which the new heuristic failed to do so. This algorithm proved to be very efficient due to the tight bounds generated by the heuristic.
TL;DR: This work gives explicit expressions and approximate power series for several common averages of the average distance to all points in a region from a designated point.
Abstract: A key quantity arising in the modeling of distribution systems is the average distance to all points in a region from a designated point. While expressing such an average as an integral can be straightforward, the evaluation of such an integral can be involved. We give explicit expressions and approximate power series for several common averages.
TL;DR: In this paper, minisum and minimax single facility location problems where the effective service distance becomes a constant when the actual distance attains or exceeds a certain value are considered.
Abstract: In this paper we consider minisum and minimax single facility location problems where the effective service distance becomes a constant when the actual distance attains or exceeds a certain value. Properties of these problems are studied, and algorithms for their solution are presented.
TL;DR: This principle is demonstrated in the context of transporting flammable liquid chemicals in bulk through New York City, where two alternative tank truck configurations are considered, depending on whether local fire department regulations or federal hazardous materials transportation regulations are followed.
Abstract: Risk assessment can be expedited and the results made more reliable by using existing information to its fullest advantage, especially when comparing relative risks. This principle is demonstrated in the context of transporting flammable liquid chemicals in bulk through New York City, where two alternative tank truck configurations are considered, depending on whether local fire department regulations or federal hazardous materials transportation regulations are followed. Spreadsheet calculations are used to estimate the risks on two different routes under average and worst-case assumptions. The results are subjected to an uncertainty analysis to help decide between the two alternatives, given the inherent randomness in the associated risks.
TL;DR: This paper presents an O ( n 3 ) time heuristic for the capacitated traveling salesmen location problem and finds a solution whose relative worst-case error equals 3 /2−3/(2 q ).
Abstract: The capacitated traveling salesmen location problem is the problem of locating one service station with servers, each having a limited capacity, q. The service units must visit each day all the calls that are registered in a service list. Each call is generated with a given probability and the service list contains at most n calls. In the paper we present an O(n3) time heuristic for the problem on networks. This heuristic finds a solution whose relative worst-case error equals 3/2−3/(2q). We also show how one can use this heuristic to solve the problem on the plane with rectilinear or Euclidean distances with the same worst-case error. In the latter case the heuristic is proved to be asymptotically optimal.
TL;DR: A model for calculating the capacity of an en route sector of an air traffic control system from the geometric point of view based on the concept of expected capacity under saturation conditions, i.e., in the presence of continuous demand for service.
Abstract: This paper presents a model for calculating the capacity of an en route sector of an air traffic control system from the geometric point of view. The model is based on the concept of expected capacity under saturation conditions, i.e., in the presence of continuous demand for service. The model could be used for planning purposes such as sector capacity calculations and capacity sensitivity analysis for different traffic scenarios. A sensitivity analysis can be performed varying such parameters as: sector geometry (number of entry points and air routes' configuration), characteristics of the sector's expected traffic (arriving traffic distribution between entry points and flight levels for each of those points, the characteristics of requests for level changes while in the sector, aircraft mix at the entry points) and air traffic control separation rules.
TL;DR: A simple approach for calculating consistent on-board itinerary flows and the corresponding loads, revenues and marginal seat values given a set of underlying demands and an assignment of seating capacities to legs is presented.
Abstract: As airlines have moved toward more concentrated “hub-and-spoke” schedules, connecting passengers have become an increasingly important part of their loads and revenues. Yet, many optimization approaches to such airline planning problems as revenue management and aircraft assignment have ignored the “cross-leg” effects of seating capacity on connecting traffic and the associated revenue. This paper presents a simple approach for calculating consistent on-board itinerary flows and the corresponding loads, revenues and marginal seat values given a set of underlying demands and an assignment of seating capacities to legs. An application of this approach to a large-scale airline network is presented and the implication of the results for decision-making discussed. Although the approach is presented in the context of airline planning, it is applicable to any transportation system in which connecting traffic plays a significant part as well as to hotel and automobile rentals.
TL;DR: This paper determines the smallest set which includes at least one optimal point for every Weber problem based on a given set of demand points, and finds the smallest possible set for p =1 or p =∞.
Abstract: It is known that the planar Weber location problem with lp distances has all its solutions in the convex hull of the demand points. for l1 and l∞ distances, additional conditions are known which reduce the set of possible optimal points to the intersection of that convex hull, the efficient set, and the points defined by a certain grid. In this paper, we determine the smallest set which includes at least one optimal point for every Weber problem based on a given set of demand points. It is shown that for 1
TL;DR: A model for regulating pedestrian flow into the Jamarat bridge may provide facility designers and managers with a quantitative tool for predicting the level of congestion at specific regions on the bridge given the specific demand flow data and a particular control strategy.
Abstract: During the Moslem pilgrimage season the Jamarat bridge becomes congested with pilgrims, due to space and time constraints. This paper aims at developing a model for regulating pedestrian flow into the bridge. The model may provide facility designers and managers with a quantitative tool for predicting the level of congestion at specific regions on the bridge given the specific demand flow data and a particular control strategy. Thus various alternatives for controlling the flow can be examined. The model is also a tool for determination of the optimal level of flow such that the number of persons in those specific regions does not exceed some predetermined limit. An optimization model is constructed and an example is included.
TL;DR: The network model presented here is designed to work with the Enhanced Traffic Management System (ETMS) project under development at the Transportation Systems Center (TSC) for the Federal Aviation Administration (FAA).
Abstract: This paper presents a network model which can serve as a framework for generating optimal global congestion-relieving strategies for the flow control problem in air traffic management. The general network model presented here addresses the global problem of optimally combining a number of local strategies to relieve multiple interdependent occurrences of congestion. While several algorithms and techniques have been or are being developed which deal with congestion at one air traffic control element for one time period, the actual flow control problem is concerned with congestion in a dynamic setting occurring at a number of different elements which are interrelated in a complex manner. The network model presented here is designed to work with the Enhanced Traffic Management System (ETMS) project under development at the Transportation Systems Center (TSC) for the Federal Aviation Administration (FAA).
TL;DR: An algorithm for determining whether m given demand points are on a hemisphere or not is presented, in which the great circle is rotated successively until the hemisphere which contains the mGiven demand points is found or it becomes known using the authors' criteria that the m givenDemand points are not on a Hemisphere.
Abstract: Location problems on a sphere can be solved easily by mathematical programming or geometrical methods if it is known that all the demand points are located on a hemisphere This paper presents an algorithm for determining whether m given demand points are on a hemisphere or not In this algorithm, the great circle is rotated successively until the hemisphere which contains the m given demand points is found or it becomes known using our criteria that the m given demand points are not on a hemisphere The convergence of this algorithm is proved, and two illustrative examples are presented
TL;DR: In this paper, the authors present a minimum cost transportation plan by simultaneously solving the following two subproblems: first the assignment of units available at a series of origins to satisfy demand at series of destinations and second, the design of vehicle tours to transport these units, when the vehicles have to be brought back to their departure point.
Abstract: The problem we consider is that of preparing a minimum cost transportation plan by simultaneously solving the following two subproblems: first the assignment of units available at a series of origins to satisfy demand at a series of destinations and second, the design of vehicle tours to transport these units, when the vehicles have to be brought back to their departure point. We present a solution method for this problem using a minimum cost flow model followed by heuristic tour construction and improvement procedures. This approach allows large problems to be solved quickly, and solutions to large test problems have been shown to be 1% or 2% from the optimum. Results are presented for a problem involving the transport of 24,000 students working on an environmental cleanup project.
TL;DR: This paper studies the bargaining between a shipper and potential carriers during the selection of a specific carrier and the resulting size of a transfer payment, when carriers' accident probabilities are proprietary information.
Abstract: This paper studies the bargaining between a shipper and potential carriers during the selection of a specific carrier and the resulting size of a transfer payment, when carriers' accident probabilities are proprietary information (i.e., the probability of accident and the safety investment of a particular carrier are not available to the shipper nor to other carriers). Optimal auction mechanism designs are used to analyze the bargaining process. When there is no likelihood of carrier bankruptcy, the shipper benefits more from joint liability with the carrier than under a rule of strict liability of the carrier. Carriers, on the other hand, free from the potential of bankruptcy, stand to benefit more from strict liability. Under conditions where carrier bankruptcy could result from an accident, the shipper benefits more from strict liability than joint liability, and the reverse is true for carriers. A liability rule which is socially desirable depends upon the safety investments by carriers, carrier asset...
TL;DR: The purpose of this special issue of Transportation Science is to focus on important current work in the areas of risk analysis, routing/scheduling of shipments, and siting of facilities for treatment or storage of hazardous wastes.
Abstract: Hazardous materials transportation is an activity of vital economic importance for any industrial society. At the same time, however, shipments of these materials create risks—the potential for harm to human health and/or the environment. The importance of hazardous materials transportation issues has attracted the attention of the research community as well as that of policy makers and the public at large. During the last decade, significant methodological advances have been made in the areas of risk analysis, routing/scheduling of shipments, and siting of facilities for treatment or storage of hazardous wastes. The purpose of this special issue of Transportation Science is to focus on important current work in this area.
TL;DR: This paper presents an analytical method to directly estimate stop probability and average delay for semi-actuated signals at low volumes, under both isolated and coordinated controls.
Abstract: Semi-actuated signals have been widely used on arterials, since they provide flexible controls for minor street traffic to reduce delays and stops. It is very important to estimate average delays and stops under such signal control in designing timing plans or evaluating operational performance. Unfortunately, the literature offers very few methods dealing exclusively with semi-actuated signals in estimating delays and stops. A common approach is to estimate average green times, then to apply a model for pretimed signals to calculate delays and stops. This method produces reasonable approximations when traffic volumes are moderate to high. When traffic volumes are low, however, this method produces biased approximations since it does not consider phase skipping due to lack of traffic demand. This paper presents an analytical method to directly estimate stop probability and average delay for semi-actuated signals at low volumes, under both isolated and coordinated controls. This method uses probability the...
TL;DR: First some properties of such facility locations are derived and then a linear time algorithm for their determination along with the associated flow pattern is given.
Abstract: Let a tree be given with supplies assigned to its nodes and weights assigned to its edges. The problem considered here is to locate a facility, so that the flow pattern which results from shipping all supplies to the facility, is such that it minimizes the largest weighted flow on any individual edge. First some properties of such facility locations are derived and then a linear time algorithm for their determination along with the associated flow pattern is given.
TL;DR: The 1990 Transportation Science Section Dissertation Prize Competition received seven nominations and the winner was Jeffery I. McGill for his dissertation “Optimization and Estimation Problems in Airline Yield Management.”
Abstract: The 1990 Transportation Science Section Dissertation Prize Competition received seven nominations. The winner was Jeffery I. McGill for his dissertation “Optimization and Estimation Problems in Airline Yield Management.” Extended abstract of all seven theses are included.