bluuebunny/crossref_metadata_2025 huggingface dataset:
Urban Network-Wide Traffic Variables and Their Relations
Authors: Ardekani Siamak , Herman Robert
Published: October 2008

Time-lapse aerial photography over the Central Business Districts (CBD) of Austin and Dallas, Texas, has been employed to determine the averages of concentration, speed and fraction of vehicles stopped and to examine the relations among such network-wide averages including the flow which was measured on the ground simultaneously. The results have indicated that the average flow in a street network may indeed be expressed as the product of the space mean speed and concentration. Simultaneous ground experiments have also been conducted in the Austin CBD to investigate the reasonableness of the assumptions of the “two-fluid model,” a curvilinear relation between the trip time and stop time per unit distance, which may be used in characterizing the quality of traffic service in urban street networks. As a result of these simultaneous ground experiments and aerial observations, the assumptions of the model have been verified. Moreover, relations between the fraction of vehicles stopped and concentration as well as between speed and concentration have allowed the two-fluid model to be used to compare the quality of traffic service in various street networks under the same level of concentration. The two-fluid model may then be used to predict, for a given change in vehicular concentration in a street network, the resulting changes in the averages of speed, fraction of vehicles stopped, flow, etc. This is particularly useful as a performance model in urban planning where for a given concentration it is desirable to predict the resulting traffic conditions.
A Family of Methods for Preliminary Highway Alignment
Authors: Trietsch Dan
Published: October 2008

The alignment of a highway is usually determined in two or even three stages. The preliminary stage, also referred to as the corridor selection, is concerned with finding a piecewise linear trajectory, which is refined in the higher stages. In this paper we present a family of methods for this preliminary design, which includes some published methods and some new ones. The new methods shown were designed to overcome some of the more obvious drawbacks of the others. Finally, one specific new method is recommended, which is “Pareto-optimal” and appealing; however, no single method within the family dominates all the others in all the parameters considered.
Average Waiting Time in Queues with Scheduled Batch Services
Authors: Özekici Süleyman
Published: October 2008

Average waiting times in queuing models are generally computed with the assumption that the arrival and service processes are independent and not related. In many applications and especially in queues with scheduled batch service times, this assumption is not valid and a formulation which relates the two processes is required. This paper proposes a model aimed at analyzing and exploiting the relationship between the arrival and service processes with emphasis on the impact of this relationship on average waiting times. The presentation is made in the context of a transportation model to motivate and validate the basic assumptions.
Increasing Model Precision Can Reduce Accuracy
Authors: Daganzo Carlos F.
Published: October 2008

In the field of logistics, a variable that is to be predicted (e.g., cost) often varies in a nonsmooth, irregular, but known manner, with various factors (e.g., distances, quantity, and density of material to be carried, etc.). This paper identifies conditions, where given approximate input factors, a prediction of the variable is less error prone if one uses a smooth approximation to the exact function of the factors. This phenomenon, which is quite prevalent, may enhance the appeal of continuous approximation models in some instances.
Optimal Minimax Path of a Single Service Unit on a Network to Nonservice Destinations
Authors: Berman Oded , Handler Gabriel Y.
Published: October 2008

In this paper we consider the problem of finding an optimal path of a single service unit that travels toward a “nonservice” destination. Two types of objective functions are examined. One objective function is the minimization of the maximum distance (or weighted distance) between the moving service unit and any demand (node) of the network. The second objective function is the minimization of the total time period that the distance (or weighted distance) between the moving service unit and any node exceeds a response time threshold λ. For these two objective functions, we present algorithms which can be calculated, respectively, in 0(n3) and 0(n3 log n) elementary operations.
Generalized Traffic Equilibrium with Probabilistic Travel Times and Perceptions
Authors: Mirchandani Pitu , Soroush Hossein
Published: October 2008

The paper studies the problem of predicting traffic equilibrium (TE) in a transportation network within the framework of decision making among discrete choices in a probabilistic and uncertain environment. Conventional approaches to predict TE typically assume that travel times are deterministic and perceived accurately by the travelers; and some new TE models have considered probabilistic travel times or inaccurate perceptions but not both. In our generalized model, which we refer to as GTESP, the travel time on each route is random and each traveler perceives, possibly inaccurately, a travel time probability distribution for each route which may vary from traveler to traveler. Each traveler uses a disutility function of travel time to evaluate each route and chooses that route which minimizes his expected disutility. GTESP is difficult to solve for general nonlinear disutility functions. However, special cases—in particular when arc travel times are statistically independent and the disutility functions to evaluate route travel times are linear, exponential, or quadratic—are solvable, at least approximately. GTESP is general in the sense that most existing TE models can be shown to be special or limiting cases of GTESP. Furthermore, this paper demonstrates, with illustrative examples, that GTESP appears to capture travelers' risk-taking behavior more realistically than existing TE models.
A Dynamic Space-Time Network Flow Model for City Traffic Congestion
Authors: Zawack Daniel J. , Thompson Gerald L.
Published: October 2008

A space-time network is developed that represents traffic flows over time for a capacitated road transportation system having one-way and two-way streets. Traffic signal lights are explicitly incorporated into the network structure so that total travel time is a piecewise linear convex function of the number of units traveling on the streets. Hence congestion effects are explicitly considered while maintaining the linear nature of the model. The first example presented has one source and one sink. There is a unimodal buildup of traffic at the source (say a factory) which enters the street network as quickly as its capacity permits and proceeds through the network, stopping at red lights when necessary, toward the sink (a residential area). Two efficient solution methods are used: a network flow solution suitable for a multiple-source single-destination network, and a shortest path solution suitable only for a single-source single-destination network. Computations show that the arrival rate has multiple peaks which are induced by the stop lights. The second example has multiple sources and one sink and gives similar results, except that the arrival rate has a single board peak which is due to the extreme symmetry of the constraints of the problem.
The Median Shortest Path Problem: A Multiobjective Approach to Analyze Cost vs. Accessibility in the Design of Transportation Networks
Authors: Current John R. , Revelle Charles S. , Cohon Jared L.
Published: October 2008

In this paper the authors introduce the median shortest path problem (MSPP). The MSPP is a bicriterion path problem with the objectives being the minimization of the total path length and the minimization of the total travel time required for demand to reach a node on the path. Potential applications of the MSPP include, among others, the location of new highways, railroad lines and subway lines and the design of airline routes. It is particularly applicable in transportation network design problems where the trade-off between operator costs and user costs is important. An algorithm is presented to identify noninferior solutions to the MSPP. This algorithm incorporates a K shortest path algorithm. The algorithm is demonstrated with a sample problem and the results are compared to those obtained using integer programming.
A Dual-Based Algorithm for Multiproduct Uncapacitated Facility Location
Authors: Klincewicz John G. , Luss Hanan
Published: October 2008

The multiproduct uncapacitated facility location problem (MUFLP) is a generalization of the classic uncapacitated facility location problem (UFLP). In MUFLP, different products are required by the customers. In addition to the fixed cost for opening a facility, there is an added fixed cost for handling a particular product. Assignment costs are incurred for satisfying a customer's requirement for each of the separate products. The objective is to minimize the total fixed costs plus assignment costs subject to satisfying all customer requirements. We propose a new dual-based algorithm for MUFLP that extends previous work for UFLP that has proved so successful. Dual ascent and dual adjustment procedures generate a good feasible solution to the dual of the linear programming relaxation of MUFLP. A feasible primal solution to MUFLP can then be constructed based on this dual solution. Like the analogous procedures for UFLP, these procedures can be used either as a stand-alone heuristic or, else, they can be incorporated into a branch-and-bound algorithm. Computational experience is given for both randomly generated and nonrandom problems with quite favorable results.
Survey Paper—A Review of Empty Flows and Fleet Management Models in Freight Transportation
Authors: Dejax Pierre J. , Crainic Teodor Gabriel
Published: October 2008

The transportation of freight, by any mode, usually generates a significant number of empty vehicle movements. Understanding and controlling this phenomenon is important for all levels of transportation and logistic system planning. In this paper, we propose a taxonomy of empty vehicle flow problems and models and review the existing literature on the subject. Major research trends and perspectives are identified and the advantages of a hierarchically integrated approach for the simultaneous management of empty and loaded freight vehicle movements are discussed.
Adaptation of a Modified Newton Method for Solving the Asymmetric Traffic Equilibrium Problem
Authors: Marcotte Patrice , Guélat Jacques
Published: October 2008

In this paper a restriction (simplicial decomposition) strategy is employed to efficiently implement a modified Newton method to solve the general asymmetric network equilibrium problem. Implementation details are discussed. Numerical results on one small-scale and one medium-scale problem, with varying asymmetry levels, are presented. Performance of the algorithms with respect to the asymmetry level of the cost mapping is assessed.
A Multiobjective Hierarchical Covering Model for the Essential Air Services Program
Authors: Flynn John , Ratick Samuel
Published: October 2008

This paper presents the development of a mathematical programming model for evaluating options for the continuance of the Essential Air Services (EAS) program, a provision of the Airline Deregulation Act of 1978. The EAS program was established to guarantee continued air service to small communities that suffered air service losses as a result of carrier withdrawals permitted by the Deregulation Act. The model has been designed to aid decision makers in allocating subsidized air services to communities in a region, given the goal of maximizing access to the air transportation system. In order to provide information on optimal service locations, service characteristics, and patterns of access, the authors have utilized a maximal covering formulation and incorporated elements of hierarchical and weighted benefit models. In addition, a stopover service option has been included in the model to permit evaluation of potential gains in economic efficiency that may be realized by utilizing stopover service, when appropriate, in place of more costly nonstop service. In addition to the coverage objective, a second objective of systemwide cost minimization is employed. By using a multiobjective approach, the trade-offs between the conflicting objectives of coverage and cost can be explored and the spatial patterns of service associated with each combination of coverage level and cost can be examined. The model is applied to a sample study of small community air service in North and South Dakota.
An Efficient Computational Procedure for the Rectilinear MAXIMIN Location Problem
Authors: Melachrinoudis Emanuel
Published: October 2008

This paper deals with the problem of locating a facility among n existing facilities so that the shortest weighted distance with respect to all existing facilities is as large as possible. The new facility is to be placed within a bounded convex region S in R2 where the existing facilities also lie. The rectilinear distance is used for a distance metric. Applications of the model include the location of an undesirable or obnoxious facility in a bounded region in which the underlying distance metric is rectilinear. Based upon the linearization of the solution space an efficient algorithm is developed that finds the MAXIMIN point by solving a sequence of LPs using Simplex. Computational results are provided. The algorithm is shown to be computationally more efficient than an existing combinatorial algorithm. The use of the algorithm is illustrated in a numerical example.
Bibliographic Section
Authors: White Peter R. , Train Kenneth E. , Mahmassani Hani S. , Feo Thomas A.
Published: October 2008

A Welfare Assessment of Transport Deregulation: The Case of the Express Coach Market in 1980, by Neil J. Douglas. Gower Publishing Co., Gower House, Croft Road, Aldershot, Hants, GU11 3HR, United Kingdom (and in USA at Old Post Road, Brookfield, Vermont 05036). 1987. 349 pp—reviewed by Peter R. White.

Blind Intersection? Policy and the Automobile Industry, by Clifford Winston and Associates, The Brookings Institution, Washington, D.C., 1987, 108 pp—reviewed by Kenneth E. Train.

Analytical Studies in Transport Economics, by Andy F. Daughety, Cambridge University Press, Cambridge, England, 1985, ix, 253 pp—reviewed by Hani S. Mahmassani.

Intermodal Freight Transportation, by John H. Mahoney, Eno Foundation for Transportation, Westport, Conn., 1985—reviewed by Thomas A. Feo.
Sensitivity Analysis for Equilibrium Network Flow
Authors: Tobin Roger L. , Friesz Terry L.
Published: October 2008

Direct application of existing sensitivity analysis methods for nonlinear programming problems or for variational inequalities to nonlinear programming or variational inequality formulations of the equilibrium traffic assignment problem is not feasible, since, in general, the solution to the equilibrium traffic assignment problem does not satisfy the uniqueness conditions required by the sensitivity analysis methods. This paper presents an approach for sensitivity analysis of equilibrium traffic assignment problems in which an equivalent restricted problem is developed which has the desired uniqueness properties; the existing methods are applied to this restricted problem to calculate the derivatives of the equilibrium arc flows with respect to perturbations of the cost functions and of the trip table. These derivatives are then shown to be equivalent to the derivatives of the original unrestricted equilibrium traffic assignment problem; therefore, the method yields the desired sensitivity analysis results.
Freeway Traffic Data from Time-Lapse Film
Authors: Persaud Bhagwant , Hurdle Van Olin
Published: October 2008

This paper describes an economical method for obtaining speeds, flows and densities from low quality time-lapse film that is unsuitable for the more common data reduction techniques, most of which require vehicle tracking. The method is developed from some very basic ideas and is illustrated in a description of a recent application—a study involving 16-mm time lapse film coverage of a 1400 m long freeway segment in Toronto, Canada. Average speeds were comparable to those obtained by tracking individual vehicles.
The 1-Center Problem: Exploiting Block Structure
Authors: Chen M.-L. , Francis R. L. , Lowe T. J.
Published: October 2008

A block of a graph is a maximal nonseparable subgraph. We show how the knowledge of block structure can be used to help solve the nonlinear 1-center problem on graphs which are more general than trees. We give an efficient algorithm which either finds a unique 1-center at some vertex, or else localizes the search for all 1-centers to a single block. The algorithm makes use of an associated graph, called a blocking graph, which is a tree, and iteratively orients arcs in the blocking graph to “point the way” to a block which contains all 1-centers.
Algorithms for Voting and Competitive Location on a Network
Authors: Hansen Pierre , Labbé Martine
Published: October 2008

Consider a network with weights associated to its vertices. When a facility must be located through a voting procedure, these weights may be interpreted as the numbers of users located on the vertices. When a facility must be located in a competitive setting, i.e., when a concurrent facility will be located later and will capture all clients closer to it, these weights may be viewed as the purchasing power of the clients. A Condorcet point is any point of the network, i.e., a vertex or a point on an edge, such that the set of vertices closer to any other point has a total weight not larger than the half sum of the weights of all the vertices. A Simpson point is a point of the network which minimizes the largest total weight of the set of vertices closer to another point. Polynomial algorithms are provided to determine the sets of Condorcet and of Simpson points of a network.
Bibliographic Section
Authors: Daskin Mark S. , Evans Leonard , Hall Randolph , Pearce Charles E. M. , Newell Gordon
Published: October 2008

Locational Decisions: Methodology and Application, J. P. Osleeb and S. J. Ratick, editors. Annals of Operations Research, Volume 6, J. C. Baltzer AG, Scientific Publishing Co., Basel, Switzerland, 1986—reviewed by Mark S. Daskin.

Road Accident Statistics, by T. P. Hutchinson, Rumsby Scientific Publishing, Adelaide, P.O. Box 76, Rundle Mall, South Australia—reviewed by Leonard Evans.

The Time Factor in Transportation Processes, by Ignacy Tarski, Translated by Olgierd Wojtasiewicz, Elsevier, Amsterdam, and Wydawnictwa Komunikacji i Łączności, Warsaw, 1987—reviewed by Randolph Hall.

Urban Spatial Traffic Patterns, by Rodney J. Vaughan, Pion Limited, London, 1987, 334 pages—reviewed by Charles E. M. Pearce.

Continuous Location of Transportation Networks, by K. C. Mosler, Texts and Monographs in Economic and Mathematical Systems, Springer-Verlag, 1987, 158 pp + x—reviewed by Gordon Newell.
Estimating Fleet Fuel Consumption for Vans and Small Trucks
Authors: Newman P. W. G. , Alimoradian B. , Lyons T. J.
Published: October 2008

A fleet fuel consumption model for commercial vans and small trucks is developed based on a survey, completed by truck drivers in the normal course of their duty. The model uses engine displacement, vehicle mass and average speed to predict fuel consumption for petrol and diesel trucks. It explains 77.4% of the variance for diesel and 86.3% for petrol trucks respectively, with the mass term dominating the regression. The model was found to predict within 1–20% of the actual fuel consumed by three instrumented trucks undergoing a controlled series of tests. As a fleet model, it represents an inexpensive and simple tool for monitoring vehicle and traffic changes.
The Traveling Salesman Location Problem on Stochastic Networks
Authors: Berman Oded , Simchi-Levi David
Published: October 2008

In this note, we consider the traveling salesman location problem on stochastic networks in which the length of links are not deterministic. In particular, we show that several available solution methods for deterministic networks can be modified to solve the problem on stochastic networks as well.
Bibliographic Section
Authors: Radwan A. Essam , Button Kenneth , Boske Leigh B. , Nelson Paul T. , Furth Peter G. , Odoni Amedeo R.
Published: October 2008

Traffic and Highway Engineering, by Nicholas Garber and Lester Hoel, West Publishing Company, St. Paul., Minn., 1988, 959 pp—reviewed by A. Essam Radwan.

The Spatial Impact of Technological Change, edited by John F. Brotchie, Peter Hall and Peter W. Newton, Croom Helm, London, 1987—reviewed by Dr. Kenneth Button.

Public Regulation: New Perspectives on Institutions and Policies, edited by Elizabeth E. Bailey, The MIT Press, Cambridge, Mass., 1987, 404 pp—reviewed by Leigh B. Boske.

Market Centers and Retail Location: Theory and Applications, by Brian J. L. Berry and John B. Parr with Bart J. Epstein, Avijit Ghosh, and Robert H. T. Smith, Prentice Hall, Englewood Cliffs, N.J., 1988, 230 pp—reviewed by Paul T. Nelson.

Managing Public Transit Strategically, by Gordon J. Fielding, Jossey-Bass, San Francisco, CA 1987; and Public Transport: Its Planning, Management and Operation, 2nd ed., by Peter White, Hutchinson Education, London, U.K., 1986—reviewed by Peter G. Furth.

Cities and Their Vital Systems: Infrastructure Past, Present, and Future, edited by Jesse H. Ausubel and Robert Herman, National Academy of Engineering, National Academy Press, Washington, D.C., 1988—reviewed by Amedeo R. Odoni, Editor.
An Analysis of Inventory and Transportation Costs in a Constrained Network
Authors: Benjamin Julian
Published: October 2008

The need to minimize inventory, production and transport costs has long been recognized by operations researchers. Traditionally, stages in materials handling have been optimized separately. This paper analyzes the complete materials handling process from production at supply points to consumption at demand points. Reasonable assumptions are made concerning production, inventory and transport costs along with production constraints and demand requirements. A local optimum is found using a generalized reduced gradient algorithm. Initial upper and lower bounds to the solution are also derived and a heuristic is introduced which finds a solution using linear network algorithms. The reduced gradient algorithm and the heuristic are applied to a hypothetical corporate sourcing problem. The problem is a small subset of the problem of acquiring and distributing new items. Results of this analysis show that for certain cases, the value of the reduced gradient algorithm solution is very close to the value of the lower bound and that there is a substantial improvement (as high as 21%) over the separate optimization solution. It is further found that the heuristic provides similar solutions to the reduced gradient algorithm but at much greater computational efficiency. It is concluded that simultaneous optimization should be considered when inventory and transport strategies are developed and that the overall advantage of simultaneous optimization depends on the magnitude of the parameters.
Traveling Salesman Facility Location Problems
Authors: Bertsimas Dimitris J.
Published: October 2008

We consider two generic facility location problems, the traveling salesman facility location problem (TSFLP) and the probabilistic traveling salesman facility location problem (PTSFLP), both of which have been a subject of intensive investigation recently. Concerning the TSFLP, we first improve the worst-case bound of the best-known heuristic for the problem on networks and observe that it is optimal under the triangle inequality to locate the facility at a node, which always requires a visit. Concerning the PTSFLP, we reduce it to the solution of n probabilistic traveling salesman problems and moreover, we propose two polynomial time heuristics one for networks and one for Euclidean problems which are at most a factor of O(log n) from both the optimal TSFLP and the PTSFLP. A by-product of our analysis is an O(n2) algorithm which solves the PTSFLP in a general network given an a priori probabilistic traveling salesman type of tour, thus improving the best-known algorithm by a factor of n. After the examination of the worst case behavior of the proposed heuristics we examine their average behavior. For Euclidean problems in which customer locations are random, we prove that the heuristic proposed above is asymptotically optimal, the PTSFLP is asymptotically very close to the TSFLP and the heuristic we are proposing is within 25% of the optimal TSFLP.
The Maximum Availability Location Problem
Authors: ReVelle Charles , Hogan Kathleen
Published: October 2008

A probabilistic version of the maximal covering location problem is introduced here. The maximum available location problem (MALP) positions p servers in such a way as to maximize the population which will find a server available within a time standard with α reliability. The maximum availability problem builds on the probabilistic location set covering problem in concept and on backup covering and expected covering models in technical detail. MALP bears the same relation to the probabilistic location set covering problem as the deterministic maximal covering problem bears to the deterministic location set covering problem. The maximum availability problem is structured here as a zero–one linear programming problem and solved on a medium-sized transportation network representing Baltimore City.
The Covering Salesman Problem
Authors: Current John R. , Schilling David A.
Published: October 2008

The primary purpose of this paper is to introduce and mathematically formulate the covering salesman problem (CSP). The CSP may be stated as follows: identify the minimum cost tour of a subset of n given cities such that every city not on the tour is within some predetermined covering distance standard, S, of a city that is on the tour. The CSP may be viewed as a generalization of the traveling salesman problem. A heuristic procedure for solving the CSP is presented and demonstrated with a sample problem.
Locating a Point of Minimum Variance on Triangular Graphs
Authors: Kincaid Rex K. , Maimon Oded Z.
Published: October 2008

In this note the convexity of the variance measure for triangular graphs is established, and an expression for the point that minimizes the variance on an edge is given. A transformation of triangular graphs into trees provides an efficient means to implement these properties via a postorder search of a tree. The result is a linear time algorithm that determines a point of minimum variance for any triangular graph whose edge lengths satisfy the triangle inequality.
A Review of Sensitivity Results for Linear Networks and a New Approximation to Reduce the Effects of Degeneracy
Authors: Powell Warren B.
Published: October 2008

Estimating the reduced cost of an upper bound in a classical linear transshipment network is traditionally accomplished using the shadow price for this constraint, given by the standard calculation c̄ıj = cij + πj − πı. This reduced cost is only a subgradient due to network degeneracy and often exhibits errors of 50% or more compared to the actual change in the objective function if the upper bound were raised by one unit and the network reoptimized. A new approximation is developed, using a simple modification of the original reduced cost calculation, which is shown to be significantly more accurate. This paper summarizes the basic theory behind network sensitivity, much of which is known as folklore in the networks community, to establish the theoretical properties of the new approximation. The essential idea is to use least-cost flow augmenting paths in the basis to estimate certain directional derivatives which are used in the development of the approximation. The technique is motivated with an application to pricing in truckload trucking.
Competitive Location with Random Utilities
Authors: de Palma André , Ginsburgh Victor , Labbé Martine , Thisse Jacques-François
Published: October 2008

This paper studies m firms competing on location over a finite subset of vertices of a graph, with the aim of attracting consumers located at some vertices of this graph. It is shown that firm i (i = 1, …, m) wants to establish its mi facilities at the mi-median of the graph whose vertices are weighted by consumers' purchasing power provided that consumers' tastes are sufficiently dispersed in probabilistic terms among the different firms. Examples based on some standard network configurations illustrate the property.
The Estimation of Multinomial Probit Models: A New Calibration Algorithm
Authors: Kamakura Wagner A.
Published: October 2008

This study proposes the estimation of Multinomial Probit models using Mendell-Elston's approximation to the cumulative multivariate normal for the computation of choice probabilities. The accuracy of this numerical approximation in computing probabilities is compared with other procedures used in existing calibration programs. Finally, the proposed estimation procedure is tested on simulated choice data.
Minimal Time Vessel Routing in a Time-Dependent Environment
Authors: Perakis Anastassios N. , Papadakis Nikiforos A.
Published: October 2008

We examine the two-dimensional minimal time routing problem for a vessel traveling from an origin to several ordered destination points. The sailing space is characterized by time-dependent routing properties. The controls are the power setting and the heading. For the vessel performance model, we prove that the optimal power setting always takes its upper permissible value. Moreover, appropriate first variation considerations result in local optimality conditions which, combined with global boundary conditions, form the framework of our “broken extremal” approach. The algorithmic implementation of the methodologies developed is also discussed. In particular, we emphasize that if the departure time from the origin location is known, the problem becomes much easier than the one with unspecified departure time. Elliptical bounds for the optimal state evolution are derived, significantly reducing the dimensionality of the problem. Finally, we present numerical examples based on the above methodologies.
The Maximal Expected Covering Location Problem: Revisited
Authors: Batta Rajan , Dolan June M. , Krishnamurthy Nirup N.
Published: October 2008

The Maximal Expected Coverage Location Problem (MEXCLP) addresses the problem of optimally locating servers so as to maximize the expected coverage of demand while taking into account the possibility of servers being unavailable when a call enters the service system. In this paper, an attempt is made to relax three of MEXCLP's assumptions: servers operate independently, servers have the same busy probabilities, and server busy probabilities are invariant with respect to their locations. We embed the hypercube queueing model in a single node substitution heuristic optimization procedure, to determine a set of server locations which “maximize” the expected coverage. Our empirical findings indicate that there is disagreement between the expected coverage predicted by the MEXCLP model and the hypercube optimization procedure. There is substantial agreement, however, between the locations generated by the two procedures. We also consider a simple “adjustment” to the MEXCLP model, based upon random sampling of servers without replacement; the same adjustment has been used previously to derive a hypercube approximation procedure. We discuss modifications and enhancements to the MEXCLP's heuristic solution procedure for this adjusted model. Our empirical findings indicate that there is better agreement between the expected coverage predicted by the adjusted model and the hypercube optimization procedure. The locations generated by the adjusted model, however, are of the same overall quality as those generated by the MEXCLP model. Readers should view the results of this paper in light of the fact that we are able to relax the MEXCLP by assuming that the operating characteristics of the service system fit the description of the hypercube queueing model, such as Poisson arrivals and exponential service times, which may not be strictly true in practice.
Bibliographic Section
Authors: Vuchic Vukan R. , Zenios Stavros A.
Published: October 2008

Urban Railways and the Civil Engineer, Institution of Civil Engineers Conference, Thomas Telford House Ltd., London, U.K., 1987—reviewed by Vukan R. Vuchic.

Parallel Processing for Supercomputers and Artificial Intelligence, edited by Kai Hwang and Douglas DeGroot, McGraw-Hill, New York, 1989—reviewed by Stavros A. Zenios.
Dynamic Traffic Equilibrium with Discrete/Continuous Econometric Models
Authors: Mannering Fred L. , Abu-Eisheh Sameer A. , Arnadottir Audur T.
Published: October 2008

A procedure is developed to simulate the spatial and temporal distribution of traffic flows on a simplified highway network for home-to-work commuter trips. The procedure is based on a discrete/continuous econometric framework in which travelers' choices of route and departure time are modeled. Equilibrium traffic flows are determined using the estimated econometric models in a classic supply/demand equilibrium. The potential usefulness of the approach is demonstrated through a number of simulation runs in which equilibrium traffic flows are determined under network capacity constraints and alternate signal timing strategies.
Public Facilities Location under Elastic Demand
Authors: Perl Jossef , Ho Peng-Kuan
Published: October 2008

While most of the existing work on public sector location models has been developed in the context of emergency facilities, the location problem of nonemergency facilities differs in the location objective and in the elastic nature of demand. The proper location objective under elastic demand is that of maximizing Consumers' Surplus (CS). Based on a proposed framework, we formulate the CS location objective under different demand functions, representing different demand behaviors. We prove that the CS function is convex and therefore the search for optimal locations can be restricted to nodes. We present integer programming formulations of the Maximum Consumers' Surplus Location problem (MCSLP) and its generalization which includes fixed facility cost. A computational analysis compares the location behaviors under elastic and inelastic demands, and investigates the effects of demand function (demand behavior) on location behavior.
Technical Note—Optimizing the Schedule for a Fixed Vehicle Path with Convex Inconvenience Costs
Authors: Dumas Yvan , Soumis François , Desrosiers Jacques
Published: October 2008

We present an algorithm that solves the problem of finding the vehicle schedule which minimizes total inconveniences for travel along a fixed path, where service times at nodes are constrained by time windows and where inconvenience is modeled using convex functions of the service times. This problem occurs as the last step or as a sub-problem in many common approaches to solving routing and scheduling problems. We show that the complexity of the algorithm, expressed as a number of unidimensional minimizations, is on the order of the number of nodes for convex inconvenience functions. For linear and quadratic functions, this complexity is linear in the number of nodes. We present extensions to the case where linear costs are applied to waiting time, and also to the case where the service time variables are discrete.
Technical Note—Conical Volume-Delay Functions
Authors: Spiess Heinz
Published: October 2008

The widely used BPR volume-delay functions have some inherent drawbacks. A set of conditions is developed which a “well behaved” volume delay function should satisfy. This leads to the definition of a new class of functions named conical volume-delay functions, due to their geometrical interpretation as hyperbolic conical sections. It is shown that these functions satisfy all conditions set forth and, thus, constitute a viable alternative to the BPR type functions.
Allocation of Airline Seats between Stochastically Dependent Demands
Authors: Brumelle S. L. , McGill J. I. , Oum T. H. , Sawaki K. , Tretheway M. W.
Published: October 2008

This paper examines the problem of allocating airline seats between two nested fare classes when the demands for the classes are stochastically dependent. The well known simple seat allotment formula of Littlewood which requires the assumption of statistical independence between demands is generalized to a formula which requires only a much weaker monotonic association assumption. The model employed here is also used to examine the problems of full fare passenger spillage and passenger upgrades from the discount class.
Routing in Point-to-Point Delivery Systems: Formulations and Solution Heuristics
Authors: Leung Janny M. Y. , Magnanti Thomas L. , Singhal Vijay
Published: October 2008

We develop an optimization-based approach for a point-to-point route planning problem that arises in many large scale delivery systems (for example, less-than-truckload freight, rail, mail and package delivery, communications). In these settings, a firm which must ship goods between many origin and destination pairs on a network needs to specify a route for each origin–destination pair so as to minimize transportation costs and/or transit times. Typically, the cost structure is very complicated. The approach discussed in this paper exploits the structure of the problem to decompose it into two smaller subproblems, each amenable to solution by a combination of optimization and heuristic techniques. One subproblem is an “assignment” problem with capacity constraints. The other subproblem is a mixed-integer multicommodity flow problem. We propose solution methods based on Lagrangian relaxation for each subproblem. Computational results with these methods and with a heuristic procedure for the multicommodity flow problem on a problem met in practice are encouraging and suggest that mathematical programming methods can be successfully applied to large-scale problems in delivery systems planning and other problems in logistical system design.
Technical Note—Heuristics for Delivery Problems with Constant Error Guarantees
Authors: Altinkemer Kemal , Gavish Bezalel
Published: October 2008

In this paper Q Iterated Optimal Tour Partitioning, and Best Optimal Tour Partitioning algorithms are studied and analyzed for their worst case error. Both algorithms are based on partitioning an optimal traveling salesman tour in order to generate a feasible solution to the unit weight delivery problem. They have a worst case error bound of 2 − 1/Q where Q is the maximal number of customers a vehicle could visit and N is the total number of customers. Similar worst case error bounds are shown when the algorithms are applied to an α-optimal traveling salesman tour.
Selected Abstracts for the 1989 Transportation Science Section Dissertation Prize Competition
Authors: Powell Warren B.
Published: October 2008

The 1989 Transportation Science Section dissertation prize competition attracted 10 dissertations. The winner was Dimitris Bertsimas for Probabilistic Combinatorial Optimization Problems. Honorable mentions were awarded to Yiannis Koskosidis and to Paul M. Thompson. Special recognition was awarded to Chryssi Malandraki and Cynthia Barnhart.
On the Set of Optimal Points to the Weber Problem
Authors: Drezner Zvi , Goldman A. J.
Published: October 2008

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<p<∞ a certain part of the convex hull is the smallest possible set, but for p=1 or p=∞ the known conditions do not necessarily yield the correct set. Finally, we find the smallest possible set for p=1 or p=∞.
Technical Note—Some Average Distance Results
Authors: Stone Richard E.
Published: October 2008

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.
Modeling and Analysis for Hazardous Materials Transportation: Risk Analysis, Routing/Scheduling and Facility Location
Authors: List George F. , Mirchandani Pitu B. , Turnquist Mark A. , Zografos Konstantinos G.
Published: October 2008

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.
Liability Rules and Hazardous Materials Transportation
Authors: Watabe Akihiro
Published: October 2008

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 levels and the level of (common) knowledge of the accident probability of individual carriers.
Bibliographic Section
Authors: Jara-Díaz Sergio R. , Hanson Susan , Stopher Peter R.
Published: October 2008

Transport Carrier Costing, by Wayne Kenneth Talley. Gordon & Breach Science Publishers, New York, 1988, 389 pp.—reviewed by Sergio R. Jara-Díaz.

Gender, Transport, and Employment: The Impact of Travel Constraints, edited by Margaret Grieco, Laurie Pickup, and Richard Whipp. Gower Publishing Company, Brookfield, Vt., 1989—reviewed by Susan Hanson.

Travel Behavior Research: Fifth International Conference on Travel behavior, edited by the International Association for Travel Behavior, Avebury, Gower Publishing Co. Ltd., Aldershot, England, 1989, 284 pp.—reviewed by Peter R. Stopher.
Introduction to Special Issue on Hazardous Materials Transportation
Authors: Turnquist Mark A. , Zografos Konstantinos G.
Published: October 2008

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.
The Hierarchical Network Design Problem: A New Formulation and Solution Procedures
Authors: Pirkul Hasan , Current John , Nagarajan V.
Published: October 2008

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.
An Algorithm for Calculating Consistent Itinerary Flows
Authors: Phillips Robert L. , Boyd Dean W. , Grossman Thomas A.
Published: October 2008

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.
Technical Note—Traffic Equilibrium Paradoxes
Authors: Catoni Stefano , Pallottino Stefano
Published: October 2008

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.
The 1990 Transportation Science Section Dissertation Prize Competition
Authors: Powell Warren B.
Published: October 2008

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.