bluuebunny/crossref_metadata_2025 huggingface dataset:
A Stochastic Formulation of the Dynamic Assignment Problem, with an Application to Truckload Motor Carriers
Authors: Powell Warren B.
Published: October 2008

The dynamic assignment problem arises in a number of application areas in transportation and logistics. Taxi drivers have to be assigned to pick up passengers, police have to be assigned to emergencies, and truck drivers have to pick up and carry loads of freight. All of these problems are characterized by demands that arrive continuously and randomly throughout the day, and require a dispatcher to assign a driver to handle a specific demand. We use as our motivating application the load matching problem that arises in long-haul truckload trucking, where we have to assign drivers to loads on a real-time basis. A hybrid model is presented that handles the detailed assignment of drivers to loads, as well as handling forecasts of future loads. Numerical experiments demonstrate that our stochastic, dynamic model outperforms standard myopic models that are widely used in practice.
Fast Algorithms for Single-Sink Fixed Charge Transportation Problems with Applications to Manufacturing and Transportation
Authors: Herer Y. T. , Rosenblatt M. J. , Hefter I.
Published: October 2008

The single-sink fixed-charge transportation problem has many applications in the area of Manufacturing and Transportation—These include the supplier selection problem, the product distribution/fleet selection problem and the process selection problem. In this paper we investigate the single-sink fixed-charge transportation problem. We develop implicit enumeration procedures to solve this problem. These procedures include both domination rules and lower bounds. We also show how the domination rules can be integrated into the lower bounds so as to get even better lower bounds. We test our procedures against the best pre-existing procedure and thereby demonstrate that problems which were previously computationally intractable can now be easily solved.
Facility Layout to Support Just-in-Time
Authors: Kamoun Mahdi , Yano Candace Arai
Published: October 2008

In this paper, we develop a heuristic algorithm based on Benders' Decomposition to solve a version of the facility layout problem with decentralized shipping/receiving (s/r). Multiple s/r areas are allowed along the perimeter of the facility and each department can be serviced by the closest s/r area. Our work on this problem was motivated by just-in-time systems which require that frequent trips be made with small move quantities. In such circumstances, the use of decentralized s/r areas can significantly decrease material handling costs. We study a version of the problem in which the dimensions and locations of rectangular departments must be determined (subject to constraints), and each department must be simultaneously assigned to the nearest s/r area. The objective is to minimize the total cost of moving materials between pairs of departments, and between the departments and their respective s/r areas. Computational results for problems with up to 30 departments are reported.
A Tabu Search Heuristic for the Vehicle Routing Problem with Backhauls and Time Windows
Authors: Duhamel Christophe , Potvin Jean-Yves , Rousseau Jean-Marc
Published: October 2008

This article describes a tabu search heuristic for the vehicle routing problem with backhauls and time windows. In this problem, the set of customers is partitioned into two subsets: linehaul customers where a given quantity of goods is delivered from a central depot, and backhaul customers where a given quantity of goods is collected and transported to the depot. Mixed routes with both linehaul and backhaul customers are constructed. A variant of this problem is examined where linehauls must precede bachhauls on each route. Furthermore, the time of beginning of service at each customer location must occur within a particular time interval. Computational results are reported on a standard set of test problems, and comparisons are made with other heuristic approaches and with optimal solutions.
Controlled Optimization of Phases at an Intersection
Authors: Sen Suvrajeet , Head K. Larry
Published: October 2008

This paper presents a general purpose algorithm for real-time traffic control at an intersection. Our methodology, based on dynamic programming, allows optimization of a variety of performance indices such as delay, stops and queue lengths. Furthermore, optimal phase sequencing is a direct by-product of this new approach. These features make the new methodology a powerful tool for intersection control. We demonstrate the usefulness of the approach by a simulation experiment in which our intersection control algorithm is interfaced with a well established simulation package called TRAF-NETSIM. Our study compares the controlled optimization of phases methodology with fully-actuated as well as semi-actuated control. We show that consistent reductions in delay may be possible by adopting the new algorithm.
Bibliographic Section
Authors: Allsop Richard , Harrison Robert
Published: October 2008

Transportation and Traffic Theory—Proceedings of the 13th International Symposium on Transportation and Traffic Theory, Lyon, July 1996. Edited by Jean-Baptiste Lesort. Oxford: Pergamon 1996, xv + 758 pp—reviewed by Richard Allsop.

Roads in a Market Economy, by Gabriel Roth, Ashgate Publishing Limited, Avebury Technical, Aldershot, England, 1996, 272 pp—reviewed by Robert Harrison.
Tributes to Robert Herman
Authors: Ardekani Siamak A. , Mahmassani Hani S.
Published: October 2008

Robert Herman, a past president of ORSA and one of the founders and the first chairman of the Transportation Science Section, passed away in Austin, Texas, on February 13, 1997. Herman is internationally recognized as the originator of traffic science. His contributions span the entire 40 years of scientific activity in this field.
Projected Dynamical Systems in the Formulation, Stability Analysis, and Computation of Fixed-Demand Traffic Network Equilibria
Authors: Nagurney Anna , Zhang Ding
Published: October 2008

This paper proposes, for a fixed demand traffic network problem, a route travel choice adjustment process formulated as a projected dynamical system, whose stationary points correspond to the traffic equilibria. Stability analysis is then conducted in order to investigate conditions under which the route travel choice adjustment process approaches equilibria. We also propose a discrete time algorithm, the Euler method, for the computation of the traffic equilibrium and provide convergence results. The notable feature of the algorithm is that it decomposes the traffic problem into network subproblems of special structure, each of which can then be solved simultaneously and in closed form using exact equilibration. Finally, we illustrate the computational performance of the Euler method through various numerical examples.
Integrated Routing and Scheduling in Hazardous Materials Transportation
Authors: Nozick Linda K. , List George F. , Turnquist Mark A.
Published: October 2008

Recognition of time-varying patterns of accident rates and exposure parameters can be used to improve routing and scheduling decisions for hazardous materials shipments. An integrated routing/scheduling approach can be used to reduce overall risk, and find preferred solutions in a multiobjective context. We describe a method for performing an integrated routing/scheduling analysis, and illustrate its use in a case study. We also construct estimates of the “value of information” for incorporation of this time-dependent data.
Modeling the Increased Complexity of New York City's Refuse Marine Transport System
Authors: Richetta Octavio , Larson Richard C.
Published: October 2008

The New York City Department of Sanitation operates the world's largest refuse marine transport system. Waste trucks unload their cargo at land-based transfer stations where refuse is placed in barges and then towed by tugboats to the Fresh Kills Landfill in Staten Island. In the early 1980s, the city commissioned the development of a computer-based model for use in fleet sizing and operations planning. As a result of the complexities introduced by environmental regulation and technological innovation, the marine transport system operations changed and the existing model became obsolete. Based on the success achieved with the first model in 1993, the city commissioned the development of a new model. In this paper, we present a PC-based model developed to meet the increased complexity of the system. Analysis performed for validation and calibration of the model demonstrates that it tracks well the operations of the real system. We illustrate through a detailed design exercise how to use the model to configure the system in a way that meets the requirements of the refuse marine transport system.
Bibliographic Section
Authors: Gendreau Michel
Published: October 2008

World Transport Research—Proceedings of the 7th World Conference on Transport Research edited by D. Hensher, J. King, and T. Oum, Pergamon, Oxford, U.K., 4 volumes, (434 + 524 + 616 + 516) pages—reviewed by Michel Gendreau.
Queue Spillovers in Transportation Networks with a Route Choice
Authors: Daganzo Carlos F.
Published: October 2008

This paper explores some of the traffic phenomena that arise when drivers have to navigate a network in which queues back up past diverge intersections. If a diverge provides two alternative routes to the same destination and the shorter route has a bottleneck that generates a queue, one would expect that queue to stabilize at an equilibrium level where the travel time on both routes is roughly equal. If the capacity of the alternative route is unlimited then this network can accommodate any demand level. However, if the bottleneck is so close to the upstream end of the link that the equilibrium queue cannot be contained in the link, then the trip time on the queued route cannot grow to match that on the alternate route. This means that the alternative route can never be attractive, even if the queue spills back past the diverge, and that drivers approaching the diverge will act as if the alternative route did not exist. As a result, a steady flow into the system greater than the capacity of the bottleneck will cause a queue to grow all the way back to the origin (blocking it). The final result is an “oversaturated static state” where the queue regulates the input flow into the system. Curiously, if the bottleneck capacity of this network is reduced below a critical level (or is eliminated altogether) then the alternative route becomes attractive again and the system cannot reach the saturation point. This phenomenon is explored in the paper, where it is also shown that: i) a network can become permanently oversaturated/undersaturated as a result of a temporary increase/decrease in link capacity, ii) even under the most favorable assumptions, and in contrast to the equivalent assignment problem with point queues, a network can be stable both in an oversaturated and an under-saturated state, and iii) temporary endogenous disturbances can permanently reverse the saturation state of a network. These findings suggest that in certain situations the time-dependent traffic assignment problem with physical queues is chaotic in nature and that (as in weather forecasting) it may be impossible to obtain input data with the required accuracy to make reliable predictions of cumulative output flows.
TSS Dissertation Abstracts—Abstracts for the 1997 Transportation Science Section Dissertation Prize Competition
Authors: Labbé Martine
Published: October 2008

The TSS Dissertation Prize Competition is the oldest and most prestigious competition for doctoral dissertations in the transportation science area. This is the report on the 1997 competition. Eligible doctoral dissertations were those completed and submitted between June 1, 1996 and May 31, 1997 in the area of transportation science. To be considered, a dissertation had to be nominated by the thesis supervisor. This year, 17 dissertations were submitted for consideration by the ludging committee which was chaired by Professor Martine Labbé, Université Libre de Bruxelles, Belgium. There were two first prize winners. Dr. Gregory D. Glockner of Georgia Institute of Technology and Dr. Sarah Stock-Patterson of the Massachusetts Institute of Technology. An honorable mention was awarded to Dr. Kalidas Ashok of the Massachusetts Institute of Technology. Extended abstracts for the 17 dissertations are provided below, winners first and then, in alphabetical order, by author.
Flight String Models for Aircraft Fleeting and Routing
Authors: Barnhart Cynthia , Boland Natashia L. , Clarke Lloyd W. , Johnson Ellis L. , Nemhauser George L. , Shenoi Rajesh G.
Published: October 2008

Given a schedule of flight legs to be flown by an airline, the fleet assignment problem is to determine the minimum cost assignment of flights to aircraft types, called fleets, such that each scheduled flight is assigned to exactly one fleet, and the resulting assignment is feasible to fly given a limited number of aircraft in each fleet. Then the airline must determine a sequence of flights, or routes, to be flown by individual aircraft such that assigned flights are included in exactly one route, and all aircraft can be maintained as necessary. This is referred to as the aircraft routing problem. In this paper, we present a single model and solution approach to solve simultaneously the fleet assignment and aircraft routing problems. Our approach is robust in that it can capture costs associated with aircraft connections and complicating constraints such as maintenance requirements. By setting the number of fleets to one, our approach can be used to solve the aircraft routing problem alone. We show how to extend our model and solution approach to solve aircraft routing problems with additional constraints requiring equal aircraft utilization. With data provided by airlines, we provide computational results for the combined fleet assignment and aircraft routing problems without equal utilization requirements and for aircraft routing problems requiring equal aircraft utilization.
The Preferential Bidding System at Air Canada
Authors: Gamache Michel , Soumis François , Villeneuve Daniel , Desrosiers Jacques , Gélinas Éric
Published: October 2008

This paper describes the Preferential Bidding Problem solved in the airline industry to construct personalized monthly schedules for pilots and officers. This problem consists in assigning to crew members pairings, days off, annual leaves, training periods, etc., while considering a set of weighted bids that reflect individual preferences. This assignment must be done under strict seniority restrictions: the construction of a maximum-score schedule for a particular crew member must never be done at the expense of a more senior employee. This research and development project has resulted in the Preferential Bidding System that has been used at Air Canada since May 1995. The solution process is summarized as follows. For each employee, from the most senior to the most junior, a so-called residual problem is solved: given an employee and a set of unassigned pairings, the solution to an integer linear program determines the employee's maximum-score schedule while taking into account all the remaining employees. The residual problem is solved by column generation embedded in a branch-and-bound tree. Integer solutions are obtained by using very efficient cutting planes, without which it would have been impossible to solve some of these residual problems.
Combinatorial Issues in Air Traffic Optimization
Authors: Fondacci Rémy , Goldschmidt Olivier , Letrouit Vincent
Published: October 2008

The current airway network used by aircraft is composed of a set of segments that intersect on special points defined by radio beacons emitting signals from the ground. This network leads to excess flight length, which for the European network is estimated to be 8%. In the near future, the Global Positioning System, which can determine precisely the location of aircraft, might allow the design of a network without using any ground fixed radio beacons. Therefore, we can project a new skyway network with straight airways between airports, allowing an airway to change level one or more times between its origin and destination to avoid potential conflict points. We present some segment set combinatorial issues to achieve such a network. In particular, we propose heuristics or algorithms for the problems of the maximum clique, the coloring, the N-coloring, and other more general problems of coloring of a set of segments. Finally, we discuss some results based on actual data analysis.
A Tactical Decision Support System for Empty Railcar Management
Authors: Sherali Hanif D. , Suharko Arief B.
Published: October 2008

In this paper, we present a tactical model to assist in the task faced by the railroad industry on a day-to-day basis of centrally managing the distribution and repositioning of empty railcars for shipping automobiles. The problem involves a group of eight principal automobile manufacturers (shippers) who have pooled their autorack resources (railcars for shipping automobiles) to improve utilization and reduce the number of empty miles logged. However, this consolidation gives rise to various equity and priority issues related to timeliness in service, particularly in the case of shortages. Accordingly, our model takes into account such practical issues, including uncertainties in transit times, priorities with respect to time and demand locations, multiple objectives related to minimizing different degrees of latenesses in delivery, and blocking considerations. We investigate the performance of two principal models that have been developed for this purpose. The first model, TDSS1 incorporates all the identified features of the problem except for blocking (a consolidation of shipments from any origin to only a limited number of destinations), and results in a network formulation of the problem. The second model, TDSS2 extends TDSS1 by further including blocking considerations, and results in a network flow problem with side constraints and discrete side variables. We then show how the resulting mixed-integer-programming formulation can be enhanced via some partial convex hull constructions. To accommodate the strict run-time limit requirements imposed in practice, 21 principal heuristics are developed and tested to solve this problem. By examining the performance of these procedures with respect to speed of operation and the quality of solutions produced on a test bed of real-world problem instances, we prescribe a solution strategy for implementation in making production runs.
Modeling Train Delays in Urban Networks
Authors: Higgins A. , Kozan E.
Published: October 2008

The reliability of urban passenger trains is a critical performance measure for passenger satisfaction and ultimately market share. A delay to one train in a peak period can have a severe effect on the schedule adherence of other trains. This paper presents an analytically based model to quantify the expected positive delay for individual passenger trains and track links in an urban rail network. The model specifically addresses direct delay to trains, knock-on delays to other trains, and delays at scheduled connections. A solution to the resultant system of equations is found using an iterative refinement algorithm. Model validation, which is carried out using a real-life suburban train network consisting of 157 trains, shows the model estimates to be on average within 8% of those obtained from a large scale simulation. Also discussed, is the application of the model to assess the consequences of increased scheduled slack time as well as investment strategies designed to reduce delay.
TSS Dissertation Abstracts—Abstracts for the 1998 Transportation Science Section Dissertation Prize Competition
Authors: Ardekani Siamak A.
Published: October 2008

The TSS Dissertation Prize Competition is the oldest and most prestigious competition for doctoral dissertations in the transportation science area. On behalf of the TSS dissertation prize committee, I am pleased to provide this report on the 1998 competition. Eligible doctoral dissertations were those completed and submitted between June 1, 1997 and May 31, 1998 in the area of transportation science. To be considered, a dissertation had to be nominated by the thesis supervisor. This year, eight dissertations were submitted for consideration by the judging committee, which was chaired by Professor Siamak A. Ardekani, The University of Texas at Arlington, and consisted of: (1) Professor Jay Jayakrishnan, University of California at Irvine; (2) Professor Srinivas Peeta, Purdue University; (3) Professor Paolo Toth, University of Bologna-Italy; (4) Professor Garrett J. van Ryzin, Columbia University I would like to extend my sincere thanks to the judges for the time and effort they devoted to the difficult task of judging these entries. The quality of all the theses submitted was excellent and the choices were difficult. The awards were announced at the Fall meeting of INFORMS in Seattle. The First Prize winner was Dr. Gianpaolo Ghiani of The Universita degli Studi di Napoli “Federico II.” An honorable mention was awarded to Dr. Robert L. Hoffman of the University of Maryland at College Park. It is important to remember that the submissions to the TSS Dissertation competition are already distinguished by the fact that they have been nominated for the award. Each makes a unique and valuable contribution to transportation science, and allentrants and their advisors deserve warmest congratulations.
The Underlying Markov Decision Process in the Single-Leg Airline Yield-Management Problem
Authors: Lautenbacher Conrad J. , Stidham Shaler
Published: October 2008

We introduce the terms dynamic and static, respectively, to identify the prevailing approaches to the single-leg airline yield-management problem: those allowing customers of different fare classes to book concomitantly (dynamic), and those assuming that the demands for the different fare classes arrive separately in a predetermined order (static). We present a coherent frame-work linking these seemingly disparate models through the underlying dynamic program common to both. We develop a discrete-time Markov decision process formulation mirroring that of Janakiram et al. Transp. Sci. 33, 147–167 (1999) to solve the single-leg problem without cancellations, overbooking, or discounting. Borrowing a result from the queueing-control literature, we prove the concavity of the associated optimal value functions and, subsequently, the optimality of a booking limit policy. We then apply this same technique to the more influential papers from the single-leg literature, at once unifying the static and dynamic models and establishing the connection between the yield-management and queueing-control problems. Finally, we propose an omnibus formulation that yields the static and dynamic models as special cases.
Revenue Management: Research Overview and Prospects
Authors: McGill Jeffrey I. , van Ryzin Garrett J.
Published: October 2008

This survey reviews the forty-year history of research on transportation revenue management (also known as yield management). We cover developments in forecasting, overbooking, seat inventory control, and pricing, as they relate to revenue management, and suggest future research directions. The survey includes a glossary of revenue management terminology and a bibliography of over 190 references.
An Exact Method for the Vehicle Routing Problem with Backhauls
Authors: Mingozzi Aristide , Giorgi Simone , Baldacci Roberto
Published: October 2008

We consider the problem in which a fleet of vehicles located at a central depot is to be optimally used to serve a set of customers partitioned into two subsets of linehaul and backhaul customers. Each route starts and ends at the depot and the backhaul customers must be visited after the linehaul customers. A new (0–1) integer programming formulation of this problem is presented. We describe a procedure that computes a valid lower bound to the optimal solution cost by combining different heuristic methods for solving the dual of the LP-relaxation of the exact formulation. An algorithm for the exact solution of the problem is presented. Computational tests on problems proposed in the literature show the effectiveness of the proposed algorithms in solving problems up to 100 customers.
Advances in the Continuous Dynamic Network Loading Problem
Authors: Xu Y. W. , Wu J. H. , Florian M. , Marcotte P. , Zhu D. L.
Published: October 2008

The continuous dynamic network loading problem (CDNLP) consists in determining, on a congested network, time-dependent arc volumes, together with arc and path travel times, given the time-varying path flow departue rates over a finite time horizon. This problem constitutes an intrinsic part of the dynamic traffic assignment problem. In this paper, we present a formulation of the CDNLP where travel delays may be nonlinear functions of arc traffic volumes. We prove, under a boundedness condition, that there exists a unique solution to the problem and propose for its solution a finite-step algorithm. Some computational results are reported for a discretized version of the algorithm.
Parallel Tabu Search for Real-Time Vehicle Routing and Dispatching
Authors: Gendreau Michel , Guertin François , Potvin Jean-Yves , Taillard Éric
Published: October 2008

An abundant literature about vehicle routing and scheduling problems is available in the scientific community. However, a large fraction of this work deals with static problems where all data are known before the routes are constructed. Recent technological advances now create environments where decisions are taken quickly, using new or updated information about the current routing situation. This paper describes such a dynamic problem, motivated from courier service applications, where customer requests with soft time windows must be dispatched in real time to a fleet of vehicles in movement. A tabu search heuristic, initially designed for the static version of the problem, has been adapted to the dynamic case and implemented on a parallel platform to increase the computational effort. Numerical results are reported using different request arrival rates, and comparisons are established with other heuristic methods.
Letter to the Editor—Comments on “Queuing Systems with Transport Service Processes”
Authors: Hofri M. , Shlifer E.
Published: October 2008

In his paper, Pearce presents a method for determining the stationary probabilities of a G/Mt/1 system, the service mechanism being such that it operates regardless of whether or not customers are present. This note is an attempt to correct his results.
The Distribution of Traffic Volumes
Authors: Vaughan Rodney J.
Published: October 2008

The distribution of hourly volumes is described and its form and characteristics are discussed. Theoretical models of the distribution are derived so that an estimate of the distribution may be obtained if only a fraction of the traffic data for the year is known. Depending on the size of this sample different estimation procedures are recommended. The hour has long been the conventional counting interval used for traffic counts over long periods. Other counting intervals are considered to determine if the hour is the best unit. The distribution of daily traffic volumes is found to be best represented by a displaced gamma distribution.
A Branch-and-Bound Algorithm for Determining the Minimal Fleet Size of a Transportation System
Authors: Martin-Löf Anders
Published: October 2008

The problem of determining a schedule for a traffic system of, e.g., bus or air lines that uses a minimum number of vehicles is treated. The various trips are required to start within given time intervals and have given origins, destinations, and travel times. It is shown that the problem can be formulated as an integer LP problem, but not of the simple network flow type. A rather simple branch-and-bound procedure is devised for its solution, which has been tested with favorable results.
An Empirical Model for Multilane Road Traffic
Authors: Miller Alan J.
Published: October 2008

Before we can construct models for multilane traffic flow, we must be able to describe single-lane traffic. This paper considers some of these methods of description including the use of headway and counting distributions. Another method of describing point processes is by means of product densities. These are essentially joint probabilities of two or more vehicles passing a point at different specified times. Product densities have been used in many fields including particle physics, ecology, and road traffic. The idea of using product densities is simple and attractive, but they do have two major disadvantages: except in simple cases, headway distributions are very difficult to derive from product densities, and product density estimates for different time lags are correlated, so that tests of hypotheses are not easy to perform. An alternative to product densities is proposed. For want of a better name these are called termination rates. The termination rate after lag τ is the probability of a vehicle passing a point in a small interval of time, divided by the length of the small interval and conditional upon the last vehicle having passed a time τ previously. These are very similar to mortality rates for humans or scrappage rates for commodities with limited life-times. The interrelations between these statistics are quoted but not derived. Various sets of data are used to illustrate the less common statistics. Some analysis is given of a sample of data from the Congress (now Eisenhower) Expressway in Chicago. Variance to mean ratios are used to show that there is a strong correlation between lanes even though the autocorrelations of headways within lanes are very small. Bivariate termination rates have been estimated for each lane. Given a vehicle in one lane, it was found that the expected number of vehicles in a neighboring lane within 2 or 3 sec was enhanced by about 10–15 percent.
Letter to the Editor—Pareto and Traffic
Authors: Greenberg Irwin
Published: October 2008

An examination of vehicular relative velocity data leads to the conjecture that the stable Paretian law might be used to describe the distribution. An implication of this concerning the headway distribution is derived and an alternative interpretation of the data is mentioned.
Letter to the Editor—Comments on “The Multiple Terminal Delivery Problem with Probabilistic Demands”
Authors: Uebe Götz
Published: October 2008

In a recent paper (Tillman, F. A. 1969. The multiple terminal delivery problem with probabilistic demands. Trans. Sci. 3 192–204.) Tillman proposes a heuristic for the problem of supplying demand points P1, P2, …, Pn from m terminals T1, T2, …, Tm. Since no restrictions are imposed on the terminals, the problem is to select the cycles that join the demand points and each terminal from which these demand points receive their supplies.
The Author's Reply—A Note on the Multiple Terminal Delivery Problem with Probabilistic Demands
Authors: Tillman Frank A.
Published: October 2008

In response to a letter to the editor by Götz Uebe, of the “Institute für Ange-wandte Mathematik, Technische Hochschule Mü nchen, Munich,” concerning my paper, “The Multiple Terminal Delivery Problem with Probabilistic Demands,” Trans. Sci. 3 192–204 (1969), there is a need for further elaboration of several points in the paper. For this discussion assume all demands are deterministic. The discussion holds for both deterministic and probabilistic situations.
The Analysis and Interpretation of Gap Acceptance Data
Authors: Ashworth Robert
Published: October 2008

Alternative methods of analysing gap acceptance data are considered with a view to removing the bias implicit in the situation in which minor road vehicle drivers exhibit consistent behavior and all accepted and rejected gaps are taken into account. Simulation techniques are used to show that some of these suggested methods are invalid, but verification is obtained for a method derived by the author in an earlier paper that simply requires the displacement of the gap acceptance curve time scale by an amount equal to the product of the variance of the observed gap acceptance distribution (sec2) and the major road volume (veh/sec). This, it is contended, is easier to apply than an alternative method of estimating the critical gap distribution parameters given by McNeil and Morgan. A theoretical relation is determined between the mean of the critical gap distribution and the Raff critical lag that shows the two to be equal only when the gap acceptance curve takes the form of a step function.
Some Properties of Presence Detectors
Authors: Newell G. F.
Published: October 2008

Presence detectors on highways record whether or not there are any cars on some nonzero length section of highway. The absence of cars is used as a criterion for switching a vehicle-actuated signal. The problem considered here is the following. Cars pass the detector according to a Poisson process, at velocities that are independent, identically distributed random variables. Starting at some arbitrary time origin, how long will it be before the detector of length L is empty for the first time. It is shown that, in most cases, this time is nearly the same as if all cars had the same velocity q/k, q = flow, k = spacial density, and is rather insensitive to the distribution of the velocities.
Letter to the Editor—A Discrete-Time Model for a Traffic Intersection
Authors: Griffiths J. D. , Thomas R. H.
Published: October 2008

Ideas introduced by Oliver and Bisbee are used in the consideration of a more realistic model of a T-junction. Results are shown to be in close agreement with those of Tanner, but are obtained by a simpler analysis.
The Economic Applications of the Distribution of Traffic Volumes
Authors: Vaughan Rodney J.
Published: October 2008

A method for estimating costs and benefits to commuters, over a period of time, is developed in this paper. The method will account for the variation of traffic volumes over the period of time considered. The cost structure of a transport mode is taken as a function of the volume of traffic on that mode. The distribution of traffic volumes is then used to measure the costs and benefits to the user and the state over a year. Commuters are divided into different social classes according to the value they place on the attributes of the different transport modes. Next the method is used to evaluate different road pricing schemes. Finally the road system is examined both as a public utility and as a public enterprise.
The Minimum Fleetsize for a Suburban Railway System
Authors: Salzborn Franz J. M.
Published: October 2008

A mathematical method is developed for minimizing the number of railcars that is needed for the peak operations of a suburban railway system by cutting railcars back from stations along the lines in an optimum way. A secondary objective is the minimization of the total driver time. A mathematical proof is given of the fact that the total number of railcars required is equal to the maximum number of railcars simultaneously in operation; and this theorem leads to the formulation of the minimization problem as a set of linear zero-one-programs. A case study demonstrates the practical usefulness of the method by applying it to an existing railway system.
Letter to the Editor—Comments on a Heuristic Algorithm for the Multiple Terminal Delivery Problem
Authors: Lam Tenny N.
Published: October 2008

The limitations of a heuristic vehicle routing procedure proposed by Tillman for the multiterminal delivery problem are investigated. Because of limitations in the assignment of demand points to terminals, the procedure does not guarantee the optimality of its solution even when the solution consists entirely of single demand point-terminal linkings.
Variability in Round-Trip Times for an Elevator Car During Up-Peak
Authors: Gaver Donald P. , Powell Bruce A.
Published: October 2008

The variability in the round-trip time of an elevator car is studied. Using the derived analytical expressions for the variance of round-trip time, we can evaluate the usefulness of solutions obtained from an optimization procedure in which round-trip time was assumed constant. Also, it is shown by numerical examples why passenger-carrying capability can be increased by operating a single bank of cars as two independent banks.
An Airline Overbooking Model
Authors: Rothstein Marvin
Published: October 2008

A model for determining airline overbooking policies is presented. The problem is formulated as a nonhomogeneous Markovian sequential decision process. Solutions that are optimal in several different senses are obtained with the aid of dynamic programming. An example based upon airline data illustrates the character of the policies and the sensitivity of the model with respect to certain parameters.
Determining Optimal Container Inventory and Routing
Authors: Horn William A.
Published: October 2008

Generalizing work of Samuel and Ullmann, this paper shows how to determine the optimal number and routings of containers used to move mail among several cities. Critical assumptions are (a) periodic demand patterns and linear transportation costs (for full or empty containers, or uncontainerized mail) between each city-pair, and (b) constant fixed cost per container in the system. The optimization problem is transformed into a network flow linear program for which efficient solution methods are known.
Operational Delays Induced by Random Exogeneous Events
Authors: Sivazlian B. D.
Published: October 2008

Exogeneous events occurring as a Poisson process are assumed to cause stoppages in the normal operation of convoys, road vehicles, or equipments. The operational delay experienced by each stoppage is assumed to have an exponential distribution. By introducing appropriate state variables, a hyperbolic partial differential equation is set up; expressions are obtained for the probability that at a given time the operation has registered at most a given number of cumulative performance units (e.g., distance) and for the probability that the operation has registered a given number of cumulative performance units on or before a specified time.
Book of Interest
Authors: Koenigsberg Ernest
Published: October 2008

Planning Tools for Ocean Transportation by I. M. Datz, Cornell Maritime Press, Inc., Cambridge, Maryland, 1971, XV + 168 pages, $10.00.
Application of Simulation to Assessment of Component Changes on Rear End Highway Accidents
Authors: Carlson William L.
Published: October 2008

This paper illustrates the simulation method of evaluating the effect of system component changes on highway crash reduction. The evaluation procedure presented uses operating characteristics of a component as input, and compares the performance of alternative components in emergency traffic conflict situations. It is shown that Monte Carlo simulation of the model may be an efficient technique for comparing component alternatives. The examples presented involve (1) the emergency braking capabilities of two populations of vehicles in emergency car-following situations, and (2) two different rear lighting systems.
Regulatory Models for Pricing and Evaluation of Transport Services
Authors: Charnes A. , Cooper W. W. , Kirby M. J. L. , Raike W.
Published: October 2008

A variety of objectives and constraints are presented for use by a regulatory agency in pricing public services and evaluating capacities under conditions where the demands are random variables with probability distributions that depend on prices in different parts of the system. The models studied include a maximization of the joint probability of achieving at least specified levels of consumers' surpluses in these interacting markets, as well as models that constrain the choices of prices and services to ensure that these surpluses are satisfied to at least specified levels of probability, while observing expected fair return constraints for the producers. Chance constrained programming formulations and reductions to deterministic equivalents are developed to use for evaluating levels of service, etc. Some new “coefficients conditions” establishing concavity for quadratic forms are stated and proved in the Appendix to this paper. This also establishes convexity for the deterministic equivalents developed in this paper and hence provides access to Kuhn-Tucker and other conditions that depend on convexity. This then yields yet another (dual) problem that is also deterministic and that makes it possible to extend the procedures for constraint evaluations in terms of their welfare and regulatory implications.
Analysis of Traffic Flow on a Signalized One-Way Artery
Authors: Preparata Franco P.
Published: October 2008

This paper concerns itself with the kinematic analysis of traffic flow on a signalized one-way artery. Using as mathematical model the continuum flow theory of Lighthill-Whitham-Richards, the flow pattern is carefully investigated under the assumptions of parabolic volume-density diagram and constant flow on the artery. The interesting symmetry existing between fluid and congested regimes is noted and used in proving various results. The delay caused by an interruption of arbitrary regimes is analyzed as a function of space and time. It is shown that an interruption of an arbitrary regime is equivalent to a particular interruption of a corresponding uniform regime: this provides a very simple and general method for delay computation. The delay caused by a periodic interruption (traffic signal) is bounded by and is asymptotically equal to the duration of the red signal; moreover, both the maximum and the average delay at fixed distance from the signalized intersection are increasing functions of the cycle time. It is further shown that the results concerning the delay function apply to all convex volume-density diagrams.
Control Strategies for an Idealized Public Transportation System
Authors: Osuna E. E. , Newell G. F.
Published: October 2008

Vehicles load passengers at a single service point and, after traversing some route, return for another trip. The travel times of successive trips are independent identically distributed random variables with a known distribution function. After a vehicle returns to the service point, one has the option of holding it, or dispatching it immediately. Passengers arrive at a uniform rate and the objective is to minimize the average wait per passenger. The problem of determining the optimal strategy (dispatch or hold) for a system of m vehicles is formulated as a dynamic programming problem. It is analyzed in detail for m = 1 and m = 2. For m = 1, the optimal strategy will hold a vehicle if it returns within less than about half the mean trip time. For m = 2, and for a small coefficient of variation of trip time C(T), the optimal strategy will control the vehicles so as to retain nearly equally spaced dispatch times, within a range of time proportional to C4/3(T).
Letter to the Editor—Productivity Increases in the U.S. Airline Industry: Comments
Authors: Mayberry John P.
Published: October 2008

There seem to be errors of two types in the paper “Sources of Productivity Increases in the U.S. Passenger Airline Industry,” by Neil B. Murphy Trans. Sci., 3, 233–238 (1969).
Letter to the Editor—Note on a Criterion for Head-of-the-Line Priority Expressway Merging for Buses
Authors: Marcus Allan H.
Published: October 2008

Suppose that an expressway on-ramp is two lanes wide up to some point (“merge” point) and then narrows to one lane at the ramp nose. The priority scheme is to give exclusive use of the left lane of the ramp to buses, and to give buses priority right-of-way at the merge point. Assume that buses and cars arrive independently and Poissonwise. Well-known results about priority queues show that this priority scheme is preferable to the standard nonpriority scheme if the ratio of expected ramp delay times for buses and cars is less than the ratio of average “cost” per vehicle per unit delay time.
On a Ramp-Flow Assignment Problem
Authors: Wang C. F.
Published: October 2008

The formulation of ramp-flow assignment problem in the operations of controlled expressways during the rush-hour period is presented here. In order to discuss the problem on a quantitative basis, a simple unidirectional expressway system with multiple entrance-ramps has been selected as the model. When the flow throughout the system can be maintained below the bottleneck capacity of the expressway, the condition of steady flow prevails, and the model may be regarded as a dynamic process in the direction of flow. The ramp-flow regulation problem in an expressway system is then formulated as a multistage decision process by considering the ramp-flows as decision variables. Various criteria for selecting the optimum ramp-flow assignment are discussed and their implications in the regulation of rush-hour traffic are illustrated through a simple example. In the example, the technique of dynamic programming was used successfully to determine the optimum policy that minimizes the system congestion period and the results led to the conclusion that the two-switching policy is the best optimum policy with respect to the stated objective for a three-stage process.
Letter to the Editor—A Note on the Minimum Fleetsize for a Suburban Railway System
Authors: Proll L. G.
Published: October 2008

A formulation of the problem of optimizing the operations of a suburban railway system with a given peak timetable is presented that has computational advantages over that given by Salzborn. The solution proposed by Salzborn for his case study is shown to be nonoptimal.
A Time-of-Day Model for Aircraft Scheduling
Authors: Miller James C.
Published: October 2008

This paper describes an aircraft scheduling model which accounts for indivisibilities in production (airplanes, flights), capacity costs due to peak demand, and consumer preferences regarding the time of day flights are scheduled. Application of the model to real-world routing problems is not intended, as the scope is limited to a system comprised of a single city pair. However, the model does make possible a detailed examination of the economic welfare aspects of various routing criteria and the degree of realism in the assumptions made. Cost functions formulated from CAB data, along with hypothesized characteristics of air travel demand, form a data base for the model. Results are included to show the effect on economic welfare of utilizing a model which fails to incorporate passenger preferences as to the time of day flights are scheduled.
Demand for Travel to Canada by American Citizens
Authors: Askari Hossein
Published: October 2008

In this paper, different empirical models for explaining car travel to Canadian provinces by American citizens are estimated. The results indicate interesting substitution and complimentarities in travel that have important policy implications. Furthermore, the results have implications for future travel to Canada given rising incomes and the shifting of the United States' population center.
An Algebra for the Analysis and Design of Transportation Networks
Authors: Baligh Helmy H. , Dellinger David C. , Volpp Louis D.
Published: October 2008

A transportation network algebra is developed as a set of definitions and rules of logic needed to create a useful, integrated theory for systematic design and development of networks. A network is viewed as the output of the physical components of the transportation system. The algebra is based on the concept of a direct trip as a function, and an indirect trip as the result of the composition of these functions. Special forms of network addition are developed and theorems related to the properties of networks are proved. The algebraic operations and theorems permit the composition and decomposition of networks and the systematic, efficient, and sequential generation of networks and their evaluation. The theorems are on some of the properties to be used in their evaluation, such as: connectedness, coalescence, and the criticalness of stations and trips.