bluuebunny/crossref_metadata_2025 huggingface dataset:
Constructing Railroad Blocking Plans to Minimize Handling Costs
Authors: Newton Harry N. , Barnhart Cynthia , Vance Pamela H.
Published: October 2008

On major domestic railroads, a typical general merchandise shipment may pass through many classification yards on its route from origin to destination. At these yards, the incoming traffic, which may consist of a number of individual shipments, is reclassified (sorted and grouped together) to be placed on outgoing trains. Each reclassification incurs costs due to handling and delay. To prevent shipments from being reclassified at every yard they pass through, several shipments may be grouped together to form a block. A block has associated with an origin–destination pair that may or may not be the origin or destination of any of the individual cars contained in the block. The objective of the railroad blocking problem is to choose which blocks to build at each yard and to assign sequences of blocks to deliver each shipment to minimize total mileage, handling, and delay costs. We model the railroad blocking problem as a network design problem in which yards are represented by nodes and blocks by arcs. Our model is intended as a strategic decision-making tool. We develop a column generation, branch-and-bound algorithm in which attractive paths for each shipment are generated by solving a shortest path problem. Our solution approach is unique in constraining the classification resources of each yard and simultaneously solving for different priority classes of shipments. We implement our algorithm and find near-optimal solutions in about one hour for the blocking problem of a large domestic railroad, in which the paths that shipments may take in the physical network are restricted. The resulting network design problem has 150 nodes, 1300 commodities, and 6800 possible arcs (blocks). We test the robustness of our solution on 19 test instances that are variations of the data for the real-world problems. If shipments are restricted to following one of a limited number of paths in the rail network, then, in four hours or less, our algorithm finds solutions within 0.4% of optimal for all test cases. Furthermore, the solutions obtained are no more than 3.9% from optimal even if all possible paths are allowed.
Models and Algorithms for Container Allocation Problems on Trains in a Rapid Transshipment Shunting Yard
Authors: Bostel Nathalie , Dejax Pierre
Published: October 2008

Multimodal transport of containers can be an alternative to the road transportation but it requires to be competitive in terms of quality of service and price. In rail–rail container terminals, new techniques are developed to facilitate rapid transfers of the containers between trains. In this article, we address the problem of the optimization of the operations management of rapid rail–rail transshipment shunting yards. We are interested specifically in the optimization of containers allocation on trains (for the initial loading and their reloading after transshipment). We have developed a class of models with different levels of complexity and realism and we have proposed optimal and heuristic methods to solve them. The experimental results on realistic datasets are very promising in terms of the minimization of the container moves in a terminal as well as the use and sizing of the handling equipments.
2-Path Cuts for the Vehicle Routing Problem with Time Windows
Authors: Kohl Niklas , Desrosiers Jacques , Madsen Oli B. G. , Solomon Marius M. , Soumis François
Published: October 2008

This paper introduces a strong valid inequality, the 2-path cut, to produce better lower bounds for the vehicle routing problem with time windows. It also develops an effective separation algorithm to find such inequalities. We next incorporate them as needed in the master problem of a Dantzig–Wolfe decomposition approach. In this enhanced optimization algorithm, the coupling constraints require that each customer be serviced. The subproblem is a shortest path problem with time window and capacity constraints. We apply branch and bound to obtain integer solutions. We first branch on the number of vehicles if this is fractional, and then on the flow variables. The algorithm has been implemented and tested on problems of up to 100 customers from the Solomon datasets. It has succeeded in solving to optimality several previously unsolved problems and a new 150-customer problem. In addition, the algorithm proved faster than algorithms previously considered in the literature. These computational results indicate the effectiveness of the valid inequalities we have developed.
Solution to the Continuous Time Dynamic Yield Management Model
Authors: Liang Yigao
Published: October 2008

We formulate the yield management problem as a continuous time, stochastic, dynamic programming model. We derive an expression for the expected revenue in terms of the stochastic booking processes and the control policies. The solution to the problem is found by maximizing the expected revenue over the possible control decisions. The solution is for an arbitrary number of fare classes and arbitrary booking curves. In particular, it requires no assumptions on the order of arrivals from different fare classes. The solution can be expressed in terms of a double recursion complex. At each node of the complex, the upper limit of a one-dimensional integral is solved to find a critical time for each fare class and for each value of remaining capacity. The critical times are the only values that need to be stored in the reservation control system to achieve optimal real-time control. This simple result is somewhat surprising given the complexity of even the static programming versions of the problem. We derive simple expressions of expected revenues and bid prices, which provide useful information to the user of a yield management system.
An Optimal Routing Algorithm for a Transfer Crane in Port Container Terminals
Authors: Kim Kap Hwan , Kim Ki Young
Published: October 2008

This paper focuses on how to optimally route transfer cranes in a container yard during loading operations of export containers at port terminals. Decision variables are the number of containers that a transfer crane picks up at each yard-bay and the sequence of yard-bays that a transfer crane visits during a loading operation. This routing problem is formulated as a mixed integer program. The objective function of the formulation is to minimize the total container handling time of a transfer crane, which includes setup time at each yard-bay and travel time between yard-bays. Based on the mixed integer program, an optimizing algorithm is developed.
Decomposition of a Combined Inventory and Time Constrained Ship Routing Problem
Authors: Christiansen Marielle
Published: October 2008

In contrast to vehicle routing problems, little work has been done in ship routing and scheduling, although large benefits may be expected from improving this scheduling process. We will present a real ship planning problem, which is a combined inventory management problem and a routing problem with time windows. A fleet of ships transports a single product (ammonia) between production and consumption harbors. The quantities loaded and discharged are determined by the production rates of the harbors, possible stock levels, and the actual ship visiting the harbor. We describe the real problem and the underlying mathematical model. To decompose this model, we discuss some model adjustments. Then, the problem can be solved by a Dantzig–Wolfe decomposition approach including both ship routing subproblems and inventory management subproblems. The overall problem is solved by branch-and-bound. Our computational results indicate that the proposed method works for the real planning problem.
A Maritime Global Route Planning Model for Hazardous Materials Transportation
Authors: Iakovou Eleftherios , Douligeris Christos , Li Huan , Ip Chi , Yudhbir Lalit
Published: October 2008

We consider the strategic level routing problem of hazardous materials in marine waters over a multicommodity network with multiple origins–destinations. The problem is motivated by the fact that selecting optimal routes by each origin–destination pair or by each type of material is myopic and may result in overloading certain links of the transportation network and, consequently, in poor overall system performance. We employ a network flow model, instead of the traditional shortest path formulation, to capture the multicommodity, multiple origin–destination nature of the problem. An efficient two-phase solution approach is proposed. The proposed solution methodology is illustrated through a single hazmat problem followed by a large scale case study of the marine transportation system of oil products in the Gulf of Mexico.
Performability of a Congested Urban Transportation Network When Accident Information is Available
Authors: Sansò Brunilde , Milot Luc
Published: October 2008

This paper presents a framework to assess a performability measure in an urban transportation network given the possibility of an accident condition. This framework needs the evaluation of network performance during the accident state. Such an evaluation is highly influenced by the duration of the accident and by information provided to the users during the accident state. To model such conditions, we propose to solve a set of modified user-equilibrium problems. Results were obtained on a test network representing the links between downtown Montreal and the South Shore suburbs. Accidents were studied on bridges linking the downtown area to the South Shore.
Formulation and Estimation of Combined Network Equilibrium Models with Applications to Stockholm
Authors: Abrahamsson T. , Lundqvist L.
Published: October 2008

Combined network equilibrium models of trip distribution, modal split, and route choice are formulated and estimated for the Stockholm region. These models take into account the feedback effects among three stages of the classical four-step model. A simultaneous structure of the mode and destination choices is studied together with nested combined models reflecting conditional choice probabilities. In the traditional combined model, mode choice is assumed conditional on destination choice. The reverse combined model, in contrast, considers destination choice conditional on mode choice. User-optimal traffic assignment is integrated with these approaches to modeling travel demand in network equilibrium models. The three combined models are estimated using the full-information maximum likelihood technique implying that all preference parameters are estimated simultaneously. The models are estimated on medium-size travel and network data for the Stockholm region in 1986. The results suggest a rejection of the traditional nested model because of incorrect relative values of the estimated cost-sensitivity parameters. The reverse nested model is preferred, even if the overall goodness-of-fit is better for the traditional nested model. An application to a future scenario for the year 2020 is included.
Continuous-Time Airline Overbooking with Time-Dependent Fares and Refunds
Authors: Chatwin Richard E.
Published: October 2008

We analyze a model of airline overbooking in which customer cancellations and no-shows are explicitly considered. We model the reservations process as a continuous-time birth-and-death process with rewards representing the fares received and refunds paid and a terminal-value function representing the bumping penalty. The airline controls the reservation acceptance (birth) rate by declining reservation requests. Assuming that the fares and refunds are piecewise-constant functions of the time to flight, we demonstrate that a piecewise-constant booking-limit policy is optimal, i.e., at all times, the airline accepts reservation requests up to a booking limit if the current number of reservations is less than that booking limit, and declines reservation requests otherwise. When the fare is constant over time or falls toward flight time, the optimal booking limit falls toward flight-time.
Simple Decentralized Feedback Strategies for Route Guidance in Traffic Networks
Authors: Pavlis Yannis , Papageorgiou Markos
Published: October 2008

The paper presents a feedback route guidance strategy for complex, meshed traffic networks. Essential components of the strategy are simple, decentralized control laws of the bang-bang, P, or PI types that may be designed based on trial-and-error. Simulation investigations demonstrate the efficiency of the proposed strategy for two example networks under several scenarios of demand and incident conditions. Feedback route guidance, though exclusively based on measurable instantaneous travel times (no predictions, no demand nor origin–destination information are provided), is shown to equalize experienced travel times along any couple of used alternative routes in the network, and to considerably reduce travel delays compared to the no-control case.
Objectives and Benchmarks for Kinetic Theories of Vehicular Traffic
Authors: Nelson Paul , Raney Bryan
Published: October 2008

Criticisms and accomplishments of the Prigogine–Herman kinetic theory are reviewed. Two of the latter are identified as possible benchmarks against which proposed novel kinetic theories of vehicular traffic can be measured. Various kinetic theories that have been proposed to eliminate perceived deficiencies of the Prigogine–Herman theory are assessed in this light. None are found to have yet been shown to meet these benchmarks.

Possible objectives and applications for kinetic theories of vehicular traffic are considered. Among these is the traditional application to the development of continuum models, with the resulting microscopically based coefficients. However, the focus is upon direct applications of the kinetic theory (e.g., the kinetic distribution function). It is concluded that the primary applications are likely to be found among situations in which variability between instances is an important consideration (e.g., travel times, or driving cycles).

It is suggested that cellular automata can provide a useful framework for testing of proposed kinetic theories of vehicular traffic. This possibility is illustrated by the initial results from an ongoing project intended to illuminate the basis for the recent result that the equilibrium solutions of (a mild generalization of) the Prigogine–Herman kinetic model comprise a two-parameter family, at sufficiently high densities. (And thus the corresponding traffic stream model displays the observed scatter at such densities.) These studies are based on the simple cellular automaton CA-184-CC.
System Optimum, Stochastic User Equilibrium, and Optimal Link Tolls
Authors: Yang Hai
Published: October 2008

Previous studies have shown that the Wardropian system optimum may not necessarily be supported as a (logit-based) stochastic user equilibrium (SUE) by finite and meaningful link tolls. This paper demonstrates that the classical principle of marginal-cost pricing is still applicable in a network under SUE from the standpoint of economic benefit maximization within the context of the classical consumer behavior theory. The marginal-cost link tolls are shown to be meaningful from both economic and behavioral viewpoints, and therefore proposed to be a good alternative to drive a SUE flow pattern toward system optimum.
The Directed Rural Postman Problem with Turn Penalties
Authors: Benavent Enrique , Soler David
Published: October 2008

In this paper, we introduce a generalization of the directed rural postman problem including new features that can be encountered in practice when routes have to be operated on a street network: some turns are forbidden and other turns are allowed but with some penalties. This new problem is called the directed rural postman problem with turn penalties (DRPP-TP); we present some complexity results and three heuristics for the DRPP-TP: two of them are constructive, whereas the third one is an improvement heuristic. We also present a transformation of the DRPP-TP into an asymmetric traveling salesman problem (ATSP) that allows us to solve the problem exactly using an existing ATSP code. Computational results on a set of instances with up to 180 nodes and 666 arcs, are given.
A Preferencing Model for Trip Distribution
Authors: Kirby Ronald F.
Published: October 2008

The trip distribution model formulated in this paper uses the basic concepts and notation of utility theory. Each trip origin is considered to rate the trip destinations available in order of perference, and each trip destination is considered to rate the trip origins. It is shown that in pairing trip origins with trip destinations in the distribution process, a “stability” condition should be satisfied, and that two particular stable trip distributions, termed “origin-optimal” and “destination-optimal,” are of particular interest. Conditions under which “like” trip origins and “like” trip destinations may be grouped together are then discussed. Finally the model is illustrated using trip data for the small city of Launceston, Tasmania.
On the Flow Capacity of Automated Highways
Authors: Bender J. G. , Fenton R. E.
Published: October 2008

Virtually all proposed systems for highway automation have at least one mode in common—steady-state car following. The nature of this mode is extremely important, as it can determine the upper limit of flow capacity of an automated highway. This limit is explored for a linear headway controller, and a fundamental relation between the effective vehicle response time and the permissible traffic stream density is obtained. The required intervehicular spacing with a linear headway controller is shown to be proportional to the effective vehicle time constant for small-signal inputs; thus, one can achieve small spacings and high flow rates by reducing this parameter to 1 sec or less. However, the vehicle is then highly responsive to small changes in lead-vehicle speed—possibly resulting in both passenger discomfort and poor fuel economy. These shortcomings can be avoided by using a linear velocity controller for automatic car following.
Maximum Inventories in Baggage Claim: A Double Ended Queuing System
Authors: Browne James J. , Kelly James J. , Le Bourgeois Philippe
Published: October 2008

The new generation of larger aircraft will compound the difficulties of designing and operating effective baggage claim facilities. A mathematical model based on uniform arrival rates for passengers and baggage is described and formulas are obtained for computing maximum expected queue lengths of both passengers and baggage for any number of passengers and bags per passenger. The flexibility of the model, its uses, and possible extensions are discussed.
A Cost-Effectiveness Study for Strategic Airlift
Authors: Mihram G. Arthur
Published: October 2008

This paper presents the motivation for the construction of a digital computer simulation of the American military's strategic airlift system, the author's analysis of that system preparatory to the simulation design, and the currently anticipated application of the model to studies of strategic mobility. Emphasis is placed on the estimation of the airlift productivity function for its subsequent utilization in appropriate strategic mobility models employed by the Joint Chiefs of Staff and by the Office of the Assistant Secretary of Defense (Systems Analysis). Those variables suspected of being primary contributors to gains in marginal airlift productivity are delineated in a description of the modules constituting the model. Finally, a sketch of an hypothetical experimental design, permitting the systems analyst to specify sequentially model iterations so as to obtain valid statistical estimates of desired marginal productivities, serves as a conclusion to the paper.
Safety Considerations for a High Density Automated Vehicle System
Authors: Lenard Michael
Published: October 2008

Simulation on the digital computer was used to evaluate systems safety for high-density traffic of automatically controlled vehicles. The response of vehicle-borne and wayside emergency control systems to sudden failure of a moving vehicle and failure to detect a stalled vehicle ahead was investigated. The number and severity of the resulting collisions were used as measures of the system’s ability to cope with accidents. The capacity and safety performance of the wayside control system was found to be distinctly superior to that of the vehicle-borne system. For a desired lane capacity, the most reasonable operating speed depends primarily on vehicle length. Finally, the results indicate that significant (systems') safety benefits are obtained if vehicles are able to maintain their speedy movement for a short time after a collision.
Further Studies on Single-Lane Bus Flow: Transient Characteristics
Authors: Herman Robert , Lam Tenny , Rothery Richard
Published: October 2008

The results of a series of experiments carried out to determine the transient characteristics of a platoon of buses starting and stopping along an exclusive right of way are reported. By using a six-bus platoon on a 2½-mile test facility, the effects of such factors as platform spacing, station spacing, speed, delay, etc., on platoon dynamics were investigated. The space-time trajectories of the lead and last vehicles have been examined in detail and a number of interesting features describing the bus platoon dynamics are presented. In particular, the results indicate that the dynamics of this cyclic operation of starting at one position and stopping at another is highly predictable. The motion of the platoon through such a cycle can be described in terms of a starting transient, a steady state, and a stopping transient, each of which is made up of simple and qualitatively describable features. Furthermore, the “smoothness” of the acceleration of a platoon to a steady state is found to be strongly dependent on starting delay, vehicle performance, and intervehicle spacing at the starting position. In addition, the experimental observations have been compared with the theoretical results obtained from numerical solutions of the linear car-following model of single-lane traffic flow.
Letter to the Editor—Locating Stepping-Stone Paths in Distribution Problems Via the Predecessor Index Method
Authors: Glover Fred , Klingman D.
Published: October 2008

This paper presents an explicit procedure for finding improving cycles or paths in the distribution model. The procedure developed may be incorporated in the row-column sum method. When this is done, both the row and column numbers and the predecessor index numbers may be determined simultaneously, a fact which contributes to the rapidity of the method. The chief difference between our method and other labeling procedures derives from the fact that the ordinary procedures are implemented in a “dual” framework and are concerned with identifying a flow augmenting path that maintains dual feasibility.
The Spectral Analysis of Speed Fluctuations on a Freeway
Authors: Lam Tenny , Rothery Richard
Published: October 2008

Two completely independent sets of observations of speed histories collected in the center lane of a freeway facility are analyzed using spectral analysis techniques. These observations were obtained from two entirely different vantage points, one from within an instrumented vehicle moving with the traffic stream, and the other from fixed roadway sites. This information has been used to calculate the autocorrelation, coss-correlation, and spectral density functions. These calculations demonstrate that a strong correlation, exists between the speed histories at locations separated by distances up to about 0.8 mi. Furthermore, it is shown that for both data sets the dominant frequencies are those with periods in the range of 3 to 6 min. The calculations are also used to obtain an estimate of the speed of propagation of fluctuations in a traffic stream with respect to the roadway. This speed of propagation is estimated to be 12 mph. However, because of the short duration of the samples used, such results therefore are only indicative.
Expanding a Nondemographic Factor Modal Split Model
Authors: Sommers Alexis N.
Published: October 2008

Expanding an earlier nondemographic factor modal split model, the author applies a revised model to business travel from Washington, D.C., to New York and Philadelphia. Actual businessman survey data is used to calibrate the model and to predict the future market shares of both hypothetical and contemporary intercity travel modes operating in this section of the Northeast Corridor.
A Multivehicle Tanker Scheduling Problem
Authors: Bellmore M. , Bennington G. , Lubore S.
Published: October 2008

The Dantzig and Fulkerson Tanker Scheduling Problem is concerned with the determination of the minimum size and optimal routing of a fleet of homogeneous tankers needed to meet a prescribed schedule of deliveries. This problem has been formulated as a network flow problem. Later formulations consider an existing nonhomogeneous tanker fleet and relax the fixed shipping schedule. These problems are treated as multicommodity minimal cost flow problems. This paper further extends the problem to consider differing carrying capabilities of the vehicles and formulates a mixed integer linear program that permits partially loaded tankers. A branch-and-bound enumerative scheme in conjunction with a decomposed linear program with network sub-problems is presented.
A Queuing Model for Car Passing
Authors: Morse Philip M. , Yaffe Harold J.
Published: October 2008

A model is developed for the flow of automobiles in one direction along a two-lane, country road. The model takes into account the fact that cars differ in speed, that slower cars accumulate queues behind them, and that the rate of escape from such a queue, by passing the lead car, depends on the speed of the lead car, on the nature of the road, and on the density of traffic going in the opposite direction. Equations for the stochastic steady state of the system reduce to an in-integral equation for the mean queue length, as a function of lead-car speed and of a queue-delay parameter. Solutions are obtained, with tables and graphs, for two different assumptions regarding the dependence of passing delay on lead-car speed. In both cases the model exhibits a sudden change from sparse-traffic conditions, where queuing is rare and delay of the faster cars is minimal, to the dense-traffic conditions where nearly all cars find themselves trapped in a slow queue, as the passing-delay parameter is increased beyond its transitional value. Such a sudden “phase-change” in traffic character is typical of actual traffic under the specified conditions. Measured dependence of queue length on lead-car speed checks nicely with the model, for sparse-traffic conditions.
Integer Programming Methods for a Vessel Scheduling Problem
Authors: Appelgren Leif H.
Published: October 2008

In a previous paper, Appelgren (Appelgren, L. 1969. A column generation algorithm for a ship scheduling problem. Trans. Sci. 3 53–68.), a decomposition algorithm for a class of vessel scheduling problems was presented. In some problems, the algorithm gives fractional solutions that cannot be interpreted as feasible schedules. This paper treats two integer programming methods that can be used to resolve these cases. The cutting plane method that was first tested was abandoned because it was not able to solve all the test problems. The second method is a branch-and-bound algorithm, where the branching is performed on one of the “essential” fractional variables and where the bounds are obtained by the decomposition algorithm. All fractional problems that have been found by simulation or in regular use of the algorithm have been solved, mostly with one branching only. There are fundamental difficulties in combining these integer programming methods with the Dantzig-Wolfe decomposition, since the constraints generated in the master program have to be taken into account in the solution of the subprograms. The success in this case is due to the simple structure of the master LP problem.
Dispatching Policies for a Transportation Route
Authors: Newell G. F.
Published: October 2008

Suppose that a given number n of vehicles (buses, trains, etc.) maybe dispatched at any times from some source to serve passengers along a route. The arrival rate of passengers is some given (nonconstant) smooth function of time, typically having one or more peaks. One wishes to choose the dispatch times tj, j = 1, …, n in such a way as to minimize the total waiting time of all passengers. It is shown that if the capacity of the vehicles is sufficiently large to serve all waiting passengers and n is large, then the optimal flow rate of vehicles (reciprocal of the headways) and the number of passengers served per vehicle, both vary with time approximately as the square root of the arrival rate of passengers. If the vehicles have limited capacity, their dispatch schedule will be distorted so that certain vehicles are dispatched as soon as they are full.
A Mathematical Programming Model for the Combined Distribution-Assignment of Traffic
Authors: Tomlin J. A.
Published: October 2008

The traffic assignment and distribution problems are customarily treated as though they were independant rather than related and interacting. In this paper a combined traffic distribution-assignment model is formulated as a mathematical program, based on the equilibrium traffic distribution model and a linear programming assignment model. The behavior of this model using the Dantzig-Wolfe decomposition principle is investigated and illustrated by means of an example. A number of areas for extension are indicated and an alternative formulation that has certain advantages is also given.
A Computer Control Scheme for Critical-Intersection Control in an Urban Network
Authors: Ross D. W. , Sandys R. C. , Schlaefli J. L.
Published: October 2008

In periods of traffic congestion, residual queues at intersections or the blocking of lanes limit the efficiency of synchronized signalization. A computer control scheme is developed that concentrates upon providing real-time, traffic-responsive corrective action for a “critical intersection,” defined as a point in the network at which primary driver routes cross or those where congestion has arisen for other reasons, such as in the aftermath of an accident or stall. The sub-optimal scheme attempts to minimize the total delay, measured in vehicle-seconds, not only to all users of the intersection but also of accumulated delay at downstream intersections. Within upper and lower limits on the cycle time, the control of the traffic signal is variable split and variable cycle-length in response to traffic needs. A simulation evaluation of the method is given via several test cases, using as a base case actual traffic data from San Jose, California.
Optimum Ambulance Location in Semi-Rural Areas
Authors: Volz Richard A.
Published: October 2008

As large medical centers become ever more capable, the existence of well equipped, well staffed, and rapid emergency ambulance service becomes increasingly important. This paper presents a method for determining the optimum location of ambulance stations to minimize the average response time to emergency calls. A new point-to-point driving time model is introduced, and a computer optimization algorithm used to determine the optimum locations. A constraint that the average response time to any point in the service area be less than some specified minimum is also considered. The method is applied to Washtenaw County, Michigan.
A Model of Nodal Entropy in a Transportation Network with Congestion Costs
Authors: Scott Allen J.
Published: October 2008

An elementary model defining maximum entropy populations for a set of nodes is developed. These nodes are connected by a simple transportation network to a central point where all work places are concentrated. A congestion cost function is defined for network arcs. Then the model yields an equilibrium solution that identifies nodal populations as an entropic function of the total cost of the journey to work.
Environmental and Social Costs Impacts of Northeast Corridor Transportation System Technologies
Authors: Dienemann Paul F. , Lago Armando M.
Published: October 2008

Rational decision making in the transportation sector cannot be undertaken without consideration of the important externalities or third party effects. This paper presents the quantification of the incommensurable and imputed monetary values impacts of the transportation system technologies planned for the Northeast Corridor on: noise, air pollution, aesthetics, safety, and air and highway congestion. A final tableau of social benefits summarizes the imputed monetary values of incremental environmental and social impacts of the following modes—high-speed rail, tracked air cushion vehicles, STOL, and VTOL—over the social costs of a 1975 base case composed of auto, bus, conventional air, and the continuation of current demonstration rail projects underway. The magnitudes of environmental and external nonuser benefits are compared with the magnitudes of direct benefit categories represented by net revenues and value of users' time savings.
On-Line Estimation of Traffic Densities from Time-Series of Flow and Speed Data
Authors: Gazis Denos C. , Knapp Charles H.
Published: October 2008

A method is discussed for estimating the number of vehicles on a section of a roadway from speed and flow measurements at the entrance and exit points of the section. The method consists of obtaining rough estimates of this count at regular intervals, and then filtering random errors of these estimates by means of a sequential correction scheme. Emphasis is placed on economy in instrumentation and data processing.
Three-Dimensional Representation of Traffic Flow
Authors: Makigami Yasuji , Newell G. F. , Rothery Richard
Published: October 2008

If one numbers vehicles consecutively along a roadway and draws the space-time trajectory of each vehicle on the same x − t graph, then this family of curves can be interpreted as the contours of a three-dimensional surface for which the third dimension is vehicle number n. The intersection of the surface with planes of constant x are the cumulative arrival curves, n vs. t, at the location x. If the surface is smoothed, the orientation of the tangent plane at any point determines the flow q, density k, and car velocity v. All commonly observed properties of traffic flow have simple geometric interpretations in this three-dimensional model.
On the Mean Speed in the “Boltzmann-Like” Traffic Theory: Analytical Derivation
Authors: Herman Robert , Lam Tenny
Published: October 2008

In a Boltzmann-like description of traffic developed by Prigogine, et al., the speed distribution has been expressed as an implicit function in terms of its own mean. In order to determine the speed distribution, it is, therefore, necessary to first determine the mean speed of the distribution. In this paper, the mean speed of the steady-state speed distribution is investigated. The mean speed is determined on the basis of the intersection of two functions; one of the functions is given by the desired speed distribution, which is a description of the goals that drivers want to attain in traffic; the other function is given by the concentration-dependent traffic parameters of the model. These parameters give a description of the restrictions that drivers exert on each other in the process of attaining their individual goals. Since the model is basically a description of the interaction between these two conflicting traffic characteristics, the effect on the mean speed due to each characteristic can hence be investigated separately through the properties of the corresponding function. In addition, all the parameters in the model, at least for the determination of the mean speed, can be effectively consolidated into a single parameter. Consequently, such a formulation of the mean speed would allow easier analysis of the assumptions and validation of the predictions.
Propagation of On-Ramp Density Waves on Uniform Unidirectional Multilane Freeways
Authors: Munjal P. K. , Pipes L. A.
Published: October 2008

This paper presents a generalized analysis of the effects of on-ramp time varying flow on unidirectional n-lane freeways. The analysis incorporates the speed-density relations for every lane, which are then used to set up separate continuity equations for every lane and are coupled by some reasonable lane-changing hypotheses. The paper assumes the same wave velocities (uniform freeway) for the perturbed flow in each lane of a freeway. Using the generalized n-lane analysis, the paper then predicts the relative propagation of density perturbations in time and space in different lanes of a two-lane, three-lane, and four-lane freeway. The corresponding relaxation distances from the on-ramp, where the initial perturbation had started, have been defined and compared for the two-lane, three-lane, and four-lane freeway. The above studies have then incorporated the effects of controlled ramp flow by suitable mathematical expressions that simulate controlled ramp flow.
Vehicle Interaction Criteria from Time Series Measurements
Authors: Pahl Juergen , Sands Terry
Published: October 2008

Vehicle interaction criteria are derived as a function of flow rate for each lane of a two-lane one-way highway. The data used were obtained from time series measurements at the flow rates of 1,479, 2,311, and 3,505 vehicles per hour. The basic approach is to study the dependency between successive speeds introduced by the interaction process. This study has shown that the phase of traffic flow for which vehicle interaction occurs can be defined in terms of time headway. A statistical analysis is used to determine the time headways below which vehicle interaction occurs (at the 1 per cent significance level); the resulting values vary between 2.5 sec and 4.3 sec depending on lane number and traffic flow rate. Plots of mean absolute relative speeds versus time headway show the effect of vehicle interaction as a function of time headway.
The Traffic Assignment Problem for Multiclass-User Transportation Networks
Authors: Dafermos Stella C.
Published: October 2008

In a recent paper a traffic assignment model has been constructed in which the cost on a link may depend not only on its load, but also on the loads on other links of the network. In this paper it is shown that this model is also capable of handling the case of several classes of users in the same transportation network each of which has an individual cost function and, at the same time, contributes to its own and other classes' cost functions in an individual way. Typical applications arise not only in street networks where vehicles of different types share the same roads (e.g., trucks and passenger cars) but also in other types of transportation networks (e.g., telephone networks). An algorithm is constructed for finding the system-optimizing flow pattern for such a multiclass-user transportation network.
Rectangular Distance Location under the Minimax Optimality Criterion
Authors: Wesolowsky George O.
Published: October 2008

Various versions of the Weber problem deal with the location of facilities in a system with fixed destinations or customers. The object is to minimize the sum of transportation costs, which is represented as the sum of the weighted distances in the system. This paper finds the optimum location for facilities where the object is to minimize the maximum weighted distance in the system. Rectangular distances, which are more appropriate for urban transportation than straight line distances, are used in the model. Optimization is achieved through parametric linear programming.
Minimum-Cost Paths for a System Composed of Ordinary Routes and a Special Network of Cheap Routes
Authors: Blumenfeld Dennis , Landau Matthias
Published: October 2008

An algorithm is presented for determining the minimum-cost paths through a system consisting of ordinary routes and a restricted network of cheap routes. The number of computations required using the algorithm is in general considerably less than for a comparison of all possible paths for each journey.
A Man-Machine Approach Toward Solving the Generalized Truck-Dispatching Problem
Authors: Krolak Patrick , Felts Wayne , Nelson James
Published: October 2008

The literature of various disciplines including engineering, operations research, and management science contains many problems that would have widespread application if methods could be found for solving problems of reasonable size. In general, these problems are combinatoric in nature; moderate to large-scale problems in this class have resisted solution by currently existing algorithms and heuristics. A partial list of these well known problems includes the traveling-salesman problem, the generalized truck-dispatching problem, board wiring, and the construction of minimum cost communication networks with various survival or redundancy demands. The authors report on a man-machine approach for solving the generalized truck-dispatching problem. Their results indicate that the technique is more accurate than previously reported heuristics. They further comment on application of the man-machine technique to other routing, scheduling, and network problems.
The Augmented Predecessor Index Method for Locating Stepping-Stone Paths and Assigning Dual Prices in Distribution Problems
Authors: Glover Fred , Karney D. , Klingman D.
Published: October 2008

The augmented predecessor indexing method provides an efficient way to update the basis and cost evaluators in adjacent extreme point solution methods for transportation problems. The method extends the predecessor indexing method, which was designed to exploit an ancestry relation in the basis tree, by showing how to exploit a more elaborate “family relation,” commonly known as a binary tree representation in computer list processing. This representation, sometimes called the “triple-label method,” was first suggested for application to network optimization problems by Ellis Johnson, who examined its use in the context of maximal flow problems. The augmented predecessor indexing method shows how to take special advantage of this representation in the context of the transportation problem, elaborating Johnson's work by providing an efficient method for characterizing successive basis trees with minimal relabeling. Moreover, we show how this procedure can be applied to update the transportation cost evaluators simultaneously without calculating current node potentials (as ordinarily required in the “stepping-stone” and related basis exchange algorithms), thus greatly speeding the arithmetic calculations.
Optimum Sample Sizes for Transportation Surveys
Authors: Vaughan Rodney
Published: October 2008

Formulas are given for determining the cost and accuracy of a given sampling scheme. Home-based, work-based and roadside surveys are examined. As in any estimation problem, one may optimize either cost or accuracy but not both. For any required accuracy, formulas are given to minimize the survey cost. It is difficult to obtain a measure of accuracy that leads to tractable mathematics; however, a formula is given that will minimize a linear combination of the sample variances of the estimators of the traffic flows. Some approximations are made that lead to simple formulas for determining the sample size. An example for a home-based survey is worked assuming preliminary estimates given by the gravity model.
Approximate Localization Theorems for Optimal Facility Placement
Authors: Goldman A. J.
Published: October 2008

The problem is that of locating a flow-receiving facility in a region, so as to minimize the weighted sum of distances between sources and facility. It is shown here that if a subregion S both generates “sufficiently much” of the region’s total flow, and admits entry via specified “gate” points without “too much” circuity, then (a) S contains at least one “near-optimal” location for the facility, and (b) no strictly optimal location can lie “too far” from S.
Letter to the Editor—A Mathematical Model for Platoon Formation
Authors: Kleinman Stephen
Published: October 2008

Under single-lane no-passing conditions it may be assumed that a vehicle's actual speed si is given by si = min[v1, v2, …, vi], where the vj represent the desired speeds of the vehicles ahead. If the desired speeds are assumed to be identically distributed random variables then several properties of the resulting platoon structures are independent of the particular density function. Several of these results are presented.
Books of Interest
Authors: Lam Tenny N. , Dawson R. F. F.
Published: October 2008

Review of books: (1) Pedestrian Planning and Design by John J. Fruin, Metropolitan Association of Urban Designers and Environmental Planners, New York, 1971, 206 pages, $5.95; (2) Economic Appraisal of Transport Projects: A Manual with Case Studies by Hans A. Adler, Indiana University Press, Bloomington/London, 1971, 190 pages, $2.95.
Temporal Expansion of a Transportation Network—I
Authors: Frey Sherwood C. , Nemhauser George L.
Published: October 2008

A model is developed for determining the optimal timing of investment in the capacity of a transportation network for which there is a finite planning horizon. The model is long term and macroscopic in nature and is limited to single-mode transportation systems in which there is a unique path connecting each origin-destination pair. The form of the optimal solution for the special case of a two-link serial network is presented. Conditions, that may be checked in application, are developed that allow the optimal solution to be calculated by solving a sequence of independent, unconstrained optimization problems. If these conditions are met, the necessity for forecasting cost and demand data for the whole planning period is eliminated.
Letter to the Editor—A Note on Fleet Routing Models for Transportation Systems
Authors: Salzborn Franz J. M.
Published: October 2008

This note is a comment on the paper by LEVIN and discusses the problem of fleetsize minimization for transportation systems. A simpler and more compact formulation of this problem results in an Integer Program of considerably reduced size, that can more naturally serve as a basis for finding suitable branch-and-bound methods for its solution.
Geometrical Solutions for Some Minimax Location Problems
Authors: Elzinga Jack , Hearn Donald W.
Published: October 2008

Four closely related minimax location problems are considered. Each involves locating a point in the plane to minimize the maximum distance (plus a possible constant) to a given finite set of points. The distance measures considered are the Euclidean and the rectilinear. In each case efficient, finite solution procedures are given. The arguments are geometrical.
Minimax Location of a Facility in a Network
Authors: Goldman A. J.
Published: October 2008

The problem is that of locating a facility in a network N so as to minimize the largest of its distances from the vertices of N. A method is given that either solves the problem, or else reduces it to an analogous problem for a single “cyclic component” of N. When N is acyclic (a tree), a very efficient solution algorithm results. Partial analogs of these results are given for a “weighted-distance” extension of the problem.
Application of Kalman Filtering to the Surveillance and Control of Traffic Systems
Authors: Szeto Michael W. , Gazis Denos C.
Published: October 2008

The methodology of the discrete-time, extended Kalman filter is applied for the estimation of densities and the control of critical traffic links. The methodology is tested using traffic data obtained at the Lincoln tunnel of New York City. Two algorithms are tested, one involving density estimation alone and one combining density estimation with a formalism for the determination of optimal control. The results indicate that the first algorithm gives very good density estimates. The second algorithm yields a less accurate density estimate, but has the advantage over the first that it is amenable to an analytical optimization investigation.