bluuebunny/crossref_metadata_2025 huggingface dataset:
A Methodology for Accurately Predicting Demand for Airlift of Military Cargo to Overseas Destinations
Authors: Billion William E. , Regan Lawrence G.
Published: October 2008

Recent developments in aircraft technology will create greater airlift capabilities at lower costs. How will this increased capability be effectively utilized by the Department of Defense? Time-series extrapolations of air-cargo demand have been made in the past for the civil sector of our economy and similar projections have been proposed for military airlift planning. These proved less than successful when compared with actual tonnages generated. This paper will explore a different methodology for predicting airlift demand in the military establishment. Basic data, consisting of approximately 3.8 million commodities and millions of shipments recorded on magnetic automatic data processing tapes, are obtained from all DOD supply management activities. Two information files are established. One is a catalogue file reflecting the physical characteristics (weight, cube, price, etc.) of the commodities that influence total distribution costs of delivering the items to overseas destinations. The second is a demandfile containing the actual volume and traffic flow of the commodities. From these files, total distribution costs for air and surface movement are computed by a mathematical model for each commodity to determine the break-even air rate. The economically air-eligible commodities are then correlated with the volume and traffic flow to determine the elasticity of demand at various air ton-mile rates. Based on known operating costs of new aircraft, logical requirements for airlift can be established. At the same time, criteria for selecting air-eligible commodities are based on economic considerations, thus producing the least-cost method of supplying overseas activities.
A Stochastic Model for Multilane Traffic Flow
Authors: Holland Homer J.
Published: October 2008

A probabilistic model to determine a variety of steady-state quantities describing the behavior of traffic on two-lane, four-lane, and six-lane highways is proposed. Faster cars form queues behind slower cars while waiting for an opportunity to pass; the occurrence of passing opportunities is governed by the characteristics of the traffic in adjacent lanes. The effects of entrances and exits, and of hills and curves on the traffic stream are also considered. Computational procedures are outlined and several sample calculations are made.
Queuing Systems with Transport Service Processes
Authors: Pearce C. E.
Published: October 2008

A common practical variant of the usual single-server queuing sysetm has a service mechanism that operates regardless of whether or not customers are present. The equilibrium behavior of such systems is considered in the case of negative exponential services and a general class of stationary but not necessarily recurrent inputs. The equilibrium queue length distribution is related to that in the associated systems with the standard service facility.
Pedestrian Crossing Time in Determining Widths of Signalized Traffic Arterials
Authors: Vuchic Vukan R.
Published: October 2008

Widening of traffic arterials at signalized intersections is often done with the intention of increasing vehicular capacity of the intersection. An analysis of the impact of increased pedestrian crossing time resulting from the widening (particularly on undivided arterials) on capacity is presented. It is shown that when signal cycle length is fixed, pedestrian crossing time imposes an upper limit on vehicular capacity of the arterial, so that its widening yields diminishing increases in capacity. There is a width beyond which capacity decreases. Relatively simple formulas and diagrams for deriving maximum capacity taking the pedestrian factor into account are presented. Short of adjustments at other points of the street network, grade separations, etc., provision of a protected pedestrian island in the middle of the arterial is suggested as the only acceptable solution to this problem.
Some Circumstances in Which Vehicles Will Reach Their Destinations Earlier by Starting Later
Authors: Smeed R. J.
Published: October 2008

Since the speed of travel on a road usually decreases as flow increases, there are often advantages in extending the period over which travelers on a road system begin their journeys, but, since travelers often wish to reach their destinations almost simultaneously, there are also advantages in reducing the period over which they spread their journeys. This suggests that there may be an optimum period during which vehicles should begin their journeys on a road system in order to reach their destinations within the shortest possible time. An analysis of the situation suggests that, if n vehicles spread their entry times into a road system uniformly over a period of time t and travel an average distance l, then the time from the first vehicle entering to the last vehicle arriving at its destination is a minimum when (l/v2)(dv/dq) + (t2/nl) = 0, where v is the average speed when the flow is q vehicles per unit time. The average journey time (also measured from the entry time of the first vehicle is minimal when (l/v2)(dv/dq) + (t2/2nl) = 0. These considerations have been applied to the case of vehicles entering a city center during peak travel periods. The calculations suggest that the “optimum” duration of entry times is associated with a particular average speed of travel, which is itself dependent on the value of fA/n, where f is the fraction of the surface area A of the city center used for roads.
Flow Dependent Traffic Assignment on a Circular City
Authors: Lam Tenny N. , Newell G. F.
Published: October 2008

Consider a circular central business district of a city with n evenly spaced radial streets and m circular streets. We assume that during the evening rush hour driver origins are all inside the city and exits at the circumference with a joint distribution that depends only upon the relative angle between original and final radii, and the radial coordinate of the origin. Travel time on any directed link is assumed to be a function of the flow along that directed link and the radial coordinate of the link. For a flow of Q vehicles per hour leaving the city, our problem is to find an assignment of drivers to paths such that every driver follows a path of minimum travel time between his origin and exit. This extends some work of Smeed who considers a similar model with no flow dependence of the travel time and a uniform distribution of origins. It is first shown that this circularly symmetric system gives rise to a circularly symmetric optimal flow pattern. This flow pattern can be generated by assigning each driver to a path that uses at most one of the circular streets. Eventually the assignment is expressed explicitly as a function of 2(m − 1) unknown parameters that satisfy a system of equations and/or inequalities. The general solution of these equations were not found, but solutions were obtained for a number of special cases that showed the effect of congestion at the center and the effect of a belt expressway. Differential equations were also obtained for n → ∞ and m → ∞.
Books of Interest
Authors: Hauer Ezra , Bullen A. G. R.
Published: October 2008

A review and recommendation of the books Transportation and Traffic Engineering: Proceedings of the Sixth International Symposium on Transportation and Traffic Theory, D. J. Buckley, editor, A. H. & A. W. Reed, Sydney, 1974, 816 pages, $29.50; The Multi-Lane Traffic Flow Process, Jens Rørbech, Ministry of Public Work Road Department, Copenhagen, 1974, 241 pages, no price given.
On the Fastest Route for Convoy-Type Traffic in Flowrate-Constrained Networks
Authors: Moore Michael Hart
Published: October 2008

Flows of convoy-type traffic through networks whose arcs are characterized by both travel times and flowrate constraints are investigated. Suggested here, in particular, is the notion of a “flowrate-constrained fastest path”—a path by means of which the entirety of a volume of traffic, initially located at a source, node, can arrive at a sink in as short a time as possible when all traffic must flow along the same path and rates of flow along arcs are limited by flowrate constraints. Unlike the usual fastest path problems (those in networks without flowrate constraints), flowrate-constrained fastest times and paths both depend, in general, upon the initial volume of traffic at the source node. Several theorems about flowrate-constrained fastest times and paths are stated and proved; it is shown, for example, that such paths are independent of source volume whenever this volume is sufficiently large. Two algorithms for finding flowrate-constrained fastest times and paths are given.
Models of Single Lane Time Headway Distributions
Authors: Branston David
Published: October 2008

The movement of traffic past a point is compared to the output of a queuing system having random input. A generalization of the queue output model leads to a suitable headway model: this model is a mixture of two distributions, representing following and nonfollowing headways, in appropriate proportions. Thin model is compared with several others that have been suggested; when used with a lognormal distribution of following headways, it gives the best overall fit to data from the M4 motorway, England, and two-way roads in Indiana, USA. For each site, the parameters of the following headway distribution can be assumed constant. The mean following headways are 1.3 sec and 1.6 sec for the M4 fast and slow lanes respectively, and 2 sec for the Indiana sites. The standard deviation of logarithms of following headways is 0.4 for both M4 lanes and 0.45 for the Indiana sites. For most samples, the reciprocal of the mean interbunch gap λ can be approximated by λ = λ* − 1/2 λ*3/2, where λ* is the flow rate, and the proportion of the following vehicles ψ can be approximated by ψ = ρ − 1/2(ρ − 1)λ*3/2, where ρ is the traffic intensity.
Route Constrained Fleet Scheduling
Authors: Orloff Clifford S.
Published: October 2008

This paper attempts to provide some insight into the structure of a large class of fleet scheduling problems. Scheduling under fixed due date constraints is shown to be easily solved using a new formulation of the problem. Scheduling under flexible due date constraints is shown to be inherently complex, and strong evidence is given for asserting that no efficient (polynomial bounded) algorithm exists for solving this problem exactly. A fast heuristic approach is described which has worked well in some school bus scheduling applications.
Letter to the Editor—Savings Approach to the Multiple Terminal Delivery Problem
Authors: Matthäus Fritz W.
Published: October 2008

For the solution of the multiple terminal delivery problem a formula for the actual savings is presented and a method of solution based on these actual savings is described. This method is simple both conceptually and computationally and gives results that appear to be “good.”
Statistical Aspects of Injury Severity Part II: The Case of Several Populations but Only Three Grades of Injury
Authors: Hutchinson T. P.
Published: October 2008

Those types of accident in which a high proportion of casualties are killed are usually those in which also a high proportion are seriously injured. This paper is concerned with the quantification of this correlation. In particular, it was found (using British data) that the variation in injury severity in a number of situations can be described by alterations in the exponent of an exponential distribution of severity, with the boundary between slight and serious injury occurring at one-third the distance from the origin of the boundary between serious and fatal injury.
Minimax Multifacility Location with Euclidean Distances
Authors: Elzinga Jack , Hearn Donald , Randolph W. D.
Published: October 2008

The problem considered is that of locating N new facilities among M existing facilities with the objective of minimizing the maximum weighed Euclidean distance among all facilities. The application of nonlinear duality theory shows this problem can always be solved by maximizing a continuously differentiable concave objective subject to a small number of linear constraints. This leads to a solution procedure which produces very good numerical results. Computational experience is reported.
The Traveling Salesman Location Problem
Authors: Burness Robert C. , White John A.
Published: October 2008

The problem of locating a single new facility relative to m existing facilities has been studied extensively under the assumption that trips are always made between the new facility and a single existing facility each time a trip occurs. A variation of the problem is the traveling salesman location problem, which involves a traveling salesman who services m customers. Each time a trip occurs the salesman visits one or more customers during the trip. Thus, 2m − 1 different itineraries can be formed, each occurring with a given probability. The new facility, which is the starting and ending point of each itinerary, is to be located such that the expected distance traveled per unit time is minimized. An iterative procedure is presented for solving the traveling salesman location problem; computational experience with the procedure is provided.
Queuing Models for Multiple Chamber Locks
Authors: Glassey C. Roger , Ross Sheldon M.
Published: October 2008

Several models for predicting mean waiting times of river traffic at a multiple chamber lock were developed and tested. Mean waiting times predicted by the M/G/1 model differed significantly from observed times. Analysis of possible causes of failure of this model suggested a limited queue length M/G/1 model for one chamber, from which more accurate predictions were derived. For the two chamber system, an M/G/1 model with random batch size was developed. This model yields a lower bound for mean waiting time. These last two models can be used to predict system performance under various operating conditions.
Books of Interest
Authors: Saunders Patsy B. , Beckmann Martin J.
Published: October 2008

Review of books: (1) Facility Layout and Location: An Analytical Approach, Richard L. Francis and John A. White, Prentice-Hall, Inc., Englewood Cliffs, N.J., 1974, 468 pp, $17.95; (2) Urban Travel Demand: A Behavioral Analysis, Thomas A. Domencich and Daniel McFadden, North-Holland Publishing Company, New York, 1975, 218 pp, $24.95.
Determining Cost vs. Time Pareto-Optimal Frontiers in Multi-Modal Transportation Problems
Authors: Srinivasan V. , Thompson G. L.
Published: October 2008

This paper provides a framework for choosing modes of transportation (rail, highway, air, etc.) by taking into account the conflicting objectives of minimizing total transportation costs and average shipment times. An efficient algorithm using the operator theory of parametric programming is presented for determining the Pareto-optimal or efficient curve denoting the minimum attainable value for the second objective for differing values of the first objective. The algorithm also provides the optimal routes, modes of transportation, and the corresponding shipping amounts for every efficient point.
Railyard Modeling: Part I. Prediction of Put-Through Time
Authors: Petersen E. R.
Published: October 2008

An analytic model of railyards has been developed and is reported in two separate studies (Parts I and II). This paper (Part I) is a macroview of yards describing the major operations performed within a yard and how different yards may be classified for modeling purposes. The yard operations are analyzed as queuing phenomena and modeled using known queuing relations. These queuing models are then used to calculate the probability distribution of put-through times, and their moments, for each major type of traffic. These, distributions are compared with observed histograms. Part II will describe how the process rates in the queuing models are related to the physical configuration of the yard, the yard resources, the marshaling rules, and the traffic intensities.
A Rectilinear Distance Round-Trip Location Problem
Authors: Chan Albert W. , Hearn Donald W.
Published: October 2008

The problem considered is that of finding the location of a facility in the plane so that the maximum weighted rectilinear round-trip distance between the facility and N pairs of existing facilities is minimized. The round-trip distance is the total distance traveled starting from the new facility via a pair of existing facilities and back to the new facility. An efficient one-pass solution procedure is developed for finding all the optimal locations to the problem, and is compared computationally with the simplex method. Two special cases are investigated, namely, when the existing facilities lie on a line, and when all the weights are equal.
The “Hub” and “Wheel” Scheduling Problems
Authors: Arisawa Sanji , Elmaghraby Salah E.
Published: October 2008

We pursue the analysis of the Hub Operation Scheduling Problem (HOSP) over the finite and infinite horizons. The demand is assumed deterministic and stationary. We deduce the minimum fleet size VT that satisfies all demands for 1 ≤ T ≤ ∞, as well as the optimal schedule that minimizes lost sales for a given fleet size smaller than VT. Reintroducing the costs of empties and of delayed sales or, equivalently, the cost of empties and the gains from shipments, we resolve the issues of optimal allocation and optimal schedule over a horizon T ≤ ∞. Finally, we generalise the above results—still under the assumption of deterministic, stationary demands—first to the case in which each city communicates with its two “adjacent” cities (this is the “Wheel” problem) and then to the general network problem in which each terminal may communicate with any other terminal.
On Stochastic Models of Traffic Assignment
Authors: Daganzo Carlos F. , Sheffi Yosef
Published: October 2008

This paper contains a quantitative evaluation of probabilistic traffic assignment models and proposes an alternate formulation. First, the concept of stochastic-user-equilibration (S-U-E) is formalized as an extension of Wardrop's user-equilibration criterion. Then, the stochastic-network-loading (S-N-L) problem (a special case of S-U-E for networks with constant link costs) is analyzed in detail and an expression for the probability of route choice which is based on two general postulates of user behavior is derived. The paper also discusses the weaknesses of existing S-N-L techniques with special attention paid to Dial's multipath method and compares them to the suggested approach. The proposed model seems reasonable and does not exhibit the inherent weaknesses of the logit model when applied to sets of routes which overlap heavily. The discussion is supported by several numerical examples on small contrived networks. The paper concludes with the discussion of two techniques that can be used to approximate the link flows resulting from the proposed model in large networks.
A Sensitivity Analysis of Multicommodity Network Flows
Authors: Jarvis John J. , Martinez Oscar Mejia
Published: October 2008

Given the multicommodity flow solution for a current transportation or communication network, planners often require some kind of heuristic measure of the effectiveness of new links which might potentially be added to the network. Exact procedures are usually prohibitive or expensive to use. This paper suggests the use of the dual variables associated with the new arcs. The paper also develops an efficient method for determining these dual variables from the current solution.
On p-Centers in Networks
Authors: Hakimi S. L. , Schmeichel E. F. , Pierce J. G.
Published: October 2008

This paper presents some improvements and some generalizations of existing techniques for computing a 1-center of a network and a p-center of a tree. For a network with n vertices and |E| edges the amount of computation to find a 1-center is shown to be at most 0(|E|n2 log n) in the vertex weighted case and 0(|E|n log n) in the vertex unweighted; for a p-center of a tree (p > 1, unweighted case), the bound is 0(np−1).
A Model and an Algorithm for the Dynamic Traffic Assignment Problems
Authors: Merchant Deepak K. , Nemhauser George L.
Published: October 2008

A discrete time model is presented for dynamic traffice assignment with a single destination. Congestion is treated explicitly in the flow equations. The model is a nonlinear and nonconvex mathematical programming problem. A piecewise linear version of the model, with additional assumptions on the objective function, can be solved for a global optimum using a one-pass simplex algorithm—branch-and-bound is not required. The piecewise linear program has a staircase structure and can be solved by decomposition techniques or compactification methods for sparse matrices.
Properties of the Equilibrium State in Transportation Networks
Authors: Hall Michael A.
Published: October 2008

The Wardrop equilibrium problem for urban road networks is considered. It is shown that the (unique) equilibrium total flow vector is a continuous function of the input traffic flows. Under fairly weak conditions it is proven that the total origin to destination travel costs are also continuous functions of the input traffic flows. It is then shown that each origin to destination cost is a monotonically nondecreasing function of its own input flow when other inputs are held fixed. Finally, it is demonstrated by means of simple examples that the equilibrium total flow vector and origin to destination travel cost functions are not differentiable at certain (possibly difficult to predict) points in the set of feasible input flow vectors and that the cost functions do not in general possess such other potentially useful properties as convexity or concavity. These results are important to an understanding of the sensitivity of the equilibrium state to variations in input data.
A Single Facility Rectilinear Location Problem with Multiple Criteria
Authors: McGinnis Leon F. , White John A.
Published: October 2008

The problem of locating a single new facility in the plane relative to several existing facilities is treated. Simultaneous consideration is given to minisum and minimax criteria. Rectilinear distances are assumed. In addition to linear programming formulations, search procedures are developed based on the special structure of the location problems examined.
Scheduling Dial-a-Ride Transportation Systems
Authors: Stein David M.
Published: October 2008

An analytic investigation into the fundamental aspects of scheduling “Dial-a-Ride” transportation systems is conducted. Based upon simple mathematical models that focus on the combinatorial nature of the problem, a class of algorithms is derived for which performance can be measured in a precise asymptotic probabilistic sense. The approach yields many qualitative insights and the resulting transportation schemes have many attractive practical features. For example, they have modest computational requirements, are decentralized, and are easy to visualize and implement.
The Effect of Small Cars on the Capacity of Signalized Urban Intersections
Authors: Steuart Gerald N. , Shin Bu-Yong
Published: October 2008

Time headways between vehicles being discharged from a queue at a signalized urban intersection is a measure of the intersection’s capacity. An event recorder actuated by tape switches on the road surface is used to measure headways at various signalized intersections in Toronto. The headways during saturation flow are related to the size of the vehicles and it is found that vehicles follow a small car with a closer headway than a full-sized car and a small car follows a vehicle closer than a full-sized car. The combined effect when both the lead and following vehicles are small cars is found to yield the smallest headways. This combined effect is most significant for the vehicles at the beginning of the queue. As a result, it is estimated that the capacity of a signalized intersection is increased by up to 15% for a stream of small cars over a stream of full-sized cars.
A New Algorithm for Tree Modification in the Primal Transportation Problem
Authors: Harris Britton
Published: October 2008

Primal methods for the transportation problem of linear programming require substantial bookkeeping to deal with constant updating of a tree describing the shipments in the current feasible solution. This paper suggests a new means of bookkeeping which is useful for long narrow problems. The method builds on previous work by the same author which reduces the number of records to be updated. The new methods reduce the number of items which have to be maintained for a replication of the tree and simplify some steps in updating the remaining items.
Solving Singly Constrained Transshipment Problems
Authors: Glover F. , Karney D. , Klingman D. , Russell R.
Published: October 2008

This paper develops a primal simplex procedure to solve transshipment problems with an arbitrary additional constraint. The procedure incorporates efficient methods for pricing-out the basis, determining certain key vector representations, and implementing the change of basis. These methods exploit the near triangularity of the basis in a manner that takes advantage of computational schemes and list structures used to solve the pure transshipment problem. We have implemented these results in a computer code, I/O PNETS-I. Computational results (necessarily limited) confirm that this code is significantly faster than APEX-III on some large problems. We have also developed a fast method for determining near optimal integer solutions. Computational results show that the near optimum integer solution value is usually within 0.5% of the value of the optimum continuous solution value.
Efficient Solutions in Multiobjective Tree Network Location Problems
Authors: Lowe Timothy J.
Published: October 2008

Much of the literature involving the location of one or more new facilities on a network is concerned with minimizing a single objective function subject to constraints on the location variable. Here, we consider the problem of locating a single facility on a tree network where there is more than one objective function to be minimized. A constructive method is given for finding the efficient set of solutions when the objective functions are convex and the constraints define a convex set. Partial results are given for the case where the feasible region is not a convex set.
A Multidimensional Perceptual Study of Road Safety
Authors: Neidell Lester A. , Wright Paul
Published: October 2008

Previous road safety research has focused on aggregate physical road characteristics and the socioenvironment of drivers. The research reported here analyzed individual perceptual data obtained in an experimental setting. Wide angle movies were taken of 12 road segments and shown to panels of licensed drivers. Three panels were utilized: (1) ordinary drivers, (2) students enrolled in a traffic engineering course, and (3) experts in traffic safety. Individual panel members rated each of the 12 segments on several characteristics thought to be related to traffic accidents. These evaluations were compared to actual accident data for the road segments using regression and scaling. Individual differences scaling models indicated that both lexicographic and compensatory models could be used to represent perceptual differences.
Markov Models of Signpost Sensor AVL Systems
Authors: Larson Richard C.
Published: October 2008

Certain cities are installing signpost sensor AVL (automatic vehicle location) systems. Such systems provide a fixed signpost sensor at a fraction ρ of intersections; when a vehicle drives through one of these intersections, its position is detected (usually by electronic means) and updated on a master file of estimated vehicle locations. In applications one is interested in system performance as a function of ρ, sensor layout, and vehicle turning behavior. Thin paper develops Markov models for computing (as a function of these characteristics) the probabilistic behavior of the distance traveled between successive passings of sensors. The measure of performance used to compare alternative systems is the coefficient of variation of distance traveled between passings. It is shown that intuitively appealing rectangular sensor layouts are often dominated by other layouts, including (in some cases) totally random positioning of sensors.
The Statistical Interpretation of Predictions with Disaggregate Demand Models
Authors: Daganzo Carlos F.
Published: October 2008

This paper discusses an element of forecasting with disaggregate demand models that has received little attention so far; namely, the extent to which the accuracy of the final prediction depends on the accuracy of the calibration process. The paper introduces a numerical technique to evaluate approximate confidence intervals for the expected number of people using a transportation facility and approximate prediction intervals for the actual usage. It is shown that, unless the magnitude of the variance of the estimated parameters is considerably small, the predictions that result may be biased and the resulting confidence intervals, inaccurate. The degree of accuracy that can be obtained with different parameter variances is illustrated numerically for the binary probit model.
Stable Phase-Plane and Car-Following Behavior as Applied to a Macroscopic Phenomenon
Authors: Ceder Avishai
Published: October 2008

An attempt is made to furnish plausible explanations for some observed traffic-flow phenomena, based on known behavior of a pair of cars in a car-following situation, A fundamental psychophysical approach is applied deterministically in assessing actual driver performance.

Observation of driver behavior in the traffic stream indicates that there are trajectories which loop clockwise in the phase (spacing/relative speed) plane. Based on these observations, and on a car-following equation appropriate for a two-regime (free-flow and congested-flow) phenomenon, an approximate limit cycle in the phase plane (switch-type behavior) is derived. The enveloping curves to these limit cycles may represent actual relatively close spacing conditions. It is realized that the intersection point of an approximate enveloping curve and a threshold curve for detecting relative speed at a given spacing has an important property, and may be associated with the critical spacing which represents transition between the congested-flow and free-flow regimes.
Letter to the Editor—Transportation Programs at the Center for Transportation Studies, M.I.T.
Authors: Manheim Marvin L.
Published: October 2008

I bring attention to some special transportation programs that should be of special interest to readers of Transportation Science. The Center for Transportation Studies at MIT will offer a coordinated set of seven Transportation Programs during August 1979. These programs are designed for transportation scientists and analysts, managers, planners, and engineers in both industry and government, as well as university faculty. Each of the courses will discuss current management, planning, policy and research issues in its subject area, and will describe new methodologies for analysis of these issues. For most of the Programs offered, students may attend one or both weeks.
A Strategy for Distance Control of Motor Vehicles
Authors: Köhler U.
Published: October 2008

Problems of distance control occur when approaching a slower moving vehicle and when following it; the two procedures differing from one another kinematically. These kinematic differences between the approaching and the following range were compiled and analyzed by measurements of the traffic flow on highways. With the results of these observations and on the basis of the car following theory, the author has developed a strategy for distance warning indicators built into motor vehicles and has calculated the effect on capacity of such a strategy.
Locations of Medians on Stochastic Networks
Authors: Mirchandani Pitu B. , Odoni Amedeo R.
Published: October 2008

The definition of network medians is extended to the case where travel times on network links are random variables with known discrete probability distributions. Under a particular set of assumptions, it is shown that the well known “facilities at nodes” theorems of Hakimi and of Levy can be extended to such stochastic networks. The concepts are further extended to the case of stochastic oriented networks. A particular set of applications, as well as mathematical programming formulations of the problem, are also discussed briefly.
Graph Structures Underlying Submatrices of Network Flow Tableaux
Authors: Rardin Ronald L. , Rosenthal Richard E.
Published: October 2008

This paper analyzes the substructure of linear programming tableaux for capacitated transshipment problems. Specifically, it demonstrates that submatrices of these tableaux correspond in a precise way to certain “contractions” of the transshipment network. The results are couched within the GNET/Depth network data structure of Bradley, Brown and Graves or the predecessor/thread/distance structure of Glover, Klingman, et al. An application to fixed-charge network problems is described.
Changes in Car Ownership and Travel to Work Patterns in England and Wales between 1966 and 1971
Authors: Davies E. M.
Published: October 2008

Data for over 40 variables relating to all the towns in England and Wales with populations of over 50,000 in 1966 and 1971 have been subjected to component analysis. Cluster analysis was then used on the component scores. The objective was to identify the most influential factors which differentiate between the populations of the towns. Details of the construction of a socioeconomic index are given, and this paper investigates in particular the relationship between such an index and car ownership rates. The changes in the travel to work mode over the 5-year period are described. Individual towns with extreme values on each variable are indicated.
Airport Capacity and Delays
Authors: Newell G. F.
Published: October 2008

The following is a survey and critique of the literature on airport capacity. It was originally written as a set of lecture notes for a university course on airport planning. The purpose is to describe, in as simple a way as possible, how the capacity of a runway configuration depends upon the strategy for sequencing various types of operations (heavy or light arriving or departing aircraft), the runway geometry, the instrument flight rules, etc.
Aggregation in Spatial Choice Modeling
Authors: Kitamura Ryuichi , Kostyniuk Lidia P. , Ting Kuo-Liang
Published: October 2008

This paper presents a spatial interaction model based on the utilitarian choice model that describes the individual tripmakers' choice of destination locations for their trips. The use of asymptotic properties of the distribution of the perceived utility of each destination zone yielded, a multinominat probit model of destination zone choice. This multinominial probit structure allowed the model to assume arbitrary degrees of similarities in the individual's preceptions of destination locations within or among the traffic zones. A few additional assumptions made it possible to generalize this destination zone choice model to a spatial interaction model representing relative frequencies of interzonal movements. The numerical analysis showed that the violation of an asymptotic assumption used in the model derivation does not cause significant errors in the model.
The Common Transport Policy: A Case of Lost Direction?
Authors: Whitelegg John
Published: October 2008

The European Economic Community (E.E.C.) has, since its inception, pursued “common” policies in areas which have a strategic significance for the long term aims of the community. The most significant “common” policy is the Common Agricultural Policy (CAP) but of real importance for E.E.C. goals of stimulating the economy and improving the conditions of cross-frontier freight movements is the Common Transport Policy (CTP). It is argued in this paper that while the CTP has made significant progress in the “regulation,” “harmonization.” “charging for infrastructure” and related areas it has failed to recognize the wider environment of transport and in particular the ways in which transport policies are inextricably linked with other policies of the E.E.C. Successive policy statements are examined to illustrate how the E.E.C.'s view of transport can be seen to be increasingly narrow and unrelated to the central issues of community development in the period immediately preceding Economic and Monetary Union. While very critical of E.E.C. policy the underlying assumption is that transport is a core policy through and with which one can advance the central issues, as long as the links between policies are understood and the administrative machinery reflects this.
Letter to the Editor—Comments on “Car Following Headways on Freeways Interpreted by the Semi-Poisson Headway Distribution Model”
Authors: Branston David , Cowan Richard
Published: October 2008

We are disturbed by some of the misleading remarks made about our work on the generalized queueing model (GQM) headway distribution by Paul Wasielewski in his recent Transportation Science paper “Car Following Headways on Freeways Interpreted by the Semi-Poisson Headway Distribution Model” (s-PM). It is clear to us from his references to our papers (Cowan, R. J. 1975. Useful headway models. Trans. Res. 9 371–375 and Branston, D. 1976. Models of single lane time headway distributions. Trans. Sci. 10 125–148.) that he had misunderstood the arguments employed in them. Because of this we feel that he misrepresents both our work and the physical basis of the GQM. We acknowledge that Wasielewski is entitled to promote the s-PM, but if he wishes to refer to our work, then he should do so without error. We are outlining some of the errors made by Wasielewski below.
Traffic Equilibrium and Variational Inequalities
Authors: Dafermos Stella
Published: October 2008

We consider the general traffic equilibrium network model where the travel cost on each link of the transportation network may depend on the flow on this as well as other links of the network. The model has been designed in order to handle situations where there is interaction between traffic on different links (e.g., two-way streets, intersections) or between different modes of transportation on the same link. For this model, we use the techniques of the theory of variational inequalities to establish existence of a traffic equilibrium pattern, to design an algorithm for the construction of this pattern and to derive estimates on the speed of convergence of the algorithm.
A Framework for Constructing Network Equilibrium Models of Urban Location
Authors: Boyce D. E.
Published: October 2008

Recent advances in network equilibrium modeling provide efficient algorithms for solving the urban trip assignment problem. These models can be extended to incorporate the trip distribution problem with two types of variable demand functions. By reinterpreting the zone-to-zone trip variable, these models can be viewed as urban location models. This paper synthesizes these results, and shows how several urban location models can be derived from the mathematical framework based on the network equilibrium problem.
Modeling of Traffic Flow at Signalized Links
Authors: Michalopoulos Panos G. , Stephanopoulos Gregory , Pisharody Vijay B.
Published: October 2008

A rigorous mathematical modeling and analysis of the traffic dynamics downstream of traffic signals and in links between signalized intersections is presented in this paper. The approach taken here is macroscopic in nature and traffic is treated as a continuum fluid. The existence and behavior of shock waves generated periodically downstream of a traffic signal is demonstrated and analytical expressions are derived for describing their propagation along the road. The formation and dissipation of traffic queues at the downstream signal in both time and space is studied and analytical expressions are presented for describing the evolution of the tail end of the queue in time. Due to the large number of possible queue length developments, a methodology for numerical solution to the problem is presented along with numerical examples.
Computation of Equilibrium Over Transportation Networks: The Case of Disaggregate Demand Models
Authors: Sheffi Yosef , Daganzo Carlos F.
Published: October 2008

The transportation planning forecasting process has been traditionally performed on a sequential, disconnected, heuristic basis, using different methodologies for each one of the stages. In an attempt to improve this situation, a first step toward developing a unified transportation forecasting methodology is described in this paper. This is done by showing how many, seemingly different, problems can be cast as analogous route choice problems on abstract networks and studied with the same methodology. As a consequence of this analogy, it is possible to perform equilibrium analyses and to study several problems simultaneously, by choosing an adequate topology for the abstract network. The bulk of this paper is devoted to presenting an algorithm within which many of these transportation equilibrium analyses can be carried out. The conditions of equilibrium are identified and defined, and an efficient algorithm for the solution of the equilibration problem is introduced. The solution method, which uses the multinomial probit model for allocation of flow to routes, can increase the accuracy and reduce the cost of many transportation equilibrium analyses.
Scheduling Aircraft Cleaning Crews
Authors: Stern Helman I. , Hersh Marvin
Published: October 2008

In this paper a technique is developed for the scheduling of crews for cleaning aircraft interiors between scheduled flights. The cleaning requirements for each aircraft are given in terms of total man-hours work to be performed. The performance of this work is limited to an interval of time during which the aircraft is on the ground and available for servicing. A labor contract requires that each cleaning crew member must be scheduled for one meal during his work shift. Meals must be taken during cafeteria hours only. The problem is to find the crew size for each shift, and the number of workers assigned to meal and cleaning activities (a crew schedule) such that the total crew cost is minimal. The problem is formulated as a pure integer programming problem. Included in the formulation are constraints designed to avoid certain undesirable phenomenon namely: shift, job, and worker interruptions. A method of decomposing large problems into a series of smaller problems amenable to solution on computers with limited capacity is suggested. The paper includes the solution to a numerical problem derived from a case study involving a medium size international airline.
Platoon Dynamics on Signal Controlled Arterials
Authors: Michalopoulos Panos G. , Pisharody Vijay
Published: October 2008

Car path, platoon length, and flow rate equations are developed for the purpose of studying the platoon dynamics at signalized traffic links. The basic modeling is macroscopic in nature and is based on the formation of shock waves generated within the link due to the intermittent service of traffic by the signals. The analysis reveals not only platoon dispersion but also platoon compression, a phenomenon already observed but not previously described mathematically. It is demonstrated that compression does not only occur to platoons entering the link in red but also to those entering in green even in the absence of a downstream signal. Numerical examples are also presented for demonstrating the applicability of the theory.
Direct Solutions to Some Multidimensional Transportation Problems
Authors: Scobey P. , Kabe D. G.
Published: October 2008

A certain analogy that exists between the mathematical formulation of the standard (two dimensional) quadratic cost transportation problem as a minimum value problem and the mathematical formulation (as a minimum value problem) of the maximum likelihood estimation of the regression coefficient matrix of a multivariate normal linear regression model, subjected to double linear restrictions, is utilized to demonstrate that the transportation problem can be solved within the framework of available statistical linear regression theory methodology. Two known multidimensional transportation problems are solved within the framework of statistical linear regression theory methodology by converting them essentially as extensions of two dimensional transportation problems. The methodology is illustrated by numerical examples.
Influence of Demand-Quality Interrelationships on Optimal Policies for Stage Construction of Transportation Facilities
Authors: Fernandez J. Enrique , Friesz Terry L.
Published: October 2008

The time staging of investment decisions for transportation facilities has generally been analyzed using models which assume a complete independence between transportation level of service and demand for the use of the facility considered. Through the use of a dynamic optimal control model, we analyze the implications of explicitly considering the interrelationship between level of service and demand on the time staging of optimal investment decisions. This analysis leads to a more general time staging decision rule than those previously proposed in the literature; an economic interpretation of that decision rule is given. Second order conditions are developed for various cases of practical significance. Finally, a numerical example is introduced to illustrate the dramatic effect that demand-quality interrelationships can have on the optimal time staging policy.
Errata—A Single Facility Rectilinear Location Problem with Multiple Criteria
Authors: McGinnis Leon F. , White John A.
Published: October 2008

Corrections to McGinnis, L. F., J. A. White. 1978. A single facility rectilinear location problem with multiple criteria. Trans. Sci. 12 217–231.
Letter to the Editor—Note on Geometrical Solution for Some Minimax Location Problems
Authors: Chakraborty R. K. , Chaudhuri P. K.
Published: October 2008

The object of this note is to develop an alternative algorithm for solving Euclidean minimax location problems in the plane.
Linear Algorithms for Finding the Jordan Center and Path Center of a Tree
Authors: Hedetniemi S. Mitchell , Cockayne E. J. , Hedetniemi S. T.
Published: October 2008

This paper contains linear algorithms for finding the Jordan center, the weighted Jordan center and the path center of a tree. All of these algorithms take advantage of an efficient data structure for representing a tree called a canonical recursive representation. As a result, the first two algorithms are different from and faster than similar algorithms in the literature. This paper also defines a new parameter of a graph called the path center, and shows that the path center of a tree T consists of a unique subpath of T.
Trip Time Versus Stop Time and Fuel Consumption Characteristics in Cities
Authors: Chang Man-Feng , Herman Robert
Published: October 2008

An attempt has been made to evaluate the effect of traffic conditions on fuel consumption and trip time for two fixed routes in Milwaukee, Wisconsin. Data on trip time, stop time and fuel consumption obtained in Milwaukee are compared for rush hour traffic and for middle of the night very light traffic. It is demonstrated that the potential fuel savings for individual trips obtainable through improved traffic are different from route to route although they are substantial, lying in the range ≈10–30%. A comparison is made of the traffic on different routes using speed-acceleration phase plots. In addition, stop time versus trip time characteristics are compared for four metropolitan areas using a linear representation between the two variables as well as a theoretical two-fluid model which relates stop time and trip time. The parameters of the two-fluid model and in addition the observed ranges of stop time and trip time are shown to be useful for comparing the quality of traffic in different metropolitan areas: the lower the values of the parameters and smaller the ranges the better the traffic. The implication of these results on fuel consumption have also been examined.