bluuebunny/crossref_metadata_2025 huggingface dataset:
Scheduling a Fixed-Schedule, Common Carrier Passenger Transportation System
Authors: Young Dennis R.
Published: October 2008

This paper presents a method for developing efficient timetables for the operation of fixed schedule common-carrier passenger transportation systems. The ability to compute such timetables is needed in the consideration of planning alternatives for future transportation systems and for the efficient operation of existing systems. Here, timetable optimization is accomplished by maximizing an objective function consisting of three basic components: operating costs, revenues, and traveler benefits. Traveler benefits are computed using a consumer preference model that specifies a traveler's willingness to pay for alternative trips, based on the scheduling of those trips. The optimization is based on successive iterations of a dynamic programming algorithm that develops timetables for each vehicle in the system. Solutions are termed optimal to within a “first-order passenger exchange.” Examples are presented to illustrate the utilization of the methodology for computing information relevant to the development of system operating policies and to the consideration of planning alternatives.
A Barge Sequencing Heuristic
Authors: Dyer James S. , Glover Fred
Published: October 2008

This paper describes a heuristic method for sequencing barge unloadings at terminals that have regulated unloading rates or flows with the objective of minimizing the variation of a common constituent in the final combined output. The work was undertaken in response to the desire of a steel manufacturer to minimize the maximum sulfur content in coal entering the coking ovens after being mixed by the simultaneous unloading of barges onto a common conveyor. Although the problem may be given an integer programming formulation, the solution method we propose enables one to obtain optimal or near optimal solutions by hand. A hypothetical problem is solved to illustrate the procedure.
Erratum—“Maximum Inventories in Baggage Claim: A Double Ended Queuing System”
Authors: Browne James J. , Kelly James J. , Le Bourgeois Philippe
Published: October 2008

Corrections to be made to the article “Maximum Inventories in Baggage Claim: A Double Ended Queuing System” Transportation Science, Vol. 4, No. 1, pp. 64–68, February, 1970.
Some Characteristics of Traffic Leaving a Signalized Intersection
Authors: Wright C. C.
Published: October 2008

Recent studies of a single lane of traffic flow at a site near Enfield, London have led to a simple bunching model that predicts some aspects of the behavior of vehicle platoons leaving a signalized intersection where overtaking is impossible. The relation between time mean speed and flow rate at this site varied considerably with the sampling interval used; possible reasons for this effect are discussed. The experimental work is briefly described and some tentative conclusions are drawn about the nature of the fundamental relations of traffic flow.
A Moving Cell Control Scheme for Automated Transportation Systems
Authors: Wilkie Dennis F.
Published: October 2008

The longitudinal vehicle control problem associated with any automated transportation scheme is discussed. The two fundamental aspects of the problem are the logical aspect and the control aspect. The logical aspect of the problem concerns the decision of where vehicles should be at a future time, based on present system conditions, so that the level of service delivered by the system is good. The control aspect is concerned with how to control vehicles to attain and maintain their desired positions while giving a comfortable ride, not taking too long, not exceeding car capabilities, and maintaining safety. Previous work dealing with both the logical and control aspects of the longitudinal vehicle control problem is briefly reviewed. One approach to handling the logical aspects of the merging problem in automated systems assumes that vehicles occupy positions on a guideway within hypothetical “cells” that move at a constant velocity. This approach simplifies the logical aspect of the longitudinal control problem. The problem of controlling vehicles to attain and maintain an assigned cell on a guideway is modeled in the paper as a linear state regulator optimal control problem. The resulting vehicle control scheme requires less information feedback than alternative schemes, and exhibits good vehicle response characteristics. Alternative control strategies that lead to optimal control problems other than the linear state regulator are discussed, and the relative advantages of the scheme presented in the paper are pointed out.
Letter to the Editor—A Localization Theorem for Optimal Facility Placement
Authors: Goldman A. J. , Witzgall C. J.
Published: October 2008

The problem is that of locating a facility in a region, so as to minimize the weighted sum of distances between customers and facility. This note shows that a subregion containing half or more of the total “customer-weight,” if it obeys an additional restrictive hypothesis, must include at least one optimal location for the facility. Thus the search for an optimal location can be limited to such a subregion, once identified.
Fleet Selection for Public Transportation Routes
Authors: Hauer Ezra
Published: October 2008

For the same total cost, a public transport route can be served by few large vehicles or more smaller ones. The problem is posed: which out of all equi-cost fleets to select? An algorithm is proposed to guide such selection. To avoid potentially controversial value judgments, the algorithm is based on systematic reduction of the range from which the choice can be made. Considerable reduction in the range of choice can be achieved making use of the “Pareto optimum” principle alone. Analysis is based on a mathematical model describing the relation between the route fleet and characteristics of service to the passenger.
A Utility Model for Travel Forecasting
Authors: Golob Thomas F. , Beckmann Martin J.
Published: October 2008

This paper shows how the problem of predicting traveler behavior may be approached in terms of economic utility theory. A general utility maximization model on the level of individual trip-making decisions is developed from basic hypotheses regarding the costs and benefits attributed to travel disaggregated into individual trips. For predictive purposes the form of the utility functions involved must be specified, and several possibilities are explored. The functional forms of the resulting travel demand functions are then derived. In order to pursue an analysis of variations in traveler behavior and in order to perform aggregation over individuals, disturbances in the parameters of the utility functions are considered. The parameters investigated are marginal utilities and the distributions used are normal distributions. In considering binary choices, a trip demand model, a modal split model, and a destination split model are obtained from the same basic methodology. Finally, possible approaches to testing the functional relations involved and to measuring marginal utilities are discussed.
Optimal Elevator Banking Under Heavy Up-Traffic
Authors: Powell Bruce A.
Published: October 2008

An important design criterion for elevator installations in modern office buildings is the carrying capability during the morning rush-hour. It is common practice to divide the total number of cars into banks, each bank serving a common set of upper floors with an express run to the lowest of these floors. The decision process of how to allocate cars to upper floors is formulated as a dynamic programming problem. Solution to the dynamic program for a given arrangement of cars is the banking policy in which the time to fill the building completely (under heavy up-traffic) is minimized.
Merging from an Acceleration Lane
Authors: Blumenfeld Dennis E. , Weiss George H.
Published: October 2008

A model is presented for merging from an acceleration lane of finite length. It is assumed that a car in the acceleration lane travels at speed v while the traffic on the main road travels at speed V > v. A merging car reaching the end of the lane stops instantaneously. The gap acceptance function is assumed to be a step function and the distribution of headways is negative exponential. An expression for the expected delay is given. The calculations suggest that the expected delay does not depend strongly on the length of the acceleration lane, and that most of the merging occurs near the beginning of the lane. Increasing the length of the lane beyond some necessary length, say 600 ft, results in relatively little further benefit in merging.
Optimal Center Location in Simple Networks
Authors: Goldman A. J.
Published: October 2008

The general problem is that of locating a central facility in a network so as to minimize the sum of its distances from the sources of flow to it, each distance being appropriately weighted to reflect the associated flow volume and/or cost. In this paper, simple one-pass solution algorithms are given for two classes of topologically simple networks, namely those which are either acyclic or contain exactly one cycle. The first algorithm is based on a reduction procedure that may also yield useful simplification of problems involving general networks.
Scheduling and Fleet Routing Models for Transportation Systems
Authors: Levin Amos
Published: October 2008

Models of fleet routing and scheduling problems for transportation systems are formulated as integer linear programs with 0-1 variables. Detailed formulations and a solution technique of the Land-and-Doig type are presented and demonstrated on examples. The conclusion is that large scale models can be solved using this technique.
Letter to the Editor—Optimal Container Inventory for a Two-Gateway System
Authors: Samuel Aryeh H. , Ullmann Zev
Published: October 2008

The optimal size of the container inventory for a two-gateway system is determined. A rule is found, according to which containers are acquired until the last container produces savings just greater than the costs incurred due to empty trips. The actual size of the optimal inventory depends on container costs, the costs of shipping full and empty containers, the cost of shipping mail uncontainerized, and the probability distribution of the volume in each direction. Numerical results are given for two parcel-post systems.
Book of Interest
Authors: Beckmann Martin J.
Published: October 2008

Proceedings, Third International Symposium on the Theory and Practice in Transport and Economics, Rome, 23–26 September 1969, European Conference of Ministers of Transport.
A Linear Programming Model for Cargo Movement Evaluation
Authors: Gould F. J.
Published: October 2008

A linear programming model is presented for minimizing the steady state cost of moving cargo carriers over certain routes subject to numerous constraints on both the cargo and carrier movement. There are several types of cargo and carriers, transshipment is allowed, cargo and carriers are linked by capacity constraints, and requirements are specified in terms of movement from a specified origin to a specified destination. The model is fairly general in that it should be applicable to certain types of cargo movement via either air or surface transportation. Studies that can be made by use of the model include (i) cost-effectiveness analyses of policy questions (such as those involving utilization rates and frequency requirements), as well as evaluation of alternatives for (ii) mix of cargo carriers, (iii) best routes for certain carriers, (iv) mix of bases or depots, (v) transshipment policy, and (vi) physical and operating characteristics of carriers.
An Extended Traffic Assignment Model with Applications to Two-Way Traffic
Authors: Dafermos Stella C.
Published: October 2008

A transportation network is considered. The traffic demands associated with pairs of nodes and the traveling cost functions associated with the links are assumed given. An extended traffic assignment model where the traveling cost on a link becomes a function of the entire flow pattern in the network is introduced. The model appears particularly suitable for application to networks containing two-way streets, in view of its capability of taking into account delays to travelers of one lane caused by traffic on the opposite lane. It is also suitable for application to urban transportation networks, where the travel time on a link depends crucially on the delays occurring at the intersections. This in turn depends on the traffic volumes on the intersecting links. The concepts of system-optimizing and user-optimizing traffic patterns are studied. Moreover, an algorithm for the construction of the above patterns is presented and applied in an example.
On the Mean Speed in the “Boltzmann-Like” Traffic Theory: A Numerical Method
Authors: Herman Robert , Lam Tenny
Published: October 2008

A method has recently been developed by the authors for determining the mean speed of the speed distribution in the Boltzmann-like traffic theory developed by Prigogine, et al. This method has now been extended to more general functional forms assumed for the details of the interaction, relaxation, and adjustment processes. The mean speed for the more general case is again expressed in terms of the intersection of two mathematical functions identical to those previously obtained. On the basis of this method a numerical procedure for calculating the mean speed is given. For most reasonably well behaved desired speed distributions this method offers satisfactory rates of convergence and is applicable for both the “individual” and “collective” flow cases.
Letter to the Editor—Constraining Relations Among Offsets in Synchronized Signal Networks
Authors: Gartner N.
Published: October 2008

Circuit constraints on the phasing of fixed-time synchronized signal networks are defined. A method, based on a graph-theoretic approach, for deriving a fundamental set of equations characterizing these constraints is presented.
Optimum Bus Scheduling
Authors: Salzborn Franz J. M.
Published: October 2008

The paper presents a mathematical investigation into bus scheduling. The passenger arrival rate is supposed to be given; the problem is to determine the bus departure rate as a function of time. The primary objective is to minimize the number of buses that is needed. A secondary criterion is the minimization of the passenger waiting time, for which a calculus of variation technique is used. Although the paper deals mainly with a single busroute, it is also shown how the theory can be extended to the case of a pair of linked busroutes. The practical implications are illustrated by an example. The fleetsize formula that is used here is thought to be applicable to many transportation systems.
Letter to the Editor—Fifth International Symposium on the Theory of Traffic Flow and Transportation, University of California, Berkeley, June 16–18, 1971
Authors: Miller Alan J.
Published: October 2008

About 90 papers were submitted for this symposium, the advisory committee selected 30 for presentation. In the review below, reference numbers from 1 to 30 are to the presented papers in the order of presentation; higher numbers are to other references. The complete list of papers follows this review.
Queuing in Lanes
Authors: Hauer E. , Templeton J. G. C.
Published: October 2008

A queuing model is presented in which delay stems from a disparity between the order at which service is provided to customers and the order at which they may leave the system. Consider, for example, wives waiting in cars—single file—for the arrival of their husbands by a common train. A car is ready to leave when its passenger takes his seat but may have to wait for the departure of all cars preceding it in the lane. Initially, the probability function of waiting is determined for a single, finite queue. Next, the consequences of splitting the single queue into several parallel queues with identical discipline are explored. The results of the analysis are applied to a parking lot design problem.
Delay at a Fixed Time Traffic Signal—I: Theoretical Analysis
Authors: Allsop Richard E.
Published: October 2008

The various theoretical analyses that have been made of delay to traffic at a fixed time traffic signal are critically reviewed. The more practicably applicable expressions for the average delay per vehicle, especially those derived by Webster, Miller, and Newell, are examined in some detail, and this paper provides an introduction to numerical comparisons to be reported by Hutchinson in the sequel.
Kinetic Theory of Vehicular Traffic: Comparison with Data
Authors: Herman Robert , Lam Tenny , Prigogine Ilya
Published: October 2008

The steady-state solution of a kinetic theory of vehicular traffic developed to describe the time and space evolution of the speed distribution of cars on a multiple-lane highway has been examined in the light of some observational data. A method of moments has been employed to compare the theory with the data. The order of magnitude agreement obtained between the theoretically predicted ratios of lower moments and the ratios determined from the provisional data indicates that the theoretical approach and assumptions are reasonable and consistent.
Optimal Locations on a Network
Authors: Wendell Richard E. , Hurter Arthur P.
Published: October 2008

The paper considers the location of centers (e.g., plants, warehouses) on a network. Necessary conditions and sufficient conditions for optimal solutions to occur at nodes in the network are determined. The conditions include consideration of capacity constraints and the possibility that not all shipments are made via the “shortest route.” The cost functions may differ from arc to arc. A proof is given for the sufficiency of node locations in situations of multistage processing when transport costs are concave over each arc. Three sets of conditions under which it is necessary for an optimal solution to occur at a node are investigated. One set of conditions involves a production function characterization of the centers being located.
Minimum Cost Schedules for a Public Transportation Route II. Examples
Authors: Hurdle V. F.
Published: October 2008

A fleet of vehicles carries passengers in one direction on a public transportation route, then returns to the dispatch point after a travel time T. The arrival rate of passengers is a known deterministic function of time and the objective is to devise a schedule that minimizes the total cost for passenger waiting time and vehicle operations. The optimal schedules for a number of hypothetical examples are found by applying principles derived in Part I and a procedure is given for constructing suboptimal schedules in cases where it is difficult to construct the optimal schedule.
Scheduling of Toll Collectors
Authors: Byrne J. L. , Potts R. B.
Published: October 2008

The problem of rostering toll collectors for a toll facility such as a bridge, tunnel, or expressway is formulated as an integer program. The working regulations for full-time and part-time shifts give special structure to the program. An eight phase algorithm is described that exploits this special structure and enables variables to be grouped together and the integer constraints successively introduced. The algorithm has been tested for a wide variety of practical schedule problems and has proved successful in obtaining acceptable schedules in comparatively short computer run times.
Minimax Location of a Facility in an Undirected Tree Graph
Authors: Handler G. Y.
Published: October 2008

This paper is addressed to the problem of locating the absolute and vertex centers (minimax criterion) of an undirected tree graph. Based upon a convexity property of the criterion function a very simple and efficient algorithm is offered that locates the minimax point by locating first a maximax point. The minimax is at the mid-point of the maximum path from the maximax point. The vertex center is located simultaneously.
Heuristic Decision Policies for the Control of Reversible Traffic Links
Authors: Glickman Theodore S.
Published: October 2008

Mathematical models of the delays incurred in a traffic link with reversible lanes, as a function of demands for service and allocation decisions, are constructed assuming that the state of the operation is reviewed periodically. There is a penalty associated with each allocation change that is manifested as a loss of capacity. Heuristic algorithms are derived that enable the determination of decision policies that minimize the delay per vehicle during some horizon. The first phase of the determination is performed upon a basic model, in which the reversal penalties are ignored, and results in a sequence of optimal periodwise decisions. This policy is then subjected to a second phase, performed upon the lost time model, in which reversal penalties are included. Progressively better policies are generated in this phase according to the heuristic notion that an optimal policy does not differ much from the policy obtained in the first phase. The solution of the models is illustrated in a case study using actual data for the Chesapeake Bridge.
Urban Traffic Speeds—I: A Comparison of Proposed Expressions Relating Journey Speed to Distance from a Town Center
Authors: Branston David M.
Published: October 2008

One of the best descriptors of traffic in a town is its speed and some knowledge of the way that it varies is clearly of interest and importance. This paper compares the suitability of five formulas that relate journey speed to distance from a town center for six towns in England and Wales. The formula that gives the most consistently good fit to the data from the towns studied here is of the form v = a − becr, where v is journey speed at radial distance r, and a, b, c, are constants. However, a formula of the power form v = arb also provides a reasonable description of the data from the towns studied. Although not necessarily being the best fitting formula for individual towns, the ease of use and interpretation of this power function and the fact that it requires only two constants may make it preferable for many studies of the variation of speed within towns. The disadvantage that this formula predicts zero speed at a town center is of little practical importance, since in practice, it can give fairly good estimates of the time taken to reach points in the neighborhood of the town center. It is also concluded that the wide variation of speeds at any particular distance from the center of the one town for which this was examined can be partly explained by the variation between radial routes.
Calibration of Dial's Assignment Method
Authors: Robillard Pierre
Published: October 2008

The purpose of this note is to study the calibration of the probabilistic assignment method of Dial (Trans. Res. 5, 83–111, 1971). The estimation of the parameters of the method is performed using the maximum likelihood principle and uses the observed traffic data. The estimates thus obtained can be evaluated with already existing algorithms.
Locating Concentric Ring Roads in a City
Authors: Pearce C. E. M.
Published: October 2008

A mathematical analysis is made of the optimal siting of concentric ring roads in a city so as to minimize the average distance travelled off the rings. It is found that although such ring roads are more effective if they are characterized by a higher speed of travel than the rest of the city, their optimal location is largely independent of such speed. Most of the benefit of using a series of concentric ring roads can be obtained from one or two well-placed ring roads. Optimization with respect to the average overall travel distance is also considered.
Gate Position Requirements at Metropolitan Airports
Authors: Steuart Gerald N.
Published: October 2008

The number of gate positions required at an airport, or the number of flights that can be accommodated at a given number of gate positions, depends on how efficiently each gate position is used. The airlines' schedule and the airport's operating policies influence the efficient use of the gate positions. A simple stochastic model describing the behavior of flights relative to their schedule was developed based on empirical information. The model was then used to study the influence of a common scheduling practice of bank operation on the requirements for gate positions. It was found that a completely uniform schedule generates the minimum requirement. A procedure is presented to estimate the number of gate positions required at an airport.
An Integral Equation for the Semi-Poisson Headway Distribution Model
Authors: Wasielewski Paul
Published: October 2008

The semi-Poisson headway distribution model introduced by Buckley [“Road Traffic Headway Distributions,” Proc. Australian Road Research Board 1, 153–183 (1962); “A semi-Poisson Model of Traffic Flow,” Trans. Sci. 2, 107–133 (1968)] involves the decomposition of the headway distribution into components which can be regarded as corresponding to “free” and “constrained” vehicles. This model is reformulated here in order to derive an integral equation by means of which the components can be calculated directly from the observed headway distribution, thereby avoiding an arbitrary parametric representation of the constrained distribution component. The model is applied to traffic observations under high flow conditions from a British and an American freeway. The model results are interpreted as an indication of whether the freeway lane is operating at its maximum possible capacity. It is found that one lane of the British freeway had a flow very near the maximum given by the model, but the greatest observed flow on the American freeway was still less than the calculated maximum.
Probabilistic Assignment: An Algorithm
Authors: Trahan Michel
Published: October 2008

This note describes improvements to the assignment algorithm Dial presented to implement his multipath assignment method. It illustrates the advantages of Robillard's refinement over the original Dial approach in terms of savings in computation time as well as in core storage. Moreover, the note provides some figures on the necessary amount of computation time on a particular computer.
A Method for Computing Network Equilibrium with Elastic Demands
Authors: Florian Michael , Nguyen Sang
Published: October 2008

We present a new method for computing the equilibrium flows in a transportation network with elastic demands and congestion effects for a single class of users. The method that we develop in the following results from the combination of a fixed demand assignment method and an application of Generalized Benders Decomposition. We give computational results obtained with the algorithm.
A Minimax Location Problem on a Network
Authors: Dearing P. M. , Francis R. L.
Published: October 2008

We consider a network model of a system of transportation links, with nodes representing locations of existing facilities, and study the problem of finding a new facility location on the network that minimizes the maximum of linear increasing functions of the “network distances” between the new facility and the existing facilities. The problem is formulated with respect to a metric space which is defined on the network, and a number of properties of the problem are developed. The properties lead to a new, simple algorithm for solving the problem when the network is a tree, and to a new, equivalent spanning tree problem for a general network.
Book of Interest
Authors: Hickok Beverly
Published: October 2008

A review and recommendation of the book Transportation Systems Bibliography, D. E. Bierman, Council of Planning Librarians, Monticello, Illinois, 1974, 100 pages (Exchange Bibliography #561–562), $10.00.
Automatic Crew Rostering
Authors: Nicoletti Bernardo
Published: October 2008

The paper discusses the computer construction of the monthly rosters for aircrews. It is shown how the method of Ford-Fulkerson for maximizing the flow over a capacitated network can be usefully employed to solve the problem. The practical difficulties of implementing the approach in a real environment are discussed and ways are suggested to overcome them.
An Airline Overbooking Policy
Authors: Shlifer E. , Vardi Y.
Published: October 2008

The paper presents a model for determining an overbooking policy for an airline. Of the three criteria chosen, the first two ensure that the probability of a rejection and the expected rejection level do not exceed given limits, and the third determines the loss incurred by rejecting a passenger relative to the profit of carrying one, thereby permitting maximization of the expected gain. The following three cases are considered: (a) Single-leg flight carrying a single type of passenger; (b) Single-leg flight carrying two types of passengers, and (c) Two-leg flight. It is assumed that all types of passengers generate the same profit for a given flight-leg, and differ only in probability of cancellation.
Letter to the Editor—On Vertex Addends in Minimax Location Problems
Authors: Lin Chihchih C.
Published: October 2008

This letter gives a useful interpretation of vertex addends in minimax location problems. Also, Handler's solution method for this problem is extended to the case when addends are present.
Books of Interest
Authors: Lam Tenny N. , Wirasinghe Chandana
Published: October 2008

Review of books: (1) Traffic Science, Denos Gazis, editor, John Wiley & Sons, New York, 1974, 293 pp., $19.95; (2) Optimising Bus Systems in Urban Areas, Sven Erlander, editor, Linköping University, Linköping, Sweden, 1973, 296 pp.
A Behavioural Explanation of the Association Between Bus and Passenger Arrivals at a Bus Stop
Authors: Jolliffe J. K. , Hutchinson T. P.
Published: October 2008

The times of arrivals of passengers and departures of buses have been observed at ten bus stops in suburban London. The different bus stops were observed at different times of the day, but the observations at each were repeated at the same time on each of eight different days. Due to the predictability of the bus services, passengers' waiting times were observed to be about 30 per cent less than they would have been had the passengers arrived at random times. An explanation of this involves considering passengers to be of three types: a proportion q whose arrival time is causally coincidental with the bus, a proportion p(1 − q) who arrive at the optimal time (the time at which the expected waiting time is smallest), and a proportion (1 − p)(1 − q) who arrive at random. It was found that p is positively correlated with the expected gain from arriving at the optimal time as opposed to arriving at random. Furthermore, p was found to be larger at those bus stops observed in the peak than at those observed in the off-peak. A number of other results relating various parameters of the bus services are also given.
Time Dependence in Commuter Traffic Models
Authors: Pearce C. E. M.
Published: October 2008

In this paper we formulate a basic model for two-dimensional time-dependent traffic flow. The model is designed specifically to relate to the morning peak period of commuter traffic, for which the underlying ideas are relatively unencumbered. The time variation of the point value of the “travel intensity at a given time point” is considered and also the global “wave movement” that peak hour traffic will exhibit—the peak hour will not be entirely synchronous at all points over the city. It is found that under standard assumptions as to routing and the location of trip end points, a strong peak hour occurs in the form of a shock wave. The effect of changes to the routing system and trip-end distribution is also considered.
Optimization of Traffic Signal Settings by Mixed-Integer Linear Programming
Authors: Gartner Nathan H. , Little John D. C. , Gabbay Henry
Published: October 2008

Setting traffic signals in a signal-controlled street network involves the determination of cycle time, splits of green time, and offsets. Part I of this paper considers the network coordination problem, i.e., given a common cycle lime and green splits at each intersection, determine offsets for all signals. Part II considers the more general synchronization problem, i.e., determine simultaneously all the control variables for the network including offsets, splits, and cycle time. In Part I, a link performance function is developed to express the loss incurred by platoons traveling through a signal-controlled intersection us a function of link offset. Integer variables enter the formulation because of the periodicity of the traffic lights: The algebraic sum of the offsets around any closed loop of the network must equal an integral number of cycle limes. The optimization problem is formulated as a mixed-integer linear program and a test network is solved by branch-and-bound techniques using IBM's MPSX package.
Books of Interest
Authors: Kanafani Adib , Ashworth Robert , Edie Leslie C.
Published: October 2008

Review of books: (1) Principles of Urban Transportation System Planning, B. G. Hutchinson, McGraw-Hill, New York, 1974, 444 pages, $19.50; (2) Highway Traffic Analysis and Design, R. J. Salter, Macmillan, London, 1974, 378 pages, $17.50; (3) Systems Planning and Design: Case Studies in Modeling, Optimization and Evaluation, edited by Richard de Neufville and David H. Marks, Prentice Hall Inc., Englewood Cliffs, New Jersey, 1974, 438 pp, $18.95.
Rapid High Resolution Single Nucleotide Polymorphism–Comparative Genome Hybridization Mapping in Caenorhabditis elegans
Authors: Flibotte Stephane , Edgley Mark L , Maydan Jason , Taylor Jon , Zapf Rick , Waterston Robert , Moerman Donald G
Published: October 2008

We have developed a significantly improved and simplified method for high-resolution mapping of phenotypic traits in Caenorhabditis elegans using a combination of single nucleotide polymorphisms (SNPs) and oligo array comparative genome hybridization (array CGH). We designed a custom oligonucleotide array using a subset of confirmed SNPs between the canonical wild-type Bristol strain N2 and the Hawaiian isolate CB4856, populated with densely overlapping 50-mer probes corresponding to both N2 and CB4856 SNP sequences. Using this method a mutation can be mapped to a resolution of ∼200 kb in a single genetic cross. Six mutations representing each of the C. elegans chromosomes were detected unambiguously and at high resolution using genomic DNA from populations derived from as few as 100 homozygous mutant segregants of mutant N2/CB4856 heterozygotes. Our method completely dispenses with the PCR, restriction digest, and gel analysis of standard SNP mapping and should be easy to extend to any organism with interbreeding strains. This method will be particularly powerful when applied to difficult or hard-to-map low-penetrance phenotypes. It should also be possible to map polygenic traits using this method.
The Brain and Resuscitation
Authors: Sävman Karin
Published: October 2008

Perinatal asphyxia remains an often devastating event that results in death or impaired survival despite extensive resuscitative efforts at birth. The hypoxic-ischemic brain injury after severe birth asphyxia is largely dependent on a neurotoxic cascade that is initiated during reoxygenation and reperfusion. This results in secondary energy failure and neuronal death within hours to days after resuscitation. The mechanisms leading to secondary brain injury include release of excitatory amino acids, free radical formation, induction of apoptosis, and inflammatory activation. The interval between the primary insult and the development of permanent injury opens a time window for therapeutic interventions to improve brain outcome. Early identification of high-risk infants who may benefit from such neuroprotective treatment is, thus, important and is based on strict criteria for birth asphyxia combined with clinical and electroencephalographic signs of significant encephalopathy. Moderate hypothermia is the most studied intervention, and reduced impairment in survivors has been reported. Promising pharmacologic agents are being investigated, but further research is needed to determine their role in improving outcome.
Pathophysiology of Anemia During the Neonatal Period, Including Anemia of Prematurity
Authors: Widness John A.
Published: October 2008

This review summarizes the current thinking about the causes of anemia universally experienced by preterm infants in the early postnatal weeks. In addition to describing developmentally determined physiologic processes contributing to anemia of prematurity, this review discusses clinically important nonphysiologic contributors to anemia experienced by preterm infants during the neonatal period. Chief among these and an important contributor to the need for red blood cell transfusions is the heavy laboratory phlebotomy loss sustained shortly after birth, when neonatal cardiorespiratory illness is most severe. Understanding and recognizing the physiologic and nonphysiologic processes contributing to anemia encountered in early postnatal life is important in knowing which treatment and prevention modalities are likely to be most effective in different clinical situations. The evaluation of rare and uncommon acquired and genetic causes of anemia in newborns are not covered in this review.
Treatment and Prevention of Neonatal Anemia
Authors: Widness John A.
Published: October 2008

Because red blood cell (RBC) transfusion therapy remains the primary treatment of anemia encountered in early life, the basis for RBC transfusion in the treatment of symptomatic anemia is discussed in this review along with several important aspects of neonatal blood banking practices. Nontransfusion approaches to the prevention and treatment of neonatal anemia also are described. Finally, this review covers the controversy surrounding whether neonatal RBC transfusion therapy should be restrictive or liberal. The evaluation and treatment of uncommon and rare acquired and genetic causes of anemia in newborn infants are beyond the scope of this review.
Prevalence of Low Bone Mass and Deficiencies of Vitamins D and K in Pediatric Patients With Cystic Fibrosis From 3 Canadian Centers
Authors: Grey Vijaylaxmi , Atkinson Stephanie , Drury Donna , Casey Linda , Ferland Guylaine , Gundberg Caren , Lands Larry C.
Published: October 2008

OBJECTIVE. In this cross-sectional observational study, we assessed both vitamins D and K status and bone health in pancreatic insufficient pediatric patients with cystic fibrosis from 3 Canadian cystic fibrosis centers.

METHODS. Eighty-one patients who had cystic fibrosis and were clinically stable for at least 3 months were enrolled. At the time of the clinic visit, anthropometric variables, lung function, pubertal status, intake of calcium and vitamins D and K, and physical activity were assessed. Blood was taken for analysis of biochemical biomarkers of bone turnover and status of vitamins D and K, and a urine sample was obtained for calcium, creatinine, sodium, and deoxypyridoline analyses. Whole-body bone mineral content and lumbar spine (L1–L4) bone mineral density were measured.

RESULTS. The children were relatively well nourished and had moderate to mild lung disease. Low bone mineral mass defined as a z score between −1.0 and −2.0, for gender and age was detected in 38% of the children for whole body and in 28% for lumbar spine. z score less than −2.0 was observed in 7 children for both bone measures. Suboptimal vitamin D status occurred in 95% of patients; suboptimal vitamin K status occurred in 82% of patients. Measures of plasma osteocalcin and carboxy-terminal propeptide type 1 procollagen and urinary deoxypyridoline compared with reference values for age, gender, and pubertal status reflected a state of suppressed bone formation and elevated bone resorption in a large proportion of the patients.

CONCLUSIONS. Bone mass of the whole body and spine was lower than expected for chronological age in approximately one third of pediatric patients with cystic fibrosis irrespective of gender or age. This may be explained by the observation of low bone turnover for developmental stage as indicated by bone biomarkers. Suboptimal status of vitamins D and K may be key causative factors of the low bone status for age.
Impact of Intensive Care Practices on Short-Term and Long-term Outcomes for Extremely Preterm Infants: Comparison Between the British Isles and France
Authors: Bodeau-Livinec Florence , Marlow Neil , Ancel Pierre-Yves , Kurinczuk Jennifer J. , Costeloe Kate , Kaminski Monique
Published: October 2008

OBJECTIVES. The objective of this study was to compare practices of care and outcomes of infants who were born between 23 and 25 weeks’ gestation in 1995 in the British Isles and in 1997–1998 in France.

METHODS. We examined 2 population-based cohorts in the British Isles (1892 births included) and in France (456 births): the EPICure and EPIPAGE studies. The rate of follow-up was 90% at 30 months and 86% at 2 years. At 5 to 6 years, the cognitive function of 64% of the children without severe disability was assessed in the EPICure study and 57% in the EPIPAGE study.

RESULTS. The mortality rate of live-born infants was lower in the EPICure study (25%) than in the EPIPAGE study (34%) before admission to a NICU but higher in the NICU (45% vs 29%, respectively), such that there was no difference in the proportions of survivors at discharge after adjustment for gestational age. The risk for severe brain lesions was 24% among infants who were admitted to a NICU in both studies, 41% in the EPICure study versus 67% in the epidemiologic study on great prematurity (EPIPAGE) among infants who died after discontinued treatment in NICU, and 17% vs 11% among survivors at discharge. The risk for cerebral palsy at 24 to 30 months was 20% in the EPICure study versus 16% in the EPIPAGE study, whereas the risk for overall cognitive score of <70 at 5 to 6 years was 10% vs 14%, respectively.

CONCLUSIONS. Despite apparent differences in the modalities of limitation of intensive care, the outcomes of infants who were born at 23 to 25 weeks’ gestation in the EPICure and EPIPAGE studies were not significantly different.
Gestational Diabetes Hinders Language Development in Offspring
Authors: Dionne Ginette , Boivin Michel , Séguin Jean R. , Pérusse Daniel , Tremblay Richard E.
Published: October 2008

BACKGROUND. Previous studies have suggested that language is affected in infants of diabetic mothers, yet there have been no systematic investigations to address this question.

OBJECTIVE. Our goal was to compare infants of diabetic mothers and controls on language outcomes from ages 18 months to 7 years.

METHODS. This was a case-control longitudinal design with 2 birth cohorts: 1835 singletons from the Quebec Longitudinal Study of Child Development (born October 1997 to July 1998) and 998 twins from the Quebec Newborn Twin Study (born November 1995 to July 1998). Cases were 221 infants of diabetic mothers (105 singletons and 116 twins), and controls were 2612 children (1730 singletons and 882 twins) for whom at least 1 language measure from ages 18 months to 7 years was available. Exclusion criteria were gestation of <32 weeks. The outcome measures were McArthur Communicative Development Inventory expressive and receptive vocabulary and grammar at 18 months and 30 months, the Peabody Picture Vocabulary Test receptive vocabulary at 48 months and expressive and receptive vocabulary at 60 months, and Early Development Instrument teacher-assessed communication at 72 months and 84 months (kindergarten and first grade).

RESULTS. Analyses of variance (controlling for gender, socioeconomic status, and perinatal factors) revealed effects of gestational diabetes on expressive language at 18, 30, and 72/84 months. Infants of diabetic mothers scored 0.27 to 0.41 SD lower than controls and were 2.2 times more at risk of a language impairment. Genes and maternal education both moderated the effect of gestational diabetes on expressive language during this period.

CONCLUSION. Gestational diabetes hinders expressive language in offspring into middle childhood. Genes are strongly associated with the risk of delays in infants of diabetic mothers, and offspring of educated mothers are less affected.
Cumulative Violence Exposure and Self-Rated Health: Longitudinal Study of Adolescents in the United States
Authors: Boynton-Jarrett Renée , Ryan Louise M. , Berkman Lisa F. , Wright Rosalind J.
Published: October 2008

OBJECTIVE. The goal was to determine whether cumulative exposure to violence in childhood and adolescence contributes to disparities in self-rated health among a nationally representative sample of US adolescents.

METHODS. The National Longitudinal Survey of Youth 1997 is an ongoing, 8-year (1997–2004), longitudinal, cohort study of youths who were 12 to 18 years of age at baseline (N = 8224). Generalized estimating equations were constructed to investigate the relationship between cumulative exposure to violence and risk for poor health.

RESULTS. At baseline, 75% of subjects reported excellent or very good health, 21.5% reported good health, and 4.5% reported fair or poor health. Cumulative violence exposures (witnessed gun violence, threat of violence, repeated bullying, perceived safety, and criminal victimization) were associated with a graded increase in risk for poor health and reduced the strength of the relationship between household income and poor health. In comparison with subjects with no violence exposure, risk for poor self-rated health was 4.6 times greater among subjects who reported ≥5 forms of cumulative exposure to violence, controlling for demographic features and household income. Trend analysis revealed that, for each additional violence exposure, the risk of poor health increased by 38%. Adjustment for alcohol use, drug use, smoking, depressive symptoms, and family and neighborhood environment reduced the strength of the relationships between household income and cumulative exposure to violence scores and poor self-rated health, which suggests partial mediation of the effects of socioeconomic status and cumulative exposure to violence by these factors.

CONCLUSIONS. In this nationally representative sample, social inequality in risk for poor self-rated health during the transition from adolescence to adulthood was partially attributable to disparities in cumulative exposure to violence. A strong graded association was noted between cumulative exposure to violence and poor self-rated health in adolescence and young adulthood.
Does Watching Sex on Television Predict Teen Pregnancy? Findings From a National Longitudinal Survey of Youth
Authors: Chandra Anita , Martino Steven C. , Collins Rebecca L. , Elliott Marc N. , Berry Sandra H. , Kanouse David E. , Miu Angela
Published: October 2008

OBJECTIVE. There is increasing evidence that youth exposure to sexual content on television shapes sexual attitudes and behavior in a manner that may influence reproductive health outcomes. To our knowledge, no previous work has empirically examined associations between exposure to television sexual content and adolescent pregnancy.

METHODS. Data from a national longitudinal survey of teens (12–17 years of age, monitored to 15–20 years of age) were used to assess whether exposure to televised sexual content predicted subsequent pregnancy for girls or responsibility for pregnancy for boys. Multivariate logistic regression models controlled for other known correlates of exposure to sexual content and pregnancy. We measured experience of a teen pregnancy during a 3-year period.

RESULTS. Exposure to sexual content on television predicted teen pregnancy, with adjustment for all covariates. Teens who were exposed to high levels of television sexual content (90th percentile) were twice as likely to experience a pregnancy in the subsequent 3 years, compared with those with lower levels of exposure (10th percentile).

CONCLUSIONS. This is the first study to demonstrate a prospective link between exposure to sexual content on television and the experience of a pregnancy before the age of 20. Limiting adolescent exposure to the sexual content on television and balancing portrayals of sex in the media with information about possible negative consequences might reduce the risk of teen pregnancy. Parents may be able to mitigate the influence of this sexual content by viewing with their children and discussing these depictions of sex.