Search

The Operations Research Society of America/Transportation Science Section's (ORSA/TSS) Workshop "Automated Techniques for Scheduling of Vehicle Operators for Urban Public Transportation Services," seals with the development and application of automated techniques for the scheduling of vehicle operators for urban public transportation services. The Urban Mass Transportation Administration, American Transit Association, and Union Internationale des Transports Publics are cooperating with ORSA/TSS to assure the workshop's success. Authors are invited to propose papers dealing principally with the following areas, heuristic and mathematical programming approaches to the assignment of vehicle operators; strategies for crew rotation schedules; interactive computer methods; reviews of implementations of automated scheduling systems; costs and benefits of automated techniques; and comparisons with manual scheduling techniques. Short abstracts should reach by November 1, 1974 and full manuscripts by January 1, 1975.

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. [ABSTRACT FROM AUTHOR]

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

The article presents a paper, which shows how to determine the optimal number and routings of containers used to move mail among several cities. This paper extends the above system to more than two cities, with different schedules on different days and with transfer of containers permitted throughout the system. A mathematical formulation is developed that can be readily solved by known linear programming techniques. Critical assumptions are (a) periodic demand patterns and linear transportation costs between each city-pair, and (b) constant fixed cost per container in the system. The optimization problem is transformed into a network flow linear program for which efficient solution methods are known. The researchers have investigated a system where containerized mail would be sent between two cities. The problem solved in reference was that of determining the best number of containers to be sent each day between the two cities, based on (a) the distribution of mail volumes going between the cities each day and (b) the costs for sending containers, full or empty, and for sending mail by other means in case of container shortage. Thus the original convex programming problem has been converted to an especially tractable type of linear program, namely the optimization of a network flow.

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. [ABSTRACT FROM AUTHOR]

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

A wide range of signal switching policies may be adopted for control of traffic flow between a pair of intersections. One of the most import,ant traffic situations is that in which rush-hour commuter traffic travels towards or away from a city center along radial roads. Under these circumstances opposing and tangential flow may be light. Earlier papers have shown that a modified form of the Dunne-Potts switching policy might be applied to pairs of intersections carrying commuter flow. Efficient and flexible operation of the system under a wide variety of flow conditions, and with the minimum of computer surveillance, was demonstrated. The present paper reports the results of further simulation experiments and discussed tentative solutions of some of the practical problems associated with the proposed scheme. [ABSTRACT FROM AUTHOR]

This paper investigates the welfare implication of changes in the transportation system in two special areas. The first is when the origin-destination demand for transportation may be assumed to be fixed and the second case is where, considering only work trips, origins may vary but destinations may not. A technique is described that could be used to forecast the new origin-destination demand resulting from a change in the transportation system. The technique also provides an appropriate measure of the welfare implications. A particular objective of the paper is to point out the pitfalls of using transportation (generalized) cost saving as a welfare measure whenever origin-destination demand may not be assumed fixed. In this situation it is shown that the welfare measure must take into consideration the benefit derived from the increased choice in available housing sites. [ABSTRACT FROM AUTHOR]

In two papers by C. J. ANCKER, JR., A. F. GAFARIAN, AND R. K. GRAY, the structure of the headways at the passage of an oversaturated signalized intersection were studied. The statistical analysis performed by these authors seems to confirm the hypothesis that these headways are independent random variables. In this paper we consider the following simple model. Let the spacings and reaction times of the vehicles stopped at the intersection all be independent and let the trajectory relative to the start position and start time be the same for all stopped vehicles. It is shown that the head- ways at the intersection are independent if and only if this trajectory is linear in a certain region specified in the paper. [ABSTRACT FROM AUTHOR]

This paper describes the examination of an oversaturated signalized intersection with no turning permitted. During the green phase, data on the time between arrivals of successive vehicles at an intersection with no downstream bottleneck have been collected and analyzed. Measurements were made of only the vehicles in queue, i.e., vehicles that were stopped during the red phase and those that were stopped during the green phase because the starting wave had not traveled back far enough. Measurements were made only on weekdays from approximately 7:00 A.M. to 8:45 A.M. in order to restrict the sample, as far as possible, to commuters. It is shown that shifted Erlang density functions fit the data satisfactorily and that all vehicles from the third on may be considered as members of the same population with different means. The mean arrival times decrease from front to rear with all from the seventh on being the same. In addition, our statistical analysis leads us to accept the hypothesis that all interarrival times are independent. Experimental techniques and statistical methods are described. Two uses of these results are (1) to provide in- formation for Monte Carlo simulations of traffic phenomena in which oversaturated situations are being considered, and (2) to develop, as will be done in a subsequent paper, a renewal model that takes account of variability in the empyting process, and that may be used in formulating control policies for the oversaturated situation. [ABSTRACT FROM AUTHOR]

This paper presents a mathematical model for the behavior of right- turning (left-hand drive is the convention observed) vehicles at an uncontrolled intersection. The model is a development of the one proposed for this situation in a previous paper by the author. It relates to the intersection of a two-lane major road with a minor road at which vehicles on the major road have absolute priority. Completely random traffic is postulated on the major road, and congestion is caused by drivers of vehicles on the major road who wish to turn right and are unable to do so immediately because of oncoming traffic. It is not possible for following vehicles to filler to the left of a delayed vehicle. The delay distribution for vehicles in each lane of the major road is determined for the case of stochastically stationary behavior, and sonic numerical results for the mean and variance of this distribution are given. The gap acceptance mechanism used in this paper is similar to the one proposed by GAVER. Further references for this paper are discussed in the Introduction to the author's previous paper. [ABSTRACT FROM AUTHOR]

The article presents a list of papers published in the 1973 issue of the periodical. Some papers are "Announcements," "API Method Extended," "Airline Crew-Scheduling," "Air-Cargo Deployment Combat Personnel," "Aircraft Average Number Collisions," "Collision Probabilities," "Large Relative Velocity," "Special Cases, Velocity," "Air Fleet Evaluation Model (AFEM)," "Airports, Parallel Runways," "Air Routes, Potential Conflict," "Air-Route Network Planning," "Augmented Predecessor Indexing Method," "Books of Interest," "Brisbane City Council Transport Services, Note," "Broken Shifts, Bus Scheduling," "Bus Crew Scheduling," "Chesapeake Bay Bridge Traffic Control," "Column Generation Algorithm," "Combat Personnel, Equipment, Deployment," "Comparison, Steady-State and Simulation Methods," "Designing Transportation Networks," "Digital Simulation, Freeway Traffic, Long Island Expressway, New York," "Facility Location Algorithm," "Feeder Transit Lines," "Freeway Traffic, Digital Simulation," "General Networks Lemmas," "Generalized Network Problems," and "Generalized Transportation Problems."

The traffic assignment problem associated with a given transportation network is the process of distributing zone-to-zone trips on links of the network. A number of methods have been proposed to solve this problem, but none have been found to be entirely satisfactory. This paper is concerned with the nonlinear mathematical model of the problem, where the link-traveling costs are increasing functions of the link flows and no explicit capacity constraint is imposed on individual links. An efficient algorithm is developed, using a node-arc formulation of the problem. It is an adaptation of the convex-simplex method that takes advantage of the very special network structure of the traffic assignment problem formulated in this way. Numerical results obtained with a moderate size street network are presented. [ABSTRACT FROM AUTHOR]

This paper develops an analytic model of the mean running time for trains on a single track railway. Trains operating at several different speeds in each direction are permitted. Priority systems are included in the model to control train behavior when meets and overtakes occur and delay times due to implementing these priority schemes are calculated. It is assumed that the departing times for trains are independent random variables that are uniformly distributed over the time period of interest. The resulting mean running times, including delays, for each speed class in each direction are found by solving a set of linear equations. [ABSTRACT FROM AUTHOR]

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 - be-cr, where v is journey speed at radial distance r, and a, b, c, are constants. However, a form ala 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. [ABSTRACT FROM AUTHOR]

This paper presents a method for serial combination of truck trips to minimize the total cost of deadheading, subject to constraints on the allowed combinations. The problem is initially formulated as an integer transportation problem with extra compatibility constraints, and then reduced to a classical transportation problem. Modifications of the classical algorithm led to a fifty-fold reduction in computer time, and permit solution of a 1000 × 1000 problem in less than two minutes of computer time. Implementation of the method led to considerable cost savings over the older manual procedure. [ABSTRACT FROM AUTHOR]

This paper develops the dual program of the constrained multifacility location problem in which total transportation cost in the system is proportional to the sum of the weighted Euclidean distances between facilities. A decomposition solution method is presented in which the master program is linear and each subprogram is a nonlinear programming problem. Computation results are presented and discussed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this paper we apply the following general scheme to determine toll patterns for multiclass-user transportation networks: we modify the travel cost as perceived by the individual traveler by charging him a 'toll.' Then we try to determine the toll pattern in such a way that the system-optimizing flow pattern becomes at the same time user- optimizing. We discuss two toll policies: (a) Tolls are collected on a link basis. (b) Tolls are collected on a path basis. The study shows that there is a degree of freedom in the path-toll collection policy. Alternative criteria are proposed for the exploitation of the degree of freedom such as: (i) that the tolls collected be nonnegative; (ii) that the personal cost of travelers, before and after the imposition of tolls, remains the same; (iii) that certain classes are treated discriminately in order to attain some social good. [ABSTRACT FROM AUTHOR]

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 con conations 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. [ABSTRACT FROM AUTHOR]

This paper outlines an approach to analyzing the safety characteristics of vehicular ground transportation systems operated under computer surveillance and control. A quantitative index of safety is formulated, and a procedure is developed for analyzing the dependence of system safety on the significant design parameters and performance attributes. Lower bounds on the permissible minimum headway are established on the assumption of instantaneous and perfect control, so that the effects of various sensing, communication, control and actuation subsystems can be assessed independently. Time delays in emergency control-resulting from discrete sensor spacing, finite sampling time, and loss of telemetered data-are analyzed and expressions for the attendant increase in the minimum headway are developed. The general approach and the specific techniques are illustrated with numerical examples. [ABSTRACT FROM AUTHOR]

This paper deals with a car-following model relating driver reaction time, temporal headway and deceleration response to accident frequency. The central goal is to assess the sensitivity of collision probability to a shift in expected reaction time. This problem reduces to determining the sensitivity of the probability of ruin to changes in the drift of the process of cumulative differences between reaction times and temporal headways. A diffusion-type approximation is used and it is shown that additive changes in mean reaction time correspond to multiplicative changes in collision probability. A numerical example is given to illustrate the potential effects of a mere 0.1 sec decrease in mean reaction time. [ABSTRACT FROM AUTHOR]

Various versions of the Weber problem deal with the location of facilities in a system with fixed destinations or customers. The object is to minimize the sum of transportation costs, which is represented as the sum of the weighted distances in the system. This paper finds the optimum location for facilities where the object is to minimize the maximum weighted distance in the system. Rectangular distances, which are more appropriate for urban transportation than straight line distances, are used in the model. Optimization is achieved through parametric linear programming. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The article focuses on models of fleet routing and scheduling problems for transportation systems, which are formulated as integer linear programs with 0-1 variables. The topics discussed in this paper are concerned with important operational problems confronting the management of the competitive air transportation system. Some of these problems are significant for other transportation systems, including those with public-service rather than profit objectives. The problems are those connected with fleet utilization, fleet size, routing, and scheduling. Work that is related to some of these problems has been carried out by operations researchers and has been limited because, when optimal solutions were sought, computation times were excessive. The principal method of attack has been dynamic programming, which usually involves a very large state space for any real-life transportation system. The basic models are of the discrete-time rather than of the continuous-time variety. This property permits the formulation of the optimization problems as integer linear programs. The aim is to formulate a realistic model and to obtain its optimal solution

A method for estimating costs and benefits to commuters, over a period of time, is developed in this paper. The method will account for the variation of traffic volumes over the period of time considered. The cost structure of a transport mode is taken as a function of the volume of traffic on that mode. The distribution of traffic volumes is then used to measure the costs and benefits to the user and the state over a year. Commuters are divided into different social classes according to the value they place on the attributes of the different transport modes. Next the method is used to evaluate different road pricing schemes. Finally the road system is examined both as a public utility and as a public enterprise. [ABSTRACT FROM AUTHOR]

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

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/or the efficient operation of existing systems. Here, time- table 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. [ABSTRACT FROM AUTHOR]

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

The problem treated is that of locating in centers (processing facilities) in a network, so as to minimize the total transportation cost associated with their use. On the assumption that all movements occur between a vertex and a center nearest it, HAKIMI has shown that only vertex locations for the centers need be considered. The present paper shows that this conclusion remains valid under alternative assumptions more appropriate for some applications. [ABSTRACT FROM AUTHOR]

The trip distribution model formulated in this paper uses the basic concepts and notation of utility theory. Each trip origin is considered to rate the trip destinations available in order of perference, and each trip destination is considered to rate the trip origins, it is shown that in pairing trip origins with trip destinations in the distribution process, a `stability' condition should be satisfied, and that two particular stable trip distributions, termed `origin-optimal' and `destination-optimal,' are of particular interest. Conditions under which `like' trip origins and `like' trip destinations may be grouped together are then discussed. Finally the model is illustrated using trip data for the small city of Launceston, Tasmania. [ABSTRACT FROM AUTHOR]

In this paper a scientific method for the construction of timetables for a suburban railway line without branches is developed. It is shown that such timetables are largely determined by stop-schedules. Two criteria for stop-schedules have been considered: the number of inter- mediate passenger stops and the number of carriage miles. A mathematical formulation is presented and it is shown that the problems of finding optimal stop-schedules can be solved with dynamic programming. Zone-stop-schedules, a type of stop-schedule with several operational advantages, have received special attention. [ABSTRACT FROM AUTHOR]

Investigations of motorist delays at the intersection of a major and minor road have involved variations of one or the other of two merging strategies: (i) MILLER'S[8] model that assumes that a minor-road motorist makes consecutive decisions consistently, and (ii) that of WEISS AND MARADUDIN[7] that assumptions that a different, independent decision is made for each headway. In this paper we show that results for both models may be obtained easily, using the results of queuing theory, if certain reasonable assumptions are made. Simple expressions for the Laplace-Stieltjes transforms and means of the delays are derived in the case of independent major-road headways with a common, general distribution. For exponential headways, a numerical study shows the mean Miller delay to increase with the variation in the merge times, while the mean Weiss-Maradudin delay decreases. To illustrate the application of the expressions obtained, we investigate the reduction in the delay achieved by inserting a traffic island between two streams of major-road traffic. [ABSTRACT FROM AUTHOR]

Two transportation systems, following the same alignment, serve an area from which population commutes to a central point. One system has a constant speed and can be taken at any point along the line; the other has a discrete movement and can be boarded at stations only. The study analyzes the optimal station locations of the latter system for which its patronage will be maximum, assuming that passengers select systems on the basis of shorter travel time. The optimal solution, derived analytically and shown graphically on a time-distance diagram, indicates that the interstation spacings for this objective should be increasing at a decreasing rate in the direction of cumulation. Compared with the optimal interstation spacings for minimum total passenger travel time, given in a recent paper by VUCHIC AND NEWELL, this solution has a greater density of stations and, naturally, larger travel times. Sensitivity of the two solutions to various parameters is examined. Several problems to which this model would be applicable are shown and the model's realistic validity is discussed. From the optimal solution and numerical examples, several conclusions are drawn that are directly relevant to the planning of station locations for discrete public transportation systems. [ABSTRACT FROM AUTHOR]

This paper develops a dynamic programming model for selecting an optimal combination of transportation modes over a multiperiod planning horizon. The formulation explicitly incorporates uncertainty regarding future requirements or demands for a number of commodity classes. In addition to determining the optimal modes to employ, the model assigns individual commodity classes to various modes, determines which supply points serve which destinations, and reroutes carriers from destinations to alternative sources where they will be most effective. The model is formulated as an optimal discrete time stochastic control problem where cost is quadratic and dynamic equations linear in the state and control variables. This model may be solved in closed form by an efficient dynamic programming algorithm that permits the treatment of relatively large scale systems. A iso developed is an alternative, generally suboptimal method of solution, based upon wiving a sequence of convex programming problems over time. This technique may be employed for a more general class of problems. In both methods the use of 'shadow prices' that arise is discussed. [ABSTRACT FROM AUTHOR]

Hillier has described a method of selecting offsets to minimize delay in certain networks controlled by fixed-time signals. In this paper an attempt is made to extend the method by relaxing somewhat the restriction on the form of the network. The problem is expressed in terms of the theory of graphs, and an iterative process is developed for finding a set of offsets that minimizes delay over the whole network. At each stage, the part of the network already covered is extended by adding one or more links, and for the method to be viable these links must be chosen so that a certain set of intersections remains small. A method of selection of links that minimizes this set of intersections at each stage is developed. The selection of links and calculation of offsets have been programmed in Fortran. Having found one delay-minimizing set of offsets, some others that give the same total delay can be found if they exist. [ABSTRACT FROM AUTHOR]

This paper is concerned with the development of a model for planning shipping prices over various routes of a transportation network. It is assumed that over each route a 'railroad' (or other transport firm) competes directly with one other shipping firm (e.g., another railroad, a trucker) for the volume of business that is to be shipped over the route. We allow the possibility that the railroad's competition will come from different firms over different routes. The model we consider is a multiroute problem that involves both institutional and physical operating constraints. Each firm's demand depends linearly upon its own and its opponent's price. Since each competing firm sets its price policy independently and before the variable demand is known, some of these constraints cannot be guaranteed to hold with certainty. Thus they are best expressed as chance constraints. The objective of the 'railroad' is to maximize its profit subject to the constraints of the model. The solution of the model synthesizes a pricing policy for the 'railroad'; we also indicate how variations of the model can be employed in a sensitivity analysis of the suggested policy and discuss the relation between our model and other notions in game theory and chance-constrained games. An example is outlined, and the implications for a welfare-economic pricing policy considered. [ABSTRACT FROM AUTHOR]

The impact of new and improved transportation facilities on urban travel behavior is a topic seldom addressed in transportation-research literature. The paper presents a method for classifying travel behavior of urban residents and suggests a procedure for quantitatively estimating diverted traffic. An application of the method is made to a limited sample of Chicago's residents. Seven groups of residents with similar travel patterns were identified and the impact of a new expressway on each of the seven groups was estimated. The study suggests a reorientation of research activities: in addition to the analyses of aggregate traffic data a greater attention should be directed toward detailed inquiries about the travel patterns of urban residents and the spatial structure of commercial traffic. [ABSTRACT FROM AUTHOR]

When an interstate highway is completed between two cities less than 200 miles apart, some people find it more convenient to switch from air travel between the two cities to automobile or bus travel. This paper employs a multiple regression model to quantitively examine this effect of interstate highway construction on short-haul air market. Several techniques are used to isolate the impact of changing highway quality on the short-haul air market from a myriad of other influencing factors. The city-pairs chosen for the regression sample are all between 105 and 185 miles apart so that the distance variable is constrained. An 'airport use' variable is introduced to reflect changing environmental demand determinants such as income and population. The regression is run in first difference form, which eliminates multicollinearities as well as the influence of static factors. Finally, quarterly data is used rather than yearly data to provide more degrees of freedom, and quarters are compared with the same quarters in an earlier year to eliminate the effect of seasonal variations. The coefficients of the resulting regression indicate two important conclusions. First, short-haul air markets are growing only about half as fast as the air market as a whole. Second, a significant number of travelers do switch from airplane travel to automobile travel when an interstate highway is made available for a one hundred to two hundred mile trip. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This article presents information regarding the International Conference on "High Speed Ground Transportation," which is to be held on the campus of Arizona State University from January 7-10, 1975. Papers are requested on both the state-of-the-art and current research in all facets of high speed ground transportation. Fields to be emphasized include: vehicle and guideway; structures propulsion; vehicle and guideway; dynamics; communications and controls; systems optimization; noise and air pollution; regional land planning, new cities; airport access; cargo movement; finance; safety; social and legal factors. The abstract deadline is October 15, 1973, with prospective authors to be notified by November 15, 1973. Manuscripts are requested by April 15, 1974. The papers presented at the conference will be published in the "High Speed Ground Transportation Journal." The abstract limit is 500 words.

In his paper, PEARCE presents a method for determining the stationary probabilities of a G/Mt/1 system, the service mechanism being such that it operates regardless of whether or not customers are present. This note is an attempt to correct his results. [ABSTRACT FROM AUTHOR]

The article presents information for authors who want their research work to be published in the journal "Transportation Science." The submission of a manuscript is taken to be the author's representation that the manuscript has not been published or accepted for publication in books or recognized journals and is not currently under consideration by another journal. Manuscripts for publication and Letters to the Editor should be submitted to the Editor either directly or to one of the Associate Editors. Tables may be typed on sheets separated from the text. Manuscripts must be double-spaced throughout with the original in typewritten or equally legible form. Figures are required in a form suitable for photographic reproduction. Any one of a number of forms will be acceptable, e.g., original black ink drawings, or high-quality glossy prints. In mathematical expressions, authors are requested in general to minimize unusual or expensive typographical requirements. Authors should strive for conciseness and clarity. References to related previous work should be reasonably complete, consecutively numbered, and grouped at the end of the paper.

Manuscripts for publication and letters to the editor should be submitted to the editor either directly or to one of the associate editors of the journal "Transportation Science." The submission of a manuscript is taken to be the author's representation that the manuscript has not been published or accepted for publication in books or recognized journals and is not currently under consideration by another journal. Manuscripts must be double-spaced throughout with the original in typewritten or equally legible form. Figures are required in a form suitable for photographic reproduction. Any one of a number of forms will be acceptable, e.g., original black ink drawings, or high-quality glossy prints. Lettering should be uniform in size and style and sufficiently large to be legible after reduction. Authors should strive for conciseness and clarity. References to related previous work should be reasonably complete, consecutively numbered, and grouped at the end of the paper. Manuscripts will be considered for publication in this journal when copy conforming to the above instructions is furnished.