Shippers of freight face many choices and trade-offs. Two choices of particular interest are those of mode of choice and shipment size. These two choices are interdependent, and they also depend on other commodity and modal attributes. Unlike previous studies on the subject, this paper considers the dependence between unit freight charge and shipment size in deriving a shipper's economic order quantity (EOQ). It also examines the nature of this dependence, and studies the effect of market and commodity attributes on optimal shipment size. A numerical example is provided in which optimal shipment size is calculated for full truckload (TL) and less-than-truckload (LTL), and the results are compared with those of previous studies.
The main purpose of this paper is to determine and compare the design thicknesses of asphalt pavements constructed from recycled and new asphalt material. For this purpose, preliminary design charts were developed for determining the thicknesses of recycled and new asphalt pavements of similar composition. These design charts were based on the results obtained from a limited number of fatigue tests conducted in the laboratory. In these tests, cylindrical samples were examined at various temperatures, using the indirect tensile test under controlled stress condition. The values of the poisson's ratio and dynamic modulus of elasticity obtained from these tests were used as inputs, together with the properties of subgrades of various strength, into a modified chevron multi layer program to determine the pavement thicknesses. The results obtained from this limited study indicate that, for the same subgrade and equivalent axle load repetitions, the thickness of a recycled full depth asphalt pavement is smaller than that of new asphalt pavements of similar composition (a).
This paper explains a preliminary procedure that could be used in calibrating a logit model to predict the market allocation of one main commodity (meat) among the rail and truck modes. The problem arising from the fact that data are seldom available in a disaggregate form was overcome by applying existing models, equations and small scale surveys to decompose published consolidated information into disaggregated data. The calibration of the model according to this procedure was found to provide encouraging results.
Based on a finite element analysis, the authors present design charts and nomographs for determining the reinforcement in prestressed concrete deep beams with two openings of different sizes. /Author/
The application of discrete choice models (e.g., logit, probit) to study modal choice in passenger transportation has had a wide acceptance in the literature. However, little success had been reported on the application of these models to study the demand for freight transportation. This is mainly because in freight transportation a model that merely attempts to explain the choice of mode without taking into consideration other related factors, such as shipment size, is only one part of a complete model. Another type of models known as inventory-based models, which takes these factors into consideration, has been developed and applied with a greater success. However, the data requirement of these inventory models has hampered their applicability, especially in situations with limited data on goods movement. This paper presents a new approach to study the demand for intercity freight transportation. The model proposed in this paper utilizes the strength of discrete choice models (e.g., probit) in explaining the process of mode choice as one part of a complete model. The complete model is presented as a joint discrete/continuous choice model for the choices of mode and shipment size. The model is practical in that it requires the same amount and quality of data that would be required to develop a standard disaggregate mode choice model, and it can be estimated using simple two-stage estimation methods which utilizes standard probit maximum likelihood and ordinary least squares estimation techniques. Key words: disaggregate, freight transportation, maximum likelihood, mode, model, probit, shipment.
Mathematical modelling can be used to obtain girder spacings and spans which will optimize the costs of multi-span concrete bridges needed for elevated stretches of highways or mass transit structures.The total cost is expressed as a function (the objective function) of the main variables, namely, main girder spacings and spans, and a set of cost coefficients. Practical requirements impose certain constraints on the choice of the variables. These constraints are respected in the optimization process.In the development of the objective function, empirical equations are needed to express the deck slab thickness, the depth of main girders, and the pier dimensions in terms of the variables.An example is solved to illustrate the method, using a non-linear programming technique called ‘SUMT’.
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