JOURNAL OF TRANSPORTATION RESEARCH
Year:2012 | Volume:9 | Issue:2 (31)|Papers Count:7

The railway networks constitute vital routes in all of the world's countries. Occurrence of earthquake events in railway locations causes the track geometry to deviate from the standard position. Remarkably, this issue is in conflict with the safe running of the train on ballasted tracks. Consequently, the seismic evaluation of railway tracks is necessary. In this study, a three dimensional numerical model has been developed for seismic analysis of the track. In this finite element numerical modeling technique, the rails and sleepers have been modeled as beam elements and the ballast and sub-ballast layers have been modeled using a spring-dash pot with lumped mass systems. In addition, the lateral and the longitudinal track resistances have been considered in the modeling process. In the next stage, due to the model sensitivity to the track length, a critical length was derived to be representative of the critical length of the track from structural and operational points of view. For this purpose, the maximum forces and deformations of sleepers and rails were considered for critical length evaluation. In the final stage, the effects of earthquakes on tracks with various stiffness values have been assessed using the evaluated critical length. The results of the seismic analysis of the model by the Kobe earthquake show that a minimum length of 40m could be selected as a critical length for seismic analysis of the track. In addition, increasing the track stiffness causes a reduction in deformations, but it has no remarkable effect on the internal forces on the track components.

Revenue management is based on offering the right product to the right customer at the right time. Revenue management scientists have concluded that traditional tools must be restructured based on the economic crisis, which has changed customers' behavior, and also the advent of low cost carriers, which attract a significant share of the customers. These new carriers offer a simplified fare structure and lower fares, and they apply price-based revenue management techniques. Dynamic pricing has several advantages, such as increase in revenue, goal oriented pricing and leveling capacity usage among resources. One of the challenges of the parallel flight sets is aggregating demand on specific flights, which can be overcome by applying dynamic pricing techniques. In this article a dynamic pricing technique based on customer choice behavior is presented for low cost carriers. Choice-based deterministic linear programming is used for approximating marginal values of resources by dual prices. These values are applied for approximating the dynamic programming problem for pricing of substitutable products. A multinomial logit model is used for modeling customer choice behavior. The proposed system is goal oriented and charges lower prices for leisure customers and higher prices for business. Monte Carlo simulation is applied and two pricing strategies, dynamic and fixed pricing, are analyzed and their results compared. The case study results show that for ample capacity compared to demand, application of a fixed pricing strategy with a price point that has low utility leads to a noticeable reduction in the company's revenue. In the case of force for using a fixed pricing policy, different factors such as initial capacity, demand and customer utility should be considered to choose suitable prices. Simultaneously with limiting initial capacity, dynamic pricing will move towards fixed pricing with higher price points.

Public transportation planning is one of the basic factors in economic and social development modern societies. Dial-a-ride problem is a topic in the area of public transportation planning which helps to plan a more convenience passenger transportation and also to improve traffic systems. In the dynamic DARP, requests are received throughout the planning horizon and the primary objective is to accept as many requests as possible while satisfying operational constraints. In this research, we developed a two-step algorithm based on dynamic dial-a-ride problem. In the first step a new request is accepted, while in the second step the optimum route is found by creating a feasible neighborhood of the current route. The results showed that the proposed algorithm obtains a near optimum solution in a short period of time (in few minutes) with the rate of acceptance above 85 percent of new requests.

Porous asphalt has a high proportion of air voids, which is a cause of low filler and grains, and higher coarseness. The benefits of this type of grain are decreased surface reflection, lower noise pollution, reduced splash and driving problems in rainy humid weather, and a greater skid resistance. This is clearly a very important consideration in accident reduction and improvement of road safety and integrity. However, conversely some mechanical features are degraded, such as the rutting resistance, which can be considered to be a weakness of this type of asphalt mixture. Based on previous studies, porous asphalt has been shown to have a low strength against rutting. There has been a wide range of studies conducted on using geotextiles in asphalt layers, but despite this its role in increasing the resistance to permanent deformation in porous asphalt has not yet been proved. In this research study, the effect of using geotextiles in the case of permanent deformation of porous asphalt samples was examined by applying the wheel track machine. It was observed at different temperatures and both dry and saturated conditions that geotextile-reinforced porous asphalt mixture can tolerate more loading cycles, with a decrease in the depth of the rutting.

The routing problem for rapid public transit is described as the determination of the optimal place or location for stations and their alignment in a city. This can be modeled as an optimization problem, with maximization of coverage of stations as the objective function. It can then be subjected to station intervals and length of the alignment. The benefit of this is optimization of the transport network, allowing more people to use public transport, thereby reducing costs and emissions. On the other hand, heuristics offer some advantages, such as reduced complexity and their high run speed, which often attracts the attention of researchers. This paper introduces a heuristic method based on the maximization of the population coverage of stations and access to the main destinations in the city. It is therefore expected that a high level of trip coverage is the main object. This solution is a combination and development of two previous methods, known as population coverage and travel coverage. Comparing the results from this method with those from the two previous methods shows that the travel coverage achieved with the new method is increased. The study in this paper has been carried out on the transportation network in the city of Tabriz.

Transportation Infrastructure (TI) project selection is identification of alternative projects in order to maximize the net benefit to the organization and allocate limited resources among those alternatives. It is difficult to select the optimum set of proposed TI projects in an organization due to factors such as project risk, corporate goals and limited availability of TI resources for the candidate projects. TI project selection is based on Multi-Criteria Decision Making (MCDM) problems, as opposed to other project selection techniques, which have restricted applications as they generally depend on the assumption of independence among the candidate projects and criteria. In this paper, an improved TI project selection methodology is proposed that reflects interdependencies among evaluation criteria and projects, using an analytic network process (ANP) within a zero–one goal programming (ZOGP) model. To provide a systematic approach to set priorities among the multi-criteria and trade-off among the objectives, it is recommended that ANP is applied prior to GP formulation. Although GP incorporates multiple objectives and determines an optimal solution, its major drawback is that the decision maker (s) must specify goals and priorities a priori. To overcome this, group discussion is needed, and this research has proposed an integrated approach for interdependent TI project selection problems using Fuzzy Delphi, the Analytic Network Process concept and Zero-One Goal Programming. In project selection it is important to consider interdependencies among projects or criteria, to reflect the characteristics of real problems. Developing a methodology for considering interdependent factors is complex, so this paper presents a solution method through a real-world TI empirical example on an ongoing decision-making project in Taichung City, Taiwan using ANP/ZOGP. In this way, problems with multiple criteria, interdependence and resource feasibility are solved.

One of the most significant extension problems of the Vehicle Routing Problem (VRP) is the Heterogeneous Fixed Fleet Vehicle Routing Problem (HFFVRP), which aims to provide a service to a specific customer group using a limited number of vehicles. This is vital in ensuring a business can meet customer demand while simultaneously maximizing its profits. The HFFVRP is concerned with determinations of the minimum cost routes for a fleet of vehicles in order to satisfy the demand of the customer population. The fleet composition consists of various types of vehicles, which differ with respect to their maximum carrying load and variable cost per distance unit. This paper proposes a hybrid metaheuristic algorithm based on the Ant Colony System (ACS) for solving the HFFVRP, in which two local search algorithms are used as improvement methods. The proposed algorithm is tested on 13 standard instances involving from 50 to 360 customers from the literature. The computational result shows that the ACS results are competitive with other metaheuristic algorithms results for solving the HFFVRP. In addition, the proposed algorithm finds closely the best known solutions for most of the instances in which six best known solutions are also found.