فصلنامه مهندسی حمل و نقل
سال هفتم شماره 1 (پیاپی 25، پاییز 1394)

Airline crew scheduling problem is one of the important problems in the field of the operation research and generally assign crew member to trips that should be covered with minimum cost. Airline flights are usually faced with some of uncertainty events, some of these are: unpredicted bad weather, absent of aircrews without any reason etc… that indicates using of fuzzy set theory in the modeling of the problem. Airline crew scheduling problem are divide in two phase: in the first phase, find all trips that origin and destination, ending where the crews are located. trips obtained in the first phase called pairings. In the second phase the crew scheduling problem modeled by using fuzzy set theory for assigning each crew member to trips with optimized mode. and then for solving the airline crew scheduling problem which categorized in NP-hard problems the Particle Swarm Optimization Approach is proposed.

Traffic congestion as a source of daily delays, degradation of environmental quality, and nonrenewable energy consumption is said to be a major trouble in most of the world’s cities. Being discontent about traffic congestion usually persuades transportation policymakers to propose measures to reduce it. Many studies have shown that individuals’ responses to urban traffic congestion, as usually assumed by policymakers, are significantly different from their respected actual behavior. This paper adopts a behavioral approach to examine the role of travel-related variables on the mentioned difference using design of experiments principles and logit models. In this approach, five policies namely cordon pricing, parking pricing, increasing fuel cost, transit time reduction, and transit access time reduction were investigated. This study uses the stated preferences of individuals who regularly use their private cars to access their job locations in the Tehran central area to calibrate seven models of non-car mode consideration. Furthermore, the role of travel-related variables is also addressed in such mode change. Analysis of the effects of the travel related variables in considering non-car modes shows that the contribution of socio-economic variables are greater than travel-related variables in all of the investigated modes. The results show that while the contribution of travel-related variables is 43% for walk and ride considerers and 31% for taxi considerers, it is 12% for considering motorcycle, 10% for public transit accessed by either car or taxis, 5% for taxi caught by phone and 1% for taxi accessed by car.

This paper deals with the problem of allocation of emergency service vehicles (ESVs) to emergency service stations in order to maximize the expected covering of the demands. Most of the previous studies in this area assume that every call needs only one ESV; however real experiences demonstrate that these assumptions are not valid. Hence, in this paper we are going to develop a model that could dedicate more than one ESV to each call. For this purpose, we use the queue theory with batch arrivals to calculate the availability rate of ESVs in each station. A mixed integer programming model is provided to determine the optimal number of ESVs in each predetermined emergency stations. A real case study is implemented in Mashhad for finding the number of ESVs in gas emergency stations. Model is optimally solved by CPLEX and results are discussed and some analyses on parameters of the model are done.

Elastic bearings are used to improve the structural behavior of the bridges. The existence of such bearings has a considerable effect on the change of vibration behavior in bridges and beams; i.e. change of structure's natural frequencies and vibration modes. In technical texts, theoretical studies can be found on one-span bridges with elastic bearings and numerical methods are used for multi-span beams. In the present paper, the equations governing the vibration of two-span beams with elastic bearings under free vibration were deduced and equation coefficients were calculated in Matlab environment. The results were compared with the simulation results in finite element software ANSYS. Finally, changes of natural frequencies and vibration modes with change of bearing stiffness and span length were investigated. The obtained results indicated that frequency changes in the first and second modes had a descending order for low stiffness; with the increase of stiffness, this change became almost constant. However, frequency increased continuously in higher modes. Moreover, in terms of performance, elastic bearings showed their best performancein equal spans.

Due toexpansions, alterations like geometric modification, fleet upgrade, variation of wagon numbers or any other possible changes, rail industry has to be flexible and be able to perform the needed predictions. This study is an attempt to provide a tool to evaluate the performance of the rail system, regarding the details of train movements, prior to its occurrence. The provided tool is a dynamic, event based simulation model, which is developed in C# and determines the parameters of passenger or freight trains in railroads. Regarding the technical characteristics and route geometry, this tool can evaluate the outputs including train travel time in blocks, fuel consumption, trains’ average and instant velocities and accelerations, and traction and resistance diagrams. The innovations of this research lie in the novel simulation distinctiveness which is utilized in this study compared to other models used in other applications. Based on expert opinion tests and also simulation-reality comparison results, no significant difference has been observed. Tehran-Mashhad railway parameters are calculated as a case study.

Catastrophic consequences of accidents related to the hazardous materials transportation and significant growth in the use of these materials to meet the industry needs, show the necessity of studying in this field. In the context of hazmat transportation, risk is a measure of the probability and severity of harm to an exposed receptor. The purpose of this study is to provide an approach for route evaluation of hazmat based on risk analysis. To reach this goal, after route segmentation, the risk is calculated in different segments. The calculation includes quantification of two main components of risk which are probability of occurrence (frequency) and consequences of occurrence for the events related to hazmat. As an output for the approach, the critical segments of a road according to the risk of hazmat transportation can be determined. The suggested approach was applied in Haraz and Firouzkooh roads as case study.Calculating risk for segments, critical segments were determined for the roads. The total risk of the roads was also calculated and the results were used to evaluate the danger level of the roads.

Reinforcement of asphalt concrete by fibers is one of the methods for improving concrete properties. In this research, the effects of two types of fibers on the properties of a common type of asphaltic concrete have been investigated. The fibers at different contents of 0.3, 0.4 and 0.5% and three different lengths of 10, 25 and 45 mm have been used, and the properties of the mixtures such as Marshal Stability, indirect tensile strength, moisture damage and static creep behavior have been studied. The results show that the Marshal stability of all the mixtures containing fiber is higher than that of the control mixture, with the highest stability for the mixture containing 0.3% of 25 mm carbon fiber. The indirect tensile strength tests show that, for the most cases of fiber contents and lengths, the indirect tensile strength of the fiber reinforced mixtures are lower than that of the control mixture without fiber. It is also found that, the permanent strain in creep tests decreases by using fibers, with the lowest permanent strain for the mixture containing 0.5% of 10mm carbon fiber. The moisture damage tests show that the carbon fiber has a better performance than the nylon fiber. The highest tensile strength ratio is found to be for the mixture containing o.4% of 10mm carbon fibers. The moisture damage increases with increasing the fiber content and length.

Utilization of byproducts of steel production factories in civil engineering infrastructures has progressively been increased in recent years. Increased spending on highway construction from one hand and environmental issues from the other hand also promotes application of these materials. Steel slags have similar physical properties to conventional aggregates and can be used into both surfacing and base asphalt layers. In this work fatigue behavior of asphalt mixes containing EAF and BOF steel slags were evaluated at both laboratory aged and non-aged conditions. Nine sets of laboratory mixtures were prepared. Each set was treated replacing various portions of limestone coarse aggregates (≥ 2.36 mm) with EAF and BOF steel slags. Four point bending beam fatigue testing was performed in controlled stress mode at various stress levels to characterize fatigue behavior of these asphalt mixes. Two approaches were applied to analyze the fatigue tests data, one was based on stiffness and the second one was a dissipated energy concepts. Moreover, in order to evaluate long term performance of mixes containing EAF and BOF slags, the specimens were subjected to laboratory aging condition according to AASHTO PP2 standard testing method. The results showed that the inclusion of EAF and BOF slags in mixes improved fatigue life of samples considerably. For aged specimens, the fatigue life did not change appreciably. This was as a result of greater stiffness of mixes containing low percentages of EAF slag. This finding approved the hypothesis which suggest that the greater the adhesion, the greater would be mitigation of aging in asphalt mixes.

Technical, environmental and economic advantages of pavement cold recyclingtechnology are good signs of an efficient method for asphalt concrete pavements rehabilitation. Nowadays, additives are used for improving the implementation situation and upgrading the performance of cold recycled mixtures. The increasing costs of preparing the common additives such as cement and lime, and also the pollutants that result from their production processes were among the most important reasons for widely using waste additives like fly ash. In this study cold waste powder in its natural and ash form was used as an additive in the cold recycled mixture with bitumen emulsion. In addition, lime powder was separately and as a compound was used in the cold recycled mixtures. The performance of the studied mixtures was assessed by Marshall, indirect tensile strength, moisture sensitivity and resilience modulus tests. The test results showed that using coal waste and its ash, improved the mechanical features of the mixture in a way that Marshal stability, tensile strength and resilience modulus were also increased. As the matter of fact, the effects of using coal waste ash on the mechanical features of the mixtures was obviously related to the existence of more Pozzolanic materials in its chemical compounds. Further, the application of coal waste ash, reduced the moisture sensitivity of the mixture, while using coal waste caused an increase in the mixture's moisture sensitivity. Moreover, the results showed that adding 3% of lime to the recycled mix significantly caused a decrease in the moisture sensitivity. Also lime can be used as a complement for coal waste and its ash because the results showed improvement of the mechanical features and the durability of the mixture due to the occurrence of cementitious reactions specifically in the long-term.

In this paper, a new discrete-event model is presented to model the traffic system dynamic. In this model, in spite of previous models, by considering the effect of number of passengers at the platforms and in the trains on scheduling and on the demands for traveling between stations, the role of number of passengers in formulating the departure time is remarked. In this paper, an objective function based on the three main reasons for passengers’ discomforts, such as waiting and travelling discomfort, congestion discomfort, and jitter discomfort are presented. . Also, some limitation related to subway traffic system such as travelling time constraint, headway constraint and number of passengers in the train constraint, are considered as non-negligible constraints in a railway traffic system. Finally, using a Model Predictive Controller, an optimal controller is designed for rescheduling in the presence of physical constrains. To show the effectiveness of the methodology, simulation is performed by using the specifications of Tehran Metro Line 2.

Alleviating traffic congestion and improving air quality at the school zones, motivating independent decision making abilities and obtaining skills in social networking, as well as combating the increasing rate of obesity requires a comprehensive investigation of mode choice among the children in their daily trips to/from the schools. Little attention paid in the literature to educational trips of students in primary schools, besides a rather sophisticated process of decision making and modeling parameters encouraged the authors to investigate the significant variables in parental decision making regarding mode choice for the primary school students. 290 Questionnaires were distributed among students in four elementary schools (including public and private boys and girls schools) to fill out by the parents in May 2013 in Rasht. The questionnaire contained validated instruments to collect socio-economic and environmental variables as well as the mode they use to take for their kids in daily educational trips. After refining the disaggregated data, 162 questionnaires were entered into analysis and Multinomial logit model was used to explain the probability that particular modes (namely school bus, walking and the private car of household) are selected by the parents for their kids. The number of vehicles the family owns, the father occupational status, household income, gender of student, distance to school and level of physical exercise of the parents (in a weekly basis) were all recognized statistically significant in the mode type selected for the student. This means that encouraging parents to physical exercise and enhancing the quality of schools to enable parents to choose closer schools in the living area are among the policies to encourage the active mode choice by the children.