فصلنامه مهندسی حمل و نقل
سال چهارم شماره 2 (پیاپی 14، زمستان 1391)

In recent years, rail transportation industry has been receiving considerable and ever- growingattention both in theory and practice. Such attentions in our country has led to setting several particular targets in the Fifth Development Plan (e.g. constructing over 1000 kilometers of new lines per year). On the other hand, increasing the length of railways logically demands for further fleets. Presently, such fleets are supplied through other developed countries. This requires a comprehensive and regulated (effective or trustworthy) method to properly select the supplier(s). This paper is aimed at developing an approach based on Fuzzy AHP for selecting the best fleet supplier(s). In this regard, relevant criteria and options have been extracted the experts in the field. Then, the pair comparisons between criteria and between options (based on each criterion) have been performed by using experts’ comments. These comparisons are transferred into fuzzy structure and a confidence level is also considered on the decision made by each expert. Finally, following a four-step procedure, the priority of options were concluded. In the first step, the weights of criteria and options are extracted. Subsequently, the weights of decision makers are computed and then, the final weights are achieved by combining first and second steps. Finally, the priority of options is driven. The result indicates that Germany has the highest priority among other countries and there is an obvious need for modifying the current selection policies.

Travel time - volume relationships are widely used in traffic engineering and transportation planning. These relations obtained for different geometric and traffic conditions, are used in level of service analysis and traffic assignment models. The different highway physical, environmental and traffic characteristics invalidate the use of foreign regulations’ models. Therefore, to obtain native models and calibrating them seems to be necessary. This research aims to propose travel time - volume models in three regions of two lane two way highways in Iran; level, rolling and mountainous, using field and simulation data, simultaneously. Due to lack of adequate traffic data, especially in volumes near capacity, a simulation approach was deployed, and TWOPAS was used to generate the data. Data analysis was led to travel time-volume models in different terrains. Various statistical tests have shown the validity and accuracy of the obtained models. The obtained model is expressed as a combination of linear part (for v/c below 0.6) and nonlinear part (for v/c over 0.6). These models are more compatible with the experimental data and are thus able to better represent the behavior of traffic streams on Iranian roads.

This paper focuses on the reasons behind the mode choice of car commuters who work in the central part of the City of Tehran. By developing a multinomial Logit model, three main reasons behind the commuters’ car usage including car comfort, car dependency and poor public transit were investigated. The study showed that while the sampled commuters mainly use their car for its comfort, their home location and age affect their reluctance to use public transit. In fact, the non-centrally located residents and elders avoid public transit because of its low quality of services. By calibrating five binary Logit models, in terms of long access times to the stations, travel time variation, low speed, discomfort, and low security, the car commuters’ reasons for not using public transit were modeled. An in-depth analysis of the reasons reveals that the long access times to transit stations are the primary reason of individuals’ unwillingness to use public transit. This reason could be a source of insecurity in addition to its disutility. Finally, to encourage car commuters to use public transit, the study concluded with more network coverage in the city outskirt, providing more information and increasing the comfort of public transit system as the most efficient measures.

Management of transportation is one of the most important GIS applications. In this filed the network capabilities of GIS such as shortest path computation is very useful. Graph theories play an important role in GIS network analysis. Various theories such as the algorithms of computing shortest path have ever been used in different cases of graph problems. But for some important cases, there is not a good solution in primal graph. For using of dual spaces, at first the problem will be sent to a proper dual space and then after solving, the answers will come back to the primal space. In this paper, different types of dual graphs used in different sciences such as GIS, have been explained by authors. The dual graph concept for two particular problems in route specification: modeling the different costs of turns in crosses and shortest path finding between non-point origin and destination, have been used. As known, the travel time on crosses in right turning is less than left turning. In this paper it is propounded that linear dual graph can be used for modeling the left turn and right turn in a city network. A solution for finding the shortest path between non-point origin and destination was proposed. In many cases the destination or origin of the trip is not a specific point. It was shown that by changing the structure of the primal graph and its adjacent matrix, the linear or polygonal destination could be converted to a specific point. The proposed approach was implemented on the street map of a municipal district in City of Tehran. The developed application illustrated the usefulness and positive effect of discussed approach in transportation network routing.

Iranian rail network has special preferences and constraints that have persuaded transportation planners to consider these constraints in their schedules. The aim of this study is to develop a new mathematical model for train scheduling problem in the single-track railways. The model consists of both passenger and freight trains. The main innovation of the model is to develop the new constraints for assessing the capacity of the siding tracks in the stations for all trains and other new constraints specialized for the passenger trains to be stopped in one station in order to let the passengers do their prayers. The objective of the suggested model is to minimize the total delays of passenger and freight trains for both directions. In order to assess the application of the model, three test problems are solved by Lingo software. Using this model, it is possible to complement the time-tabling for single-track railways automatically.

The transportation planning process for urban areas is typically based on partition of the area into traffic zones. In transportation planning and network analysis, it is customary to use centroid nodes to represent traffic analysis zones (TAZ). In order to load trips of each zone on the roadway network, each centroid is connected to the roadway network by at least one connector. Globally there are few studies examining the impact of connectors on traffic assignment, but all of them emphasize the importance of this subject. In this paper, the effect of selecting connector nodes on traffic assignment results is studied and a new method is proposed to select connector nodes. To implement the concepts presented in a real sample, City of Mashad, Iran, was selected as the case study. The proposed method in this study emphasizes the proximity of connector node to centroid and other criteria. This proposed method is compared with two methods from the literature. In the first method the only criterion is that the connector node must be close to the centroid. The second method introduces a measure of weight for all nodes and then selects connector nodes. To evaluate the three methods, results of traffic assignment were compared to observations of traffic volume on 87 selected links. Evaluation of results shows an improvement in the goodness of fit index of the proposed method of 3.78 and 22.2 percent compared to the first and second methods, indicating more precision in replicating real world observations.

Switches in railway tracks have discrete and complicated structures. Due to this, these points are one of the most dangerous parts of a railway track. As an operational and maintenance approach it is important to evaluate and predict derailment probability in these points. As a train-track interaction problem, this phenomenon is influenced by switch geometry, switch structure and dynamic characteristic of railroad vehicle like velocity and axle load. Therefore it is important to develop a new model that contains these factors and be able to predict vehicle derailment with reasonable accuracy. In this research, by using the sensitivity analysis in described parameters, a derailment model is presented. For this goal, dynamical modeling of the chosen both freight and passenger wagon in switch track using ADAMS/RAIL is developed and the effect of the switch geometry, switch structure and operational parameters of the vehicles are studied in vehicle derailment. With the help of the neural network, the optimum mathematical model that describes the vehicle derailment and effect of the main parameters is determined.