JOURNAL OF TRANSPORTATION RESEARCH
Year:2009 | Volume:6 | Issue:2 (19)|Papers Count:8

Better accessibility is one of the most important effective factors in making decision about allocating and distributing a form, space and activities. In fact, as access is considered as a valuable factor, "activities setting" and "population settlement" are affected by these factors as two key components effectively and a spatial structure of a city is exposed to change . It means that the urban functions and activities put at points that the access is caused a more easily. People also consider this factor as a factor effecting on making a decision to select their settlement place. But it must be mentioned that in a spatial structure of a city, its center has a unique feature that from geographical point of view it is the most equivalent area and town center and from a functional dimension point of view has very much focus on activities, and accessibility subject is faced with a much sensitivity. Hence, we can expect that with improving and disturbing an access quality in town center, the effect of this factor on two components of "activities setting "and" population settlement" is appeared more evident and sensible to other town areas. Man has challenged during history to rise access to goods, places, etc… and spatial and physical situations of a city are also affected by any evolution in this field. Particularly, it was exposed to change using a new vehicles, construction, texture and size of cities. In this case, it was carried out many efforts in the field of cognition and using a land use relation (activities setting and population settlement) and transportation from second half of 20th century. But most performed studies have been paid to land use effect in producing trips and one side of effect of land usage planning has been reviewed on a transportation planning and the reflection of effectiveness of policies and decisions making has been ignored in the field of a transportation planning on a land use planning. From 1950's, with expanding a systematic attitude, this relation has been reviewed in return.Therefore, we can state that as the access requirements facilitation affects on a spatial and physical development of a city, the reverse requirement of this issue (access restriction making) can also act as one inhibitor factor and/ or changing factor of development trends.In this article, in addition to theoretical clarification of issue according to Edmond Biken theory that "People's decisions make a shape of a city", the outcomes of access restriction making on people's decision for selecting their activities place and settlement and finally the reflection of frame and spatial works of this type of decisions are reviewed in a shape of a city.In this framework, according to the initial question during a study process and using a scientific method, one analytical model was formulated for reviewing the existing requirements of Tehran center so that from this way the spatial reflections of access restriction use (Traffic ban area plan) are reviewed in Tehran center. On this basis, the effectiveness of access restriction on activities setting pattern and a population settlement pattern have been formulated and tested in the field of two assumptions for researching about the desired issue.The extracted information of commercial institutes and companies turnover and statistical records (as an index from activities setting pattern) and also population data of Tehran metropolitan city accompanied by the extracted information from an opinion polling questionnaire in the studied scope (as an index of population settlement trend) have been analyzed at the framework of research analytical model. The results show that the access restriction use as one sole policy of traffic along with other effective factors have tended to change activities setting pattern and a settlement of part of population and have followed the attenuation of town center.

Fiber Reinforced Polymer (FRP) materials are increasingly used to strengthen and retrofit of RC structures. Their high stiffness and strength-to-weight ratio, resistance to corrosion, and easy handling and installation are making FRP jackets the material of choice in an increasingly large number of seismic retrofitting projects, despite the relatively high material costs.FRP jackets provide lateral confinement to concrete which increases the strength and ductility of piers. Several empirical models are available that predict the compressive strength and the axial strain of confined concrete using FRP sheets. Comparing the models with available empirical data indicates a considerable stage of uncertainty. In this paper this uncertainty is predicted and taken into account in reliability analysis of FRP-confined piers. Based on analytical results, some recommendations are suggested to modify the strength reduction factor for design of confined piers so as to ensure the same level of reliability as for unconfined piers. Also a suggested relationship between the reduction factor and the ratio of confinement for FRP-confined piers in axial compression and axial compression with flexure is proposed. As a final approach, the effectiveness of parameters such as ratio of reinforcement, ratio of live to dead load and ratio of eccentricity have been studied.

Backcalculating layer moduli, using the deflections measured by the FWD (Falling Weight Deflectometer) device, is the basis for structurally evaluating pavements when considering maintenance and rehabilitation options. Many algorithms have been developed to perform the backcalculation.Classical pavement- subgrade system analyzes is based on multi- layer linear elastic analysis, infinite pavement layer dimensions and a semi-infinite subgrade. Linear elastic response assumptions are valid when there is no discontinuity, for example at joints in rigid pavements, or cracks. The assumed static loading conditions are also a simplification of reality.The duration of loading runs from 20 ms to 65 ms depending on the type of FWD device. The FWD provides excellent structural information if it is fully utilized. From a review of the sensor peak values for each measurement location, it becomes clear that points farther from the center of load plate attain their peak values later than locations closer to the plate. This time differences are known as phase difference of deflections and are measures of the velocity of propagation of the shockwaves. These types of time history data contain useful information that if well utilized would contribute to improved accuracy of the structural pavement evaluation. The use of only peak values discards this potentially very useful information. Most of the common backcalculation programs with elasto-static basis use an elastic layer program for forward analysis and an error optimization algorithm. In this study, the programs MODULUS6.0, ELMOD5.0, and EVERCALC5.0 have been used to perform traditional back analysis.The DBSID program, which is based on the system identification methods, was also employed for the dynamic backcalculation. System identification methods were developed by electrical engineers who were interested in determining the characteristics of a filter by using the input and output signals of the filter and an assumed model of the filter. The characteristics of the filter are changed systematically using a search technique until the model produces an output that is acceptably close to that of the filter. The procedure is in fact exactly analogous to what is being done in backcalculating the moduli of pavements. An impulse load is applied to the pavement at a remote distance; and the surface motion is sensed as signals received by two sensors, which are separated by a distance, x. the pavement between the two sensors is regarded as the filter, the characteristics of which are to be determined. The unknowns in each layer are its modulus, percent damping, thickness, and unit weight.In this study, the results of soil mechanic tests for subgrade layers have been used as a “ground-truth” to compare with the moduli values derived from the FWD data and the ones suggested by the laboratory tests. The elasto-static programs terminate when the convergence condition between deflections is satisfied. The Root Mean Squared Errors (RMSE’s) higher than 5% were not accepted. Reviewing the results is always necessary because every predicted modulus may not be acceptable. For example, the moduli which are equal to the lower or upper limit of the acceptable range are difficult to justify given the known quality of the materials.In EVERCALC program, it was found that moduli convergence usually happened earlier than deflection convergence. So the program was rerun by changing the moduli range to achieve the best deflection fit.The DBSID program tries to create the best fit between measured and computed deflection time histories. The surface moduli are most dependent on the deflection measured at the sensor in the middle of the load plate (W1 at 0 inches), so in the final evaluation, not only the RMSE have been considered, but also the peak error at the W1 sensor.In most of the DBSID output files from the different sections on the Zanjan-Tabriz highway both RMS and peak errors were high. The time histories of the measured deflections also had irregular shapes. These output files were excluded from the final conclusion.The results were classified in scatter and bar charts. Lastly, the results (the predicted moduli) of all the four programs were compared with each other and with the expected values which were extracted from the soil mechanic tests.In the end, by considering all the defined criteria, MODULUS6.0 is suggested as the most appropriate program for the cases under study.

Traveling Salesman Problem (TSP) is one of the most well known and applicable problems in combinatorial optimization that transportation makes up the most notable applications of the problem. Its definition is simple and clear while its solving is very hard. In the classic TSP, a salesman wants to find the cheapest way of visiting a number of cities in which each city must be visited exactly once. The TSP can be symmetric or asymmetric. In symmetric one, the distance between each two cities does not depend on the direction. The classic TSP is also known as finding the shortest Hamiltonian tour. In addition to the classic TSP, which is defined so far, the problem has numerous variants from which we can mention traveling salesman problem with time windows, period traveling salesman problem, selective traveling salesman problem, moving object traveling salesman problem and so on.The importance of the TSP lies in two aspects: theoretical and practical aspects. In theoretical aspect, because the TSP is one of the first problems that its NPCompleteness has been proved, i.e. there is no algorithm to solve it in polynomial time; it has become a test bed for new algorithmic ideas. In the practical aspect, its simple definition has resulted to many direct or indirect applications in different problems of various domains like transportation, production planning, and bioinformatics. In transportation domain, as our attention. General routing problems generally deal with transporting of customers/commodities on a given network using an optimal method, from which, we can mention the distribution of services/commodities from depots to customers, vehicle routing problems, production and distribution planning and so on. These problems occur in operational management while the classic TSP is the core of most of them. In fact, although the TSP has direct applications, we can also mention indirect applications of the TSP in many other problems like the vehicle routing problems, crew scheduling, and train scheduling. Because the physical costs of distribution make up a considerable amount of the total distribution costs in each economy, any reduction in these costs through improved solution methods and algorithms of routing problems results in 16 great savings and benefits to the final customers. So, in this paper we develop a successful solution method in solving the TSP and then apply it for the first time to 360 selected cities of Iran to find the shortest Hamiltonian tour. The cities had been chosen based on their economical and political importance. As a solution method, among numerous exact and approximate ones, a new combination of the ant colony system (ACS) and the local search is used. Ant algorithms with inspirations of real ants' foraging behavior are competent in solving hard optimization problems while using a local search can lead to better results. In other words, the ACS section of the proposed algorithm is rather responsible for searching the solution space while the local search part refines the search and directs it to the most promising regions by locally optimizing the solutions of the ACS section. To check for quality of the solutions, results are compared to the results of the well-known ACS. This comparison shows the complete superiority of the suggested method over the ACS. These results also can be used in future for other comparisons of different solution methods for this problem.

The geometrical shape of wheel and rail profiles are some of the most important parameters affecting wheel-rail interaction in the area of elastic contact. Contact conditions have direct effects on the wear of rail and wheel. There are main restrictions in traditional methods, like Hertz Theory, calculating two-body contact parameters in specific case of rail and wheel, so this paper studies this case by an FEsimulation model made by ANSYS. In order to verify the model, the results are compared to those of two other models which are an ABAQUS model and the Iwnicki’s 2003 model. In addition to wheel-rail contact modeling of new rail, the worn rail is modeled. Also, by using a lateral force, the contact patch in a curve is modeled in different wheel-rail contact points.Significant differences between the FE and the Hertz Theory can be observed. The results show preference of non-conical UIC wheel profile (like ORE-S1002).

Airlines are faced with some of the biggest and hardest scheduling problems known. For example, one major US carrier periodically schedules about 2700 flights per day to over 130 cities, using more than 400 aircrafts of 14 different kinds. Flight scheduling is one of the major problems for any airline company. This problem has been investigated as an optimization problem for many years. Usually, the flight scheduling problem is divided to a number of sub-problems, and fleet assignment is one of them. In this problem, given a flight time table and aircraft specifications, the type of aircraft is determined for each flight or the fleet assignment problem is the problem of assigning the right aircraft type to the rights in the timetable, while minimizing costs and satisfying various constraints. A lot of money can be saved if the right aircraft types are used. For example, in 1994, Delta Air Lines estimated that the use of a newly developed fleet assignment system would yield savings of up to $300 million over the following three years. The trade off between different aircraft types is that with a larger aircraft, more passengers can be serviced, and thus more income is generated. On the other hand, a larger aircraft consumes more fuel and is generally more expensive to operate. The fleet assignment problem (FAP) in air transportation consists of assigning fleet types to flights of a given flying schedule while respecting feasibility constraints and maximizing expected profit. Expected operational costs can be quite accurately expressed as a linear function of the FAP decision variables. The same cannot be said of expected revenues. Future revenues depend mainly on future travel demand. A particular fleet assignment (FA) then affects revenues through capacity limitations. Hence, when one expresses the expected profit as a linear function of the FAP decision variables, it is implicit that it is based on demand forecasts and that this linear function is only an approximation, a tool whose efficiency is to be judged on the profitability of the FAs found by the FAP solver. Because of this tight economic link, the fleet assignment problem is often connected to a revenue management system, which gives information about that is the best aircraft type for an individual flight, from a purely economic point of view, considering the booking situation and other things. But if the best aircraft type for each individual flight is already known, then what is the problem, you might ask. Just assign the best type to each flight, and the problem is solved. But this is obviously a typical example of a way in which one problem in a sequential solution procedure can ruin the possibilities for the following problems. It could for example mean that an aircraft would have to make a large amount of flights without passengers, so called deadheads, to operate its flights, because they are scattered geographically. This is likely not a very good solution. In recent studies, the fleet assignment problem has been modeled as a multi-commodity network flow problem with integer and real variables, and solved by conventional methods. In this research, we modify one of the existing models for domestic airline company and use Genetic Algorithm (GA), Simulated Annealing (SA) and Ant Colony Optimization (ACO) to solve it. These algorithms were implemented for the fleet assignment problem and used to solve a sample problem. Comparison of results of solving the sample problem by algorithms and GAMS software indicates that, GA, SA and ACO have good capability for solving the fleet assignment problem.

Recognition of weather events has great role in decreasing road accidents and road Maintenance costs. During recent years the role of atmospheric conditions in road safety, winter road maintenance and environmental impacts have been of great importance among researchers. Knowing the starting and ending time of snowfall is important in winter road maintenance management, safety acts of police, and more preparedness of drivers and all related to transportation systems. In this paper, based on statistics of 119 meteorological stations, we have determined probability of starting and ending of precipitation. Starting of snowfall in Iran depends on elevation, latitude and environmental factors, so that on Albors, Zagros, Khorasan and Azerbaijan mountainous regions, starting time of snowfall is usually November, however very high mountainous regions may have snowfall in October. Based on the map of distribution of special and temporal ending time of snowfall in most of mountainous regions, this event will be continued up to May. Therefore starting and duration of winter road maintenance in Iran would be determined based on analysis out puts. Finally may statistics in the country may be examined because of the importance of studying weather related road accidents (Road accidents accompanied by precipitation). In this research we have used road accidents statistics related to safety and traffic section of The Iranian Road and Transportation Organization in the period 1990 - 1998. Determining the spatial and temporal distribution of each effective factor in accidents are other objectives of this paper. As a result, the maximum number of road accidents in rainy conditions have occured in Fars, Kohkiloye va Boyer Ahmad and Hormozgan provinces. In snowy conditions most of road accidents have occured in Charmahal va Bakhtiyari, Zanjan and Tehran provinces.

In recent years, traffic accidents have been the ninth cause of fatalities in the world and the second in Iran (after heart diseases). Many individuals suffer financially from traffic accidents or lose their lives every year. Traffic accident analysis, as a powerful tool, can give valuable data regarding the cause of accidents and appropriate solutions. Such analysis would be possible at two levels; the "project" and the "network". In this paper, the analysis has been carried out at "network" (provinces) level to achieve a proper approach to increase the macro management abilities for the presentation of classified approaches appropriate to the conditions of each district. Because every province is unique, regarding driver behavior, infrastructure conditions, precautionary measures before and relief measures after an accident, classification of similar provinces for the purpose prioritization of safety measures and necessary decision making to reduce the number of fatalities in accidents deems necessary. Also, group study of similar condition provinces helps decision makers to provide similar measures for the solution of safety problems. "Cluster Analysis" is a method used for the purpose of classification. In this study, cluster analysis, using six methods, has been carried out for all provinces, on the basis of accidents data in 2004, obtained from Legal Medicine Organization (LMO). Necessary variables required for the cluster analysis, were obtained through the study of accidents data epidemiology and contain eight major groups called number of fatalities, gender, age, education, occupation, place of death, user situation and final death cause (totally 64 variables). The analysis was done in 4 clusters and the results were validated with help of "Chernoff Faces Method". The results obtained reveal that some provinces maybe classified under one group, but some other provinces, like Isfahan, need special studies.