پژوهشنامه حمل و نقل
سال پنجم شماره 1 (پیاپی 14، بهار 1387)

People are usually involved with the phenomenon of road accidents, directly or indirectly. Estimations of the international organizations show that 75% of road accidents occur in developing countries, in spite of the fact that such countries only possess 32% of motorized vehicles. The cost of road accidents is a large proportion of transportation costs sustained by different societies. The cost of road accidents is composed of different elements, in which the cost of damaged vehicles constitutes an important part. In this research-work for the first time all existed information related to the type and pertinent characteristics of rural road accidents in Iran, were compiled and it was concluded that they are not sufficient for the calculation of the cost of damage to vehicles in such accidents. Therefore, additional information was needed. These were supplied by the analysis of raw data obtained from the police and insurance departments. The main three sources for the information used in this study, were: 1- Traffic and Transportation Department of the Law Enforcement Force, 2- Insurance and Assessment Companies, and 3- State Transportation and Terminal's Organization. Based on the said analysis, the rate of presence of different vehicles in accidents and also the severity of damage to vehicles were assessed. Then, through field studies and establishing the price of vehicles in both traditional and official markets, the cost of damage to vehicles in rural road accidents in Iran, defined in current Rials of the Iranian year 1383 (21 March 2004 to 20 March 2005), was estimated. Estimation phases include: 1-determining the average number of vehicles damaged in accidents, 2- determining the price of each vehicle involved in the accidents, 3- determining the damage inflicted to vehicles involved in accidents, and 4- analyzing the results of the former phases and determining the costs of damage to vehicles in rural accidents. Given the fact that the frequency of vehicles in the country's transportation fleet is not necessarily equal to their frequency of involvement in road accidents, extensive research was concluded in this study to determine the percent of involvement of each vehicle in the accidents. In order to obtain such information 1082 accident files from police and 2101 accident files from insurance were analyzed. The results show that the average number of vehicles in each rural accident was 1.89. The rate of average damage inflicted to vehicles in rural road accidents in Iran in this study, in comparison to their price, is calculated to be equal 18.7%. This is the most delicate and detailed calculation of such cost ever estimated in Iran. This cost which is 6196.7 billion Rials (US$ 673.5 million), corresponds to more than 0.5 per cent of the country's Gross National Product. Also it is seen that this cost is greater than total budget designated to the road construction and maintenance of the country's road network in year 1383 which was equivalent to 5121 billion Rials.

With the increasing demand for public transportation due to congested city highways and streets, the rail systems and especially metro have become one of the most viable alternatives for daily commuting. While city planners are excited with the increasing public transportation ridership, they are also challenged with a higher volume of passenger flow and longer queuing lines at the existing stations and of course, metro platforms.One of the most useful features for improvement of the current situation and plans for the future, is using simulation tools to help the planner to evaluate system operation design, queue management, fare equipment design and fare policy impacts, all in virtual and real world.In this study, co- ordination of headways between entrance of passengers to metro station, and arrival of metro trains that travel by fixed scheduling is proposed. The objectives for the study are development a simulation model to analyze the passenger waiting time of urban metro stations with other modes of feeder services. Urban metro system is characterized by its comparatively short headway and fixed schedules. Thus, the behavior of passengers in urban metro is significantly different from the behavior of passengers in intercity train or bus system. If the entrance of passengers from other modes likes buses, taxies, walking and etc. To metro station considered as a major feeder system for the urban metro, passenger waiting time and related behaviors of the urban metro station should be influenced by the reliability of train scheduling that the most important part is average headway between arrival of each metro trains.So, in this study by using simulation technique, a reliable simulation model for passenger and metro train that named as "METSIM Software", where designed.Results provide planners with an analytic model for accurately quantifying the relation between passenger waiting time of urban metro system and the reliability of other variables like headway of arrival metro trains due to fixed scheduling, passenger flow entrance rate from other feeder services to the station, fare policy and the equipment that presented at ticket hall for fare collection (like ticket vending machine, waiting in queue lines for buying paper tickets or credit cards, and ticket acceptance gates).By using statistical data collected fully one normal day from three lines and 30 stations of Tehran metro and running the program of simulation model for four hours (6:00 to 10:00 AM) of a normal day, the Mathematical Relations between passenger waiting time of the stations (w) and Average headway of trains (h) where dedicated and the ratio between these two parameters as an average of the simulation run time is determined by 0.6 in accuracy of 0.95 percent for the total Tehran metro network.

Safety is one of the most important issues of transportation systems, and new technologies and complex systems increased the need for a systematic approach. Safety matters have a vital influence on railway transportation, and interacting of factors such as manpower, electric and electronic devices, mechanical faces of locomotives and trains, civil engineering issues in the infrastructure, etc. all make a framework of uncertainty. Level crossing, the most dangerous place of the railway system, has a more complex condition, because it is covered by different type of people: The employees and the public. The second group makes it much more complex, because the factor is out of railway authorities control and they really face to the danger. As it clearly could be understood, assessing safety in this situation is a real hard work, because it is needed to manage issues with different roots in a single framework and synchronization of these factors is not a simple work. This introduction implies the necessity and importance of a criteria and framework which could manage the safety issues in such different faces.Risk, as a simple, easy to understand, strong and adequate criteria, could help us to assess safety issues in different places with a single method. Risk has a double hinges those shown undesirable event happens with witch frequency and witch severity. Therefore, in this research risk was selected as a decision criteria and a framework of tolerable rates was fitted to it. The tolerable rates show risk according witch conditions will be accepted or denied. Lack of national framework for this subject forced research team to determine a local framework for RAI.The second phase of research was designing and generating set of steps and diagrams which as a chain leads to assess the risks in the scope of study. The first step of the process, hazard identification in fact is a process of identifying, predetermining of frequency and severity, and rating at end separating the high rated hazards for further studies. The second phase of this process is causal analysis that includes recognizing roots of the hazard, deceiving their frequency of happiness, determining the chain of their relationship, and at end assessing the hazard occurrence likelihood. Consequence analysis, the third phase of research, is modeling and determining the scenarios which will be happened if the hazard really occurred. The output of this phase is set of consequences and their possibilities ratio. Now is the time for assessing the estimated loss in each kind of scenarios and aggregating them with regards to their possibility ratios which are assessed in the 3rd. phase. At the end of this phase, the risk is assessed and should be compared with tolerable rates. If it is not acceptable, risk mitigation process should be applied. Risk mitigation process will be used for unacceptable risks and its purpose is reducing or eliminating risk sources or decreasing their undesirable consequences. This phase includes two main steps: Option analysis and impact analysis. Option analysis with getting help from innovative methods tries to find a new solutions and methods and its output is the list of options. The impact analysis phase tries to select the best option according to the criteria of risk reduction and cost analysis.Appling the process in Garmdarreh_Level Crossing exhibited that risk could easily demonstrate the safety state of a system and also it showed how modeling and generating causal and consequence charts can help researchers to more easily and more reliable find a solutions and options for reducing risks. The application also shows that the process capability completely covers all the hazards in the scope.

Train movement on the railway tracks causes dynamic loads and impact to the track, stress and deformation to the different elements of the tracks and vibration, etc. Since, the defects of the track structure and its components depends directly on the dynamic response, stress and deformation of the track, it naturally cause amplification.The main important types of ballast defects are ballast settlement, smash of ballast and hardening of ballast layer. The effects of deterioration of ballast on dynamic response, stresses, and deformations of track components, can be simulated by a real train-track modeling. When the ballast is not in a good condition, sleepers provide a small support. This situation can usually be seen on the railway lines. When the ballast undergoes deterioration, the sleepers suspend from the rail. This situation usually speeds up the deterioration of the track and for example, it can create surface corrugation of rail, damage or brakeage of fastenings, loss of elastic characteristic of rail pad, crack in the sleepers and uselessness of the ballast layers.Grassie [1], has analyzed a 150cm suspended sleeper on an elastic bed by the method of continuous beams, also complementary studies have been carried out by Dalburg [2] with regard to its effects on dynamic behavior of track components. He has considered the effect of unfilled distance between the sleeper and the ballast in his dynamic model and has investigated the increase of interaction forces. Also, Gaoliang [3], has implemented the train-track dynamic modeling in his investigation for replacement of sleepers in high speed lines. Hence, if when replacing a new sleeper with an old one, the track is not tamped, in reality, the replaced sleeper is suspended. It has been tried in this paper to investigate the dynamic behavior of such sleepers in the whole structure.Due to the fact that in the Iranian railway and in particular in districts such as North, Lorestan and North-East, the problem of rail corrugation, suspended sleepers due to the age of the track or replacement of sleepers, wear of the rails and deterioration of ballast exists, this paper has carried out a case study on the North-East railway district, considering the superstructure with UIC60, good and poor quality of ballast (in some section of the line), Wooden and concrete sleepers with a high speed trains of up to 160 Km/h. For this purpose a suitable model of a track with suspended sleepers has been considered and variation of rail-wheel interaction contact forces, acceleration, vibration and displacement of rail-sleeper and ballast has been investigated. The elaborated model is of a discrete supports with one suspended sleeper. The mathematical model of the track was developed through the former model [4,5], in order to undertake the possibility of suspending the sleepers.In normal situation, the track components dynamic's behavior, takes place by modeling of rail in the form of continuous beam on discrete elastic support. In practice, sometimes due to deficiency of the track bed or the ballast layer, sleepers supports do not perform well, which is termed as "loose sleeper". In this article, mathematical model of the track consisting of several suspended sleepers has been developed. According to this model, equations of motion for the track-train has been formed by considering non-linearity of wheel-rail contacts and has been solved by numerical integration in time domain. Dynamic response of track components with harmonic excitation source has been investigated. From the results it can be seen that, intensive vibrations, would cause an increase in wheel-rail contact forces, e.g. harmonic excitation of 0.4 amplitude and wavelength of 240 mm on the rail (measured in North-East railway district), shows an increase of 25.5% in contact forces (for trains of 160 Km/h) and 74% in vertical displacement of the rail. Also the results showed that; lack of one sleeper on the track would act as an excitation source and would cause irregularity in vibration (vibration acceleration, vibration velocity) for railway track superstructure components.

Retaining wall is one of the structures that have being used extensively in road and railway networks. Over time, the classical gravity walls transitioned into cantilever reinforced concrete types. A paradigm shift occurred in the 1960s with the advent of Mechanically Stabilized Earth (MSE) masses, i.e., reinforced layers of soil allowing for modular construction. The reinforcement was initially steel straps, and subsequently welded wire mesh provided an alternative. By the 1980's the MSE technology used polymeric reinforcement like geotextiles, geogrids and other polymer straps. As geosynthetics have many advantages (certainly reinforcement and drainage), nowadays designing and implementing of such retaining walls grows rapidly up and more attended.Applicability Study of Geosynthetic Reinforced Soil Walls gives an opportunity to evaluate technical and economical issues of these walls, analyze reliability of their internal stability and investigate environmental effects on their structures. This paper (based largely on Golestan special road study) will present a comparison of technical notes of different types of retaining walls, and then follow with their reliability analysis about internal stability of geosynthetic reinforced soil walls. It will then present economical analysis and compare cost data of building different retaining wall such as gravity walls (masonry block and concrete), cantilever reinforced concrete and geosynthetic reinforced soil walls. Finally it will study applicability of implementing this process for Golestan special road. This process and some results of this research will be given as follows.Comparird to gravity or reinforced concrete, geosynthetic reinforced soil walls are more flexible, and have the ability to absorb the earthquake forces much better. They can support more displacements than other wall types, so usage of them on soft soils, in areas with high possibility of earthquake and also for high height embankments are suitable and have cost effectiveness. In other part of this research, authors take economical analysis to compare results as which type of wall and in which height has alternative benefit. After examining site plan of study case base and detecting designing parameters, the denoted retaining walls were designed, then the total cost of their construction were computed and the results were illustrated in a chart. Comparison of illustrated cost data shows that cantilever reinforced concrete walls are by far the most expensive, with gravity walls (masonry block and concrete) significantly less expensive. Note that gravity walls are rarely over 6 meters in height. This limitation first comes from their high mass weight and earthquake considerations. In the other hand, supporting materials would be difficult. It is also obvious that in height between 6-10 meters, geosynthetic reinforced soil walls are the least expensive of all wall categories. Nonetheless in height less than 6-m geosynthetic reinforced soil walls have better reaction to variation of displacement and take less affect under lateral forces such as earthquake loading. By comparing economic surveys, it becomes appeared that geosynthetic's prices have a significant effect on the total cost. So if our manufactures produce these materials in the country, total cost of geosynthetic reinforced soil walls will be decreased.Last step of applicability study is considering the impact of environmental and natural issues on walls serviceability. Some of the degradation properties include sunlight (ultraviolet radiation), temperature, oxidation and hydrolysis, chemical, radioactive and biological degradation. There are several environmental issues that affect such walls, but in this certain area, floods make critical situation for wall's structure. Floods moved huge stones to wall face and soil layers may be scoured. As results of this paper reflect, geosynthetic reinforced soil walls, although, have economical benefits and its reliability is acceptable, their sensitivity to environmental issues caused not to take them as alternative to avoid golestan special road oppose concerns.

Recently, a significant increase in demand of airports caused many problems such as resulting in delay and wasting economical costs. Then, for preventing these problems, optimal use of runways is one of the best ways for complete use of available resources. Runway Operations Management is related to increase in utility of using the available runways that are bottlenecks in many airports. The main task of Runway Operations Management is: Runway Configuration Management, Runway Assignment Management and Runway Operations Planning that are assumed in this paper. A model have been developed for determined configuration due to the runway configuration for airports at any time of the year. It should be noted that airport capacity is mostly expressed as sum of landing and take off operations. Current and predicted levels of air traffic demand, raise the need for airport capacity enhancements, as well as reduction of the environmental impact (engine emissions) and the costs incurred by operational inefficiencies (fuel burn). In an effort to satisfy such a need, the presence of an automated decision support system, which includes planning and control algorithms, will be a significant contribution.One of the ways of runway capacity enhancement is increasing their numbers. Constructing of new runways is not possible because it imposes heavy costs and requires occupying urban lands. Moreover, increasing the number of runways without optimum operations planning and assignment will not be undertaken completely. Using which runway, for which operation, in which time plays an important part in the runways system capacity. For example, in an airport with the single runway, the following parameters have their own influential rules in determining operations planning: configuration of runways, arrival and departure volumes, volume and place of fixes in a time, place and number of apron gates, place and number of taxiways and exit rapid taxiways, mix of aircrafts, etc. An increase of the number, geometric complexity, runway’s orientation and location, runway crossing points and final approach of runways, workloads of the controllers is so important that without optimum operations planning and assignments, most of the capacity of the runways and ultimately the airside capacity, won’t be used. In addition, strong delays, wasting of economic resources and dissatisfaction of the airport users, among the passengers and airlines, are of the other consequences.This paper presents a procedure for considering Runway Assignment Management and Runway Operations Planning together which were considered separate till now. A scheduling model was used for this analysis which indicates a good efficiency in integrating Runway Assignment Management and Runway Operations Planning.

Capacity and delay are two most important measures in the evaluation of non signalized intersection’s performance that have been widely used in traffic improvement projects and transportation network assignment models. Because of the close relation between driver behaviors and traffic regulations with the Investigation and computation of delay and capacity in non signalized intersections the analysis of these intersections are so sophisticated. The purpose of this research is to adapt the state of the art algorithm used in HCM 2000 with Iran’s situation with respect to the gap acceptance behavior of the drivers in Iran. The data achieved from several field observations on the intersections of Tehran have been used to calibrate the gap acceptance used for the capacity and delay estimation model. Using developed countries design and operation manuals in developing countries without modification would give misleading results.

Dynamic assessment of structures is used for a variety of reasons including damage detection, seismic assessment, condition monitoring and etc. In the civil engineering field bridges are strategic structures. Dynamic assessment of large structures such as bridges usually requires high levels of energy input to excite relatively low frequency responses. In general, the excitation methods fall into the main categories of ambient and impact vibration. In the ambient excitation method, amount of force to the structure is not directly measured. But in the second method, measured-input excitations are usually applied at a single location where the force input due to impact to the structure can be monitored.This paper considers an alternative method of introducing an impulsive force to a structure by the use of two proprietary designed hammers. These hammers are used for excitation of beams, slabs and bridges.