فصلنامه مهندسی حمل و نقل
سال ششم شماره 4 (پیاپی 24، تابستان 1394)

The aim of this paper is to manage the train disruptions in block sections as well as stations to reach the desired reliability. It is necessary to note that in the case that the disruptions are not absorbed, the delays propagate from one train to the next one. Therefore, absorbing the disruptions is an important issue. In the classical method to define the buffer times in operation plan studies is to consider 5 seconds for each kilometer. In this paper, it is aimed to compute the exact amountof buffer times and locate them in convenient parts of timetables. To that end, a new mathematical model based on fuzzy approach is proposed to compute the buffer times. Moreover, the lower and upper bounds of fuzzy limits are determined by some new methods as well as a heuristic algorithm. Finally, to illustrate the applicability, and analyze the performance of the proposed method, some random examples as well as an Iranian case study are analyzed and the results are reported. The final results shows that by this new method the required buffer times are defined more precisely and consequently the computation of required number of trains as well as the number of parking lines can be done more accurate and reliable.

All-day events and accidents occur frequently in various parts of transport that it has a high cost. In the aviation industry due to expensive facilities and equipment, costs arising from accidents would be highly salient. Over fifty percent of aviation accidents, incidents of airport rampby various factors is occurs (which is the main cause of human error). The purpose of this study is to provide a model to predict project in Airport Ramp Accidents and the impact of each factor in the accident show to preventative work to be done to reduce and minimize accidents. The case study is based on data from the years 1386 to 1389 are in the airport and the general, neural network and fuzzy regression model have been used. The models are calibrated and analyze and the two variables "number of small aircraft" and "average age of planes," ", respectively, with coefficients of 0.34 and 0.29 were identified as major contributing factors in accidents and preventive strategies in this regard arises.

This study aims to predict the pedestrian accident severities and affecting factors in rural roads. An ordered logit model was applied for analyzing the factors affecting the death or injury of pedestrianaccidents in Tehran province rural roads during years 1388 to 1390. More than 50 variables were selected for describing the dependent variable. Further analysis on these variables showed that variables such as driver characteristics; time of accident; the vehicle involved in the accident; pedestrian role in accident; distance from the nearest police station; the cause of the accident scene; and the number of vehicles involved in the accident are significant in model and should be considered for predicting model. The results indicated that the type of vehicles involved in the accident, location of accident, time of accident and pedestrian guilt have a significant role in the severity of pedestrian accidents. Finally, with respect to nature of the studied variables, recommendations were proposed for enhancing the safety of pedestrians crossing thepedestrians crossing the road in Tehran province rural road.

Reinforcement of asphaltic concrete by fibers is one of the methods for improving its 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 1 mm 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 0.4% of 10mm carbon fibers. The moisture damage increases with increasing the fiber content and length.

Moisture damage or stripping is one the fundamental defects of asphaltic surface layers. Moisture damage has great effect on other defect types of asphalt surface layers. Generally, Moisture damage is loss of adhesion between asphalt binder and aggregates or loss of cohesion in asphaltbinder structure. Since hot mix asphalt is made of different components, performance improvement of each component will result better resistance against moisture damage effects. However, weight of asphalt binder as one of the components of hot asphalt concrete is not high, but hasmajor effect on the better performance, durability and stability of asphalt concrete mixtures and any change in asphalt binder performance has remarkable effects on the asphalt concrete performance. Nowadays, modifiers are used for modifying asphalt binders and upgrading its performance. Nanoparticles include Nano-clay are one of the modifier types that are used for modifying asphalt binders. Because of layered structure, Nano-clay would enhance performance properties of Nano composites. In this research, two types of Nano-clay is used for evaluating their effects on the Moisture damage resistance of asphalt concretes (montmorillonite CA and CB). Marshall Test, boiling texas test and image processing are used for un-compacted samples as well as moisture damage test (AASHTO T283) and resilient modulus test are used for compacted samples containing 0, 2, 4 and 6 percent of each Nano-clay modifier. Results show that asphalt concrete has better resistance to moisture damage by adding Nano-clay modifiers.

Every year, road traffic accidents cause direct and indirect loss in gross national product in every community. The present study aims to provide a methodology to estimate the costs of road accident fatalities in Iran. In this research, using different available methods namely the “Court Award” and the “Lost Product”, the average costs of individual road traffic fatalities have been determined, separately. The annual road fatality rate in the road network has also been estimated using 12 ARIMA(3,0,0)×(1,0,0) model of time series. Combining the each separateestimate of road fatality cost with the number of road traffic fatalities in a single measure, two measures of lost in gross national product due to road fatalities have been estimated. Finally comparing the results with the observed number of fatalities for the next years, the two methods of fatality cost estimation have been compared in terms of validity. In other hand, used method is statistical economic. Analysis of road accident fatalities by the “Court Award” method shows a descending trend of loss in gross national product followed by an ascending trend, during 2010 to 2012. Application of “Lost Product” method of road fatality cost estimation on the same database however, indicated a totally descending trend. Finally and Comparing the estimates of the two methods inferred that the “Lost Product” is a more promising method in estimating the gross national product loss due to road traffic fatalities, since the lost amount in this method remains proportional to the number of road traffic fatalities.

Transportation planning studies are generally based on dividing the study area into a set of traffic analysis zones (TAZ) based on a set of rules. Each zone is then represented by a node named centroid, which is assumed to be the origin and also the destination of all trips of that zone. Considering the sensitive and focal role of the location of centroids on traffic assignment results due to this rather big assumption which may cause large errors in results, very little research is found in the literature. Due to this research gap in this field, the current paper tries to analyze and examine the impact of centroid location on traffic assignment results. The traffic assignment applied is that of Wardrope’s user equilibrium (UE) principle implemented in VISUM transportation planning software package and the quantitative measures are those of hourly flows on different links of thetransportation network. Predicted link flows for different scenarios are compared to the observedflows on the same selected links. To discuss and analyze the implementation challenges, the real sized network of the second largest city of Iran, namely the city of Mashhad is selected as the case study. Three different methods for selecting centroids are presented to analyze their impacts on link flows. For each method, two different scenarios of choosing connector nodes are presented: in the first scenario, number of connector nodes is variable for different zones but their locations are fixed for each of the three methods. In the second scenario, having chosen the centroid according to each of the three methods, the closest node to the centroid is selected as the connector node. Results of this research, based on the comparison of predicted and observed flows on 87 links of Mashhad transportation network, show that for the assumptions of this case study, changing centroid location can cause a change in the coefficient of determination of the linear regression line of predicted-observed flow links of 1.7 percent in the first and 20 percent in the second scenario of selecting connector nodes. This noticeable impact in a real case with realistic assumptions can be considered an important confirmation of such research and also the need for further research in this rather unattended field.

In structural evaluation of asphalt pavement using FWD device, the depth temperature of asphalt layer was measured to analyze deflection data in reference temperature by means of correction coefficients. In addition to direct measurement of the temperature during the test, also some models were developed to predict asphalt layer depth temperature. AASHTO graph and Bells model are the most common of them. The main goal of this research is to evaluate Bells model to predict the asphalt layer depth temperature. So, 10 pavement sections of Kerman and Khuzestan provinces were selected and the temperature was measured in half and one-third depth of asphalt layer and also required data were gathered to use Bells model. To comprehensive evaluated of Bells model, various asphalt layer thicknesses of old and new constructed pavements were considered and depth temperature was measured in every 30 minutes of day. Linear regression analysis of Bells model versus measured depth temperature with R2=0.85 indicated that Bells model need to calibration to increase accuracy. More evaluation specified that the main reason of R2 decreasing in selected sections was the existence of new constructed asphalt pavements because determination coefficient of depth temperature based on Bells model and measured temperature in old pavements is equal 0.96. So Bells model for new constructed pavements was calibrated and corrected model was presented.

Every year, a large volume of waste materials are produced in the world, however a very small part of it take place in recycling and reusing. Recycled Asphalt Pavement (RAP) is a waste material which may have undesirable influence on its environment. Considering these materials reported characteristics, there have been introduced different strategies to reuse RAP’s. One of these applications recently noticed by the researchers is using RAP’s in cement mixtures such as concrete.As RAP is mainly gathered from roadsides and highways, so it is desirable to use them in common mixtures for roads pavement construction. Hence, Roller Compacted Concrete -a concrete mixture with unique features such as ease of application and low costs - was selected as basic mixture. In this research, after introducing two mixing ratios with two designing strengths, replacing a part of aggregates with RAPs was carried out in three states: 1-with fine and coarse aggregates, 2-with just fine aggregates, and 3-with just coarse aggregates, with ratios of 0, 10, 20, 40, and 80 %. Then, in the next step regression models with acceptable correlation coefficients were presented for prediction of compressive strength as well as allowable percentages of RAP aggregate to use in theconcrete. Valid using other types of RAPs was another work conducted in this research.

In the rail fleet Sizing problem, it is aimed to determine the optimal number of each vehicle type in transportation fleet, while optimizing system objectives. This issue has been investigated as a single-objective problem in the context of rail transportation with the assumption of homogeneity in the fleet, despite the existence of different goals in real systems. In this paper, a dual objective function is adopted after studying real-world consideration. According to the experts at the IslamicRepublic of Iran Railway Company (IRIR), reduction of the number of delays in response to requests during the course of planning is an important additional objective function, which is included in our model. The solved problem is dynamic and demands for wagons and the transportation times are assumed to be deterministic. In this paper, after presenting the mathematical model, the importance factor of each objective function is calculated taking into account theprescriptions of the experts at the IRIR Research Center and based on aggregate weighting method. In order to solve the model and find the solutions on the Pareto front, three methods based on Genetic Algorithms, Simulated Annealing, and a hybrid of those are designed and their parameters tuned, by which the rail transportation system of the IRIR is solved and the results are discussed.

Different factors affect the skid resistance of asphalt pavements. One of these factors is pavements surface temperature. Although several researchers have tried to evaluate the effect of this parameter on skid resistance of asphalt pavement, no specific result has yet been presented. In this article the effect of pavement surface temperature on skid resistance of different asphalt mixtures have been investigated. To perform this, laboratory approach was used. Four types ofasphalt mixtures including Hot Mix Asphalt, Stone Mastic Asphalt, Steel Slag, and Porous asphalt were heated in oven and their respective skid resistance value were measured in different temperatures, using a British Pendulum Device. Results indicated that skid resistance of asphalt mixturesdecreased as heating temperature increased.

Track stabilization is an indispensable issue in railway track construction within the initial months of track operation. Construction of rail track on soft and compressible formation soils causes pore water pressure to prolong the consolidation time. The passage of heavy haul trains with considerable imposed trainloads over such deposits causes excessive track settlements and significant reduction in the load bearing capacity of the track. It causes deferment in track stabilization. These deformations lead to less safety and stability of railway track systems. As a result, track maintenance will become a challenging concern. This paper presents a proper model of prefabricated vertical drains to be installed in heavy hauls. This model facilitates achieving to a proper degree of consolidation in an optimum time. In this regard, a finite element analysis was carried out to analyze substructure and superstructure of railway heavy hauls. Parameters including subgrade total consolidation time, subgrade degree of consolidation and track’s total settlement have been derived. Consolidation time for subgarde with prefabricated vertical drains has been also established. The number and distance of the prefabricated vertical drains per unit length have been determined. Furthermore, the optimum length of each drain has been identified taking advantage of sensitivity analysis on stabilized track subgrades with different lengths. Finally, a model,including the number, the distance and the length of drains has been proposed in order to install in heavy hauls.

The purpose of this paper is to evaluate the spatial accessibility of bus rapid transit in Mashhad metropolitan based on access to the system and access to three separate activities (hospitals, parks and libraries) through the system. In particular, the distribution of accessibility patterns was evaluated in relation to different socio-economic strata. The research method is descriptive analytical, and to assess two dimensions of access are used the service-area function within network analyst and the Hansen gravity model. Findings indicate that the wealthy strata have the highest walking access to the bus rapid transit and the poor strata are at the lowest level of walking access. Access scores to each of the activities through the bus rapid transit are largely influenced by the spatial distribution and Target gravity. Generally, levels of access to hospitals and parks are minimized and access to the library is more balanced. But surveying the accessibility status of all three activities indicates that access scores of 87 percent of all strata are lower than average.