پژوهشنامه حمل و نقل
سال دوازدهم شماره 4 (پیاپی 45، زمستان 1394)

Stone matrix asphalt is one of the solutions for rutting used worldwide. By providing stone on stone contact, the coarse portion of this type of mixtures bear the loads of axles and transfer them to the lower layer. The mixture of fine aggregate, filler, bitumen and additive including fiber and polymers are to fill the air void of coarse aggregate. Bitumen must hold the coarse aggregates together. As the typical bitumen is not capable of doing so, the use of additive polymers seems essential. Additives consist of fiber and polymers. In order to prevent drain down while fabricating, cellulose fiber is used. The application of elastomer-thermoplastic polymers causes the improvement of rutting resistance in high temperature. Elastomeric properties make the deformations recoverable and thermoplastic properties broaden the performance grade of bitumen. Polyethylene and ethylene-vinyl-acetate copolymers are selected in dosage of 3, 5, 7 and 4, 8, 12 percent, respectively. These polymers could be directly added to the mixture which is a common method to use them in Iran. By applying 50℃ as the ambient temperature and 450KPa as the level of the stress for creep tests, while considering high temperature condition, the most severe condition of loading is simulated. Comparing the result of unconfined creep test which is performed on the modified and unmodified specimen, concluded that polyethylene and unmodified specimen has the same creep performance while 8 and 12 percent ethylene-vinyl-acetate has the same creep result as 4 and 6 styrene-butadiene-styrene specimens, respectively.

A well-developed of air surveillance system is one of the most important factors for development and growth air transportation system.The surveillance system directly relates with the safety of air transport network including, airports, air routes, and the fleet. One of the newly developed systems is the multilateration system which is located on the ground and can accurately determine the aircraft position by its three antennas based on the signal’s time different of arrival. Due to its lower cost of capital, implementation, repair and maintenance, it started to be widely used throughout the world. In this paper using the Analytical Hierarchical Process (AHP) an attempt was made to develop a ranking model to prioritize the different surveillance system based on the safety and cost parameters. The two main system analyzed in this paper are secondary surveillance system radars (SSR) and the Multilateration system. These two systems were evaluated based on the technical and economical parameters and a ranking model was also proposed. The developed model was evaluated in the three different mountainous airports in Iran. The MLAT system shown to be the most cost effective air surveillance system for the mountainous airports. The developed model can be used for evaluation of any type of system at any set of airports.

Assessment of probability of risk occurrence to the railway system is so important because of severe cost which could be imposed to both railway administration and passengers. Wheel movement on rail is one of the factors which has significant role in overall damage of railway infrastructure. Theses interaction-based defects are divided into several categories such as wheel flat and RCF faults. Nowadays, railway administrations are interested in increasing speed and axle load of rail vehicles due to its economical advantages. Therefore, studies on wheel-rail interaction defect-base become a concern for researchers. Implementing finite element method is a major approach in determining fracture behavior of both wheel and rail. In previous studies, simulations were mainly carried out in 2D domain by considering symmetrical assumptions. The main aim of this paper is to implement FE method based on three dimensional situations with more realistic conditions to assess rail surface crack behavior which is exposed to dynamic moving load. For this purpose, stress intensity factors for different depth of crack was obtained and compared also. The results showed that by increasing crack depth and crack tip position from rail surface, the crack tip stresses and consequently stress intensity factors were decreased.

Reduce consumption of fossil fuel and that`s negative effects is one of the most important issues related to sustainable development. With increasing distance from CBD, increasing walking time to public transportation, reducing density and mixed land use, car dependence and fuel consumption will be increased in transportation sector. In this regard and reducing fuel consumption in transportation sector, understanding the proper and sustainable urban forms and analysis of the current urban forms is an undeniable necessity for planning. This paper examines the findings of an empirical study, that have been studied the effects of urban form on households travel behavior in transportation sector in three neighborhoods of Shiraz with different urban form characteristics. The variables investigated in this research include the urban form variables and households car ownership. The urban form variables in this study contain of distance from CBD, walking time to public transport, mixed land use and density. Also travel frequency, travel time; travel distance and modal choice are travel behavior variables have been studied in this article. Information about urban form variables have been extracted from GIS maps of Shiraz and data of household travel behavior and car ownership are extracted from questionnaires. Number of questionnaires in this research is 260. To examine the relationship between urban form variables and travel behavior and car ownership, correlation analysis is used. Results of this study indicate the relationship between urban form and travel behavior variables, and households residing in neighborhoods close to CBD with high density and mixed land use have a different travel behavior with residents of other neighborhoods.

Suburban passenger terminals locating processes used in most cities indicates that methods used as non-scientific and based only on expert opinion. In this paper, a mathematical model which has been developed by the authors of this paper was applied to locate suburban terminals in Tehran. First, the most important criterias in locating terminals were identified by interviewing the experts and specialists and also by completing questionnaires. To excequte this model) which is a large scale programme (, the Branch and Bank method was used on Trans CAD software. Based on the results of implementing this model, four places in Tehran were identified in order to build the terminals and analysis of technical and economic evaluation of the results have been carried out shows positive results. In this paper a comparison between the results of the proposed model in this study and the existed model in the master plan of transport and traffic of Tehran was made. The model of master plan suggests 14 locations to construct the terminal, while, proposed our model shows that construction of more than 4 terminals may not be economically justify. Considering the significant differences in functional status, the proposed method in this study clearly verifies as an effective and efficient method to locate terminal

In this study proposes an approach for pricing the urban transportation with the consideration of its external costs. This model is a static partial equilibrium model of urban transportation that incorporates three transport modes: private car, public transportation and taxi. The public transportation mode is an urban bus system operated by the public authority. The proposed model in this study is implemented using data set of Isfahan transportation network and the results are presented. The results of the research show that the optimal price of travel by private car is 851/67, while the optimal price of public transportation and taxi, in respect, are 129/31 and 1876/52. Considering to the results of the research, the optimal pricing will cause an increase in transportation prices of private car and taxi and also a decrease in price of travel by public transportation, in comparison to current prices.

In the early 1960’s, the European asphalt industry recognized a critical need for pavements which would be resistant to rutting, abrasion, and various pavement distresses induced by heavy traffic and studded tires. To address this need, roadway pavement contractors and researchers developed Stone Matrix Asphalt (SMA). After a short time of its application in Germany, this asphalt has been used in Europe for more than 20 years to provide better rutting and permannet deflection resistance and and to resist studded tyre wear. SMA is a gap-graded mix containing a high concentration of coarse aggregate, which maximizes stone-to-stone contact and provides an efficient network for load distribution. The coarse aggregate particles are held together by a rich matrix of mineral filler, fiber, and polymer in a thick asphalt film. The coarse aggregate materials are the main structure of mixture. Fibers as a stabilizer and to prevent draindown used in SMA mixtures. The main objective of this research is the investigation of the effects of cellulose and jute fibers on mechanical in stone matrix asphalt (SMA) made with lime and marble aggregates and its comparison with conventional asphalt mixtures. Also, in the optimal asphalt content, mastic draindown of SMA mixturs and resilient modulus of AC and SMA mixturs were obtained and compared. Test results have shown that optimal asphalt content of bituminous mixturs made with lime aggregates, is slightly more than marble aggregates. Also, optimal asphalt content of bituminous mixturs made with cellulose fibers, is slightly more than jute fibers. Marshal stability and marshal quotient of SMA mixturs made with lime aggregates, is morse than marble aggregates; also marshal stability and marshal quotient of SMA mixturs made with jute fibers, is more than cellulose fibers. Resilient modulus of bituminous mixturs made with marble aggregates, is more than lime aggregates, also resilient modulus of bituminous mixturs made with cellulose fibers is more than jute fibers. Mastic draindown of SMA mixturs made with lime aggregates, is less than marble aggregates; also mastic draindown of SMA mixturs made with jute fibers, is less than cellulose fibers. The dosage rate for cellulose and jute fibers shall be approximately 0.3 percent by total mixture weight of SMA, and is sufficient to prevent draindown which its permissible rate is 0.3 percent by weight of the mix. The VCA ratio for all of the SMA mixturs is less than 1, therefore provides stone-to-stone contact in the mixturs.