پژوهشنامه حمل و نقل
سال دوم شماره 4 (پیاپی 5، زمستان 1384)

Railway is a major transportation system for mass transport at high speed to connect large cities. Recently many concerns have been focused on developing new type of train and increasing the maximum speed moreover to cope with the congested situations and environmental problems of railroads and roadways. One of the most important structural problems to meet the social demands would be to solve the dynamic interaction of vehicles, the rail and bridge, evaluate the running safety, and assume excellent riding comfort at high-speed operation.The dynamic response of railway bridge under moving load has been studied both theoretically and experimentally for many years. Recently, more sophisticated models that consider various dynamic characteristics of the moving vehicle have been used. Traditionally in studying the dynamic response of a vehicle-bridge system, two sets of equations of motion can be written, one for the vehicle and the other for the bridge or rail. It is interaction force existing at the contact point between the two subsystems that make the two sets of equation coupled. One feature with this kind of contact problem is that the contact points move from time to time. To solve these two sets of equations, procedures of an iterative nature can generally be followed one drawback of this approach is that the computation involved in the iteration process can be significantly large. The converge rate is likely to be low, when dealing with the more realistic case of a bridge bearing a series of vehicles in motion. From literature review, it is clear that most of the existing procedures cannot be efficiently adopted in the analysis of general vehicle-track-bridge systems. In this paper, a finite element formulation to solve the dynamic response of vehicles, the rail and a general bridge is presented. The interaction between wheel and rail is completely considered here. A mechanical model to describe the interaction between the wheel and the rail that is connected directly with the bridge is described. For the vertical and rolling motion, constraint equation to connect wheel-set and the rail are given. The equations become time-dependent since wheel-set move on the rail at high speed. For the transverse and yawing motions, constitutive equations to describe the relationship of interaction forces and relative velocities between wheel and rail are given in a form to be treated in the finite element solution procedure. The numerical method of solving the equation of the motions of vehicle-track-bridge systems effectively under the constraint and constitutive equation to express the interaction between the wheel and rail is discussed.A computer program, DTVBI has been developed for the nonlinear analysis on vehicle-track-bridge interactions. Numerical examples are demonstrated to assume the validity and effectiveness of the proposed method. Case study carried out on concrete three-span bridges with continuous girders by using mechanical model and presented analytical method. The results of calculations showed that a track effect on running comfort of passengers (lateral and vertical accelerations of rolling stocks) is very important. Track effects on bridge dynamic responses depend on their span length and in bridges with spans smaller than 25m have considerable effect, however, in bridges with larger spans have less effect.

Many damages to the structure of bridges occurred during the past earthquakes, are mostly the result of underestimation of seismic forces. For this reason, seismic isolation can be effectively used in designing or retrofitting the bridges in high seismic zones. The objective of this paper, along with the study of characteristics of electrometric isolator that can be manufactured in the country, is to briefly present design guidelines of these isolators and to investigate the effects of key parameters like elastic stiffness, inelastic stiffness and yielding force of isolators on seismic performance of five typical highway bridges.Based on the results obtained in this research, seismic isolators have a significant role in reduction of seismic forces and displacements of the typical bridges, protecting sub structural elements which are usually weak and brittle. The larger the bridge lateral stiffness, the more effective will be the seismic isolation. The primary elastic stiffness and yield force of isolators are the key factors in isolation efficiency and its hysteretic damping.By decreasing the elastic stiffness of isolators, the bridge response will decrease while the absolute displacement of the bridge deck will increase. This drawback can be compensated by increasing yielding force and damping of isolators by inserting other types of passive devices. Optimum design can be found through numerical investigation. It is eventually concluded that elastomeric seismic isolators can be effectively used in designing new bridges or retrofitting existing bridges, according to the performed design and analysis of bridges in this paper. Experimental studies on seismic isolators are recommended as a complementary to numerical procedure to ensure desired lateral performance of isolated bridges.

One of the effective factors in road safety and accident reduction is to combat road surface slipperiness. The greater the coefficient of friction at the contact patch, the greater will be the degree of vehicle control in bringing it to a halt, thus helping reduce accidents.Asphalt pavements are used extensively throughout the world in general, and in Iran in particular. Thus, in this research hot asphalt mixes (3 types) have been studied for their relative performance in skid resistance. In this research, British Skid Resistance Tester (commonly known as the Pendulum) has been used to evaluate the skid resistance of laboratory made samples and the macrotexture of these surfaces have been measured using the sand-patch technique.In this research, by keeping the aggregate type the same, three types of asphalt mixes that is; pervious macadam, stone mastic asphalt and asphalt concrete are made and evaluated that are different in respect of macrotexture, nominal size, aggregate grading and the percentage of large to small aggregate fractions. Samples made measure 30 x 30 cm with a thickness of 5 cm which are the same as a complete wearing course layer in the field. As asphalt pavements are extensively used in Iran and in the world in addition to mechanical specifications of the asphalt mix the skidding resistance should also be considered. The results show that:1.Among the porous asphalt, SMA asphalt, and the asphalt with continuous grading (concrete asphalt), the porous asphalt is advantageous from the skidding resistance point of view.2.The nominal size of the mix affects the skid resistance of the size, and in the range of 4.75 to 19 mm. nominal size that were studied in this research. The less the nominal size of the mix, the more will be its skid resistance.3.Investigations show that the content of aggregates passed through sieve No. 4.75mm. affects the skid resistance of the nominal size measured by the English pendulum and the skid resistance of the aggregates has a reversed relationship with the aggregates passed thought the same sieve.4.In the asphalt with continuous concrete asphalt grading, the reduced skid resistance between nominal size of 4.75 and 9.5 mm. is not considerable, however it is influential on other parameters like Marshall Stability

Motorcycles are mostly used in city and intercity travels in the country and their utilization has recently grown significantly. Using motorcycles have not unfortunately been associated with appropriate planning, therefore it has brought up so many problems through which the most important one is the increased number of accidents and the consequent damages and mortalities. Due to the complexity of cars and vehicles accident, the number of research studies in this respect has not been satisfactory in the world. In our country no research study has been implemented up to now.In this research study that part of it has been presented in this paper, a comprehensive database including all the information on geometric design of roads, specifications of traffic, specifications of the vehicles involved in accidents in 241 intersections in Tehran have been collected. This database was prepared by utilization of the Database of Tehran Vehicles Accidents, as well as Tehran Comprehensive Studies on Transportation and Traffic. By using this database some models were made for the purpose of predicting motorcycles accidents in the studied intersections, as well as the probability of motorcycles involvement in the intersections accidents. The logistic regression was used for modeling. Results show that factors like the intensity of accidents, dryness of the pavements, existence of the special bus lines, locating the intersections in the forbidden traffic areas, are amongst the most important factors that have the greatest effects on the motorcycles involvement in Tehran accidents in intersections. Using the motorcycles involvement probability parameter in accidents and application of public linear models and appropriate transfer functions have resulted a model by which the prediction of the number of motorcycles accidents in the city intersections would be possible. The accuracy of the model is descriptive of the fact that the attempts performed in predicting the motorcycles accidents have been quite successful.Based on the obtained results, regarding the probability of motorcycles involvement in accidents there are some factors influencing the whole process. These factors are the route grading, traffic volume, the difference between the input and output of routes, two sidedness of the routes and finally, the width of the roads. These factors have the greatest effects on the number of accidents in Tehran intersections.

Train scheduling problem is one of the severe problems in rail transport planning. Mathematical programming, simulation, expert systems, heuristic and meta-heuristic methods, and combinational methods are amongst techniques for train scheduling. This paper develops an algorithm to train scheduling problem using Ant Colony System meta-heuristic. At first, a kind of train scheduling problem is formulated in a mathematical model and then the algorithm based ACS is presented to solve the problem. The problem is considered as a traveling salesman problem wherein cities represent the trains. ACS determines sequence of trains dispatched on the graph of TSP. According to the sequence as well as removing trains collisions incurred, train scheduling is determined. Numerical examples in small and medium size are solved by using the algorithm and compared to exact optimum solutions to check for the quality and accuracy. To analyze the solution results obtained, they are compared with those of exact optimization method of the train scheduling model. For this purpose, computations are carried out for 45 problems including 3 to 8 trains and 2 to 8 track sections. Comparison of the solutions shows good enough quality and time savings. Sensitivity of the run times of the algorithm with respect to variation of number of track sections as well as with respect to variation of number of trains have been shown and compared with those of exact optimization method. To clarify use of the proposed algorithm, a problem with 30 trains and 4 track sections is solved to illustrate the solution. Structure of the paper is as follows: section 1 presents a hierarchical process of rail transport planning and ant’s behavior which gives inspiration for ant algorithms, is presented. Section 2 reviews the literature of the train scheduling problem and then the manner of creating, developing and applying the ant algorithms is put forward. Section 3 presents the proposed ACS-based model and solution method using ACS for train scheduling. In this section a mathematical model for train scheduling on a single track line is presented. Section 4 illustrates the analysis of the model. This chapter compares the solution results obtained from the model with those of exact optimization method of the train scheduling. Section 5 presents a case study that supports the qualified results of the model. This section describes how to determine the ACS algorithm parameters and section 6 summarizes the paper.

Accurate estimation of delay is difficult because of the randomness of traffic flow and large number of factors affecting intersection capacity. Existing delay models provide only approximated point of estimates of signalized intersections. Identification and evaluation of probability distribution of delay can be beneficial in understanding the nature of its variability at signalized intersections. In this study travel time delay data at three per-timed signalized intersections in Tehran, Iran were evaluated. The main purpose of this research is to present a delay distribution prediction model based on the data collected at some signalized intersections in Tehran. For this purpose the following steps have been taken:1. Literature reviews on queuing theory and existing delay models, well as well as theoretical support for the study.2. Sampling and data collection regarding delay of vehicles in some fixed time signalized intersections in Tehran.3. Determination of delay distribution functions by existing vehicles delays values obtained from the data. For this purpose the frequency of delays (data) in various intervals was calculated and then, based on the obtained histogram of the data, a few distribution functions (i.e. Weibull, Gamma, Beta, Normal, Erlong, Triangular, Exponential and Uniform) were fitted to this data and consequently the best delay distribution function was obtained. 4. Presentation of a model for predicting the delay time in some signalized intersections in Tehran.Hence, delay probability distribution functions were developed for each signalized intersection using Arena simulation software. Results of simulation show that Weibull distribution function provided better fits for delay data at all three intersections. The two parameters of this distribution were estimated by "average delay" and "g/c" ratio.