JOURNAL OF TRANSPORTATION RESEARCH
Year:2006 | Volume:3 | Issue:1|Papers Count:7

Due to the large number of urban trips and the importance of people's value of time, transportation planners are quite concerned about the design of efficient transportation systems. Therefore, the need for a new and efficient transit system for large cities is a must. Light Rail Transit (LRT) is one of transit alternatives for such cities. One of the important issues in the context of LRT development is network design. The core of the problem, which is designing a transit network capable of transporting a large number of people efficiently and cost effectively, is highly complex. In operations research, the problem belongs to the class of network design problems, but due to their very large sizes, integrality restrictions and non-linearity, they can not be solved by means of standard network design methods. There is not yet any analytical method available to solve this problem. Gendreau and his co-researchers have expressed the fact that design of a rapid transportation system is a procedure accompanied by complex trend of decision-making, multi-restraint and multi-objectives, uncertainty, non-measurable elements, heavy investment, and long period activity. They have then concluded that the standard traditional methods of network design are insufficient for such complex problems with big dimensions. Nonetheless, however, operation research methods might be of great importance and help at different stages of design, by developing and utilizing tools for production and evaluation of alternatives. Usually in practice, a two-stage procedure is used in locating the railway line, as following:1- Developing the efficient answer, considering the basic criteria, and2- Locating the best line amongst the existed alternatives by evaluating them and considering both measurable and non-measurable criteria ...

In this paper results of the information collection application regarding the occurrence of approaching a model that predicts the accidents intensity. The modeling method used in this research is based on the logistic regression or its substitutes like Probit and dual Logit. At the first stage, by using the public Probit model and defining a parameter with four grades that is illustrative of the intensity of accidents, the independent parameters to be considered have been selected using the results of statistical Wald test.At the second stage, the intensity parameter has been converted to a dual parameter and by using the various compositions of independent parameters, various models for accidents intensity have been approached by dual Logit method.In this research, the modeling principles by logistic regression method have been analyzed and the substitute methods have also been comparatively investigated, and the effect of various independent accident parameters on the accidents intensity has been studied. The study of the effect of parameters on the intensity of accidents showed that there are some reasons responsible for the accidents. It is shown in this paper that applications of the results of Logit and Probit models regarding prediction of motorcycles accidents are almost the same and both are statistically credible.Various parameters regarding the climatic conditions, drivers' conditions, vehicles conditions etc… are the inputs of the system as independent variants and the effect of those variants that according to statistical test are credible, have been investigated. Results of this research not only have provided the possibility for prediction of motorcycles accidents intensity using Probit at 4 grade intensity, but also showed that some parameters are mostly responsible for the intensity of accidents.These factors include the vagueness of the driving licenses of the guilty drivers, occurrence of the accidents between 4-6 am, involvement of buses or mini buses in the accidents, occurrence of accidents in highways or ring roads, crashing of motorcycles with heavy vehicles and inefficiency of traffic signs. These are the major parameters responsible for the increased intensity of motorcycles accidents and should be considered in safety programmes regarding motorcycles drivers.

Restoration of a rough texture to a smooth road surface was widely achieved by means of surface treatment. Soon after the Second World War was over, increased interest over the past twenty years in surface treatment by mechanical re-texturing has resulted in the fact that many companies make investments in manufacturing and developing re-texturing machines to operate on the roads and other paved areas.It should be emphasized that there is no need for structural maintenance by the time a road surface becomes slippery. Re-texturing offers the potential for economically increasing a pavement's surface life without the addition of new material. Surface re-texturing of heavy traffic roads often and potentially offers the means of cost effective maintaining adequate resistance to skidding. There are about 14 different ways of mechanical treatment methods among which many of them are based on bush hammering and sand blasting techniques.There is no justification yet on the way one method is more effective than others and why one method is preferred. To overcome this problem, a laboratory apparatus has been designed and a methodology of its operation has been developed by the author of this paper. The apparatus is of a simple design consisting of a table to the side of which the BS 812 road wheel is mounted, exposing one specimen at a time for the use of pendulum for PSV determination, and also for the use of the needle gun and shot blasting treatments.Effective parameters affecting the quality of the end product of the two types of re-texturing treatment i.e. simulated Bush Hammering and Sand Blasting has been evaluated and compared. Robustness of treated aggregate has been examined using thin sections through aggregate and analysis by optical microscope and surface roughness has been assessed using scanning electron microscope. When some aggregates have undergone re-texturing treatments it has been found that some of them end up with significantly higher performance in terms of their re-textured pendulum value, durability of the surface re-textured and its polished stone value (PSV), compared to others. A survey has been carried out in order to determine appropriate methods to retexture samples under 7 laboratory conditions, also find the most suitable ways of aggregates being re-textured and giving enhanced subsequent performance. Parameters affecting the quality of the produced end product of the two types of re-texturing treatment i.e. simulated Bush Hammering and Sand have been evaluated. Robustness of treated aggregates has been examined using thin sections through aggregate and analysis by optical microscope and surface roughness has been assessed using scanning electron microscope.

Routes should be designed with a comprehensive and long term approach so that they create cost effective road networks. The accurate location and details of the roads can't be specified all at once in one stage. Thus alignment is specified in various stages, using different-scale aerial maps and photographs. The first step in the design of road corridors is determination of general route model considering the sequence to the access points. The purpose of this research is to present an economically optimum model for this matter.In this paper after describing a short history of the past studies in the field of road routing, the current methods are evaluated and consequently two mathematical models are presented for route location in plain areas. In the first method the harsh and difficult areas are not modeled. A major point of road corridor design is that the road should be so designed that it could not pass through forbidden protected military or environmental fields. The major capability of the second method is predicting these areas in the optimum road corridor. In rolling and level areas, the costs are mostly dependant on the length of the road. All the costs (including construction and operation), are converted to the unit cost of the road length. Due to different conditions in various roads, the total cost factor will change in different areas. In addition to the construction costs, the operation cost in the design period for each of access points is an important factor in the cost function of the road. Therefore, the importance of the points to which we should have access to, is the major factor for the shortness of the path. The operation cost per kilometer of access road for each point is determined by factors like passenger and goods traffic volume. The total cost function in the analysis of this research is equal to construction and utilization costs. Therefore, in an intercity road or railroad network, the minimum construction cost is a form of the network in which in addition to the appropriate connection of the urban areas, natural resources and industrial centers, the length of the roads are optimal.In this research the mathematical non-linear programming has been used for modeling. These methods convert the problem to a mathematical model and then solve them. Converting a problem to a mathematical model increases the ability to investigate it, and therefore, provides better opportunities to get benefit of a variety of mathematical programs.An important application of the presented mathematical models is therefore their utilization in provision of master highway and railroad corridor plans in plain areas. Such corridors may also be used in route location projects in larger scale maps, in plain areas. The presented model in this paper yields the final route corridor in a way that economic, social and political requirements of the project are fulfilled. All the cost parameters of the route length can enter the model. The natural and geographical phenomena like valleys, mountains, lakes, lagoons, soft soils, environmentally protected areas, are able to be included in this model.

Analysis of elastic buckling of Monosymmetric I–Section (MIS) is rather difficult, and it requires special attention at various stages. Investigations on elastic buckling of I-section of bridges, are mostly concentrated on symmetrical coupled I-sections, and on lesser extent on MIS. When buckling occurs in a beam with MIS, cross–bending stresses and twist bending occur about rotating axis of the member. This bending twist causes changes in twisting stiffness of the member.In this paper, theory of side–twist buckling of beams with I-sections together with MIS and important parameters affecting buckling capacity of continues beams are studied. Eleven two – span beams which were divided into three groups are chosen. Most of the beams had thick and short flange and thin webs, therefore twisting occurs in web, and buckling in flange similar to stiff members.In compression flanges three modes of buckling: twisting, lateral and vertical buckling may occur. Considering lateral buckling of compression flange, only rotating strength of sections and also column reaction of compression flanges resist lateral buckling. In general, rotating resistance of sections and column reaction of compression flanges act together. Here, the shear buckling resulted from shear stresses, which is very important, is also considered. Thin plates of web, can stand tensile stresses, but they are weak in compression stresses, and buckle under stresses less than yield stresses of plate.Furthermore, for analysis of the beams, a nonlinear computer program NISA II was used, all the beams had the same mesh, boundary conditions, and two equal spans (6m) except for these beams in which the effect of different spans was required (L1= 5, 6m L2= 2, 3, 4 and 5m).In order to have confidence in the results, the beams were analyzed under static loads. For this purpose maximum deflection that occur under the loading points, were obtained from the program, and then the results were compared with theoretical results. The results indicate that the chosen model has yielded good results.To study the effect of monosymmetric (0.1, 0.3, 0.5, 0.7 and 0.9), in the first 5 beams, the width of top flange was changed while the rest of parameters, remain constant. In other six beams only the thickness of top flange was changed.Also, to study the effects of loading conditions on buckling strength, load on first span kept constant, then load on second span changed from zero up to the load of the first span (P2/P1=0.25, 0.5, 0.75 and 1.00). The other important parameter is the effect of span ratio, therefore buckling load with respect to different span ratios was obtained for L2/L1=0.4, 0.5, 0.67, 0.8 and 1.00. Similarly the effects of span ratio were obtained for uniform distributed load. The effect of biaxial stresses on MIS was obtained and the results are plotted on different figures. Finally the figures of critical loads versus each of the considered parameters are prepared based on the obtained results. It was found that buckling load of such beams is increased by increasing the width of top flange, provided the length of spans being equal and the other geometric characteristics of section and boundary conditions remain constant. Furthermore, if the ratio of concentrated applied loads in mid-spans is about 0.8, the maximum buckling capacity of section will be obtained.

Mass-Spring systems are widely used as the most effective LRT systems in urban areas. When considering this system in railway superstructure, vibration-prone regions and dense residential areas are among the most feasible and efficient design options. Similar to vehicle suspension system, a part of the mass of the track structure can be dynamically sprung, in railway superstructure mass-spring systems.In this system, a spring element is needed which is often chosen from rubber or poly-urethane materials. The characteristics of the sprung mass in terms of weight, live loads, rigidity and etc. are influential in vibration damping and elastic properties of the system. The elastic element in these systems contributes more than just a spring element. Since many of mass-spring systems are adapted in slab tracks (ballast-less tracks), they can also be used to increase the elasticity of the track system which in turn results in lower dynamic loads, better deflection behavior and lower maintenance costs. In this regard, in MSS systems, the improvement of the system elasticity as well as vibration damping behavior should be considered. The fields of application of Mass-Spring system can be extended in Iranian railway network and urban railways. Dense urban and rural residential areas, ancient areas, auditoriums, concert halls, studios, labs and buildings containing precise measurement devices are sensitive to railway vibration and should be protected against transmitting ground motions resulting from passing trains.Iranian major cities are experiencing a heavy urban railway construction. In some ancient cities like Isfahan, the national heredities should be protected from the oncoming vibrations resulting form moving LRVs after operation. In this regard the need of an efficient vibration damping system has been realized, among which the mass-spring systems are noticeable. In this paper, a simple as well as accurate analysis method for these systems is developed. The results of vibration and elastic analysis of the mass-spring system used in Isfahan are presented and are compared with the international criteria and standards. The Scandinavian vibration criteria adapted from Swedish Transport Research Center are used to preliminary evaluate the vibration impacts of the LRT line on the vibration-prone buildings and ancient construction. In this paper vibration damping criteria of -20ΔdBv is suggested for ancient cities.This criterion should be fulfilled in LRT tracks in working frequency domain above 50 Hz. The use of Poly-Urethane elastic layers and minimum weight of the sprung mass of 6 ton/m are also recommended in this paper. The natural frequency of LRT MSS system should be as low as 18 Hertz to be efficient. In the mean time, a soft track system (in terms of track modulus) should be avoided. On this basis in this paper the vibration analysis of the system is accompanied by track deflection analysis. For operation reasons, the maximum dynamic and static track deflection are limited to 3 and 4 cm. respectively.