JOURNAL OF TRANSPORTATION RESEARCH
Year:2007 | Volume:3 | Issue:4|Papers Count:10

With the rapid expansion of motor vehicle use in the world, road traffic-related deaths and injuries are rising sharply. More than one million people died at road traffic crashes in the year 2000 all around the world and according to the World Health Organization (WHO) that number could nearly double by 2020. Also the rate of serious injuries is estimated to be 20 times that of road deaths. In Iran, more than 28,000 people died in road accidents during year 2005. This is a very large number in comparison with the world road traffic deaths rate regarding its overall road length. Iranian traffic police department statistics shows about 70 percent of road crashes occur in the last 30 km of roads length near cities named "City Entrance Zone". There are some reasons available for this fact:Mixed Traffic: Because of locating different factories, workshops, farms, etc. near cities, different vehicle types comprising passenger cars, three wheels and heavy vehicles are available in "City Entrance Zone".More Access Roads: Many rural or industrial zones are located near big cities; therefore many access roads will be available in "City Entrance Zone".Different Behavior: The trips in City Entrance Zones have different situations; some of them are generated from the city, some of them will end in that city and the others will pass the city through another city, so drivers will have different behaviors in these zones.In this paper, some road parameters are discussed to find their influences on road accident rates.Moreover, road safety index (RSI) is defined versus road accident rate. With the analysis of accident data which obtained from traffic police department and gathering data from 14 road sections, and by using SPSS software, a model generated which shows the relationship between road accident numbers and road parameters (such as road traffic volume, road width, number of access roads and junctions, road vertical slope and city population). This model predicts road accident probability in any other road section and can be used in efficiency estimation of road safety solutions.

This paper describes a FE simulation of the behavior of mechanically stabilized cohesive earth walls under seismic loads and the effects of reinforcements in reduction of deformations under earthquake loads were studied. In this manner, different heights and different systems of reinforcement were considered.First of all, the maximum height of cohesive vertical slope was estimated without any reinforcement. In other words, five different types of cohesive soils were considered and their maximum stable heights were calculated. Then a geotextile reinforcement system was designed for each wall with the recommended method in the research. Also, to be reassured about the better design of the reinforced walls under seismic loads (considering that the used method for design was merely regarded static loads) the walls were modeled and their stress-strain behaviors were obtained under Saint Jose earthquake loading. After some try and error steps, and finding the safety factors in each step, the optimized design was gained. After that, to evaluate the effects of reinforcements in reduction of deformation in retaining systems some comparisons were made between the reinforced and non-reinforced walls with different heights (6m, 8m, 10m, 12m and 14m) The results of stress-strain analysis were tabulated and related curves were presented. The results clearly show that the reinforcement systems force a full control on displacement specially at the top and the middle of the walls which are the critical zones in retaining walls behavior under seismic loads. Finally it was shown using reinforced system in vertical cohesive slopes with common height, under seismic loads, can reduce the X components of deformations more than 90%.

Rapid improvement in vehicle manufacturing technology has caused increases in vehicular speed, thus making ever increasing needs for improvements in vehicle break and skid resistance of road surfaces. International studies have shown increase in average speed, resulted greater damages when accidents occur. Concrete surfaces in general and road surface characteristics in particular have not neen improved in the same manner and wet skid resistance is generally low.The main aim of this research which has been carried out at Tarbiat Modares University is to evaluate the effect of concrete surface macro texture and its type, nominal size and effect of aggregate shape on skid resistance. In this research, the skid resistance is measured by using British portable skid resistance tester, commonly known as British pendulum and macro texture is measured using the sand-patch method.Skid resistance is an important factor for reduction of raod accidents. When this resistance is less than the optimum limit, special provisions should be considered for the surface areas. The best practice for controlling the skid risk is prevention. This means that during construction of the roads, it is necessary to achieve a suitable and long life skid resistance, by taking into account the principal techniques. The present research and its findings showed that the following points are of great importance:1. The diagrams 5 and 7 illustrate the fact that the skid resistance has a direct, relationship to the size and shape of aggregates. Aggregates with largest sizes (4.75mm) created the highest resistance.2. Diagram 3 shows that the troweled surfaces (lacking the macro texture) have had the minimum skid resistance.3. It also shows that the macro texture developed on the surface of concrete road through harsh brush and fine aggregates with size 2.6mm. has had the best skid resistance.

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Rock falls cause extensive damage in mountainous areas. Many factors are responsible for this natural phenomenon amongst which earthquakes, active faults, atmospheric and climatic conditions, weathering etc.. .are the most important ones. From the falling potential point of view, all mountainous areas are not the same and there are differences in risk factors. These factors are evaluated using various parameters that are divided into three main categories; geological and rock mechanics, climatological, and traffic parameters. There are various methods for risk analysis of roads. Applying these methods may prevent or reduce the effects of natural disasters. Due to the fact that Iran is located on a risk prone zone from natural disasters point of view, also because of its population density and natural disasters high risk, prevention and mitigation of risk is of great importance.Knowing the types and potential of the rockfall at slopes is the main step for preventing hazards. The risk evaluation methods are divided into optical risk evaluation, risk evaluation by GIS data, tree risk analysis and RHRS method. Having studied all the methods and their comparisons, the RHRS is considered as the most comprehensive and accurate method for mountainous roads in Iran and used in this case study (Karaj - Chalous Route). In this method initially the various regional, geological and traffic data were gathered and then those parameters required for rating of risk evaluation of rockfall incidents were calculated and rated. Finally the total parameters were considered as the total rating of the terminals where the higher the rate, the higher is the risk of slopes rockfall. Results obtained from the rating of rockfall risk within the 20 Km danger zone of the mentioned route were as follows: Traffic parameters must certainly be considered in risk analysis and evaluation of rockfall accidents in mountainous areas. Aspects such as sight destination, speed of the vehicle, traffic volume and the road width have great influences on determination of rockfall risks.Usually by increasing the traffic parameters, the rokfall risk is also increased in various terminals. As long as the rockfall risk is the result of combination of many parameters, therefore, the increasing of traffic parameters adds to the total rating of rockfall risk at different terminals. By studying and comparing the total rating of various terminals, also considering the total traffic rating, it became clear for the researchers that half of the ratings related to rockfall risk in mountainous roads were due to traffic parameters, and the remaining half was related to geological and climatological parameters which shows the significance of these parameters in risk analysis of rockfall accidents in mountainous roads. Due to the low width of the road and the limited spacing between mountains that the road passes through, installation and construction of guardrail ditches was not possible in most locations of the road, therefore the rating of this parameter was considered as the worst (100) among others. In rating of rockfall risk, some other aspects like the existence of substitute roads, routes to the relief centers, weathering etc ... were considered so that a more accurate investigation could be carried out for the area and the selected terminals.

Updating and predicting different types of Trip Generation Models (TGM) is always known as a challenge in different studies. Trip Generation (TG) is the first and one of the most important stages between fourfold trip demand prediction stages that its goal is to estimate the total number of generated trips from one source. Researchers such as Ortuzar and Willumsen emphasized that more non-congestion trip generation models have better prediction and adaptation ability. So in many years to validate different ideas, experts have invented variety of models and they always try to estimate the number of generated trips in a better method helping newer model presentation. Also they try to decrease the previous models problems and defects as much as possible.At this research a new method using fuzzy logic was presented to predict the number of generated trips using trip generation data in City of Rasht, in north Iran. For configuration of the fuzzy model four important parameters have to be considered: household structure, family size, car ownership and income. Data of these parameters are integer and converting the integer numbers to fuzzy form is meaningless. Therefore, three parameters; household structure, family size and car ownership were normalized to income that is one of the most important parameters at trip generation. Then to develop fuzzy model, the ratio of household structure, family size and car ownership to income was used as input functions and the ratio of number of generated trips to income was used as output function. The basic idea at this method is using fuzzification-defuzzification procedure and selecting input-output function based one data of one research in City of Rasht.One of the more common methods to develop TGMs is step-wise regression method. To represent very high accuracy of proposed fuzzy method, this model was considered and compared with step-wise regression analysis, step by step. Because of three parameters: family size, car ownership and income were identified as the most effective parameters in TG, at first fuzzy model was developed versus these three parameters, then proposed model was developed using four parameters: household structure, family size, car ownership and income. To compare with step-wise regression method, 4-variable step-wise regression equation was used. As we predicted before, the results of 4-variable and 3-variable step-wise regression equations do not have any differences, because these correlation coefficients have only 0.1% difference. The result of fuzzy model with 4 parameters and 3 parameters represent that these two models have differences remarkable and using household structure-parameter as an extra input leads to exact accurate results. To compare, these two methods, fuzzy model and step-wise regression analysis, were performed on 20 groups of random statistical data of City of Rasht that was selected with MATLAB software. Result of these comparison shows that in step-wise regression method except one that can originate from data dissipation maximum error was 22%, but fuzzy method approximately without error leads to very accurate results. Fuzzy method error was zero for all data except one. In addition to fuzzy method leads to correct and very accurate results for all ranges of data, but step-wise regression method results correctly only for given ranges of data. Another benefit of fuzzy method is that this has less mathematical complexity with the compare of step-wise regression method.According to above-mentioned consideration, it can be concluded that proposed fuzzy method at this research has high accuracy compared to other methods and this model is one of the most assured methods for prediction of generated trips.

The general aim of Hot Mix Asphalt Design is selection of the most suitable and economic mixture of aggregate and bitumen which can maintain the properties of asphalt mixture in a definite range. Until now different methods have been developed for Hot Mix Asphalt Design including Marshal Method, Modified Marshal Method, HVeem Method and Superpave Method.At the time being, the Hot Mix Asphalt Design is based on the Marshal Method in Iran. In Marshal Method, the optimum bitumen content is based on the mean of the bitumen content which obtained from highest Marshal stability, highest density and the most suitable air voids in Asphalt content. This bitumen content is not necessarily the optimum bitumen content. In this paper a nonlinear programming model is developed to determine the optimum bitumen content from Marshal or modified Marshal Method. To do that, first of all the equations which relate the effective parameters in Hot Mix Asphalt Design such as density of mixture, Marshal stability, flow, Asphalt content, air voids, VMA, void filled with bitumen versus bitumen content using method of least squares and from a quadratic polynomial equation. Then based on these equations and using a nonlinear multi objective programming model, the optimum bitumen content is determined in such a way that given hot mix Asphalt has all of the requirement mentioned in the design guide and has a highest density and Marshal Stability. Since the optimum bitumen content is definitely between the maximum and minimum bitumen content used in the test (4 to 7 percent), it is possible to first determine all allowable solutions (bitumen contents which satisfy all of the constraints), then evaluating objective function in each allowable solutions. The most optimum value of objective function and also optimum bitumen content can be determined. To evaluate the presented model a program was written in MATLAB. Then based on results obtained from a Marshall mix design method and using the above model, the optimum bitumen content was determined.Finally, application of this method is described using an example and then optimum bitumen content was determined based on the results of a real Marshal test.

Many bridges built in the past 50 years are reinforced concrete. Because of their normal deterioration, the introduction of new safety standards, and the increasing traffic volume and loads, a high percentage of the older bridges require rehabilitation or expansion. Often, the choice between constructing a new bridge and rehabilitating the existing one must be made. An essential factor in making a sound decision is knowledge of the strength of the bridge in its existing form. Unfortunately, the inelastic response, load distribution characteristics, and ultimate strength of bridges can not be realistically assessed by use of simplified procedures currently used for design and evaluation. Prediction of this behavior ultimately requires extensive experimental tests or advanced analytical techniques. In many cases, analytical methods are more economical and expedient than laboratory or field testing, and a number of researchers have extolled the potential of using finite element analysis to predict bridge response.The primary objective of this study is to establish and demonstrate a convenient, reliable, and accurate methodology for analyzing reinforced concrete structures with particular emphasis on Reinforced Concrete Bridge and develop a capability for predicting stress and strain distribution through the thickness of bridge decks. A secondary objective of the analytical evaluation include the development of a finite element model that could correctly represent global bridge behavior and accUl1telypredict strains, stresses and displacements in the deck. A specific objective is to investigate the enhancing effects of compressive membrane action on the ultimate flexural strength of bridges.A nonlinear finite element program, NONLACS2, developed by Kheyroddin, was selected as the basic platform for this study. The next step was to demonstrate how reinforced concrete is modeled within NONLACS2 and to validate the results predicted by the NONLACS2 program by comparing them with relevant experimental data and accepted design calculations. The finite element model of a reinforced concrete beam, simply supported, and subjected to a uniformly distributed load, was initially investigated. Further verification of the validity of finite element models of reinforced concrete components were demonstrated by comparing the predicted response of the model with experimental results obtained from laboratory tests of a two-way reinforced, simply supported, concrete slab. Tests on existing slab and beam bridges around the world have shown that many of these structures possess a greater load capacity than current design codes predict they should have. Many researchers attribute the additional capacity to a phenomenon known as compressive membrane action. Compressive membrane action occurs as a result of in plane restraints that restrict the horizontal expansion of the bridge deck as it deflects vertically. For this purpose, finite element modeling of slabs with idealized end restraints has been carried out.With the information acquired through the research proposed in this paper, a more complete understanding of the nonlinear behavior of RC bridges was obtained. This would allow a more realistic assessment of the flexural strength of these bridge types to be made. Some important points can be noted. The type of end restraint imposed on a slab significantly affects its load deflection behavior. The ultimate load capacity of a slab with fully restrained ends is almost five times greater than that of a simply supported slab. The stiffness of the horizontally restrained slabs is also significantly greater. The behavior of slabs with pinned ends depends greatly on the height at which the horizontal support acts. T-shape beam have a high lateral strength rather than rectangular beam and cause decreasing of deflection of deck. The stiffness of the T-shaped beams was largely responsible for the mode of failure.