پژوهشنامه حمل و نقل
سال چهارم شماره 3 (پیاپی 12، پاییز 1386)

Lead and cadmium are heavy metal pollutants released by vehicles which are propagated into the urban environment by traffic flow. To study roadside soil pollution and to determine the traffic parameters affecting levels of lead and cadmium in soil, Isfahan was selected for a case study. In this city, soil samples were collected from 13 roadside sites and traffic parameters were determined. The traffic parameters studied include total traffic volume, daily traffic volume, total traffic volume to road oriented width, total traffic volume to total traffic capacity, speed, and aspect ratio. Average lead and cadmium concentrations in soil at distances from 0 to 50 meters from the road edge were found to be higher than background values, thus failing to meet maximum acceptable agricultural soil standards. The regression analysis of concentrations in stream soils versus selected traffic parameters showed that the total traffic volume was the parameter with the highest impact on soil metal content. Also, it was observed that lead and cadmium concentrations (as dependent variables) decreased logarithmically with increasing distance (as one of the independent variables) while each of the lead and cadmium concentrations increased linearly and exponentially, respectively, with increasing total traffic volume (as another independent variable). The regression models developed in this study can be used for predicting lead and cadmium levels in roadside soil in terms of distance from road edge and total traffic volume. The results obtained from this study may be used in urban traffic control, transportation management, urban design and architecture, and urban land use planning.

Crushed asphalt is made by recycling of asphalt pavements (by crushing or milling the old materials). This material may be used in making new asphalt mixes. Using crushed asphalt in making new asphalt, reduces the consumption of new materials and thus results some savings in capital as well as natural resources. The main objective of heating the crushed asphalt in the process of hot mix recycling is to change the hard state of asphalt to soft and liquid state and thus making the possibility of segregation of the aggregates in the asphalt mix. Not to mention that too much heating may also result corrosion or burning of the bitumen. Meanwhile heating the asphalt less than the required time, may result incomplete mixing of crushed asphalt components with aggregates and new bitumen materials. In this paper the effect of temperature changes and heating periods of crushed asphalt on some parameters like real gravity, Marshall Stability and indirect tensile strength of recycled crushed asphalt have been evaluated. Also the Marshall Stability and indirect tensile strength of recycled asphalt mix have been compared to similar amounts in the ordinary asphalt mixes. The obtained results are as follows:1-Heating time and heating temperature of crushed asphalt influence the real gravity, Marshall Stability and indirect tensile strength of the asphalt mix. These influences are meaningful, by other words; the occurred changes in the mentioned parameters are not accidental, but affected by the developed changes in time and temperature of heating process.2-Taking into account the Marshall Stability diagrams and indirect tensile strength of asphalt mixes on the basis of heating time and temperature parameters of crushed asphalt, it is considered that the average amounts of both parameters, at the heating time of four hours and heating temperature of 160◦ have reached their maximum level. By other words, those parameters that are indicative of hardness and strength of asphalt mix, at the mentioned time and temperature have reached their maximum level.3-Results show that the recycled asphalt mix has had considerable Marshall Stability and tensile strength. For instance the Marshall Stability of the recycled asphalt mix at 4-hour heating time and 175◦ heating temperature has approximately reached 3700 Kg. Also the indirect tensile strength of the asphalt mix at 4-hour heating time and 160◦ temperature has approximately reached 26 Kg/cm2. Comparison of the mentioned amounts with the same amounts in ordinary mix asphalt (without crushed asphalt) it can be resulted that making use of crushed asphalt in asphalt mix increases the strength and hardness of the asphalt mix to a considerable extent. 4- Relatively intensive slump of real gravity, Marshall Stability and indirect tensile strength diagrams at the point of 8-hour heating time and 175◦ temperature shows that at the mentioned point the properties of asphalt mix have considerably changed. The reason for these changes is developing considerable changes in the properties of crushed asphalt, due to the high temperature and long period of heating.

A review of data on road accident shows that approximately 50-60% of accidents occur on two lane rural roads. The other surveys reveal that half of these accidents happen on the road curves. It is very important that designers pay special attention to this matter. Road network has an important role for the transportation and carriage of goods and safe passage of vehicles. It is important to design a road according to guidelines of geometric designs of roads, with particular emphasis on safety. This research work has led to introduction of models for prediction of road accident on curves on two lane rural roads. This is a step forward for determining the location of accident black spots. A vast and through literature review was carried out to investigate factors affecting the road accident. Parameters, which had the most effect, were identified as geometry of road, radius of curvature, super elevation, curve length and sight distance. Accident data were collected for Khorasan province in Iran, data collected were analyzed and models were developed, the models were checked and calibrated for parameters mentioned above. The results obtained show that models are valid for identifying the accident black spot on two lane rural roads.

In this research, generalized linear models are used for modeling the trip modal split of Tehran residents. Characteristics of trip and traveler are used for calibrating the model. 434 questionnaires are distributed between a random sample of students of Tehran. Selected students were asked to fill one questionnaire form about trips of their family and the other questionnaire about trips of their neighbor. The gathered data of questionnaires are analyzed and using a log linear model, effect of trip destination, trip goal, and trip time on the modal split is studied. Sample size is determined as it can produce the necessary information with sufficient accuracy. It is emphasized that the sample size is dependant to the information and accuracy which is needed for decision making. It has been shown that a sample size of 400 families in Tehran is enough for determining the trip goals. For determining the trip destinations, Iran is divided into 8 regions and trip destination of Tehran residents is categorized in this regions. The ANOVA method is used for checking the effect of trip region, trip goal and trip time on the modal split. It has been shown that the 3 mentioned parameters can affect trip modal split. Analysis of gathered data shows that trip goals can be classified in the below categories: recreation, with 48%, meeting the relations and friends, with 19%, pilgrimage, with 18%, work, with 10%, and other goals including studying, business, and treatment with 5%. Using the generalized log linear models, dependency of trip region, trip goal, and trip time on the use of private car for intercity trips is studied. Pair combination of trip goal and trip time parameters, shows that most of the residents prefer to use private cars for traveling to Tehran region for recreation. In addition, most of the residents prefer to travel to the North region by their private cars for recreation.

In this research a computer model formulated on the operating principle of genetic algorithms to serve as an analytical aid for pavement maintenance engineers is introduced. Analyses are conducted to show the characteristics of important operation parameter of the program. These parameters include: (1) Parent pool size; (2) Mutation rate in offspring generation. The effects of road maintenance parameter such as choice of warning level are analyzed. Examples are presented to illustrate the application of program to the selection of maintenance warning levels. Finally the detailed maintenance and rehabilitation schedules with two objective functions; minimization the present worth of maintenance costs budget and maximization of network pavement condition index; are presented.

Wheel wear is a common problem in railway industry. Determination of the train wheel wear trend is very important in this industry, especially in subway system. That’s why; it is possible to have better maintenance planning by determining wheel wear trend. Comparison of obtained wear shows whether the wear condition will be acceptable or not, and will help to correct the direction characteristic and another parameters which are effective in wear. Life prediction is also important, so in different cases, such as wheel/rail, there are different criteria and methods for predicting the life of the components, being worn. In this paper, a method is proposed in order to determine and predict the wheel wear trend.. Determining this trend needs a complete databank of system wear condition. Therefore, in different logged distances, the wheel thickness of flange in the second line of Tehran subway was measured by gauge and by miniprof during thirty months. These information were imported to the prepared software, capable of fast and reliable processing of data. Our output data is flange wear rates in different periods and situations. By using these data, it will be possible to have better management on wheel maintenance and predict logged distance in which the wheels should be re-profiled and replaced. The period that the fleet will not be available for service can also be estimated. Meanwhile, the accuracy of results might be proved by comparing them with field measurements. Therefore, the wheel stock management parameters, wheel re-profiling and replacing timetable are obtained.

Every year, a considerable amount of money is spent on construction and maintenance of road networks. In this regard, enough care should be taken in the utilization and protection of expensive asphalt layers. One of the main causes of pavement deterioration is heavy wheel loads, which unfortunately occur very frequently in Iran. These loads reduce pavement life and result in the pavement deterioration before their predicted useful life. The damage caused by these wheel loads must be calculated so that the road authorities could compensate for imposed costs. In this study, KENLAYER software is used for analysis of pavement behavior against heavy loads. Moreover the reduction of pavement design life for each load is calculated based on allowable repetition of each load and according to Asphalt Institute criteria for fatigue and rutting strains. Finally, the equal amount of expense for each load is calculated based on the reduction of allowable repetition. Results of this research show that the weaker the body of the road, the more destructive will be the effects of heavy axes on the road. It may seem that the cost of heavy loads in freeways and expressways is more than costs of two way roads but it is not practically like this. According to some studies in USA and Canada, the costs of passing axes on low traffic roads (¬and naturally on roads with weaker pavements) may be so much higher than the costs in stronger roads. Therefore it may be claimed that when heavy loads pass through expressways and freeways less damagers would occur to the pavements