نشریه فناوری حمل و نقل
پیاپی 21 (پاییز و زمستان 1392)

One of the major challenges for the transportation system is transportation's effects on environment. The most important ones are the impacts on air quality, energy consumption and land use. Air pollution is considered as a matter of serious environmental pollution caused by transportation systems. There are problems for tunnel user's so that these kind of problems can cause and create a fire hazard, environmental effects such as global warming, ozone layer thickness reduction, reduced access to clean air, increase in density and toxic emissions from gasoline and choking, gathering dust and aerosols and decrease tunnel visibility, congestion and emissions from gasoline fires. These problems threaten mental health of tunnel users and affect tunnel traffic safety. In order to maintain an acceptable level of toxic gases and pollutants, the ventilation system needs to be designed in a way that is both economical and applicable in emergency. The tunnel’s ventilation is the most important safety measure and safety assessment of tunnels in design and improvement of the air-conditioning system. Therefore, strategies for obtaining fresh air to dilute pollutants is presented and there is an urgent need to calculate the flow rate of air. In this study, factors affecting tunnel ventilation are evaluated, so the classification of them into a number of indicators and sub-indicators can be done and in the end a tunnel safety index in ventilation will be presented.

Evaluation of crack propagation in asphaltic mixtures under traffic loading is very important. These cracks that are in relation to fracture in asphalt mixture, can be created in various forms in flexible pavements. These damages can be categorized in thermal cracks, fatigue cracks, and reflective cracks in asphalt overlay on the existing cracked pavement. Among these types of cracks, fatigue cracks divided into top-down cracking (longitudinal cracks) and bottom-up cracking (alligator cracks) can remarkably reduce pavement age. In this research, according to previous works and developed models such as Paris law, mechanism of fatigue crack propagation in asphalt mixture has been investigated, and effects of temperature, loading frequency and asphalt mixture properties have been considered on the mechanism of fatigue cracks propagation. Besides, effects of healing property of asphalt binder on the pavement performance against these types of cracks have been evaluated. According to the results, healing in asphalt binder could increase pavement age against fatigue cracking and considering J integral instead of stress intensity factor could be more appropriate criteria for evaluation of pavement age against fatigue cracking because J integral considers viscoelastic properties of asphalt mixture.

One of the main problems with accident analysis is determination of the exposure index. Exposure can be defined as a number of locations and times prone to accidents. Vehicle miles traveled, travel time, number of trips and the traffic density are some of the known exposure parameters. But given the lack of data, using these indicators is not always possible, especially when the exposure index for a particular group of drivers and vehicle is required. Due to this problem, researchers have proposed techniques to deal with indirect exposure, most of these methods are quasi-induced exposure. Assuming the quasi-induced exposure method, non at-fault drivers in two-vehicle accidents with one driver fault and one driver non at-fault, are the random sample of all drivers on the road at the time of the accident. Thus, exposure to different specifications of the drivers and riders can be obtained with distribution of non at-fault drivers and vehicle. In this study, features, applications and content validity of the results is discussed.

Due to the growing traffic problem in cities, and serious need to develop a network of road transport infrastructure in the country as one of the major economic development, building bridges seems to be an imperative need. In this research, designing two element bridges (Concrete slab and steel carrier beam) has been represented as an optimization standard problem. The final weight of the bridge deck is considered as the goal function that is composed of concrete slab weight and beam weight. Designing constraints in this problem include limitations to design concrete slab such as stress limitation in slab transverse bars and the norms of longitudinal bars and necessary limitation for designing steel area section such as slimming constraint ingredients, limitations of longitudinal stiffener, constraint of compression stiffener, limitation of cutters, stress limitation of beam section and constraint of bridge deformation. This problem consists of 22 design variables and 39 constraints. The important issue in this problem is that all of the constraints are in accordance with the AASHTO regulation agreement and journal 395 (instruction to design steel bridges). CSS and GA algorithms are used for optimization and the performances of these two algorithms in solving the problem are compared with each others. In performance of algorithms, the power to access the best result and time to solve the problem is considered. Comparison is done by using Rank sum test statistical hypothesis and t test statistical hypothesis.

In recent years, development of compressed natural gas vehicles is on the priority to reduce the consumption of petroleum products in the transport sector. One of the factors to promote this program is consideration of CNG supply, due to the need of vehicles for frequent refueling. This study investigated different scenarios, to provide solutions overcoming the lack of CNG stations in Tehran. Besides, an economic feasibility study of these projects has been reviewed. Economic evaluate n of the project has been carried out using the software COMFAR EXPERT III. Internal rate of return, for scenarios 1 to 4, equal to 5.89, 15.76, 4.78 and 12.52 percent, respectively. But these figures have no economic justification with regard to the interest rate of the country which is about 20 percent. The net present value for these scenarios are positive and their return periods are 12, 7, 12, 8 years, respectively. Comparing the indicators shows that Scenario 2, the construction of a small place with a suggested price of 3,700 Rials will be more justified.

The growth of urbanization and utilizing vehicles in most developing countries has led to increasing challenges in development of underpinnings and facilities of transportation. Among these, the way and the amount of providing space for on-street and off-street parking area is considered as one of the needs of transportation programming authorities. On the other hand, the studies about desirability of the use of parking space, have demonstrated the effect of desirable walking distance on the parking demand. The effect of environmental factors on desirability of walking distance has rarely been taken into account. In this paper, the environmental factors affecting the desirable walking distance in Ahwaz were identified. Following that, standard survey forms were designed and the statistical analysis was carried out through the statistical software. The results of the study showed that desirable weather conditions, and existence of covered walkways with appropriate width and enough light, with no obstacles on the way, were important environmental factors that increased the average desirable walking distance to at most 58 percent.

Considering the importance of transit systems in transportation and ridership in cities, management in this field has great impact on development of cities. To achieve an appropriate solution, decision makers should know about the problem. Transit performance will be improved just by detailed evaluation of the system. Many studies have been done in this field, but what characterize this evaluation from previous ones is the evaluation of bus system from two different points of view, operator and passenger. In this study, a framework for evaluating bus system performance established and applied to six urban districts of Tehran. The method is Data Envelopment Analysis, and indicators are selected based on previous studies. Considering operator and passenger points of view, this evaluation reveals roots of probable inefficiencies.