پژوهشنامه حمل و نقل
سال هشتم شماره 2 (پیاپی 27، تابستان 1390)

Bicycles, as a non-motorised transportation mode, have been widely used in developed countries. Riding a bicycle not only yields benefits to the rider, but also to society as a whole due to reduced fossil fuel consumption and pollution levels. Several factors have hindered the wide-spread use of bicycles as a mode of transport in developing countries, the most important one being the lack of infrastructure. In this research, a model is proposed to assign bicycle routes based on feasibility criteria, including BCI, BLOS, RSI, and IEI. The proposed model is implemented to assign the bicycle routes in a city that has the information required by the model. The objective function of the model is defined as the minimization of the total cost of implementation, including capital costs, costs from travel time, safety considerations and environmental costs. The model is evaluated based on the actual data collected from the city of Qom, and the results show that the proposed model is sensitive to the geometry and traffic specification of roads.

The transport sector as a prerequisite and foundation for development plays an important role in creating facilities and potential opportunities. Identification of the factors affecting the development of this sector can assist in the optimal use of the transportation sector’s capacity, as well as determination of policies aimed towards increasing the sector’s efficiency. The objective of this paper is to perform an analysis of the role of research and development in the growth of the transport sector. This analysis is based on exogenous and endogenous growth patterns and empirical studies, which are used to identify the required variables and role of the economic model for R&D expenditure on growth within the transport sector in Iran. Finally, these models are estimated using appropriate econometric techniques. According to both of these models, the labour force, rate of investment and the ratio of investment to capital stock have a positive and significant effect on the growth of the transport sector.The variables of ratio of the research credit to value-added of transport sector, index of degree of openness of the economy, changes in the price index of goods and service sector as well as the degree of government intervention also have a positive and significant role on the studied field. Dummy variables for the periods of war and revolution have a negative effect. According to the research findings, if a person is employed as an expert or specialist in the research and development sector, the knowledge rate will grow by 0.0382%, which will ultimately lead to an increase in the value added variable of growth rates for the transportation sector to 0.0494%. In another model, increasing rates of investment in R&D will result in an increased growth rate of transport to 0.042. Finally, variance decomposition of forecasting errors shows that variation in the labour force employed in occupations that are scientific, technical, and specialized have a slight role in variation of the value added variable for the transportation sector.

In this study the possibility of improving the properties of binary concrete containing pumice is investigated, by combined use with silica fumes and development of high performance mixes suitable for the harsh environment of the Persian Gulf. Ternary mixes based on the combined use of 15% and 30% pumice and 2.5%, 5% and 7.5% silica were considered. Concrete mixes were evaluated using compressive strength tests, electrical resistance tests, the rapid chloride permeability test (RCPT) and the rapid chloride migration test (RCMT) at various ages up to 180 days.The results show that simultaneous use of silica fumes and pumice overcomes the deficiency of the slow rate of strength gain that binary mixes containing pumice usually exhibit. In addition, the use of ternary mixes results in considerable improvement in durability at all ages when compared with the control and binary mixes. By using appropriate combinations of pumice and silica fumes it is possible to achieve good strength and durability characteristics at 28 days, along with excellent long term durability.

Rail joints are one of the most sensitive and vital areas of a rail, and they playa determinant role in railway tracks. Therefore, impact stress analysis that simulates when a train’s wheels pass over the tracks is one of the most basic requirements in this field. In this study, stress and displacement over the two ends of rails in a rail joint have been investigated, along with their effective parameters. Because of the complexity of this in terms of solving the dynamic analysis problem when the wheel passes over the rails and their connections, in this study an LS-DYNA solver has been implemented that allows explicit solving. In this research, the effect of axial load and speed as two important parameters has been examined, and the ratio of contact force to axial load has been computed. In addition, the effect of distance of the rail gap on the impact stress has been studied. These studies have been conducted for rail profiles that are used in Iran’s domestic rail industry (UIC60). Results show that by increasing the axial load there is an increasing the imported stress to the head rails, while by increasing the speed there is no remarkable change in stress on the head rails. To carry out this investigation, a factor has been introduced that is termed ‘impact stress factor’. This is equal to 1.435 and shows the ratio of impact stress in the rail joint to the contact stress. The results also show that the contact force in the contact area is about 3 times that of the axial load. Investigation of the rail gap distance shows that by increasing the gap distance, the impact stress is increased, but the rate decreases.

In modern times, the necessity of tunnel construction is inevitable with regards, to the development of the transportation industry, and as a result it is very important to analyse its stability while it is adjacent to some geologic features, such as discontinuities. The direct shear test is one of the most applicable geotechnical tests to investigate geological features such as joints and discontinuities. The dilation and shear behaviour of two sliding surface can be analysed with this test, and in this paper, a constant strain joint element has been presented and a combination of a slider and a shear spring have been applied to this joint element to model the plastic shear behaviour of the joint in contrast to previous joint models. Then, the direct shear test has been programmed based on the finite element method in MATLAB. Subsequently, the joint behaviour has been analysed with an increasing normal stress with various shear stiff¬ness values and JRC (Joint Roughness Coefficient). The results of this numerical study demonstrate that the shear displacements reduce with an increase in shear stiffness, and consequently the dilation decreases as well. Meanwhile, by increasing the normal stress, the joint experiences more dilation in spite of a reduction in the rate of increasing the dilation. Moreover, the peak shear stress and shear strength of the joint have been increased as the JRC increases, but the effect of the normal stress on the shear strength increases with greater significance than with the JRC. Also, the increase in JRC has a direct relationship with dilation increase in the joint.

Expansion of transportation as an infrastructural sector is influenced by the improvement of technology, growth and development. This expansion leads to further economic development by providing improved, increased and easier access to the inputs and financial resources of other zones. For identification of factors affecting the quantity of demand for air travel, which is one of the most important subsectors of passenger transportation, a gravity type model is created using panel data, consisting of 21 of Tehran’s one-head province-pairs during 1379-85.Real air fares, real bus fares, real per capita income, population and distance are considered as the effective factors in the model. The findings indicate that all of these are significant at the 95% confidence level, except real bus fares. Air travel is classed as normal goods, and demand is inelastic with respect to real air fares and distance, and elastic with respect to population.

The classical vehicle routing problem (VRP) is one of the most important combinatorial optimisation problems, and has received much attention from researchers and scientists. This problem involves routing a fleet of vehicles, each visiting a set of customers such that every customer is visited exactly once and by exactly one vehicle, with the objective of minimizing the total distance travelled by all the vehicles. The vehicle routing problem with simultaneous pickups and deliveries (VRP_SPD) is an extension to the VRP, where the vehicles are not only required to deliver goods to customers, but also to collect some goods from the customer locations.Ant Colony Optimisation (ACO) is a probabilistic technique that simulates the ants’ food-hunting behaviour, which is used for solving problems that do not have a known efficient algorithm. The Ant Colony System (ACS) is one of the most famous metaheuristic algorithms, which differs from the other ACO methods due to its transition rule and updating pheromone. This paper proposes an improved ACS, mixed with a 3-opt local search for solving the VRP_SPD. The proposed method is different to the common ACS with regards to the coefficient pheromone and heuristic information for the ant visibility measure. This process will avoid the premature convergence and generate better solutions. The proposed algorithm is tested on 34 standard instances available in the literature. The computational result shows that the proposed algorithm improves the four best-known solutions of the benchmark problem, and it is competitive with other metaheuristic algorithms for solving the VRP_SPD.

Although there have been considerable progressions in increasing the safety of the freeway, the importance of freeway accidents and their human and economic costs have made study and modeling of freeway accidents imperative for recognition of the effective factors on their severity. The severity modeling of freeway accidents enables researchers to survey and analyze the effective factors with regards to their severity.In this research, the Tehran – Karaj freeway is used as a case study, and incident information from 1384 to 1387 has been collected from associated organizations. With attention to the nature of driving accidents, many different parameters are effective in causing these accidents and their severity. In this research, ordinal profit regression modeling is employed for analysis to understand the influence of the variables associated with an accident. This study also uses SPSS software to develop the prediction model.The results indicate that the severity of accidents is related to the driver’s age, meaning that drivers under 35 years old are factors that increase the severity of crashes. Accident severity is also influenced by traffic volume, where a traffic volume less than 4000 VPH has an impact on increasing severity of accidents. Another conclusion is also presented, where it is shown that nonconformity to following distances has a significant impact on the severity of accidents on the freeway.