JOURNAL OF TRANSPORTATION RESEARCH
Year:2010 | Volume:6 | Issue:4 (21)|Papers Count:9

Today, existence of several access driveways to Iranian main roads has become one of the main problems of the national roads network. As the design, operation and monitoring conditions in such roads do not match the existing standards; many dangerous spots are formed in these roads.The main goal of this research is to determine the impact of access density on accident rates in Iranian roads. For this purpose, at the first phase, the terminology of access roads, their characteristics and also design and operation parameters were taken into consideration and defined. Then, by considering road accidents trends, those parameters which directly have impact on accidents were theoretically introduced and considered. Then the descriptive statistical analysis and statistical regression models were presented in order that the relation between roads accident rate and main relevant factors causing accidents (of which we can refer to access driveways), become clear. The main results of this research are as follows:- Changes in the density of access driveways can directly affect the rate of accident with the same ratio.- Less density in access driveways will result in smoother incremental trend of accident rates.- When access density increases and passes some specific limit, the accident rates increase remarkably.- In roads where there are a lot of access driveways, after some specific maximum limits, with an increase in access density, the accident rates decrease. Therefore, there are also other important factors causing accidents, especially in roads with many access driveways.

Transportation, which has a specific division in production economics and service systems, has a great value in a gross national product (GNP) in every country. Thus, most researchers worked on improving routes, omitting unimportant transportations, or replacing shortcut routes. For these reasons, they have developed a traveling salesman problem (TSP) and a vehicle routing problem (VRP). The classical and deterministic VRP seeks routes with the lowest cost from a depot to a geographically dispersed customers’ set with known demands. Usually in the VRP, monopoly in an environment is the first assumption in solving the problem. Also attending to the competitors for getting better success is important. In the real-world situation, customer’s cash is limited, and a competitor that reach to customers earlier than others can receive the maximum cash. So, providing the specific service to customers earlier than other competitors is very important. In this paper, getting the maximum cash is considered in our presented model with a competitive environment. In the best of our knowledge, the VRP with maximizing cash in the objective function has not been considered in the literature. Thus, we consider a bi-objective model that minimizes the total distance travelled and maximizes the cash flow in a competitive environment. These objectives conflict with each other (i.e., the better one of them, the worse the other). So for facing to this difficulty, a weighting method is needed to integrate these objectives into a single minimization cost function. The presented mathematical model is solved by the Lingo 8 software for various test problems. Since exact solutions of VRPs that belong to the category of NP-hard problems are not practical in large scale, a hybrid simulated annealing (SA) algorithm embedded with genetic operators is proposed in order to obtain an efficient solution in a reasonable computational time. Furthermore, a real case study is carried out to validate our presented model and the related results are reported. Finally, the remarkable conclusion is presented.

Highway bridges are the most important members of transportation network, which play the key role of lifelines at the time of natural disasters like earthquakes. Several solutions for rehabilitation of highway bridges have been proposed by engineers among which seismic isolation solution seems to be a good solution from the practical point of view.Replacement of existing elastomeric bearings with lead-rubber seismic isolators is a solution that exempts the substructures from expensive retrofit work. Since the use of seismic isolators increases the displacements of the deck, more exact estimation of the displacements is essential to provide enough gap distance at the end of girders. In case of underestimation of the gap, there is a high probability of collision between two adjacent decks or deck and abutment. Such collision causes not only seismic isolation to be non-effective but also harmful for bridge health and serviceability. Deck fall and abutment rotation are some of the results.In this paper, for more exact estimation of the deck displacements, a coupled plasticity model has been used for nonlinear modelling of the seismic isolators. Earthquake excitation also has been applied bidirectional in two orthogonal (longitudinal and transverse) directions simultaneously. A comparison between the results of coupled plasticity-bidirectional excitation and uncoupled plasticity-unidirectional excitation has been carried out. The results show that the deck displacements are estimated unrealistically in the uncoupled plasticity-unidirectional excitation modelling (common engineering practice) relative to the coupled plasticity-bidirectional excitation modelling.

Finding the location of airport is an important factor to reduce transportation costs. In this paper we want to find the location of an airport in the Semnan province of Iran. We use the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) method and the algorithm of finding the center of a tree to find the best location of airport. To model this problem consider a graph which its vertices and edges represent the cities and roads, respectively. TOPSIS is one of the well-known methods for multiple attribute decision making. We first use this technique to determine the weights of cities. Then an algorithm of solving center location problem in a tree is applied to find the location of airport in the Semnan province. The center location problem is one of important problem in the location theory; this problem asks to find the location of a facility in the graph such that the maximum weighted distances from vertices of graph to this facility is minimized. In this research we consider the five cities and assign ten attributes to each city. According these attributes the weights of vertices are determined by TOPSIS method. After solving the center problem in the graph of Semnan province we find that the optimal location of the airport in this province is in the road between the cities Damghan and Semnan which it is distance from Damghan is 16 KM.

The most important operational decision related to transportation in the supply chain planning is the routing and scheduling of deliveries. Vehicle Routing and Scheduling Problem (VRSP) is a significant task in both supply chain planning and distribution optimization. A very large body of research and modeling literature has been devoted to address VRSP. But most of them concentrated on hypothetical or simplified problems and disregarded many practical aspects of such problems. On the other hand, many practical problems have been tackled by different commercial systems for this class of problems, but little has been published about them. The primary objective of this paper is to develop a flexible algorithm for solving complex real VRSP arises in practice.VRSP can be simply defined as: planning efficient flow of goods between facilities by a fleet of carriers through the transportation networks. This statement reveals the main components or objects of VRSP problems, namely, goods, facilities, carriers and transportation networks. Each object may have its owners, who impose their objectives and restrictions to the problem. For example, drivers may be considered as the owners of vehicles who may impose working time or region constraints.In developing the algorithm, the most important criteria have been flexibility and speed. Most of new algorithms developed by researchers are problem specific. They might improve the quality of results at the expense of reducing the flexibility of algorithm to handle new constraints or increasing its computation time.Among various families of heuristics for optimization problems, Tabu Search (TS), Genetic Algorithms (GA) and Simulated Annealing (SA) have shown promising performance to solve various combinatorial problems. TS have several features which make it suitable candidate for real life complex cases. Robustness, simplicity and flexibility are the most important features of TS. In our experiences, the flexibility of GA is questionable and SA needs complicated parameter adjustment to gain high quality results. Therefore, we selected TS as framework for developing optimization algorithm.In TS algorithm, during the search process, current solution may deteriorate from one iteration to the next. To avoid cycling, recent explored solutions are temporarily declared forbidden by putting their selected attributes in the Tabu list. The TS algorithm has been evolved over time and several innovative features are included in this algorithm by researchers to enhance its performance.In the proposed algorithm, a cheapest insertion routine has been used for building initial solution. Neighborhood structure is another component which heavily influences the behavior of the algorithm. In order to improve the quality of solution or speed up the algorithm, numerous enhanced neighborhood structures have been proposed by researchers. Practical experiments show that a combination of relocation, exchange and 2opt* can provide high quality results within low computational time. We have examined more complex routines like CROSS and 3-opt, which resulted in no meaningful value and higher computation time. Since the problem contains contradicting objectives, using specific to artificially help the algorithm in finding better solutions is harmful and reduces the effectiveness of the algorithm.In order to evaluate the performance of proposed algorithm optimization engine, a comprehensive experiment is conducted on a set of standard problem available in the literature. In this experiment we have used the (CMT) 14 standard VRP benchmark instances. These problems contain 50 to 199 cities in addition to depot. Our intention was to demonstrate the capability of proposed algorithm on classical VRP for which enormous research and experiments has been done. The performance of proposed algorithm is compared with several best known advanced heuristic algorithms.The average deviation of proposed algorithm results from the best known solutions is 0.55 percent. In three instances, it provides the best known solutions. This experiment shows that the proposed algorithm can provide comparable results with sophisticated TS algorithm for classical VRP.  Since the proposed algorithm is designed for real complex problems, we believe that it can easily attain higher quality solutions than algorithms which are designed and tested for standard problems.  Most of available algorithms are quite specific and need special modification for more complex cases.The computation time of algorithms can not be compared directly, since they have run on different machines. Its average run time for the proposed algorithm on CMT set is 0.5 minutes, which is also an outstanding performance. This experiments shows that the proposed algorithm can provide high quality results comparing to the leading edge heuristic algorithms.

Transportation is one of the most important economic sectors, which the performance of the other economic sectors is highly depends on it. High gasoline consumption in this sector has been an issue in Iranian economy. Because of high gasoline consumption there is not any alternative for the government unless the import of gasoline which this could lead in trade deficit. Moreover as a result of economic habitation it would be more tangible. Because of some facts such as low price of gasoline in Iran, none existence of a suitable substitution, high consumption and its effects on macroeconomic variables it would be necessary to investigate the main factors which affects the gasoline's consumption in transportation sector. Therefore this study aimed to estimate long and short- term gasoline consumption function in transportation sector in Iran.In this area, one of the studies that was carried out by Esmailnai, A. (1999) employed data from 1967-1998 for Iran, The results indicate that the demand for gasoline is inelastic with respect to price and income. Naji Eltony (2003) in Kuwait also found same results. Furthermore Khaksari, A & Ardebali, P.(2006), Gaskari, R. Eghbali, A. Eidani, M.(2005), Khatai, M. Eghdami, P.(2005), Zaranejad, M. Ghapanchi, F.(2007), Norozi, H. Salgi, M.(2006), Pagolatous, J.H.(1986), Johanson, T. & Totto, L.(1983), Adegbulugde, A. & Dayo, F.(1986), Akinboade, O. Ziramba, E. Wolassa, L.(2008) also studied the gasoline consumption in transportation sector and its sub sectors such as road, rails and so on.In this study oil-group price index to calculate real price was studied. The investigation of nominal and real price of gasoline for the period over 1974-2006 shows that in spite of increasing nominal price of gasoline between these years, the real price decreased. Also, results showed that the average growth of gasoline consumption in transportation sector was 8.4%.In order to estimate the short and long term demand function of gasoline in transportation sector of Iran the Auto Regressive Distributed Lag (ARDL) method has been used.  This method in spite of providing coefficient of long term model would give the error correlation term too. To estimate the model the MICROFIT 4.0 package has been used.This study aimed to estimate short-term and long-term gasoline demands in transportation sector during the periods (1974-2006) using ARDL method by considering real price of gasoline, GDP, number of cars and average lifetime of cars as independent variables. The dummy variable is defined for 1981 & 1982 which in these years the consumption of gasoline has decreased. When the variables of interest are non-stationary or exhibit a unit root, the procedures of conventional econometric technique may not be appropriate pointed out that in the presence of non-stationary variables, an OLS regression might become a spurious regression, thereby leading to biased and meaningless results. It is important to test stationary of time-series data to set up an appropriate methodology in the formation of econometric models. Therefore, prior to testing a long-run equilibrium relationship between gasoline consumption and dependent variables, the Augmented Dickey–Fuller tests were carried to examine the presence of a unit root for all study variables. Results of ADF tests for stationary are showed that gasoline consumption and average lifetime of cars are stationary in level, I (0) and other variable are stationary first differences, I (1).Results indicate that gasoline price elasticity in short-term is -0.04 while in long-run is meaningless, because of the fixed nominal price and a lack of suitable substitution for gasoline in transportation sector. Short-term & long-term income elasticity for gasoline is 0.57 and 0.89, respectively.  We also found that the short-term & long-term elasticity of gasoline for number of cars is 0.33 and 0.51, respectively.  For average lifetime of cars the short-term & long-term elasticity is 0.15 and 0.24, respectively. The result also shows that income had more effects and the cars average life time had the least effect on gasoline consumption in short and long term. The lagged error correction term was significant with expected negative sign (-0.64).The CUSUM and CUSUMSQ tests on gasoline consumption in transportation sector have been done and the results showed a stabilization of coefficient in confidence level 5%.By conclusion, low price elasticity of gasoline resulted in low efficiency of price policy. Therefore liberalization of gasoline price and omitting of its subsidy could increase the efficiency of price policy. Meanwhile the liberalization of gasoline price could decrease the high consumption. Because of the fact that there is no any suitable substitution for gasoline in transportation sector the demand for gasoline is inelastic with respect to price and income. Hence, substitution of gasoline with CNG would be a good solution. Since there is a strong and positive relation between the number of cars and imports in recent years it would be useful to develop and diverse public transportation such as subway, tram, bus, and so on. The results presented that there is also a strong and positive relation between average lifetime of car and the amount of gasoline consumption, therefore, declining average lifetime of cars and scrapping old car are recommended.

This paper aims to solve railway crew scheduling problem that is concerned with building the work schedules of crews needed to cover a planned timetable. The proposed model is a two-phase procedure. For the first phase, the pairing generation, a depth first search approach is employed to generate a set of round trips starting and ending at home base. The second phase deals with the selection of a subset of the generated pairings with minimal cost, covering all trips that have to carry out during a predefined time period. This problem, which is modeled by set covering formulation, is solved with a genetic algorithm. In order to check for quality and validity of the suggested method, we compare its results with the final solutions that are produced over the 6 test problems of Beasley and Cao (1996). Comparison of the results indicates good quality and solutions.

Existence of vast mountainous areas in Iran has caused construction of many tunnels for connection of the provinces and regions of the country. Maintenance of road tunnels in Iran has been performed in the past with traditional method and only based on observational and occasional inspections. The most important factors in determining the appropriate method of maintenance has been experiences of the operators and the life cycle and prioritization of tunnels based on their present situation in road network have not been paid attention.In order to achieve the goals established for the administration, operation and maintenance of a tunnel it is necessary to have one or more systems to collect the relevant information and make it available at all times. Such a system is termed a Road Tunnel Management System (RTMS).Nowadays, with regard to increasing age of tunnels, maintenance is not solely sufficient and establishment of a system for management and systematic maintenance of tunnels is necessary. Tunnel Management System is a valuable tool which helps the directors in performing optimum maintenance in tunnels, allocating appropriate financial support and alarms tunnel owners in critical conditions.In some countries, national regulations refer to tunnel operations. This requires the production and delivery of documents and reports to various authorities on the condition and maintenance undertaken on the tunnel structures and safety equipment. This may include all the maintenance work and inspections done by the operator. The inspection and maintenance records must be easily retrieved for examination by these authorities. Such systems may be manual, but it is more efficient if they are computer based.This paper has been prepared based on the results of a research programme to establish a system for road management in Iran. In this paper after defining the concept of Road Tunnel Management System (RTMS) and main goals of its establishment, the main stages in this regard have been defined and considered separately. The methods of gradation of tunnel components after inspections in conjunction with structural, electrical and mechanical systems gradation tables have been presented. Finally, the method of RTMS software operation has been explained.