پژوهشنامه حمل و نقل
سال نهم شماره 3 (پیاپی 32، پاییز 1391)

Highways are one infrastructure facilities that play a vital role in transportation. There are several approaches for the highway management; such as Intelligent Transportation System (ITS), which control technologies to improve traffic flow quality in transportation networks. Different methods have been developed such as ramp metering (RM), variable speed limits (VSL), route recommendation and variable message signs (VMS) are recognized as the most effective for relieving traffic congestion. This research paper discusses the optimal coordination of variable speed limits and ramp metering in a highway traffic network. The control problem is to determine the optimal combination of control variables that result in the best network performance. Efficiency of this problem was evaluated based on the total time that a vehicle spent in the network. The applied co-ordination approach incorporates the macroscopic traffic flow model METANET and genetic algorithm. The proposed model was implemented on a highway network. The results showed that applying this model to the highway networks could prevent traffic breakdown and therefore, the satisfied traffic flow could be achieved.

The aim of this study is to analyze the time headway distributions of vehicles on multi-lane highways under heavy traffic flow conditions. In this study, the driver behavior was assessed when selecting headways at daytime and nighttime peak hours. The field-data was collected at the Shahid Kharrazi six-lane highway in Isfahan, which was under uninterrupted flow conditions. The primary survey shows that a high percentage of drivers do not consider safe headways; but instead use a car-following process, which leads to an increasing risk-ability of drivers and causes a safety reduction. The chi-squared method was used to test the goodness of fit of the statistical models on headway distributions, and the results show that the lognormal model with a shift of 0.24 seconds is an appropriate model for headways of the passing lane. In addition, the gamma distribution with a shift of 0.69 seconds was a good fit to headway data collected from the middle lane. The dissimilarity of headway models is due to different behaviors of drivers in the lanes during traffic peak hours; as the pattern of car-following in the passing lane is different to that in the middle lane. The majority of drivers in the passing lane tend to follow the vehicles in front even at high speeds. This has triggered the difference in capacity. In addition, the results obtained from a comparison of models during day and night hours show that at high levels of flow rate in night hours, the drivers choose headways that are safer than during daytime hours.

Optimizing the railway capacity is one of the most important goals in the train scheduling field, and literature shows that optimizing the use of the existing railway capacity is a more cost-effective solution than capital investment on upgrading or installing new railway infrastructure. The sequence of dispatching trains and stopping schedules are the main factors that can affect the railway capacity on double track lines, and in this thesis, a train sequencing and stop scheduling problem is studied in order to maximize the use of existing railway capacity. The main decision variables are the sequence of dispatches from the origin station and the selection of the best station for the scheduled stops in order to minimize the makespan. This research proposes a flexible flow shop scheduling formulation, which considers block section and station as single and parallel machines. In addition, an integer programming model is presented for solving the train sequencing problem in double track railway lines by considering the station infrastructure and stopping schedule policies in Iran’s railway systems. The problem is of very high complexity, and therefore a greedy randomized adaptive search procedure (GRASP) is used for finding the near optimal solution. Three meta-heuristic algorithms based on GRASP are developed and tested on randomly generated test problems, and the output results show the effectiveness of the proposed meta-heuristic algorithm in solving real-sized problems.

The global population is booming, and Iran is no exception. This additional capacity is placing considerable strain on many aspects of human life; in particular on transport. Fossil fuels will continue to play an important part of the transport fuel mix, and therefore the limited and dwindling reserves need to be optimized for economic, social and environmental reasons. The goal of this research is to determine the gasoline transport capacity from ports of the country and local refineries to different destinations throughout Iran. It is the aim of the study to determine an optimization alternative for the gasoline transport capacity from and to each specified destination by applying the trans-shipment model. The goal is to minimize transport expenses due to sending gasoline from two sources to seventy seven destinations, by using forty seven intermediate points and 6,076 decision variables (transport direction). By achieving this goal, industry is confronted with demand and supply restrictions, simplicity of use and non-negative portable gasoline capacity. Referring to the results obtained, the expense of 73% of gasoline transport by pipe-line was 70%, and for road transport of 23%, it came to 25% of the total gasoline transport expenses. Share of transfer by ship for 3.4% yields an expense equal to 5%, and in addition the results show a 17% cost saving of the gasoline distribution expense in 1387.Urban highways are one of the most important infrastructure facilities that play a vital role in daily transportation. There are several approaches for the management of urban highways; one of which is the Intelligent Transportation System (ITS), which integrates advanced information and control technologies to improve traffic flow in transportation networks. Different methods have been developed to improve the performance of highway networks, among which control strategies such as ramp metering (RM), variable speed limits (VSL), route recommendation and variable message signs (VMS) are recognized as the most effective for relieving traffic congestion. This research paper discusses the optimal coordination of variable speed limits and ramp metering in a highway traffic network. The control problem is to determine the optimal combination of control variables that result in the best network performance. Efficiency of this problem was evaluated based on the total time that a vehicle spent in the network (TTS). The applied co-ordination approach incorporates the macroscopic traffic flow model METANET as a prediction model, and a genetic algorithm as an optimization algorithm to co-ordinate the RM and VSL in a highway network. The proposed model was implemented on a highway network with two ramps and two VSLs upstream of each one. The results showed that in cases where ramp metering is insufficient to prevent congestion, variable speed limits can prevent a traffic system breakdown and maintain a higher outflow. In other words, optimal co-ordination of ramp metering and VSLs can significantly reduce congestion and result in a lower total time in the network for vehicles. The results have been compared with a previous study in this field and have been shown to be more beneficial, due to the use of the GA in comparison to the search methods used previously in the literature.

With the advent of modern globalization and advances in technology, there has been a considerable increase in the prevalence of air transport. It is clear that the confidence in the quality of air transportation systems requires evaluation of airports’ performances. The purpose of this paper is to evaluate the efficiency of airports by way of DEA (Data Envelopment Analysis). This system requires inputs of quantity of human resources, terminal menstruation, band length, alongside outputs such as number of flights, number of transferred passengers and amount of cargo. This data is used in the DEA technique to classify the airports according to their efficiency and non-efficiency groups. Then, the study identified source airports for non-efficiency airports, along with the sensitive index effects on the efficiency of airports to determine the potential for airport improvement. Emam, Mehrabad, Ahvaz, Rasht, Sari, Gorgan and Birjand airports had the maximum efficiencies. The quantity of human resources of each airport was identified to be the less sensitive index, and terminal menstruation was identified as the most sensitive index for the efficiency of Iran airports. Finally, the study employed a crossing efficiency evaluation technique for ranking the airports, which showed Ahvaz airport in the first rank and Mehrabad airport in the bottom placing rank.

Providing adequate surface frictional resistance is a major requirement in the construction of concrete pavements. The choice of surface finishing treatment method is an important factor, which directly affects the skid resistance properties of the pavement surface. Furthermore, there are currently no widely accepted guidelines or procedures for identifying and selecting methods of texturing concrete pavements that consider all the relevant technical, environmental, economic, and safety issues. To this end, the aim of this study was to investigate the functional relationship linking the macrotexture characteristics and skid resistances of concrete pavements, which required mixtures to be designed with consideration of three different grading aggregates based on the difference in nominal maximum aggregate size (NMAS). With acceptance of these three mixtures, the study consisted of an experimental program that involved skid resistance testing of laboratory prepared specimens, which were textured using the tining method in plastic concrete. The British Pendulum Tester and Sand Patch Method were then applied for microtexture and macrotexture measurements, respectively. Tines were raked in three different widths and with four different spacings, and British pendulum tester experiments were performed on transverse, skew and longitudinal tined surfaces. The results demonstrated that the skid resistance of a concrete surface is significantly affected by the macrotexture. In addition, this paper finds that the friction value increases with an increase in tine width and decrease in tine spacing. Furthermore, the maximum friction was achieved when the pendulum move direction was perpendicular to the tine direction.

As car travel becomes more and more prevalent, it is vital that research is conducted in order to improve safety, and in particular, this research is focused on the effect of driver types. In this study, 1611 drivers were studied by way of questionnaires, and is aimed towards examining the properties of those drivers on the basis of demographic and personality criteria (age, gender, education and type-A personality), and the effect that they may have on safety indicators (driving behavior, accidents and ticketing rates). Based on the above criteria a 36-level scale of drivers was produced. Subsequently, in order to categorize 36 driver ‘states’ into significant and homogeneous groups, a Cluster analysis and statistical significant test (Mann-Whitney U) were conducted on their driving behavior, accident and ticketing rates. Finally, the results revealed that a 4-level index for driver safety is appropriate, and also that there is no significant difference among those levels on the basis of lapse and error behaviors. Moreover, the validation of the results was inspected by way of 158 random questionnaires, which were left over until the study end, which confirmed the obtained index. This index will be an important tool in order to assess drivers’ risk potentials so as to improve safety and management planning.