Journal of Transportation Engineering
Year:2016 | Volume:8 | Issue:1|Papers Count:11

Coarse aggregate constitute main part of Stone Matrix Asphalt mixtures (SMA). In consideration appropriate workability of SMA to rutting it is required excellent lock and bind between coarse aggregate particles, bitumen and fibers are required, to fill the gaps and voids. Although there are numerous recourses of gilsonite in Iran, but there are limited studies about this modifier. So, there is a need to investigate the effects of using this material as a modifier. In this study different percentage of Gilsonite (0%, 5%, 10% and 15% compared to the total asphalt binder used in mixture) was used and bitumen characteristics including softening point, penetration test and viscosity were examined. The performance tests including, marshal stability, flow, resilient modulus and dynamic creep test are carried out on unmodified and modified SMA mixtures with UTM system. According to the results of laboratory tests and assessment of the results it can be said that by increasing the Gilsonite to the SMA mixtures, Marshal stability of specimens increases, in addition resilient modulus and dynamic creep parameters have significant increase which leads to enhancement in rutting performance.

Using fibers to reinforce bitumen is a new method to improve mechanical properties of asphalt-concrete. Economical competitive advantages, easy to work and improvement of physical and mechanical properties are the benefits of reinforcing asphalt-concrete by using fibers in comparison with other modifiers, e.g. polymers. This paper investigates the adhesion of aggregates to fiber-reinforced bitumen. This concept has been described in two parts including theoretical and experimental sections. In the former section, pull-out force of aggregate through a fiber-reinforced bitumen has been modeled by using "force-equilibrium method" and "slippage theory of short fiber composite theory". In the later section, polypropylene and polyester fibers of 12 mm length at 0.1%, 0.2% and 0.4% were used to reinforce 60-70 bitumen. Both of lime and quartz aggregates were considered in experimental design. Consequently, the instron tensile tester was modified to perform pull-out tests. Pull-out test measured the force required to pull-out the aggregate through the bitumen and/or fiber-reinforced bitumen. The experimental results showed that the proposed model can predict the pull-out force of fiber-reinforced samples.

Scheduling vehicles’ runtime and dwell time is one important phase of designing and developing public transportation systems. Apart from trains’ headway time in subway systems, parameters such as time and rate of acceleration when trains startup or brake and also their dwell time at stations influence scheduling design criteria including passengers travel time, economic efficiency of the service and the amount of energy consumed. Since these criteria are not positively correlated, Tehran subway line no.1 service schedule has been optimized using NSGA-II in this study. To achieve this goal, the problem was modelled first and objective functions of optimization procedure were formulated based on scheduling criteria. Then, by performing the multi-objection algorithm, solutions occurred on the Pareto Front was obtained. Since the number of solutions obtained by NSGA-II are numerous, K-Means analysis was used to cluster solutions. Centroids of each cluster could be considered as candidate solutions that one of them will be chosen by decision makers as the preferred solution. Results of the study show that using the suggested approach would output a wide variety of solutions and provide possibility of choosing the final solution based on decision preferences for the decision maker. Calculated objective functions for candidate solutions were compared with those for current subway schedule that resulted in the preferred solution to be chosen which leads to passengers travel time and economy loss of the system decreasing by 7.16 and 5.13 percent respectively.

Location-Routing problem is an interesting subject in the literature due to its various applications for real world problems. This paper proposes a two-echelon bi-objective model under the assumption of characteristics including multi commodity, simultaneous pickup and delivery and soft time windows. The first objective function aims to minimize transportation costs besides location costs, while the second objective function minimizes fuel costs. Various approaches such as robust optimization have been developed in the literature to deal with uncertainty. The proposed model accounts for the uncertainty in customers’ demands in terms of different scenarios and the problem is formulated as a mixed integer linear programming model using p-robust approach. Finally, a number of sensitivity analysis are conducted by applying the historical data of a spare part distributer company. The results imply that a slight increment in expected cost of system results in decreased scenario costs.

Skid resistance characteristics of road marking materials affect road safety appreciably. The two componenet road marking materials that are extensively used in pedestrian crossings should have skid resistance properties in order to assure safety of both pedestrians and cyclists. In this research evaluation of skid resistance and other physical properties of a two-component road marking material (that is extensively used in Tehran), were determined. Several mineral additives were used, namely Waste Glass, Silica and Leka (an expanded clay). British pendulum testing was conducted on all the samples and their skid resistance values (SRV) were determined. In addition to skid resistance, abrasion resistance, reflectivity and also adhesive properties of the samples were determined.Testing results showed that conventional road marking materials had poor skid resistance characteristics. With using the above mentioned additives the problem could be partially solved. Comparing the results it was shown that among the various additives, waste glass had performed better. In fact, the results showed that application of %10 waste glass resulted in SRV increase from 21 to 40. This also reduced abrasion resistance of the road marking material for some 10 percent and provided greater reflectivity.

This paper deals with the school bus routing problem (SBRP). This problem is a variant of the vehicle routing problem where three simultaneous decisions that have to be made: determining the set of stops to visit, for each student which stop he should walk to and the latter case occurs when determining the routes visited with the chosen stops, so that the total traveled distance is minimized. In the standard VRP all stops to visit are given, but in school bus routing problem, is assumed that a set of potential stops is given, as well as a set of students that can walk to one or more of these potential stops. The school buses used to pick up the students and transport them to school have a finite capacity. Ant Colony Optimization (ACO) is a meta-heuristic for combinatorial optimization problems. In this paper, artificial ant colony is developed. its successful application to the SBRP and finds optimal or close-to- optimal solutions of large instances of the SBRP in very limited computing times is shown.

Significant cost is associated with road accidents, traffic jam, waste of runoff, and polluted water which negatively impact on environment. All of these problems are produced due to expansion of cities and impervious surfaces. Pervious concrete pavement is an effective tool to overcome these problems. There have not been enough studies conducted on physical and mechanical properties of aggregates to date. The main purpose of this paper is to investigate the effect of aggregate size on physical and mechanical properties of pervious concrete pavement. First of all, sufficient mix designs have been produced using only coarse aggregates. Then, cylindrical and beam samples have been taken and applied to execute compressive, tensile, flexural, and infiltration tests. The test results have been analyzed with regards to aggregate size. It is concluded that with similar water to cement ratio and cement content, the greater the size of aggregate, the less the compressive, tensile, and flexural strength and the more the infiltration rate.

Wheat is one of the strategic goods has a significant share of household portfolios. Due to the high volume of wheat transportation in our country and the importance of providing timely, more attention needs to the distribution system of wheat. Current system for wheat distribution is direct shipment and there is no planning for wheat transportation. Due to the high volume of wheat transportation in different months, using the distribution points seems to be practical. For this reason, we are going to use hub-location approach for distributing wheat in the country. As results shows, the new distribution network will significantly reduce transportation costs. For modeling the wheat transportation network, we use hub location models with fix costs, so the number of optimum hubs will be determined. Also this model considers the characteristics of wheat distribution network such as seasonal production and various modes for transportation of wheat. For solving the problem, CPLEX software is used. Other outputs of model are determination the optimal paths from the original points to hubs, hubs to hubs, and hubs to destination points for each period. Also the types of transportation modes between hubs are determined. Finally this study ended with Sensitivity Analysis of different parameters and conclusion.

Since models of transport demand have shifted from trip-based to activity-based approaches, prediction of activities and their duration has gained further importance. Activity duration is an important component of activity participation behavior of individuals, and therefore, an important determinant of individual travel behavior. Since duration data is non-negative and often censored, it follows non-normal distributions, hence, linear regression is not a suitable model. Duration models offer vaster suitability for this kind of data and thus have been used for behavioral analysis of individual trips. Since for the past two decades, shopping has been under spotlight as indispensable diurnal activities for human, the current paper has tried to compare the results of several approaches with their different modeling assumptions, by modeling duration shopping activity concurrent with recognition of influential factors on duration variable and proper distributions for such data. case study of this research, is the shopping trips of 2 and 3 home-based trip tours data obtained from inquiry a sample of Qazvin residents comprising personal and household information, the characteristics of transport networks and the features of susceptible sites for doing shopping activity which constitute 99 percent of Qazvin's citizen's daily travels. The analysis and analogy of modeling results indicate estimation of parametric approach with regard to goodness of fit, is better than other approaches and suitable distributions has used for shopping activity duration data is log-logistic distribution. Considering that scale parameter estimated of model is lower than one, the hazard curve is non-monotonic and an inverted U-shape. Worker's female than male and male than other, has associated lower duration to shop with significant difference (p=0.005). Non- motoric travel modes has positive influence to reduction of shopping duration (p<0.05). In addition, covariates such as distance and commercial destination travel attraction, are significant portion to increase of shopping activity duration (p<0.05).

In order to consider the effect of loading time and temperature on the stiffness modulus of asphalt mixtures in current mechanistic-empirical pavement design methods, such as Mechanistic-Empirical Pavement Design Guide (MEPDG), the quasi-static analysis assuming elastic behavior of asphalt mixtures is employed instead of dynamic analysis assuming viscoelastic behavior of asphalt mixtures. In current procedures, quasi-static analysis of pavement is commonly accomplished by dynamic modulus. Nevertheless, previous studies have shown that the dynamic modulus is greater than the resilient modulus due to consideration of rest period for determination of resilient modulus of asphalt mixtures. Due to this reason, utilizing dynamic modulus for quasi-static analysis of pavements results in decreasing reliability of pavement design. This paper aims to propose a new method for quasi-static analysis of flexible pavements on the basis of resilient modulus master curves of asphalt mix under three loading waveforms of square, triangular and haversine. In the proposed method, the resilient modulus master curves under different loading waveforms are developed based on measured complex moduli and by employing linear viscoelastic theory. Comparison of fatigue life and rutting life resulting from the quasi-static analysis of pavement based on the dynamic modulus and resilient modulus shows that the pavement life is overestimated when the dynamic modulus master curve is used instead of resilient modulus master curves. Also, this paper shows that for more accurate quasi-static analysis of flexible pavements and to consider loading waveform as well as the rest period on the stiffness of asphalt materials, the dynamic modulus values should be used with the assumption of f=1/2mt instead of f=1/t.

In this paper, the effects of varying tire pressure and axle load on the responses of cracked asphalt pavements are investigated. Traditionally, linear elastic methods are used for pavement analysis and determination of pavement responses. Three dimensional Finite Elements method using ABAQUS has been utilized for modeling and analysis of cracked pavement under dynamic loading. Pavement responses including the maximum tensile strain in asphaltic layer, the maximum compressive strain on the sub-grade, the maximum vertical deflection of surface, and the stress intensity factors under standard 8.2 ton single axle load at different tire pressures of 80, 100, 120 and 150psi and single axle at different loads of 5, 8.2 and 15ton, all at the same tire pressure of 100psi, have been evaluated. Longitudinal top down and bottom up cracks with the similar geometry and position relative to the load have been considered for evaluation. All pavement materials have been modeled with linear elastic behavior. The results show that the pavement responses increase with increasing tire pressure and axle load with higher values for the cracked pavement compared with the pavement without crack. The rate of variation of the pavement responses with tire pressure and axle load is different for the sections with top down and bottom cracks, with, generally, a higher rate for the top down crack. In addition, it is found that the top down cracking results in higher tensile strain, surface deflection and stress intensity factor in mode I than the bottom up cracking, while the compressive strain on the sub-grade and stress intensity factor in mode II is higher on the pavement with bottom up cracking. The tensile strain in asphalt layer and the compressive strain of sub-grade in cracked sections is found to be up to 60% higher than in the control section without crack.