پژوهشنامه حمل و نقل
سال نوزدهم شماره 1 (پیاپی 70، بهار 1401)

Determining the numerical value of the safety effectiveness of countermeasures or the Crash Modification factor (CMF) is one of the issues that has received considerable attention in recent years in the world. In this regard, several studies have been carried out to determine the CMF for converting intersection to roundabout in different countries. The results of these studies have led to a reduction of about 35 to 70 percent of crashes at the intersections. Since there is no serious study regarding determining CMF of constructing a roundabout and the percentage of crash reduction due to this countermeasure in Iran, the researchers are seeking to determine the CMF and reduction percentage of the crashes due to this measure in Iran. For this purpose, Salman Farsi roundabout of Ilam city was evaluated. AADT rates were obtained from the available traffic counts and crash data from the police. For determining CMF, empirical Bayes method was considered. The reason for using empirical Bayes method is its high efficiency in removing the phenomenon of regression to mean and other time-alteration factors and the high precision of this method is due to the use of SPF in order to reasonably estimate the frequency of crashes in the period prior to countermeasure. During studying, a SPF from AASHTO 2010 was used. Using this tool and predicting crashes before and after the construction of the roundabout, as well as calculating the frequency of expected crashes before and after it, the effectiveness of safety was calculated. The results for crash frequency is as crash CMF and crash frequency reduction percentage indicates a CMF of 0.68, implying a 32 percent reduction in crash. The statistical significance evaluation of this reduction shows that the 32 percent reduction of crashes after constructing roundabout is significant at 90 percent confidence level.

Travel time and its variation are among important aspects of transportation that are used as key indicators to evaluate network performance in transportation planning. Studies show that traffic congestion is an important factor effecting travel time reliability and is divided into two categories: Recurrent and Non-Recurrent. Studies show that Traffic incidents, Work zones, Weather, Demand fluctuations, Special events, Traffic control devices and bottlenecks are the seven major factors which cause travel time changes. This article aims to examine how changes in transit geometry (number of lanes), accidents, traffic volume, and weather conditions can affect travel time reliability. In order to do so, a variety of machine learning methods were used to study and model the Virginia highway network, including Support Vector Regression, Nearest Neighbor regression, and Decision Tree regression. The results of this study showed that these tools can reflect the changes in the average travel time to an appropriate extent. Among these methods, performance of the Nearest Neighbor was the best (coefficient of determination 0.85 and error 0.0012 for training set and coefficient of determination 0.57 and error 0.0014 for test set and stable performance equal to 1.47).

this research aimed to investigate the effects of using waste polyethylene terephthalate (PET) on the resilient modulus of asphalt concrete. To this end, waste PET was added into asphalt concrete at different dosages of 0, 2, 4, 6 and 8% (by the weight of binder) and the resilient modulus of the mixtures was evaluated at different temperatures of 5, 25 and 45°C. Coarse and fine PET particles were added into asphalt concrete. Response surface methodology in Design Expert software was utilized for designing of experiments, developing a model for prediction of resilient modulus and evaluating the main and interaction effects of different factors on the resilient modulus of asphalt concrete. A polynomial model was well fitted to the test results relating temperature and PET content to the resilient modulus. Analysis of variance in Design Expert software implies that the model is highly capable for prediction of resilient modulus. Temperature, PET content and PET size are found to be effective on the resilient modulus. The resilient modulus of the mixtures was found to increase with increasing PET size and content, while it decreases with increasing temperature. However, the decrease of resilient modulus with PET size is not significant. It was found that there is no interaction between temperature and PET content with PET size, while interaction effect was found between temperature and PET content. Higher reduction of resilient modulus with increasing temperature was found to be in the mixtures containing higher PET content.

Identifying road segment at risk of accidents offers a special approach to safety professionals to better understand crash patterns and enhance road safety management. Conventional methods for identifying accident hotspots and crash patterns are not strong enough to take into account the spatial properties of crash data in the model. Traffic accidents with a spatial nature tend to be spatially dependent, Spatial models describe the predicted value of the crash pattern in space, which can be due to changes in the remarkable properties of the local environment Reflects crash densities better and provides a more realistic picture of crash distribution. In this study, all the main suburban axes of Hamedan province based on spatial accident data from 2017 to 2019 using kernel density distribution methods, geographical weighted regression, (GWR) geographical weighted Poisson regression(GWPR) have been studied. The results of the models show that the geographically weighted Poisson regression(GWPR) model has better results for predicting crash locations than other models.

The tourism sector is considered by policy makers because of its positive external implications for other sectors of the economy such as services and industry, and its positive effects on employment and economic growth. The revenue generation of the country's tourism industry, in addition to being a function of economic variables including exchange rate and per capita income of the country, depends on the services of the transport and hotel sectors, the state of political and economic stability of the country and the presence of historical and natural attractions of the country.The present paper examines the factors affecting the tourism sector of selected developing countries with emphasis on transport infrastructure in the tourism development sector for the period 2000-2015. The results of the research indicate that the development of transportation in the air and rail sectors has had a positive and significant impact on the tourists entering the countries. Also, the tourism registered in the UNESCO Organization, the political stability of the host countries, per capita gross domestic product and the exchange rate have had a positive impact on the arrival of tourists.

Existence of soft soil layers and high ground water level in the Qom Salt Lake area have caused deflection more than allowable limitation in Tehran- Isfahan high speed track railway. Due to reduce deflection of track railway in this area, improving the stiffness and strength of the soil beneath will be done by means of concrete pile group. But also, due to the high speed of train, resonance phenomenon is expected to happen. Despite conducting some researches on the effect of improving soft ground by pile in recent years, but there are ambiguities about performance of pile on the increasing critical speed of the track-ground system which track has been experienced large dynamic amplification as the train speed approaches that speed. So first, the bearing capacity of pile and soil layers geotechnical parameters have been determined by comparing the numerical modeling results of single pile with data obtained from in situ compressive loading test on that in this paper. Afterwards, the effect of the geometrical dimension pile group on the dynamic behavior and critical speed of track-ground system has been investigated under various speed of train (60-450 km/h) using 3D finite element model. The results indicate that resonance phenomenon has been occurred at speed of 100 km/h, which is equal to Rayleigh speed of first subgrade layer. However, improving of soil layers by pile group increases the value of the critical speed to 250 km/h.

After applying the logit model as a route choice model in early stochastic traffic assignment algorithms, other models have been developed to overcome its theoretical weakness in considering path overlap. These models maintain the closed-form and computational convenience of logit, while not requiring simulation and computational efforts of probit. The purpose of this paper is to evaluate the most important of these models in comparison with each other. The models under consideration are Multinomial-logit (MNL) model, two modified MNL models called C-logit and PS-logit, and two models from the generalized extreme value family called cross-nested logit (CNL) and Paired-Combinatorial logit (PCL). These comparisons were performed at different levels of network congestion (origin-destination demand) and different values of perception variance of network users (scaling parameter) and were also compared with results of deterministic traffic assignment. Results of a nine-node and the Nguyen network show that as the congestion level increases, general patterns of link flows of stochastic assignments approach the deterministic assignment link flows; While the difference of these link flows in four models that consider the effect of path overlap increases compared to MNL model. Also, as the variance of user perceptions increases, the difference of link flows of stochastic assignments relative to the MNL model and relative to the deterministic assignment increases. Besides, results of the studied models for the Sioux-falls network show that path flows in stochastic assignments have much more entropy than the deterministic assignment, and therefore stochastic models produce more probable answers in this regard.

In Iran, the Code 415 is used to study the geometric design and road safety. There are no specific manuals to design military roads. This paper is aimed to optimally design the radius of horizontal curves in military roads under more realistic conditions. For the purpose of road geometric design in the Code 415, the minimum radius of horizontal curves is calculated based on the point mass model. In the real world, vehicles move like a multi-dimentional mass not a rigid one, therefore the equation presented in the code 415 can be questioned. This doubt seems to be reasonable, since in reality, the forces acted on each single tire differes as vehicle passes the horizontal curve. So, in order to analyze more accurately, 112 scenarios are considered in this research. The scenarios include different slopes, grades, rollover indices, load transfer indices, lateral friction factors in the horizontal curves. The results showed that considering the dynamic limitations of lateral acceleration, Rollover index, load transfer index, Roll rate, lateral friction factor, the proposed radius in this paper can be lower than the proposed radius in 415 by 95.6 percent. These proposed radii of of horizontal curves are suitable and widely used in difficult operational-military routes.

Driving accidents are a serious problem in the world. Human, the road, the vehicle and the environment are the four causes of driving accidents. The most effective cause of accidents is the human factor. Therefore, in the field of traffic safety, social science studies, especially psychology studies, are necessary. Any attempt to get to know the personality and improve driving behavior can save many lives. Personality tests are used to identify a person's personality. The research instrument was a questionnaire consisting of three sections: demographic questions, high risk driving behavior questionnaire and Myers-Briggs personality test. Traffic high-risk behaviors included 38 items that were classified into four factors: aggressive behavior, fatigue and distraction, lack of agreeableness and lack of attention to their health. And personality preferences obtained from the Myers-Briggs test include (Extrovert-Introvert, sensor-intuitive, Thinker- Feeler and Perceiver -judger). Multivariate regression was used to measure the predictive power of the number of accidents. The results of regression analysis showed that among the personality dimensions of Myers-Briggs test, the perceptual variable has the most significant predictive power of accident variable. Also, among the high risk driving behaviors, aggressive behavior and distraction have the most significant predictive power of accident variables.

Securing traffic flows in cities is one of the most important goals of urban transportation planning. Among the country's metropolises, Qom city with a large volume of traffic flows in the city, along with the illegal behavior of some drivers while driving, is lacking. The required traffic equipment and ... The safety factor of traffic flows in some passages in the city has been significantly reduced, although the urban management system of Qom has taken appropriate measures to improve the safety of intra-city transportation so far. Unfortunately, during the three years (2014-2015), more than 17,000 accidents have been registered within the legal limits of Qom, of which more than 95% occurred as injuries and the rest as deaths and damages. More than 17,452 accidents, of which 89 the percentage of these accidents has been recorded as injuries. More than 53% of all accidents occurred between 12 noon and 8 pm, and the daily analysis of accidents revealed that more than 32% of accidents occurred on Saturdays and Tuesdays. 58% of all accidents in Qom are related to accidents, one of which is motorcyclists, and 36% of all accidents are related to not paying attention to the front, 24% are related to non-compliance with the right of way. On average, during the last three years, more than 88 fatal accidents have occurred in the city of Qom. And the necessary measures have been proposed..

Asphalt pavement cracking is one of the most common pavement failures that can be caused by fatigue and aging of asphalt mixtures under environmental conditions and traffic loads, causing other damage to asphalt pavements. For this reason, investigation of fracture behavior and precise evaluation of mechanical fracture parameters of asphalt mixtures and its effective parameters can assist pavement engineers in designing and constructing high-quality pavements. In this study, semicircular bending specimens (SCB) were used to evaluate the impact of experimental loading rates on different fracture mechanics parameters of asphalt mixtures at intermediate temperatures (25 ° C). The main objective of this study was to determine the most appropriate loading rate for SCB testing at an intermediate temperature, taking into account the coefficient of variation of the test and with specimens with geometrical characteristics of diameter and thickness, 15 and 3 cm and crack length equal to 18 mm. For this purpose, SCB samples were subjected to loading rates of 0.5, 1, 3, 5, 20, and 50 mm / min and Peak Load parameters for cracking of asphalt samples (PL), Fracture Energy of asphalt samples (FE). Flexibility Index (FI) and Cracking Resistance Index (CRI) were evaluated. The results showed that as the loading rate increased, the amount of PL and FE for the asphalt mix failure always increased, but FI and CRI did not show a significant increase with the loading rate. Based on the results of the experiments and evaluation of the coefficient of variation (COV) of the parameters mentioned, loading rates of 3 and 5 mm / min are recommended for use in the SCB test.

Overloaded vehicles damages roads and road structures such as bridges and destroys the country's high-cost road network, which is built at a high cost. Overloading more than the standard capacity of vehicles is one of the effective factors in damaging the roads. In general, the phenomenon of overloading of freight vehicles is common in developing countries where traffic control measures are poorly implemented. On the roads of the country, according to the studies, it is predicted that on average, at least “between” 5% to 10% of the trucks have overload conditions. This is one of the most important factors in reducing the service life of road pavement. In this paper, the results of data analysis collected from the weigh-in-motion system (WIM) and the effect of overloaded vehicle on flexible pavement are presented. By calculating the equivalent axial loads and damage factor (DF) to the road pavement, the remaining service life (RSL) of the pavement has been determined by considering Overloaded truck impact. The analysis showed that the damage factor obtained from WIM information is to the extent that it reduces the service life of the pavement.

The construction of different paths on fine-grained soil beds is often inevitable and, it is necessary to select and design suitable methods of soil improvement. One of these methods is shallow soil mixing with different additives such as lime and Nano-clay. These particles can improve the physical and chemical properties of the soil as much as possible and make changes on a microscopic scale. In this paper, the stabilization of fine-grained soil beds and their strength properties due to the addition of Nano-clay and lime mixing are investigated. For this purpose, the series of unrestricted compressive strength tests, Atterberg limits, density, PH and microstructural tests including X-ray diffraction (XRD) and scanning electron microscope (SEM) have been performed on the mixture of soil with Nano-clay and lime with different adding percentages at 7, 14 and 28-day curing period. The obtained results indicate that the optimum soil properties were obtained by adding 3% lime and 3% Nano-clay during the 28-day curing period and according to the results of microstructural analysis, it was found that soil resistance increased due to the formation of calcium silicate hydrated gel with reducing the voids and increasing the contacts between soil particles.

Traffic accidents, as one of the most important threats to human beings, have shown themselves as a dangerous phenomenon. The impact of various factors on the incidence of accidents with different contributions has made it difficult to reduce the consequences of this unpleasant event in the safety analysis. Calibrated simulation models by taking into account the interaction effects of factors such as various behavioral characteristics of users in interaction with road have the potential to assess the safety performance of traffic facilities in different situations. Identifying the effective calibration parameters in simulation models due to their different impacts according to the purpose of the study as well as computational constraints is one of the essential steps in the calibration process. This study aims to provide a solution to identify the effective calibration parameters in the safety microscopic simulation model. For this purpose, 4 detectors located at the Mashhad-Sabzevar-Tehran route and vice versa with 23 accidents and 306 traffic records were selected as case studies and by deriving geometric information from available databases, the simulation model of the study area was built in the SUMO microscopic simulation software. By logically executing the simulation model on selected accidents, the effective calibration parameters in the car-following model, as well as the lane-changing model, were identified and by adjusting them in multiple scenarios, the simulation model in the case study routes was calibrated and validated with the use of the safety effective calibration target parameters such as Surrogate Safety Measures (SSMs). Among all the parameters of the simulation model, the global parameters of the normal distribution of permissible speed coefficient index with a mean and standard deviation of 0.95 and 0.10, respectively, and also local parameters of the cooperative, assertive and keep right lane-changing indexes were identified as effective.

One of the most important by-products of steelmaking and refining processes is steel slag. It is necessary to determine the geotechnical engineering properties of steel slag and assess their potential use in road and railways embankment constrictions. In this paper, the shear strength properties of steel slag were studied. Two types of steel slag, Blast Oxygen Furnace (BOF) and Electric Arc Furnace (EAF) slags that generated in Esfahan Steel Company and Mobarakeh Steel Company are used in this paper. The grain size distributions range of the test specimens have been selected under the characteristics of the road pavement and the existing laboratory facilities. In this study, two slags (BOF, EAF) with two grain size distribution and two difference compaction energy (standard and modified compaction) and the effect of saturation in California bearing ratio were evaluated. The results of the atterberg limits test showed that the material is none plasticity. The results of the compactions tests showed that dry unit weight varied between 1.94 to 2.74 gr/cm3 and optimum moisture content varied between 8% and 12.5%. Based on the California Bearing Capacity (CBR) tests, the CBR varied between 88 to 199 for BOF slags and 185 to 490 for EAF slags in socked and unsoaked conditions. In this study, direct shear experiments were performed on two types of granulation under four vertical stresses of 25, 50, 100 and 150 kPa in dry, submerged and dry-submerged. Based on the results, the above slags have an internal friction angle between 28 and 68 degrees and the adhesion of these materials was between 0 to 32 kPa. These results showed that steel slag has a much higher shear strength than natural soil and, according to the results of experiments, can be used as a material in engineering embankments.

A critical research area overlooked in previous studies on nano-silica material is the understanding of how its physical characteristics influence its final behavior as a composite when added to the asphalt binder. This study aimed to understand the feasibility of modifying the nanosilica with asphalt binder based on the asphalt binder characteristics. 60/70 penetration grade asphalt cement was prepared by adding (2%, 4% and 6%) of nanosilica by weight of asphalt. Properties of nanosilica material and asphalt cement were first examined. To prepare the modified asphalt binder was heated at 140C, blended by mechanical mixer at a speed of 2000 rpm for different mixing durations (30 to 60) minute. The modified asphalt binder was examined for rheological properties including penetration grade, softening point temperature, penetration index, Brookfield rotational viscosity and ductility test. Results shows that the modified asphalt binder stiffness increases based on rheological properties and sensitivity of temperature decreases with increasing nanosilica percentage. A 4 % nano silica by asphalt weight enhanced the conventional properties of the modified asphalt binder and became proper in hot weather conditions. While ductility of modified asphalt decreases with increasing nano silica percentage, due to stiffness and agglomeration increased. Finally, longer mixing time to more than 60 min had an adverse effect on the ductility property and lead to agglomeration of nanosilica modified asphalt binder.

This research investigates the way nano-silica (NS) and Gilsonite additives affect the performance behaviors of asphalt binders and SMA mixtures. A 60/70 type of asphalt binder, Gilsonite (0, 3, 5, and 7% by the weight of asphalt binder), and nano-silica (0, 2, 4, and 6% by the weight of asphalt binder) are utilized. The physical and rheological behaviors of modified asphalt binders are evaluated by rotational viscosity (RV), dynamic shear rheometer (DSR), multiple stress creep recovery (MSCR), bending beam rheometer (BBR), and linear amplitude sweep (LAS) tests. The performance properties of mixtures are evaluated by the application of four-point bending (FPB) fatigue, resilient modulus (Mr), indirect tensile strength (ITS), dynamic creep, and wheel track tests. In order to analyze the data statistically, a two-factor analysis of variance (ANOVA) is evaluated. The rheological behavior test outcomes depicted that Gilsonite utilization and NS additives enhance the rutting and fatigue resistances of asphalt binders. Gilsonite utilization decreases the low-temperature resistance of asphalt binders, while NS improves that. Storage stability test outcomes reveal that Gilsonite utilization enhances the storage stability of asphalt binders. Also, the application of NS leads to enhance phase separation. The MSCR test results demonstrate an enhancement in the high-temperature performance of virgin asphalt binder at different levels of stress by adding Gilsonite and NS. Moreover, NS utilization enhances the rutting resistance of samples. Based on the LAS test, Gilsonite utilization and NS additives enhance the fatigue properties of asphalt binder.

Tunnel design and construction in developed and developing countries have been widely considered by government officials to maximize the use of underground space. Meanwhile, the presence of groundwater, crushed rock masses and faults are among the problems of the tunnel passage that seriously affect the underground space. If for any reason the tunnel route cannot be changed, the tunnel can be designed and implemented in the vicinity of the fault with safety solutions. The accuracy of the correct design of these tunnels is due to the passage of the fault through or near the tunnel, which are of special economic and safety importance. Therefore, in this article, the effect of the fault around the Noghre Kamar tunnel located in Markazi province with different directions and different distances on a tunnel was investigated, and these results and suggestions can have significant recommendations for designers. This analysis has been investigated using finite element numerical modeling (Plaxis) and finite difference (FLAC).The results show that with increasing the distance of the fault from the tunnel axis, the amount of displacement and damages are significantly reduced and with increasing the thickness of the fault, the opposite is true. The average maximum displacement obtained from Plexis and Falak software is 17 and 17.5 cm, respectively, in the case of a 90-degree fault with a width of 3 meters, and in the case where the fault intersects the tunnel at a 45-degree angle, it is 13 and 13.5 cm, respectively. Also, the total stress changes in the position where the fault intersects the tunnel at an angle of 45 degrees is the minimum and in this position the maximum value of the safety factor is obtained.

Rutting is identified and used as the first failure mechanism in most important design conditions of flex- ible pavements. Bitumen can play a decisive role as one of the main materials used in asphalt mixtures, and modifying the properties of bitumen can greatly delay these failures and minimizing them in some cases. In this study, the PG 64-22 bitumen was modified using 2, 4 and 6% weight percentage of nano- silica and the effect of this modifier on reducing rutting failure was evaluated compared to the control sample. The rutting parameters including non-recoverable creep compliance (Jnr ) and the recovered creep (R%) were also evaluated, and then the effect of nano-silica on the improvement of these parameters at high temperatures was evaluated by simulating dynamic loading using Dynamic Shear Rheometer (DSR) and performing the MSCR test at 3 temperatures of 58, 64 and 70 C. After investigating the bitumen behavior in the non-linear viscoelastic state, a significant effect was observed in the rutting parameters. So that, as a result of nano-silica addition, the cumulative strain decreased compared to the control sam- ple and this decrease became more by increasing the modifier percentage, resulting from increasing the creep recovery at the end of each creep cycle. It was also concluded that, the increase in temperature in high and low stresses, has a negative effect on decreasing deformation recovery percent (R%) and the non- recoverable creep compliance (Jnr), both in unmodified and modified bitumen samples, but importantly, the amount of nano-silica effect on the improvement of these parameters was negative, which was dis- cussed in detail in this study. Also, at a certain temperature, increasing the percentage of nano-silica modifier significantly increased R%, and also significantly decreased the Jnr. In the following, the differ- ence of creep recovery in high and low stresses of Rdiff and the difference of the non-recoverable creep compliance in high and low stresses of Jnr diff significantly improved, indicating a reduction in the sensi- tivity of asphalt samples to the applied stress and also a significant increase in resistance of the samples against rutting.