فهرست مطالب

Transportation Engineering - Volume:3 Issue: 4, Spring 2016

International Journal of Transportation Engineering
Volume:3 Issue: 4, Spring 2016

  • تاریخ انتشار: 1395/05/03
  • تعداد عناوین: 6
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  • Ali Abdi, Mahmoud Saffarzadeh, Arsalan Salehikalam Pages 237-251
    Stop and go traffic that leads to oscillate traffic flow frequently is observed on congestion flow. Unexpected reasons such as lane – changing maneuvers, lower speeds of leader vehicle and moving bottleneck cause stop and go traffic and amplifying delay and environment impacts. Stop and go traffic exactly can’t be modeled by traffic models, and also car following models based on kinematic flow theory can’t be implied correct perception of stop and go traffic. Based on asymmetric microscopic theory and trajectory data of NGSIM, traffic flow can be classified into five phases according to speed and movement of the vehicle: Free flow, acceleration and deceleration, stationary and coasting phases. Analyzing stop and go traffic based on asymmetric theory of acceleration and deceleration phase will result to classify them into three cases: generation, growth and dissipation of traffic waves. Analyzing of traffic oscillation implies that stop-and-go traffic is relatively small and can’t be propagated upstream unless the following traffic is also near D-curve; while the effect on lane changes are greater, and can propagate even the following traffic is not near the D-curve. In this paper, using time window in trajectory data clarify relation between the total number of lane changes and stop-and-go waves for congestion traffic. Analyzing net lane changes inside the searching window for incoming and outgoing lane changes about growth and dissipation of traffic waves indicate how characteristics of stop-and-go waves are intimately related to driver’s asymmetric behavior of acceleration and deceleration. The comparison result on the growth and dissipation indicated that under the same net lane changes, growth wave case occupy the regions in fundamental diagram, flow – density diagram, deceleration curve, and dissipation wave case occupy the regions of flow – density, acceleration curve.
    Keywords: Traffic oscillation, stop, and, go traffic, asymmetric theory, lane, changing maneuver, acceleration, deceleration wave
  • Hamid Reza Behnood, Mashyaneh Haddadi, Shadrokh Sirous Pages 253-266
    The main objective of this study is to estimate a part of road traffic injury costs including costs due to fatality and disability, which are related to lost social products. Lost output consists of costs, which are related to losses of national product or lost-income in death, hospitalization or physical disabilities. In recent years, the Disability-Adjusted Life Years (DALYs) has been used as an appropriate criterion to measure mortality and disability burden from different diseases. The DALYs index for a definite disease is defined as total years of life lost due to a premature death (YLL) and the years lost due to disability (YLD) for the disease. The distribution of fatalities and disabilities in age intervals takes advantage of official references including Legal Medicine Organization reports on road fatalities and Harvard University surveys in road-crash-related disability dispersion in Iran. According to this distribution, life expectancy can be determined for the used age distribution in this study. This study indicates that the highest amount of the life years lost due to road fatalities belongs to the age range of 11-29 years old in Iran for whom, an average value of lost useful life is estimated more than 12 years. The total output value or lost product due to death or disabilities by traffic injuries is estimated approximately 1.4 Billion USD in 2011. As a social cumulative criterion, it stands for the second cost contributing factor after medical costs. The study has shown that the lost output is identified as the main part of costs imposed on each individual killed by a road traffic injury.
    Keywords: Road traffic injuries, economic cost, lost output, gross domestic product
  • Hadiuzzaman*, Ahsanul Karim, Mizanur Rahman, Tanweer Hasan Pages 267-275
    In most of the developing countries, the metropolitan organizations do not assess the safety consequences of alternative transportation systems and one of the reasons is the lack of suitable methodology. The goal of this paper is to develop practical tools for assessing safety consequences of arterial roads in the context of long-term urban transportation plans in Dhaka city, the capital of Bangladesh. The researchers used the generalized linear modeling approach to develop separate models to predict number of crashes for different levels of crash severity for major arterial segments which have the highest crash rates. The models used five independent variables - length of segment, traffic volume, number of access road, design speed and roadway width - all of which are usually collected or predicted by transportation planners. The study reveals that roadway width and design speed are the governing factors for non-lane based traffic on urban arterials for controlling crashes. The crash prediction models presented in this paper can enable Dhaka’s transport planners to evaluate the safety impact of alternative road networks with regard to the costs and benefits in long-term planning context.
    Keywords: Crash prediction, regression models, negative, binomial distribution, poisson distribution, fatal accident
  • Eugene Vida Maina*, Albert Forde, R. Michael Robinson Pages 277-288
    Optimally minimizing delay times at signalized intersections can significantly improve both traffic flow and safety. However, most traffic flow optimizing tools do not measure the effect on safety. This study uses nonlinear programming (NLP) algorithms to optimally minimize delay times and employs both Safety performance functions (SPFs) and empirical Bayes (EB) before-after methodology to measure the impact on safety presented as a Crash Modification Factor (CMF). A crash modification factor (CMF) is a multiplicative factor used by transportation practitioners to compute the expected number of crashes at specific study site(s) after a countermeasure has been proposed or is implemented. Using 2013 traffic data from seventeen signalized intersections located in Virginia Beach, the results show that optimally minimizing intersection delay times can result in a safety improvement of approximately 26.46% that is a CMF of 0.735. This result is not conclusive, but the significance of the findings shows the need for further investigations and potential inclusion in the future editions of the Highway Safety Manual (HSM).
    Keywords: Safety, crash modification factors, delay, safety performance functions, empirical bayes
  • Arash Sadrayi, Mahmoud Saffarzadeh*, Amin Mirza Boroujerdian Pages 289-300
    Pedestrians are among the most vulnerable road users. Speed of vehicles is considered as one of the major causes of danger for pedestrians crossing the street. Therefore, it is of utmost importance to devise suitable solutions to reduce speed of vehicles. One of these solutions is installation of Pedestrian Refuge Islands (PRI) in very wide midblocks. With regard to fluctuations in pedestrian and vehicle traffic volume in traffic hours, there are different variations in collisions between vehicle and pedestrian. In this article the effect of constructed PRI in Tehran on speed of vehicles and consequently their effects on probability fluctuations of fatal accidents are determined. Speed of vehicles in two phases of before and after arriving to the PRI is assessed. Additionally, speed of vehicles in non-observed volumes of vehicle and pedestrian are calculated using Aimsun.v6 simulation software. Paired T-test is applied to compare average speed of vehicles before and after the PRI. The results revealed that except for traffic volumes of 3000-4000 veh/h and 400-600 ped/h in other volumes reduction of average speed of vehicles as a result of PRI is significant. Also, the results show that in all volumes, these equipment reduce the probability of fatal accidents to under 10%. According to the results, it is recommended that PRI should be installed in mid blocks where traffic volume of vehicles in each lane is less than 750 veh/h.
    Keywords: Pedestrian refuge island (PRI), before, after studies, fluctuations of speed of vehicles, probability of pedestrian fatal accidents
  • Hasan Taherkhani*, Farshad Firoozei, Jafar Bolouri Bazaz Pages 301-312
    Cold-in-place recycling (CIR) is an environmentally sustainable alternative for preservation of asphalt pavements. A major disadvantage of this practice is the lower strength of the cold-in-place mixtures. Addition of cement into this type of mixture is a method for increasing its bearing capacity. The effect of cement content on the mechanical properties of the cold-in-place recycled asphalt mixtures has been investigated in laboratory. Different percentages of cement have been added to the recycled asphalt mixtures mixed with an optimum percentage of emulsified bitumen and moisture, and the indirect tensile strength, resilient modulus, dynamic stiffness and fatigue life have been measured. Due to the problem of fabrication of beam specimens, traditionally, the fatigue behavior of cold-in-place recycled mixtures has been investigated using dynamic indirect tensile loading. In this research, a method has been developed for making fatigue beams of the mixture. It is found that the fatigue life, dynamic stiffness, indirect tensile strength and resilient modulus of the mixtures increase with increasing cement content.
    Keywords: Cold, in, place recycled asphalt mixtures, cement, fatigue, resilient modulus, dynamic stiffness