1,720,969 research outputs found
Multi-criteria appraisal of multi-modal urban public transport systems
No full textThis study proposes a multi-criteria decision making (MCDM) modelling framework for the appraisal of multi-modal urban public transportation services. MCDM is commonly used to obtain choice alternatives that satisfy a range of performance indicators. The framework embraces both compensatory and non-compensatory approaches including lexicographic, Simple Additive Weighting (SAW), technique for order preference by similarity to the ideal solution (TOPSIS) and Concordance Analysis. These methods are applied on survey data collected through a questionnaire in Teheran, Iran. The survey encompassed passengers, operators and the wider community and inquired about the perceived attributes of three urban public transport modes: regular bus (RB), bus rapid transit (BRT) and rail rapid transit (RRT). The aforementioned MCDM techniques were applied to rank the performance of the three studied transit modes. The outputs of this study are instrumental in supporting planning decisions and prioritizing measures to improve public transport services.Transport and PlanningCivil Engineering and Geoscience
Using taxi GPS data for macroscopic traffic monitoring in large scale urban networks: Calibration and MFD derivation
No full textA two-Fluid Model (TFM) of urban traffic provides the macroscopic description of traffic state. The TFMs parameters are hard to calibrate, particularly for the dynamic traffic conditions. This leads to the TFM often being used to compare the quality of service through the plot of stopping time versus trip time of the vehicles in the network. Recently, the taxi GPS data has been applied to predict the traffic condition at the network level. Despite the network-wide coverage of the taxi GPS probe data, the penetration rate of taxis in the network traffic is still a vital and challenging issue for traffic estimation purpose. It is necessary to estimate penetration rate of taxis by combining with other data sources. Here, we propose a novel approach to fill two gaps: TFM parameter calibration and the taxis penetration rate. This method stretches the description of TFM to a zone size. The method is applied to real Changsha city GPS data, calibrating the parameters. The macroscopic fundamental diagram of the large-scale city is derived. For the Changsha case, running speed is the super-linear power law of the fraction of running cars; the fraction of stopping time is nearly linear power law of density, which can be an alternative of the density. The proposed method enables the calibration of TFM parameters and macroscopic traffic monitoring at urban scale using only GPS data.Transport and Plannin
Comparison of On-Line Time-Delayed and Non-Time-Delayed Urban Traffic Control via Remote Gating
No full textRecent studies demonstrated the efficiency of feedback-based gating control in mitigating congestion in urban networks by exploiting the notion of network fundamental diagram (NFD). The employed feedback regulator of proportional-integral(PI)-type targets an operating NFD point of maximum throughput to enhance the mobility in the urban road network during the peak period, under saturated traffic conditions. In previous studies, gating was applied directly at the border of the protected network (PN), i.e. the network part to be protected from over-saturation. In this work, the recently developed feedback-based gating concept is applied at junctions located further upstream of the PN. This induces a time-delay, which corresponds to the travel time needed for gated vehicles to approach the PN. The resulting extended feedback control problem can be also tackled by use of a PI-type regulator, albeit with different gain values compared to the case without time-delay. Detailed procedures regarding the appropriate design of related feedback regulators are provided. In addition, the developed feedback concept is shown to work properly with very long time-steps as well. A large part of the Chania, Greece, urban network, modelled in a microscopic simulation environment under realistic traffic conditions, is used as test-bed in this study. The reported results demonstrate a stable and efficient behaviour and improved mobility of the overall network in terms of mean speed and travel time.Transport & PlanningCivil Engineering and Geoscience
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Examining perimeter gating control of urban traffic networkswith locally adaptive traffic signals
No full textTraditionally, urban traffic is controlled by traffic lights. Recent findings of the Macroscopic or Network Fundamental Diagram (MFD or NFD) have led to the development of novel traffic control strategies that can be applied at a networkwide level. One pertinent example is perimeter flow control (also known as gating or metering), which limits the rate at which vehicles are allowed to enter an urban region. This paper studies to which extent a combination of adaptive traffic control and gating improves the traffic flow. To this end, combinations of gating and traffic signal timing tested implemented in a microsimulation. It is found that gating is much more effective than adaptive signal timing for high traffic loads. Adaptive signal timing can improve the network performance by increasing the maximum flow and increasing the critical accumulation, i.e. the number of vehicles inside a protected network for which the performance is maximized. The latter helps to reduce queuing outside the protected network.Transport and PlanningCivil Engineering and Geoscience
Combination of traffic-responsive and gating control in urban networks: Effective interactions
No full textRecent findings regarding macroscopic relationships of urban traffic measures such as the Macroscopic or Network Fundamental Diagram (MFD or NFD) have led to the development of novel traffic control strategies that can be applied at a network-wide level. One pertinent example is perimeter flow control (also known as gating or metering), which limits the rate at which vehicles are allowed to enter an urban region. In general, these gating strategies seek to prevent a network from becoming congested and maximize network efficiency/productivity by maintaining an optimal accumulation of vehicles within the network. Several studies have found that NFDs are more well-defined (i.e., have less scatter and show better overall network performance) when adaptive traffic signals are installed that dynamically respond to local traffic conditions. A combined gating and adaptive traffic control scheme can leverage the more reproducible macroscopic traffic patterns achieved with adaptive signals to provide more robust and efficient gating control. The purpose of this paper is to explore the benefits of combining perimeter gating with locally adaptive traffic signals through micro-simulation of the Chania, Greece traffic network. Two adaptive traffic signal strategies are considered with the feedback-based gating strategy: (1) a simple volume-based strategy and (2) a modified version of the SCATS algorithm. The results of the combined gating/adaptive signal control scheme are compared to gating under fixed traffic signals and the implementation of adaptive signals only. Overall, the study finds that travel delays and congestion can be considerably reduced with the combined strategy. This is because the adaptive traffic signals allow the network to achieve higher network productivity while the gating control allows the network to maintain this higher efficiency for a longer period of time than if left uncontrolled. The results are promising for the implementation of perimeter gating strategies in practiceTransport and PlanningCivil Engineering and Geoscience
Urban network throughput optimization via model predictive control using the link transmission model
No full textDeveloping practicable and efficient real-time signal control strategies for urban road networks is a major challenge with significant scientific and practical relevance. For the sake of practical feasibility, many urban traffic control strategies are based on simplified models. In this way, a trade-off can be made between controller accuracy, and (computational) complexity of the controller. However, designing a controller which operates efficiently with low computational time under different traffic conditions (i.e. under-saturated, saturated and over-saturated) remains a challenge. Several linear and quadratic model predictive control approaches are described in the literature to tackle this problem without considering the shock-wave dynamics of spill-back under over-saturated conditions. The principal contribution of this paper is the formulation of a linear model predictive controller that takes the shock-wave dynamics into account. This is realized by modeling the traffic dynamics in a link using the link transmission model. The performance of the proposed controller is compared with two other existing strategies. The total time spent by all the vehicles in the network and the computation time have been applied as performance indexes for the appraisal of the control strategies. Simulation results show that the control strategy proposed in this paper achieves better throughput under over-saturated conditions within comparable, low computation time.Transport & PlanningCivil Engineering and Geoscience
Lane changing and speed interaction on freeways: An analytical microscopic study
No full textUnderstanding the influence of lane changing manoeuvre on the capacity, stability, and breakdown of traffic flows is a crucial issue. In a recent study, four distinct lane change strategies on freeways have been empirically found: (1) Speed Leading; (2) Speed Leading with Overtaking; (3) Lane Leading; (4) Traffic Leading. To the best of our knowledge, combining speed choice and lane preference is not currently considered in most driving behaviour models. The principal aim of this paper is to investigate the impact of the forenamed lane change strategies on freeway traffic operations. The developed strategy-based lane change model has been implemented in a microscopic simulation environment. The study revealed that different lane change strategies may have various impact on the lane flow distribution and consequently on the freeway capacity. It has been seen that an unbalanced distribution of flow on a multi-lane freeway may lead to reduction of capacity. In addition, it has been found that the lane change rate variates under different lane change strategies. The highest traffic stability has been observed under speed leading and speed leading with overtaking strategies.Transport and PlanningCivil Engineering and Geoscience
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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