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Author: Koohong Chung
Publisher:
ISBN:
Category : Dissertations, Academic
Languages : en
Pages : 68
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Book Description
Author: Koohong Chung
Publisher:
ISBN:
Category : Dissertations, Academic
Languages : en
Pages : 68
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Book Description
Author: Koo Hong Chung
Publisher:
ISBN:
Category :
Languages : en
Pages : 128
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Book Description
Author: Jittichai Rudjanakanoknad
Publisher:
ISBN:
Category : Dissertations, Academic
Languages : en
Pages : 84
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Book Description
Author:
Publisher: Transportation Research Board
ISBN: 0309129265
Category : Technology & Engineering
Languages : en
Pages : 268
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Book Description
"Reliability of transport, especially the ability to reach a destination within a certain amount of time, is a regular concern of travelers and shippers. The definition of reliability used in this research is how travel time varies over time. The variability can apply to the travel times observed over a road segment during a specific time slice (e.g., 3 to 6 p.m.) over a fairly long period of time, say a year. The variability can also pertain to the travel times of repeated trips made by a person or a truck between a given origin and destination. Agencies are increasingly aware of the issue of reliability, although the transportation industry as a whole as yet lacks a firm understanding of the causes and solutions to failures of reliability. As the agenda for the SHRP 2 research on travel time reliability took shape, it became clear a fundamental study was required to be able to talk about travel time reliability in a meaningful way"--Foreword.
Author: Srinivasa Srivatsav Kandala
Publisher:
ISBN:
Category : Traffic congestion
Languages : en
Pages : 109
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Book Description
Traffic congestion is a major externality in modern transportation systems with negative economic, environmental and social impacts. Freeway bottlenecks are one of the key elements besides the demand for travel by automobiles that determine the extent of congestion. The primary objective of this research is to provide a better understanding of factors for variations in bottleneck discharge rates. Specifically this research seeks to (i) develop a methodology comparable to the rigorous methods to identify bottlenecks and measure capacity drop and its temporal (day to day) variations in a region, (ii) understand the variations in discharge rate of a freeway weaving bottleneck with a HOV lane and (iii) understand the relationship between lane flow distribution and discharge rate on a weaving bottleneck resulted from a lane drop and a busy off-ramp. In this research, a methodology has been developed to de-noise raw data using Discrete Wavelet Transforms (DWT). The de-noised data is then used to precisely identify bottleneck activation and deactivation times, and measure pre-congestion and congestion flows using Continuous Wavelet Transforms (CWT). To this end a methodology which could be used efficiently to identify and analyze freeway bottlenecks in a region in a consistent, reproducible manner was developed. Using this methodology, 23 bottlenecks have been identified in the Phoenix metropolitan region, some of which result in long queues and large delays during rush-hour periods. A study of variations in discharge rate of a freeway weaving bottleneck with a HOV lane showed that the bottleneck discharge rate diminished by 3-25% upon queue formations, however, the discharge rate recovered shortly thereafter upon high-occupancy-vehicle (HOV) lane activation and HOV lane flow distribution (LFD) has a significant effect on the bottleneck discharge rate: the higher the HOV LFD, the lower the bottleneck discharge rate. The effect of lane flow distribution and its relationship with bottleneck discharge rate on a weaving bottleneck formed by a lane drop and a busy off-ramp was studied. The results showed that the bottleneck discharge rate and lane flow distribution are linearly related and higher utilization of the median lane results in higher bottleneck discharge rate.
Author: Xingan David Kan
Publisher:
ISBN:
Category :
Languages : en
Pages : 105
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Book Description
On-ramp metering at freeway bottlenecks is an effective method of reducing a freeway system's delay because empirical studies have previously shown that metering can prevent capacity drop, or reduction of outflow as a result of queue formation. However, arterial traffic signals that facilitate access to freeway on-ramps operate independent of the traffic conditions on the freeway on-ramp. Consequently, the traffic signals employ long signal cycle lengths and thus long green durations to maximize capacity at the arterial signalized intersections, which result in long platoons of freeway-bound traffic advancing toward the on-ramps. This often causes queue spillback on the freeway on-ramps and the surface street network. Queue override, a function that terminates or significantly relaxes the on-ramp metering rate whenever a sensor placed at the entrance of the on-ramp detects a potential queue spillover of the on-ramp vehicles on the adjacent surface streets, has become a widely accepted method of resolving queue spillback on the freeway on-ramps and nearby surface streets. Unfortunately, queue override releases the queue into the freeway and negates the benefit of ramp metering during the peak hours with recurrent freeway congestion. Video data collected downstream of freeway/on-ramp merge in San Jose, California show that the bottleneck discharge flow diminishes when queue override is activated for a sustained period of time. Observations over a two-week period suggest that queue override reduces the bottleneck discharge flow by an average of 10%. Recently, there has been significant interest in integrated corridor management (ICM) of facilities comprised of freeways and adjacent arterial streets. Significant benefits can be realized by preventing queue override and effectively storing the queued vehicles on the nearby arterial surface streets if the arterial traffic signals can account for traffic conditions on freeway on-ramps and avoid sending long platoons to the freeway on-ramp. A signal control strategy was developed and evaluated in this study. The algorithm takes available on-ramp storage and freeway ramp metering rate into account and dynamically reduces the cycle length and adjusts the green durations to prevent on-ramp queue spillback and mitigate unnecessary delay in the conflicting arterial directions. The proposed algorithm was tested through simulation and the results show that the proposed strategy reduces the freeway and system-wide delay even under fluctuations in traffic demand, at a modest penalty on the on-ramp bound traffic.
Author: Md Hadiuzzaman
Publisher:
ISBN:
Category : Traffic congestion
Languages : en
Pages : 239
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Book Description
Over the past few decades, several active traffic control methods have been developed and implemented to mitigate freeway congestion. Among them, Variable Speed Limit (VSL) is considered the most efficient control method. In addition, the latest advances in Intelligent Transportation Systems (ITS) have made it feasible to implement predictive freeway control. The successful implementation of such control requires an accurate macroscopic traffic flow model that can predict all the important traffic dynamics. To avoid violation of the equilibrium traffic state assumption and to improve traffic state prediction accuracy in the VSL control situation, this research proposes a 2nd order model, DynaTAM-VSL, which drops parameterization of the METANET's FD; instead, it includes speed limit-dependent parameters in the speed and density dynamics. The validation results with the 20-s loop detector data confirmed that, compared to the existing models, the proposed model better simulates traffic flow. With the validated model, this research investigates the impact of control parameters and demand levels on total travel time and throughput under the coordinated VSL control and determined a range of the demand / bottleneck capacity ratio, when VSL simultaneously improves both of the mobility parameters, which resolved the existing paradoxical results. This research also proposes an isolated VSL control strategy that aims at avoiding capacity drop at recurrent freeway bottlenecks. To evaluate the effectiveness of the control strategy, a base model of the 11-km test site: Whitemud Drive (WMD), Edmonton is calibrated within a microscopic traffic flow simulator to reproduce real-world traffic conditions, while the control strategy is implemented to evaluate its impact. The sensitivity analysis of the control strategy on safety constraints and VSL update frequencies demonstrates promising results to support practical implementation. Considering its flexible use in macroscopic simulation, a 1st order traffic flow model, CTM-VSL, is proposed. Unlike the 2nd order models, it is parsimonious: it only includes parameters that can be estimated using routinely available point detector data. However, the model is valid only for the condition of perfect compliance by drivers to VSL control, since it shares same properties of the CTM model. To update the storage capacity of an upstream segment of a VSL sign, a real-time queue estimation model is proposed. Despite the simple structure of the CTM-VSL model, the VSL control shows comparable results with the DynaTAM-VSL in terms of improving mobility parameters. Finally, this research distinguishes the relative contributions of driver compliance levels (CLs) and a predictive VSL control with different CLs to improve traffic flows. Several CL-to-VSL strategies are modeled with a fixed co-efficient of variance of speeds obtained from static speed limit on WMD. The CLs include speed distributions for aggressive, compliant, and defensive drivers. It is proven that the mobility benefits from the VSL control are not at the expense of increased collision probability and vice-versa.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 21
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Book Description
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Recurrent congestion is a continually growing problem on urban freeways. Facility expansions cannot keep pace with the growing vehicle demand. Low-cost mitigation measures are one way to alleviate the congestion at recurring bottleneck locations. Low-cost measures typically have a life of approximately 10 years and costs ranging from $8,000 to $2.45 million. While benefits have been realized in field applications, there hasn't been a lot of study regarding the performance of these measures in terms of added capacity. While modeling has long been a tool for planning and analyzing freeway networks, there has been little reported regarding its use for estimating the benefits of low-cost freeway improvements. In this study, the author tested proposed treatments at two sites using both a macroscopic and microscopic model. Because empirical performance information of these measures is not available, a quantitative analysis would not be reasonable since confidence in the values reported would be low. Current bottleneck identification methods typically either predict breakdown in real-time, or analyze detector data off-line. In order to identify bottlenecks from recorded aggregated data in an off-line model, criteria were generated to identify active bottlenecks and analyze the models' performance in an empirical and qualitative manner. Application of the criteria has been shown to provide reliable bottleneck identification to the calibrated pre-treatment case and expected results in the post-treatment cases.
Author: Hani S. Mahmassani, Jiwon Kim, Ying Chen, Yannis Stogios, Andy Brijmohan, and Peter Vovsha
Publisher: Transportation Research Board
ISBN: 0309274508
Category :
Languages : en
Pages : 268
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Book Description
This report from the second Strategic Highway Research Program (SHRP 2), which is administered by the Transportation Research Board of the National Academies, explores the underlying conceptual foundations of travel modeling and traffic simulation, and provides practical means of generating realistic reliability performance measures using network simulation models.
