[PDF] Proactive Integrated Control For Relieving Freeway Congestion eBook

Author : Xu Wang
Publisher :
Page : 229 pages
File Size : 34,89 MB
Release : 2015
Category : Ramp metering (Traffic engineering)
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Active bottlenecks limit traffic flow on freeway corridors. To relieve bottleneck severity, ramp metering (RM), variable speed limit (VSL) and their integration are often implemented to control the on-ramp and mainline input flow. Currently, freeway operation has become proactive based on short-term prediction. Macroscopic traffic flow models are often applied as prediction models in proactive traffic control strategies. Prior to field implementation, the models need to be calibrated and validated carefully to ensure that they represent real-life traffic situations. This study proposes modifications for METANET model to adapt it to the unpredictability of bottleneck activation during peak hours. The modified model is calibrated and verified its improvement of model prediction accuracy from segment-specific parameters. The modified model is validated that it can replicate traffic state evolutions during peak hours and be applicable in proactive traffic control practice. Weaving maneuvers (i.e., intensive lane changes) are a major cause of bottlenecks during high-demand periods. To consider weaving impacts in RM, this study introduces a proactive optimal RM algorithm that uses dynamic weaving capacity at weaving segments. Sensitivities of capacity and capacity drop are applied to dynamically estimate weaving capacity within a macroscopic traffic flow model. The proposed traffic flow model conducts estimation in a model predictive control (MPC) frame-work. The proposed RM algorithm is evaluated in macro-simulation and its effectiveness is enhanced by real-time estimated weaving capacity. The RM control research reveals a need of theoretical methods for weaving capacity estimation. This study then defines a linear optimization problem to solve weaving capacity and then establishes a lane-changing model to constrain the weaving flows. The proposed method is evaluated and analyzed for sensitivity with field data from two weaving segments. The capacity estimates from the proposed model are consistent with those from the HCM 2010 model and with field observations. Moreover, the weaving capacity is sensitive to weaving maneuvers. The proposed method is finally applied to estimate the real-time maximum discharge flow rate; the estimates match field measurements. Next, this study presents a proactive integrated control of RM and VSL, with goals to improve network-wide travel time and traffic flow. By decoupling the traffic prediction and simulation models, the possible control error sources are analyzed. The evaluation reveals the proactive integrated control achieves an amelioration in total time spent (TTS) up to 13.65% and an increase in total travel distance (TTD) up to 3.41%. The isolated and integrated controls benefit the traffic network in different extent under different demand scenarios. In addition, control rate profiles are analyzed in detail and found that RM is activated during slight congestion and the most congested situation to assist VSL. Through the integration, the infrastructure utility is maximized. Speed transition zones are complex when dynamically created and shifted by VSL. This study then attempts to represent speed limit effect and estimate real-time driver compliance at speed transition zones. The field data from two speed transition zones are investigated for temporal and spatial variations of speed and driver compliance using statistical tests. After selecting several key factors from statistical tests, a linear regression is established to rank the contributions of the selected factors and other general factors proposed by previous research. The regression results confirm speed limit value, surrounding traffic speed and existence of activated speed enforcement or education devices contribute more to driver compliance. Finally, this study reports the preliminary VSL test and details its implementation procedure on Whitemud Drive, Edmonton, Canada. DynaTAM-VSL software is designed to realize all necessary functions for VSL filed implementation. The preliminary test is conducted, and the VSL control performance and reliability are evaluated. The results for before-and-after VSL control are finally analyzed in depth. The analysis compares average traffic speed, standard deviation of speed, total travel time and total travel distance. The results from this study confirm that VSL can relieve recurrent traffic congestion.

Author : Jennifer Gray
Publisher :
Page : 46 pages
File Size : 38,56 MB
Release : 1990
Category : Electronic traffic controls
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This paper is an executive summary for the project entitled "Segment-Wide On-Line Control of Freeways to Relieve Congestion and Improve Public Safety". The project consisted of a number of working papers that examined various areas of freeway on-line control. Working papers are documented in the References section at the end of the report. The three major areas investigated include: monitoring of traffic detection information and incident control strategies; detector diagnostics; and ramp entry control strategies

Author : Hani S. Mahmassani
Publisher :
Page : 4 pages
File Size : 17,65 MB
Release : 1998
Category : DYNASMART (Computer file)
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This study focuses on traffic congestion, primarily that occurring on freeway corridors in metropolitan areas. Lack of coordination in the operation of various components of the system is often a major source of inefficiency, resulting in greater delays to motorists than what might be achievable with the existing physical infrastructure. The main objective of the study is to improve corridor network management by coordinating the various control elements in a freeway corridor, for both recurrent and nonrecurrent congestion situations.

Author : Karteek Kumar Allam
Publisher :
Page : 95 pages
File Size : 23,1 MB
Release : 2015
Category :
ISBN :

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Heavy traffic flow entering the freeway mainline can cause or worsen congestion on the freeway mainline due to interrupted on-ramp traffic. In order to address this problem, Freeway ramp metering systems are usually deployed to improve the traffic flow on urban freeways. These systems are attended to improve the flow on the freeway by regulating the on-ramp rate entering the freeway. However, amongst all the possible factors contributing to traffic congestion on freeways and arterials connected via ramps, lack of coordination in the operation of various system components is a major source of inefficiency at freeway and ramp conjunctions. Various ramp metering algorithms have been developed in an attempt to solve the unsystematic problem in coordinating the control of freeway, and arterials. Nevertheless, most of the algorithms control actions were selected based on either pre-defined plans or detected traffic condition. Implementation of the algorithms on the field is also a concern because of its excessive data requirements of these algorithms. Furthermore, existence of a range of flow rates in synchronized flow traffic can cause breakdown due to internal perturbations. Many algorithms failed to address the issue of worsening freeway congestion due to upstream traffic at the on-ramp. This research will formulate an integrated ramp metering control algorithm, using real time traffic measurements. Multiple priority objectives are explicitly set up to delay the congestion due to internal perturbations, maintain the throughput of freeway, and to prevent on-ramp vehicles from overflowing into arterials. This algorithm is also formulated to minimize the delays and control the shockwave propagation from the merge location of the on-ramp and the freeway. In order to measure the effectiveness, the proposed algorithm is compared with a traffic responsive algorithm, such as ALINEA (Asservissement LINeaire d'Entree Autoroutiere), and proposed recommendations accordingly. Considering the importance of gap acceptance and internal perturbations in the current research, calibration of the simulation model was conducted. For this purpose, video data was collected capturing the traffic at the merge location of the freeway and on-ramp, from which the accepted gaps and headways of the vehicles merging into the freeway have been extracted. This was given as an input to the VISSIM simulation model for calibration. The simulation test results indicate that the proposed integrated ramp metering algorithm is more effective than the ALINEA and Fixed Time ramp metering algorithms in terms of reducing the system delays and travel time on the freeway, and minimizing the freeway breakdown. Additionally, the proposed algorithm works efficiently at the ramp traffic flow of no more than 580 veh/hr. In other words, the ALINEA likely outperforms the proposed algorithm as the ramp traffic exceeds 580 veh/hr. The contribution of the research will be reflective of the following aspects: 1) developing a method with a supportive algorithm for minimizing the shockwave propagation by dampening shockwave formation of mainline freeway traffic; 2) developing a method with a supportive algorithm to reduce mainline freeway shockwaves by dispatching vehicles from the on-ramp at a flow rate that can best fit in the observed gaps to be available from the freeway traffic; 3) identifying the minimum accepted gaps at the merge location from video observation to develop appropriate gap acceptance parameters; and 4) developing an integrated computing system to provide a fundamental platform for further functionality expansion in the future for study of a multiple-ramp situation at a freeway system.