ATTAP analyzed field data collected from one of the intersections with dilemma zone protection system(DZPS). The analysis focused on short-term impacts from the deployed system on driving behaviors such as speed, decision of drivers during the onset of the yellow phase. The evaluation results also showed that the DZPS provide 100 detection rate to red light running vehicle.
Download (Design-and-Field-evaluation-of-the-Dilemma-Zone.pdf)
Authors: Minseok Kim, Hyeonmi Kim, Sungyoon Park and Saed Rahwanji
Conference: presentation at the 2014 TRB Alternative Intersections & Interchanges Symposium.
Unconventional Design: Six types of UIDs, including Superstreet (RCUT), CFI, CGT, DDI, SPUI, and DRI.
Purpose: presents the state of practice, case studies and analysis tools on unconventional designs in Maryland.
Abstract:
The Maryland State Highway Administration (MSHA) has been active in adopting unconventional design concepts at local intersections and interchanges as a feasible solution for relieving arterial congestion and improving safety. This paper presents the state of practice, case studies and analysis tools on unconventional designs in Maryland. The state of the practice focuses on six concepts consisting of restricted crossing u-turn (RCUT) intersection, continuous flow intersection (CFI), continuous green-T (CGT) intersection, diverging diamond interchange (DDI), single point urban interchange (SPUI), and double roundabout interchange (DRI). Case studies summarize the planning and design considerations that have been made for the first signalized RCUT intersection and DDI in the State of Maryland in addition to the 2nd CFI in Maryland. An overview of two analysis tools, developed as a joint research effort between MSHA and the University of Maryland at College Park, is also provided to introduce the Maryland Intersection Design & Capacity Analysis Program (MIDCAP) and Maryland Unconventional Intersection Designs (MUID) Analysis Tool. MIDCAP is useful to conduct capacity and queuing analyses based on the MSHA’s standard critical lane volume (CLV) and queuing methodology. MUID Analysis Tool contains statistical models to estimate the delay and queue in planning evaluations and models to optimize signal timings in operation analysis for three design concepts: 1) CFI, 2) DDI, and 3) signalized RCUT.
Authors: Liu Xu, Xianfeng Yang, Geng-len Chang and Saed Rahwanji
Conference: Presentation at 2015 TRB Annual Meeting
Unconventional Design: Signalized Superstreet
Purpose: Developed a set of interval-based queue models for evaluating the bay lengths among a signalized superstreet.
Abstract:
Despite the extensive implementations of Superstreets on congested arterials, a reliable tool for effective assessment of their geometric designs remains unavailable in the literature. To satisfy such a need, this study presents a convenient planning method that allows users to reliably estimate the queue size and its variation (interval) on each critical link in a Superstreet, based on the given signal plan and observed range of volumes. Grounded on a set of simulation experiments with well-calibrated network, this study also shows the significant interrelations between intersection delay and link occupancy rates by traffic queues. Hence, the estimated queue intervals in comparison with the proposed link length offers the basis for design engineers to evaluate if any queue spillover and lane blockage may occur on any critical links, and to determine if the preliminary geometric design needs to be revised, or the signal coordination between a Superstreet’s sub-intersections shall be redesigned. To assess the proposed model’s effectiveness, the study further conducts a simulation evaluation with the field data from a Superstreet in Maryland, and the results of extensive experiments confirm the reliability and applicability of the proposed model in evaluating the design of Superstreet.
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Authors: Xianfeng Yang, Yao Cheng and Gang-Len Chang
Journal: Journal of the Transportation Research Board (TRR),2015
Unconventional Design: Asymmetric Two-leg CFI
Purpose: Developed a signal optimization model for asymmetric Two-leg CFI by concurrently optimizing both the phase sequence and offsets.
Abstract:
Despite the increasing implementation of Continuous Flow Intersection (CFI) in practice, the development of reliable guidelines for its operational analysis and signal design remains at the infancy stage, especially for the popular two-leg asymmetric CFI design due to its relative low cost and desirable efficiency. To best utilize the capacity of such a CFI design, this paper presents a signal optimization model that can serve as an effective tool for engineers to design the cycle length, phase duration and sequences, and offsets for both its primary and sub intersections. By accounting for the commonly-encountered constraints of short bay length for turning movements and the interrelations between critical flow movements, the proposed model can prevent the queue spillover on left turn bays, and offer concurrent progression for both the through and left-turn flows. To ensure the applicability and effectiveness of the proposed model, this study has further used the data from a proposed asymmetric CFI in Maryland for performance evaluation. The results of extensive simulation with field data confirm that the proposed signal optimization with its capability to account for all physical constraints and flow conflicts can indeed perform as expected, that is, offering concurrent progression to both through and left-turning flows and preventing any queue from spilling over its designated bay.
Authors: Xianfeng Yang, Xiyang Song, Hyeonmi Kim, Gang-Len Chang and Saed Rahwanji
Conference: Presentation at 2014 Alternative Intersection & Interchange Symposium (Salt Lake City)
Unconventional Design: Superstreet
Purpose: Developed a planning model for the Superstreet geometric design based on the VISSIM simulated maximum queue lengths.
Download (AIIS-superstreet.pptx)
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Authors: Xianfeng Yang, Gang-Len Chang, Yang Lu, and Saed Rahwanji
Journal: Journal of Transportation Engineering 2013
Unconventional Design: CFI
Purpose: Developed a set of planning models for CFI geometry design based on the estimated maximal queue length for each link.
Abstract:
Despite the increasing use of continuous-flow intersections (CFIs) to contend with the congestion caused by heavy through and left-turn traffic flows, a reliable and convenient tool for the traffic community to identify potential deficiencies of a CFI’s design is not yet available. This is due to the unique geometric feature of CFI, which comprises one primary intersection and several crossover intersections. The interdependent relationship between traffic delays and queues at a CFI with five closely spaced intersections cannot be fully captured with the existing analysis models, which were developed primarily for conventional intersections. In response to such a need, this study presents a comprehensive analysis for the overall CFI delay, identifies the potential queue spillback locations, and develops a set of planning-stage models for the CFI design geometry. To facilitate the application of these proposed models, this paper also includes a case study of a CFI at the intersection of MD 4 and MD 235 constructed by the Maryland State Highway Administration.
Download (Development-of-Planning-Stage-Models-for-Analyzing-CFI.pdf)