查看更多>>摘要：The aim of this research was to develop operational strategies for integrating the operations between diamond interchange traffic signals and ramp metering signals. Integrated operational strategies were developed on the basis of the two commonly used diamond interchange phasing schemes: the basic three-phase scheme and the Texas Transportation Institute four-phase scheme. The key elements of the integration system and its operations include a proposed enhanced detection system and an operational algorithm. Through implementation of special signal timings at the diamond interchange, the traffic flows feeding the ramp meters can be effectively controlled and thus minimize ramp queues and the resulting need to flush the queues, which would possibly lead to freeway breakdown. The operational strategies were evaluated with VISSIM microscopic simulation under three general traffic demand scenarios— low, medium, and high—as characterized by the volume-to-capacity ratios at the metered ramps. The results of the evaluation indicated that the integrated operations were most effective under a medium traffic demand scenario in preventing or delaying the onset of ramp metering queue flush, thereby reducing freeway breakdown and system delays.
查看更多>>摘要：The use of an appropriate method in determining the left-turn signal change interval (yellow change interval plus red clearance interval) can result in signal timings that improve both safety and efficiency of an intersection. An improved framework for calculating the change interval for the left-turn movement is presented: it incorporates a comprehensive set of parameters, which are identified from a survey. Field data collected from 21 intersections in eight Texas cities were used for the basic calibration of three essential parameters within the improved framework: drivers' entering driving behavior, drivers' behavior on left-turn curves, and drivers' tolerable centrifugal force. After the basic calibration, a sensitivity analysis of the three essential parameters was conducted. Further, a systematic calibration approach was designed to extend the improved framework to a wider range of intersections with different approach speed limits, number of left-turn lanes, control types, and truck percentages. Values of the three essential parameters under different intersection attributes were calculated; they can be of direct reference for practicing engineers. Finally, the effect of intersection attributes on the yellow change and red clearance intervals was analyzed. The research recommends that the change intervals for left turns based on the proposed framework and calibration method be used by practicing engineers, which would improve both safety and efficiency of the intersection.
查看更多>>摘要：A comparison was conducted of traditional vehicle detection, in which all lanes on an approach are connected to an actuated controller through one amplifier card and input, and lane-by-lane detection, in which each lane is interfaced with the controller through separate amplifier cards and inputs. Both detection strategies were evaluated with various extension time values on the same traffic stream. A total of 430 h of data from two separate approaches was evaluated on an hour-by-hour basis. During certain time periods, lane-by-lane detection provided up to a 13% increase in efficiency. For all 930 h of observations, the median increase in efficiency was 5.2% on an approach with 51-ft-long detection zones and 3.5% on an approach with 38-ft-long detection zones. This increased efficiency corresponds to time that could be allocated to other movements or used to reduce the cycle length. The largest improvements associated with lane-by-lane detection occurred during periods with moderate volume-to-capacity ratios, with smaller benefits observed during periods of heavy or light traffic.
Avery RhodesDarcy M. BullockJames SturdevantZachary Clark...
p.134-145页
查看更多>>摘要：Many U.S. agencies have adopted video vehicle detection technology as an alternative to inductive loops. Although many product evaluations have been performed, the majority of these evaluations concentrated on freeway applications in which speed and volume were the primary evaluation criteria. At an actuated intersection, the metrics of speed and volume do not necessarily represent how well a device will operate as a presence detector. Video detection at signalized intersections was evaluated at a test intersection in Indiana. Cameras on all approaches were located at the optimal camera position recommended by the vendors, approximately 60 ft from the strain pole. Two additional cameras were located on each mast arm at slightly less optimal positions, 36 and 48 ft from the strain pole. Traditional inductive loops were also available at the intersection and were used to provide baseline data to screen for discrepancies. Each time the detectors were not in agreement, a discrepancy was noted. A digital video recording was later viewed by a human observer to determine whether the video detector or the loop detector was in error. An analysis of the data showed that video detection was found to produce statistically significantly more false detections and missed detections than the loop detectors on most phases. A small incremental increase in performance was observed when the camera was mounted at 60 ft rather than 36 ft on two of the approaches, but this marginal improvement likely does not justify the additional expense of mast arm, pole, and pole foundation associated with this camera location.
查看更多>>摘要：Gridlock along arterial systems in cold climates is often the result of adverse weather conditions, which can render the normal signal coordination plans unsuitable as a result of changes in the traffic flow parameters. The current study aims at understanding the impact of different factors on the magnitude of the operational benefits to be expected from implementing special timing plans for inclement weather. The factors investigated include (a) the characteristics of the signalized corridor, (b) the type of the simulation model used in the evaluation, (c) the level of traffic demand, and (d) the duration of the inclement weather event. To achieve the study's objective, two signalized arterial corridors are selected as case studies, and several simulation experiments are conducted. The results show that signal retiming during inclement weather can result in significant operational benefits (as high as a 20% reduction in control delay in some cases). The results also show that the benefits appear to be greatest when traffic loads are close to capacity and tend to decrease when the available capacity is exceeded. Finally, a significant increase in the benefits is realized with the increase in the duration of the inclement weather event. In one experiment, retiming the signals resulted in a 36% reduction in control delay for a 2-h snow event as opposed to only 18% for a 1-h event.
Thomas J. KimpelJames StrathmanRobert L. BertiniSteve Callas...
p.156-166页
查看更多>>摘要：Findings are presented on changes in bus running times, on-time performance, and excess passenger wait times following implementation of transit signal priority (TSP) in select bus corridors in the Portland metropolitan region. Analysis of the effectiveness of TSP is often undertaken by using simulation techniques or empirical studies that are limited in either scope or data availability, or both. The current research uses an abundance of trip-level data collected from TriMet's Bus Dispatch System, in Portland, Oregon. The study focuses on the most common performance measures of interest to both transit operators and passengers and shows that the expected benefits of TSP are not consistent across routes and time periods, nor are they consistent across the various performance measures. The authors believe that benefits of TSP will accrue only as the result of extensive evaluation and adjustment after initial deployment. In most cases, an ongoing performance monitoring and adjustment program should be implemented to maximize TSP benefits.
查看更多>>摘要：A signal control system named Real-Time/Internal Metering Policy to Optimize Signal Timing (RT/IMPOST) has been under development for several years. It is designed to compute signal timing plans for the entire range of operating conditions from under- to oversaturation for control systems ranging from first generation (GEN 1) to highly responsive advanced traffic management systems. The different flow regimes of urban traffic control are reviewed. Then the focus is on the treatment to develop cycle-based signal timing plans for inclusion in the data libraries referenced by GEN 1 real-time traffic control systems for the undersaturated-flow regime. This approach decomposes a grid network into its constituent arterial subsystems in a way that is responsive to user-specified priorities. The user may define and rank the arterial systems subsumed within a grid network so as to satisfy strategic objectives responsive to traffic demand patterns and local needs. The procedure computes optimal signal timing plans for all these arterial subsystems in a priority-ranked sequence and integrates these arterial-based timing plans to form a networkwide signal timing plan. Field and simulation test results are presented. The field tests confirm that the IMPOST timing plans improved the operational performance of traffic along an arterial system in New York State relative to a fine-tuned existing control. The simulation studies compared the performance of traffic responding to IMPOST signal timing plans with that responding to Synchro 6.0 signal timing plans. The benefits of network decomposition and of arterial priority ranking are also documented.
Srinivasa R. SunkariCarroll J. MesserHassan Charara
p.176-184页
查看更多>>摘要：A major difficulty with traffic signal operation on high-speed approaches is the dilemma faced by approaching motorists when the downstream signal turns yellow. Should the motorists stop or proceed through the intersection? Crashes that may occur at these intersections result in excessive property damage and personal injury because of the high speeds involved. The Texas Transportation Institute has developed a new system named the Advance Warning for End of Green System (AWEGS) for application at high-speed signalized intersections. Typically, dilemma zone detection strategy is based on a certain approach speed (typically the 85th percentile). AWEGS provides protection for the majority of motorists who are not covered by the dilemma zone treatment. AWEGS provides advance warning to motorists by using signs mounted on the roadside. These signs (Be Prepared To Stop When Flashing) would flash a beacon about 5 to 6 s before the onset of the yellow signal for high-speed approaches. Similar systems have been implemented in Canada and in a few U.S. states that use the trailing-green approach, which results in loss of dilemma zone protection every cycle. AWEGS, however, is almost completely independent of the traffic signal controller, and hence the signal controller would continue to provide the dilemma zone protection for which it was designed. The system was implemented at two sites in Waco and Brenham, Texas. Results of AWEGS implementation illustrated an improvement in traffic operations. AWEGS consistently enhanced the dilemma zone protection at intersections and reduced red light running by about 40%.
查看更多>>摘要：An advanced transit signal priority (TSP) control method is presented: it provides priority operation in response to real-time traffic and transit conditions. A high-performance online microscopic simulation model was developed for the purpose of predicting transit travel time along an intersection approach. The proposed method was evaluated through application to a hypothetical intersection with a nearside bus stop. The performance of the proposed method was compared with that of normal signal operation without TSP and a conventional signal priority method. The experimental results indicated that the developed method provided efficient and effective priority operation for both transit vehicles and automobiles. The proposed method significantly reduced transit vehicle delays as well as side-street traffic delay compared with conventional active priority control.
Montasir M. AbbasNadeem A. ChaudharyGeza PestiAnuj Sharma...
p.195-204页
查看更多>>摘要：Although several studies have shown the potential great benefits of traffic-responsive plan selection (TRPS) control, time-of-day operation continues to be the primary method used to select patterns for signal control applications. This practice could be largely attributed to the minimal guidelines available on the setup of the TRPS mode. An innovative framework for TRPS system setup is provided, and guidelines for implementing TRPS in a simplified manner are shown. The guidelines, developed at Texas Transportation Institute (TTI), use a comprehensive approach that incorporates a multiobjective evolutionary algorithm and a supervised discriminant analysis. Engineers can directly implement the guidelines presented as an initial design. Hardware-in-the-loop simulation is used to illustrate the performance of TTI's TRPS configuration methodology.
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