scholarly journals Operational Performance and Safety Assessment of Signalized Roundabouts

2020 ◽  
Author(s):  
Jameel Hannun ◽  
Jamal Hannun ◽  
Khaled Shamiyeh ◽  
Mohammad Ghanim ◽  
Mohamed Kharbeche
Keyword(s):  
Safety Assessment ◽  
Traffic Simulation ◽  
Field Measurements ◽  
Assessment Method ◽  
Signalized Intersections ◽  
Operational Performance ◽  
Signal Timing ◽  
Microscopic Traffic Simulation ◽  
Crash Data ◽  
Traffic Operation

Roundabouts are widely used to reduce the severity of conflicts at intersecting roads. While they tend to provide an acceptable level of traffic operation, their operational benefits are reduced when traffic demands increase. One possible and economic mitigation is to convert the roundabouts into signalized ones to accommodate the demand increase and to further reduce the conflicts. This conversion will allow the roundabouts to perform both functions (safety and operational) within acceptable levels. Accordingly, proper signal timing parameters are often required to achieve the anticipated safety and operational levels. Unlike the operational performance of signalized intersections that can be easily assessed based on field measurements, safety assessment is far more difficult due to the need of historical crash data, which would potentially take years. This study presents the use of traffic simulation to assess the operational performance as well as the safety performance of signalized intersections. At first, a well-calibrated model of a signalized roundabout located in the city of Doha is built in microscopic traffic simulation environment based on field measurements and observations. Secondly, Surrogate Safety Assessment Method (SSAM) is used to analyze the simulated vehicular trajectories to identify the type and severity of conflicts. The results revealed that the implemented signal timing parameters have a significant impact on the safety functionality of the signalized roundabouts.

scholarly journals Evaluation of the pre-detective signal priority for bus rapid transit: coordinating the primary and secondary intersections

Transport ◽  
2015 ◽  
Vol 33 (1) ◽  
pp. 41-51 ◽  
Author(s):  
Min Yang ◽  
Gang Sun ◽  
Wei Wang ◽  
Xin Sun ◽  
Jian Ding ◽  
...  
Keyword(s):  
Traffic Simulation ◽  
Limited Range ◽  
Simulation Software ◽  
Bus Rapid Transit ◽  
Signal Timing ◽  
Rapid Transit ◽  
Negative Effects ◽  
Microscopic Traffic Simulation ◽  
The Common ◽  
Traffic Operation

Since the traditional transit priority strategy can only adjust signal timing in a limited range and is not suitable for all kinds of signal timing designs, it cannot provide enough priority for Bus Rapid Transit (BRT). In addition, traditional transit priority strategy has caused serious interferences with other traffic. This study proposes a pre-detective signal priority strategy for BRT with coordination between primary and secondary intersections. By pre-detecting, the time buses arrive at the primary intersection, the signal timing of both the primary and secondary intersections, along with the offsets, are adjusted simultaneously, based on the common length and the green ratio of each phase. In this method, the signal cycle constraints are clarified, and the bus control coordination between intersections has been taken into consideration. In this paper, one direction traffic is taken as a study example to testify the effectiveness of this method. The study uses the data collected from Changzhou, China, and a microscopic traffic simulation software PTV VISSIM with four simulation scenarios defined: no signal priority, traditional signal priority, pre-detective signal priority and pre-detective signal priority with coordination. This paper selects a set of indicators to evaluate the traffic operation for both public transit and private traffic. Results show that pre-detective signal priority with coordination is the most effective, with the total bus intersection delay decreases by 67.4% and the bus headway adherence declines by approximately 40% at all the primary and secondary stations of BRT line 1. Moreover, the negative effects that could happen with providing signal priority for BRT, such as increasing the delay and length of queue of private traffic at the intersections, are significantly reduced.

Safety-Based Left-Turn Phasing Decisions for Signalized Intersections

2017 ◽  
Vol 2619 (1) ◽  
pp. 13-19 ◽  
Author(s):  
Kiriakos Amiridis ◽  
Nikiforos Stamatiadis ◽  
Adam Kirk
Keyword(s):  
Urban Areas ◽  
Primary Objective ◽  
Signalized Intersections ◽  
Safety Performance ◽  
Signal Timing ◽  
Left Turn ◽  
Crash Data ◽  
Intersection Safety ◽  
Traffic Volumes

The efficient and safe movement of traffic at signalized intersections is the primary objective of any signal-phasing and signal-timing plan. Accommodation of left turns is more critical because of the higher need for balancing operations and safety. The objective of this study was to develop models to estimate the safety effects of the use of left-turn phasing schemes. The models were based on data from 200 intersections in urban areas in Kentucky. For each intersection, approaches with a left-turn lane were isolated and considered with their opposing through approach to examine the left-turn–related crashes. This combination of movements was considered to be one of the most dangerous in intersection safety. Hourly traffic volumes and crash data were used in the modeling approach, along with the geometry of the intersection. The models allowed for the determination of the most effective type of left-turn signalization that was based on the specific characteristics of an intersection approach. The accompanying nomographs provide an improvement over existing methods and warrants and allow for a systematic and quick evaluation of the left-turn phase to be selected. The models used the most common variables that were already known during the design phase, and they could be used to determine whether a permitted or protected-only phase would suit the intersection when safety performance was considered.

Calibrating Vissim to Analyze Delay at Signalized Intersections

2017 ◽  
Vol 2615 (1) ◽  
pp. 73-81 ◽  
Author(s):  
H. Sebastian Buck ◽  
Nicolai Mallig ◽  
Peter Vortisch
Keyword(s):  
Traffic Simulation ◽  
Signalized Intersections ◽  
Level Of Service ◽  
Microscopic Traffic Simulation ◽  
Car Following ◽  
Control Delay

The level of service of an intersection is determined principally by control delay. Accordingly, control delay must be reproduced correctly when microscopic traffic simulation is used to evaluate intersections. This study demonstrated how Vissim could be calibrated for that purpose. Vissim models of four signalized intersections for which data had been collected were built. From these data, information that was extracted on headways, time to pass the intersection, and arrival distribution was used for calibration. Calibration of the headways resulted in car-following parameters for these intersections that differed substantially from the Vissim default values. An adjustment in the vehicle arrival distribution to the observed distribution was also necessary to reproduce the measured delay in the simulation.

scholarly journals An Innovative Signal Timing Strategy for Implementing Contraflow Left-Turn Lanes at Signalized Intersections with Split Phasing

2021 ◽  
Vol 13 (11) ◽  
pp. 6307
Author(s):  
Rongwei Guo ◽  
Jinli Liu ◽  
Yi Qi
Keyword(s):  
Traffic Simulation ◽  
Design Procedure ◽  
Signalized Intersections ◽  
Signal Timing ◽  
Current Signal ◽  
Clearance Time ◽  
Left Turn ◽  
Simulation Based ◽  
Time Requirements

Contraflow Left-Turn Lanes (CLLs) have the potential of being a solution for mitigating congestions at signalized intersections where split phasing is recommended or required. However, the current signal timing strategy for the intersections with CLLs cannot be directly applied at the signalized intersections with split phasing (SIWSP). To address this problem, this study proposed an innovative signal timing strategy, which is referred to as Counterclockwise Split Phasing (CSP) signal timing, for implementing the CLLs at the SIWSPs. A traffic simulation-based case study was conducted and the results indicate that, by using the proposed CSP signal timing plan, CLLs can be implemented at the SIWSP and can significantly reduce the traffic congestions caused by the high left-turn demand at this type of intersection. In addition, since the proposed CSP signal timing design procedure has fully considered the clearance time requirements for the left-turn vehicles on the CLLs, the risk associated with the use of CLLs can be controlled which makes it safe to use this innovative intersection design at SIWSPs.

Comparison between Surrogate Safety Assessment Model and Real-Time Safety Models in Predicting Field-Measured Conflicts at Signalized Intersections

2020 ◽  
Vol 2674 (3) ◽  
pp. 100-112 ◽  
Author(s):  
Mohamed Essa ◽  
Tarek Sayed
Keyword(s):  
Real Time ◽  
Safety Assessment ◽  
Traffic Simulation ◽  
Simulation Models ◽  
Signalized Intersections ◽  
Assessment Model ◽  
Vehicle Trajectories ◽  
Traffic Conflicts ◽  
Safety Models ◽  
Conflict Prediction

Traffic simulation models are frequently used to evaluate the safety of signalized intersections, especially when testing unconventional designs or investigating the effects of emerging technologies such as connected and autonomous vehicles. In this approach, vehicle trajectories extracted from traffic simulation are usually analyzed using the surrogate safety assessment model (SSAM) to estimate the number and severity of traffic conflicts. However, recent research has shown that evaluating safety using SSAM has several limitations. First, a rigorous calibration procedure must be applied to the simulation model to obtain reliable conflict results. Second, simulation models in many cases do not accurately represent actual driving behavior. Subsequently, they often fail to capture the actual mechanisms generating near-misses. This paper presents a new procedure, alternative to SSAM, for evaluating the safety of signalized intersections. The procedure combines simulated vehicle trajectories with real-time safety models to predict rear-end conflicts. The conflict prediction is based on dynamic traffic parameters, such as traffic volume and shock wave characteristics, repeatedly measured over a short time interval (a few seconds). To validate the proposed procedure, its performance was investigated in predicting traffic conflicts extracted from 54 hours of real-world video data at two signalized intersections in the city of Surrey, British Columbia. The predicted conflict results were compared with SSAM. Overall, the results showed that the proposed procedure outperforms SSAM in relation to accuracy of conflict prediction. Lastly, a case study of using the proposed procedure in evaluating the safety impact of a recently developed connected-vehicles application is presented.

A Novel Safety Assessment Method based on Fault Dependent Matrix

2019 ◽  
Vol 15 (9) ◽  
pp. 2392 ◽  
Author(s):  
Dong Haiyong ◽  
Gu Qingfan ◽  
Wang Guoqing ◽  
Zhai Zhengjun ◽  
Lu Yanhong
Keyword(s):  
Safety Assessment ◽  
Assessment Method
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