Set methods of left-turn waiting zone at signalized intersection

To maximize the number of vehicles passing by the stop-line in a cycle and improve the operation efficiency of intersection in China, the settlement of left-turn lane waiting-zone is becoming prevailing. Based on conflicting-point method, the internal mechanism of left-turn flow after stopping line was analyzed through taking postposition left-turn lane waiting-zone intersection for instance. The relationship between the first left-turn vehicle and the last vehicle of previous phase passing the conflicting point was expounded. According to the time of successive arriving of two vehicle flows at conflicting-point, the reasonable layout for waiting area of left-turn vehicles was researched when the clearance index was less than O. The results suggest that the appropriate layout for waiting area of left-turning vehicles can improve the operation efficiency of intersections.

Analysis of opposing left-turn conflicts based on traffic conflict technology

The relationship between the opposing left-turn conflict and the traffic participants was analyzed in this study. Based on the traffic conflict technology, the image data were collected in a real traffic situation. The relationship was investigated under two different conditions. The number of opposing left-turn conflicts was positively correlated with the number of left-turn vehicles while the ratio of left-turn vehicles to opposing vehicles was less than 1, and showed a positive correlation with the number of opposing-through vehicles when the ratio of left-turn vehicles to opposing vehi- cles was more than 1. In other words, the opposing left-turn risk was positively correlated with the number of the minor traffic participants, which had a negative effect on the whole traffic system op- eration.

Influence of bus stop with left-turn lines between two adjacent signalized intersections

Based on the symmetric two-lane Nagel–Schreckenberg（STNS） model, a three-lane cellular automaton model between two intersections containing a bus stop with left-turning buses is established in which model the occurrences of vehicle accidents are taken into account. The characteristics of traffic flows with different ratios of left-turn lines are discussed via the simulation experiments. The results indicate that the left-turn lines have more negative effects on capacity,accident rate as well as delay if the stop is located close to the intersections, where the negative effect in a near-side stop is more severe than that in a far-side one. The range of appropriate position for a bus stop without the bottleneck effect becomes more and more narrow with the increase of the ratio of left-turn bus lines. When the inflow is small, a short signal cycle and a reasonable offset are beneficial. When the inflow reaches or exceeds the capacity, a longer signal cycle is helpful. But if the stop position is inappropriate, the increase of cycle fails in reducing the negative effect of left-turning buses and the effectiveness of offset is weakened.

Bandwidth Maximization Approach for Displaced Left-Turn Crossovers Coordination under Heterogeneous Traffic Conditions

As one of the UAIDs(unconventional alternative intersection designs),DLTs(displaced left-turn crossovers)have been presented to mitigate traffic congestion.Although,qualitatively and quantitatively isolated UAIDs outperform their conventional counterparts,there is no simplified procedure to consider the DLTs coordination.Hence,this research investigates the coordination of consecutive DLTs under heterogeneous traffic conditions.To achieve the optimal coordination and provide an efficient coordination control,a bandwidth maximization progression approach was used.Seeking the optimal offset for each pair of consecutive intersections to guarantee the green bandwidth waves along the coordinated corridor,a mixed-integer linear program was adopted.The optimization problem was formulated and solved based on the standard branch-and-bound technique.As a real-world study case,data of three typical intersections located in an arterial corridor in Cairo,Egypt was used.PTV-VISSIM as a microsimulation platform was employed to simulate and evaluate the different signal timing plans.However,to represent the heterogeneous traffic characteristics as close as possible to the reality,different simulation parameters were tuned and validated carefully.The results emphasized the undoubted improvement of coordinated DLTs by different operational performance indices.The total travel time,average delay,the number of stops per vehicle were obviously improved.

Impact of Pedestrian Traffic on Saturation Rate of Protected Left-Turn at Urban Intersections

Heavily congested intersections in metropolitan areas in China are facing unique problems due to high travel demand and a high degree of traffic law violations. Based on a study conducted by the authors of this paper, 93% of left-turn vehicles turning left in these areas were slowed in order to avoid conflict with pedestrians. Intertwined pedestrian and vehicular flows can significantly reduce the capacity of exclusive left-turn lane group through reducing saturation flow rate, which increases the congestion at intersections. This paper investigates how the saturation flow rate of exclusive left-turn lane group is affected by the characteristics of pedestrian flow. By analyzing the imagery data collected by video cameras installed at intersections, the research team is able to obtain the characteristics of both vehicular and pedestrian flows, such as speed and spatial locations. The average operating speed at the saturation flow rate with and without pedestrian traffic is used as a direct measurement to evaluate the effect of pedestrians. Based on the statistical analysis, the paper concludes that saturation flow rate is mainly affected by the position of pedestrian in the crosswalk (inside or outside of left-turn vehicle’s trajectory), and the distance between the vehicle and pedestrians. In general, when the distance is less than four meters, the smaller the distance between vehicle and pedestrians, the larger the impact. However, there is no significant impact when the distance is larger than four meters. To accurately quantify the effect, the degree of pedestrian-vehicle impact is defined in four levels. The results show that the difference in the saturation flow rate between the best and the worst level could be 15.7%, which clearly indicates how important it is to enforce pedestrian crossing behavior.

Developing Framework to Test Driving Performance at Left-Turn Movement with In-Vehicle Advance Collision Warning Message

Left-turning traffic without a protected left-turn signal is one of the major safety concerns at urban intersections. Though an average of only l0% - 15% of all approaching traffic turns left, significantly a large proportion of left-turn crashes occur involving 21% of all intersection fatal crashes. Where traditional safety countermeasures of signal timing-phasing and use of flashing yellow light have reportedly failed to significantly reduce the rate of crashes, an in-vehicle advance collision warning message can be helpful to reduce left-turn collisions at intersections. In this study, an in-vehicle audio warning application has been designed by providing two safety warning messages (Advance Warning Message and Safe Left-turn Maneuver Message) under the vehicle to vehicle (V2V) communication system, which is triggered based on the acceptable gaps of oncoming opposing vehicles for a safe left-turn. A driving simulator test has been conducted with 30 participants to investigate the impacts of warning messages on performance measures such as speed and acceleration profiles, collision records, brake reaction distance, and intersection clearance time. Statistical results showed that with the help of these messages, all participants were able to reduce speeds and accelerations and chose suitable gaps without potential conflicts. Moreover, the results of questionnaire analysis provide a positive acceptability especially for the Safe Left-turn Maneuver Message. Based on the performance measurements, this type of safety warning messages can be recommended for possible real-road tests for practical applications.

Volume warrants for major and minor roads left-turning traffic lanes at unsignalized T-intersections： A case study using VISSIM modelling

The most common type of intersection improvement considered in Ghana is signalization. However, other actions such as the installation of left-turn lanes have been proven to improve the efficiency and safety of an intersection without the need for signalization in the short term. Warrants which guide the installation of such lanes in Ghana are adopted from elsewhere and as a result do not reflect local traffic flow conditions. This study established volume warrants based on a delay threshold to guide the installation of left- turn lanes at unsignalized T-intersections using VISSIM micro simulation tool. The VISSIM model was calibrated using traffic flow, delay, average and maximum queue length data obtained from a two-hour video recording of the case study intersection during the morning peak period. After calibration, several scenarios covering a wide range of opera- tional conditions were simulated. Using level of service （LOS） C cut off point of 25 s/veh as the maximum acceptable delay to minor road left-turning traffic, an equation y = -0.57x ＋1091 has been developed which predicts the minor road left-turn volume threshold （y） above which a minor road left-turn lane may be considered and below which a minor road left-turn lane may not be necessary for a range of major road volumes （x）. The critical delay to major road left-turning traffic was found to be 16 s/veh. Major road left-turn lane volume warrants were also determined based on this threshold delay value. The approach used in this study can serve as a guide that can be used by metropolitan and municipal road en- gineers to assess the need for left-turn lanes.

Signal timing optimization model based on dual-ring phase scheme for roundabout

A signal optimization model for roundabout was control concept were used to eliminate the conflict points proposed based on dual-ring scheme and two stop lines for left turns and weaving sections at a roundabout. A cycle length minimization problem was considered to generate optimal signal timings for roundabout, and a set of constraints to ensure feasibility and safety of the resulting optimal signal settings were proposed. Extensive experimental analyses in comparison with signalized intersection reveal that the proposed model is quite promising for application in design of roundabout signals, and the minimum cycle length can decrease from 186 s to 79 s while the capacity increases from 8 682 pcu/h to 9 011 pcu/h under high demand scenario. Sensitivity analysis with respect to the system performance show that the lane assignment plan, number of circulatory lanes and left turn ratio are three critical factors which have dominate impacts on performance of signalized roundabout

Optimal design of left-lane line extensions considering non-yielding maneuvers at the beginning of the permitted phase

In order to restrict non-yielding maneuvers of left-turning vehicles,an optimal design of left-lane line extensions is proposed to solve the problem.A field observation was conducted to collect a data set of left-turning vehicles at the beginning of a green phase at two similar intersections(one with a permitted phase and the other with a protected phase).The comparative analysis shows no significant difference in the speed distribution using either a permitted phase or a protected phase,but it reveals that a permitted phase can lead to a larger acceleration when the left-turn vehicles pass through the conflict points.Those indicate the existence of non-yielding maneuvers of left-turn vehicles at signalized intersections with a permitted phase.Optimal designed left-lane line extensions contain two types of segments,circular curves and transition curves,and they are only related to four geometry parameters of an intersection.The proposed method is easy to use and it can offer reference for intersection channelization and traffic organization.

Drivers’ Reaction of Warning Messages in Work Zone Termination Areas with Left Turn

Work-zone crashes have always drawn public attention. A number of fatalities are recorded every year nationwide within work zone areas. Most existing countermeasures have been dedicated more to the advance warning areas, transition areas, and activity areas of work zone, than the termination areas, where drivers might play less attention to safety threats. In this study, the vehicle-to-vehicle communication based left turn warning system was applied at a work zone termination area, which is immediately followed by a T-intersection. The work-zone is located on the minor road side, while left turn vehicles will be appearing from the major street through the said T-intersection. A smart phone application was designed using Android coding system to provide several types of warning messages to drivers. Corresponding scenarios were designed in a driving simulator, and 20 subjects were recruited to participate in the simulation test followed by a questionnaire survey. The subjects received a warning message when driving to the termination area of a work zone on the coming left turn vehicles. Twenty test drivers’ driving speed, acceleration rates, and break reaction distance to the warning messages were studied in four different scenarios. Results show that the smartphone application has a great impact on driving behaviors, especially the female voice and the beep tone warning, which are recommended for possible field tests. Besides, the developed smartphone applications can be further updated for practical applications of similar needs.

Left-turn phasing selection considering vehicle to vehicle and vehicle to pedestrian conflicts

Left-turning vehicle movement at signalized intersections with permissive left-turn phases creates safety concerns due to the higher chance of conflict with opposing-through vehicles and pedestrians.In this research,a simulation-based study was conducted to evaluate pedestrians’impact on traffic conflicts between left-turning vehicles and opposing-through vehicles(V-V conflicts)as well as traffic conflicts between left-turning vehicles and pedestrians(V-P conflicts)in the permissive left-turn phasing scenario.Intersections with different opposing-through volumes,left-turn volumes,number of opposing-through lanes,and pedestrian volumes were modeled in VISSIM,a traffic micro-simulator.The surrogate safety assessment model(SSAM)was used to estimate the number of V-V and VP conflicts.The effect of pedestrian presence on V-V and V-P conflicts was evaluated using simulation scenarios with and without pedestrian presence.Simulation results revealed that pedestrian presence increased both V-V and V-P conflicts.As pedestrian presence increased the total number of traffic conflicts,permissive left-turn phasing processed fewer left-turn vehicles to maintain the same level of intersection safety with pedestrian presence compared to the no-pedestrian scenario.Since current left-turn phasing decision guidelines do not consider the impacts of pedestrian presence,this research quantified pedestrian-influenced and pedestrian-involved left-turn traffic conflicts to determine appropriate left-turn signal phasing decisions to ensure safe and efficient crossing of pedestrians and vehicles at signalized intersections.This simulation-based study’s findings can be beneficial in the decision making of left-turn phasing selection as the before-after intersection safety performance analysis by collecting field data often resources intensive.

Critical Conditions for Left-Turn Lane's Stop Line Backwards Setting Under Exclusive Left-Turn Phase

Aiming at the problem that the vehicles always turn left in advance which causes heavy conflicts in the intersection and effected traffic efficiency,the solution of the left-turn lane’s stop line backwards setting was proposed,and the critical conditions on the stop line’s setting were studied.Firstly,we studied the characteristics of trajectories distribution in the release process of turning left in advance vehicles.Based on that,we proposed to move the stop line backwards to solve the problem of turning left in advance.Considering the intersection’s geometric features and the vehicle operation features,the geometric critical condition was given for setting the position of left-turn lane’s stop line.And then the model of left-turn vehicles’queuing length was established based on queuing theory and traffic wave theory.By using queuing length model,the flow restrictions of stop line backwards could be found.Assuming left-turn vehicles’arrival rate is stable in a certain period of time,the minimum green time and the maximum red time of left-turn phase were given after the stop line was set up.According to the changes of the vehicles’turning paths,the shortest yellow setting recommendation was given.Finally,the application of the critical limits used in stop line backwards setting was demonstrated.The research result could provide a theoretical basis for traffic signs and markings’setting and perfect the relevant laws and regulations.

Optimal control of automated left-turn platoon at contraflow left-turn lane intersections

Purpose–This study aims to propose a centralized optimal control model for automated left-turn platoon at contraflow left-turn lane(CLL)intersections.Design/methodology/approach–The lateral lane change control and the longitudinal acceleration in the control horizon are optimized simultaneously with the objective of maximizing traffic efficiency and smoothness.The proposed model is cast into a mixed-integer linear programming problem and then solved by the branch-and-bound technique.Findings–The proposed model has a promising control effect under different geometric controlled conditions.Moreover,the proposed model performs robustly under various safety time headways,lengths of the CLL and green times of the main signal.Originality/value–This study proposed a centralized optimal control model for automated left-turn platoon at CLL intersections.The lateral lane change control and the longitudinal acceleration in the control horizon are optimized simultaneously with the objective of maximizing traffic efficiency and smoothness。

A peer-to-peer logic environment to validate flashing yellow arrow decision support system

The flashing yellow arrow(FYA)signal display creates an opportunity to enhance the leftturn phase with a variable mode that can be changed on demand.This research develops an integrated general purpose data collection module that time stamps detector and phase state changes within a National Electrical Manufacturers Association(NEMA)actuated traffic signal controller to provide recommendations for the flashing yellow arrow left-turn mode on a cycle-by-cycle basis.115 left-turn approaches at 38 intersections with locations across the State of Florida were analyzed totaling 1370 h of video data processed including off-peak and peak conditions.Video data extraction was an essential step in developing thegap thresholds for the permissive left-turn.Actual intersection field data were obtained through loop detector mapping to the controller in the lab in real-time mode using a peerto-peer logic environment.A custom communications software was developed to retrieve instantaneous channel input data,synchronize opposing through green phase,analyze traffic information,provide the algorithm decision,and generate a real-time log recording the events to determine whether it would be optimal to switch the red arrow to a flashing yellow arrow.The algorithm determines the time interval between the successive arrivals of vehicles and computes the corresponding headway for each lane by cycle on a secondby-second basis.Peer-to-peer logic is a necessary step to verify and validate new traffic concepts prior to field-testing and offers the advantage of acquiring and analyzing realtime traffic data coupled with video feed with the benefit of a safe environment.