Left-turn Flow Research Articles

Simulation Modelling of Permitted Left-Turn Saturation Flow Rate Based on Opposing Through-Flow Degree of Saturation

This paper presents the modelling of the saturation flow rate of the permitted left-turn in an exclusive lane. In the proposed model, the total permitted left-turn saturation flow rate is determined as a sum of saturation flow rates during the effective green time and the intergreen period. Primarily, the permitted left-turn saturation flow rate during the effective green time is modelled based on the opposing through-flow degree of saturation and the number of opposing through-flow lanes. The relation between the permitted left-turn saturation flow during the effective green time and these variables was examined using data from the simulation experiments in VISSIM. To our knowledge, this is the first study of the permitted left-turn saturation flow modelling based on the opposing through-flow degree of saturation instead of the opposing through-flow rate and signal-timing parameters. The proposed model was validated based on data collected at seven intersections with a permitted left-turn served in an exclusive lane. The permitted left-turn saturation flow rate could be accurately determined based on the opposing through-flow degree of saturation and the number of opposing lanes according to the RMSE of 58.4 pcu/h.

CONTRIBUTION TO THE U-TURN DESIGN AT MEDIAN OPENINGS IN IRAQ: Al-NAJAF CITY AS A CASE STUDY

Field observations indicate that left turning vehicles at U-turn sections lead to a significantly bottleneck (congestion) at both origin and destination (opposing) roads. The bottlenecks have been observed in several U-turns such as Kufa –Najaf U-turn sections, Najaf –Karbala U-turn sections. It was found that left turn flow from U-turn leads to high congestion on both origin and destination roads. Therefore, field improvements have been done by the traffic policemen who create a temporary barrier from traffic plastic signs in order to protect left turning vehicles from through traffic in opposing direction. This study introduces new design for U-turn in order to protect both turning and through trafficto increase the level of performance. This design has been tested by using simulation model. The developed model (S-Paramics) has been calibrated using field data collected from Al-Najaf city. Then, the validation for the developed model has been implemented using another set of field data. Finally, the simulation model has been adopted to test the new design for U-turn. It was found that the new design gives higher capacity than the current design.

NEW APPROACH TO ADDITIONAL LEFT-TURN SECTIONS OF THE TRAFFIC SIGNAL REGULATION

Introduction. The paper describes methods of using the additional left-turn phase of regulation. The authors view the main foreign and domestic methods used in the specialization of the left turn in a separate phase of regulation. To propose a new approach to the specialization of the left-turn direction in a separate phase of regulation the authors investigate one of the most loaded intersections in Voronezh and determine the main characteristics of the traffic flow. Therefore, the authors suggest new parameters in choosing of the necessary method of traffic organization at controlled intersections.Methods and materials. The paper analyses the main methods, which were conditionally related to two approaches: the accident rate of the site and the characteristics of the traffic flow (speed and intensity of the left-turn flow). The authors explained that the new approach, which took into account such parameters as speed, vehicle delays and queue length, allowed effectively controlling the intersection due to the optimal choice of the necessary traffic organization method and due to the result of changes in the parameters by combining the intensity of the left-turn flow and forward flow.Results. The authors developed the approach to the additional left-turn section introduction at the controlled intersection based on a comparison of the left-turn intensity and forward flow and on the analysis of changes in the main characteristics of the traffic flow (speed, vehicle delays and queue length).Discussion and conclusions. The authors concluded that it is necessary to use the proposed approach at the stage of modeling, design and reorganization of the regulated area on the basis of changes in the main characteristics of the traffic flow.

Concurrent Progression of Through and Turning Movements for Arterials Experiencing Heavy Turning Flows and Bay-Length Constraints

Contending with congestion on major urban arterials by providing progression bands has long been a priority task for the traffic community. However, on an arterial experiencing heavy left-turn volumes at major intersections, the left-turn queue may spill back rapidly and further degrade the effectiveness of the through progression band if the left-turn volume and the limited bay length have not been accounted for in the optimization of signal coordination plan. Such negative impact from left-turn queues also justifies the need to take into account the concurrent progression of through and left-turn flows on major arterials. To address these two issues, this paper presents a three-staged signal optimization model that can circumvent or minimize the impact of left-turn spillback to the through movements and concurrently minimize the delay of left-turn flows. The proposed model firstly obtains an initial maximized bandwidth from an existing state-of-the-art method and then maximizes the portion of through bandwidth not impeded by the left-turn overflows. The delay of left-turn flows at each intersection will also be minimized under the obtained effective through bandwidth. The results from the numerical analyses have confirmed the benefits and need of including the left-turn volume and its bay length in the design of dual progression for through and left-turn movements. The simulation experiments further show a reduction in the average delay and the number of stops, by 6.4% and 5.5%, respectively, for vehicles traversing an arterial segment of six intersections, compared with the state-of-the-art model, MULTIBAND.

Development of an algorithm for choosing the specialization of the left-turn lane in the zone of a controlled intersection

The article is devoted to the methods of organization of left-turn traffic in the area of regulated intersections. As a result of the study of the world experience of arrangement of left-turn traffic at controlled intersections, the authors found that today there is no reasonable approach to the specialization of the strip, based on the study of the main characteristics of the traffic flow. The authors have developed an algorithm based on previously unused characteristics, which allows, depending on the ratio of the intensity of the conflict “direct conflicting and left-turn flow” to determine the necessary way of organizing the movement. As a result of testing the developed algorithm, the efficiency of developed algorithm of choice of specialization to allow left-turn lanes in the area controlled intersection.

Operational Analysis and Signal Design for Asymmetric Two-Leg Continuous-Flow Intersection

Despite the increasing implementation of the continuous-flow intersection (CFI) in practice, the development of reliable guidelines for its operational analysis and signal design remains in its infancy, especially for the popular two-leg asymmetric CFI design, because of the relatively low cost and desirable efficiency. For best use of the capacity of such a CFI design, a signal optimization model is presented; it can serve as an effective tool for engineers to design the cycle length, phase duration and sequences, and offsets for both its primary and subintersections. 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 queue spillover on left-turn bays and offers concurrent progression for both the through and left-turn flows. To ensure the applicability and effectiveness of the proposed model, this study further uses 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, it offers concurrent progression to both through and left-turning flows and prevents any queue from spilling over its designated bay.

Minimization of Travel Time in Signalized Networks by Prohibiting Left Turns

The direct left turn at intersections increases delays and causes more accidents in certain conditions. Prohibiting left turns could increase the capacity of the road network and reduce the delays. This research aims to analyze which left turns should be prohibited in an urban road network to increase efficiency. Stochastic User Equilibrium (SUE), with left turn prohibition, is studied in this paper, by minimizing the travel time of the network. The left turn prohibition solution, the corresponding cycle time and green times are determined. A left turn prohibition filtering algorithm (LTPFA) is developed in this paper. The core of the algorithm is that the minor left turn flows have priority to be prohibited. The LTPFA succeeds to find optimal or near-optimal result of travel time in the shorter time compared with enumerating all left turn prohibition combinations. As the total traffic demands increase, the traffic network can benefit more from the left turn prohibition.

Formation and Propagation of Local Traffic Jam

Large scale traffic congestion often stems from local traffic jam in single road or intersection. In this paper, macroscopic method was used to explore the formation and propagation of local traffic jam. It is found that (1) the propagation of traffic jam can be seen as the propagation of traffic signal parameters, that is, virtual split and virtual green time; (2) for a road with endogenous flow, entrance location influences the jam propagation. With the same demand (upstream links flow and entrance flow), the upstream got more influence; (3) when a one-lane road is thoroughly congested, virtual signal parameters everywhere are the same as that at stop line; for a basic road, the virtual signals work in a cooperative manner; (4) phase sequence is one important parameter that influences traffic performances during peak hour where spill back of channelization takes place. The same phase plan for left-turn flow and through flow would be preferred; (5) signal coordination plays an important role in traffic jam propagation and hence effective network signal parameters should be designed to prevent jam from propagation to the whole network. These findings would serve as a basis for future network traffic congestion control.

Evaluating the Impacts of Unconventional outside Left-Turn Lane Design on Traffic Operations at Signalized Intersections

This study evaluated the operational impacts of an unconventional outside left-turn lane design used at some signalized intersections in China. Using traffic data collected from 10 approaches to five signalized intersections where both traditional inside and unconventional outside left-turn lanes are installed, the research team compared turning speeds and saturation flow rates for left-turning vehicles from inside and outside left-turn lanes. The team found that vehicles turning from outside left-turn lanes had relatively higher turning speeds than those turning from inside left-turn lanes. The differences in speed were statistically significant for both passenger cars and heavy vehicles. However, the higher speeds did not result in higher left-turn lane capacity. Unconventional outside left-turn lanes provided slightly lower, but generally comparable, left-turn saturation flow rate when compared with traditional inside left-turn lanes. The differences in discharge headways from inside and outside left-turn lanes were not statistically significant. A binary logit model was developed to quantify the impacts of various factors on the probability of a driver selecting the outside left-turn lane to make a left turn. The chance of a left-turning driver choosing the outside left-turn lane would increase with an increase in the traffic volume of the major street and the queue length in the inside left-turn lane and would decrease with an increase in the distance from the upstream right-side side street to the signalized intersection. Drivers of heavy vehicles and those from upstream right-side side streets were more likely to select outside left-turn lanes.

Blocked Time of Permitted Left-Turn Lane Group with Two Opposing Lanes for Two Arrival Types

The blocked time is a portion of effective permitted left-turn green time blocked by opposing traffic until the left-turn vehicle can get an acceptable gap to complete a permitted left turn. In the Highway Capacity Manual, it is designated as the opposing approach queue clearance time, gq The blocked time, denoted as gb, is a critical parameter in estimating delay for a signalized intersection because it affects not only left-turn saturation flow but also the shape of the delay area. This paper proposes a model for estimating blocked time for a left-turn lane group with two opposing lanes for well-and poorly coordinated signals. The proposed model was developed by directly considering the arrival types. Possible platoon arrival patterns during the green interval were categorized and then used to estimate the blocked time of the left-turn lane group. A comparison of the results from the proposed model and the existing models with CORSIM results indicated that the proposed model is more realistic in estimat...

Effects of U-Turns on Capacities of Signalized Intersections

In Florida, the increased use of restrictive medians and directional median openings has generated many U-turns at signalized intersections. There is no widely accepted procedure for estimating the effects of U-turning vehicles on signalized intersection capacity. In the 2000 edition of the Highway Capacity Manual, U-turns are treated as left turns for estimation of saturation flow rates. However, the operational effects of U-turns and left turns are different. This study analyzed the effects of U-turning vehicles on the left-turn saturation flow rate. Data were collected at three signalized intersections in the Tampa Bay area in Florida. In total, the study team recorded the queue discharge times for 260 queues, including 571 U-turning vehicles and 1,441 left-turning vehicles. On the basis of the data collected in the field, a regression model was developed to estimate the relationship between the average queue discharge time for each turning vehicle and the various percentages of U-turning vehicles in the left-turn traffic stream. Adjustment factors for various percentages of U-turning vehicles were also developed by using the regression model. The adjustment factors developed in this study can be directly used to estimate the capacity reduction due to the presence of various percentages of U-turning vehicles at a signalized intersection.

Traffic Planning Models for Single-Point and Tight Diamond Interchanges

Although the single-point interchange (SPI) has been around for approximately three decades, users do not yet have a simplified procedure to evaluate its traffic performance with a similar configuration, the tight diamond interchange (TDI). Several studies have derived general results without decisive conclusions or with partial coverage to assist the users in the selection process. Simulation modeling is used to compare operational traffic performances of isolated SPI and TDI without frontage roads. Modeling was conducted on similar geometries over a wide distribution of traffic flow conditions (101 scenarios). The 101 scenarios were run for both SPI and TDI to derive control delay, stop time, and percent stops from CORSIM. The multivariate statistical comparison of all three variables showed a combined significant difference between the two interchange types, favoring SPI. TDI created more delay, stop time, and percent stops when the left-turn off-ramp flows were very high. Regression models were derived to estimate the three measures for both SPI and TDI. The models are robust and are functions of the highest flows on the cross street and off-ramps. These models are tools that can help planners in the evaluation and selection process of these interchange configurations.

Characteristics and Quantitative Analysis of Crossing Pedestrian and Bicycles Affecting the Left-turn Flow at Signalized Intersections

In this Paper, The purpose of this paper is to investigate the factors affecting saturation flow rate of left-turn traffic. The actual conditions and characteristics of pedestrians/bicycles at the conflict area where pedestrians/bicycles and left-turn vehicles cross are clarified in order to quantify the behavior of pedestrians/bicycles. The model devised in this study is expected to contribute to the development of signalized intersection planning.