Left-turn Intersections Research Articles

A Study of Safe Left-Turn Intersection Conditions for Non-Motorized Vehicles in Lhasa Based on Expansion Widths

A Study of Safe Left-Turn Intersection Conditions for Non-Motorized Vehicles in Lhasa Based on Expansion Widths

A traffic queueing model for exit lanes for left-turn intersections

The unconventional design of exit-lanes for left-turn (EFL) has been confirmed to be an effective way to increase intersection capacity when left-turn demand is high. However, because of the unique feature of EFL control, there would be a strong oscillation in the left-turn queues at signalized intersections when the EFL strategy is used, which makes the analytical evaluation of the EFL strategy very difficult. In particular, the random nature of traffic demand would make it even harder to estimate the queues. To this end, in this paper, we propose a signal state-dependent queueing model to quantify the dynamic behavior of left-turn queues at signalized intersections under EFL control. The obtained results will contribute to establishing an analytical numerical framework that gives us the possibility to study the effect of various factors on the left-turn queues at the EFL intersections and provide insight into the unique queueing behavior that is most likely to manifest this strategy. We validated the proposed model using field data, and it shows a good agreement between the estimated results and the field results. In addition, the numerical experimental results show that the obtained performance measures are practically beneficial to provide a numerical tool to quantify the uncertainty in the queues of left-turn movements with EFL control and thus enrich the guidelines for further improving the use of EFL design.

Development and Evaluation of the Dynamic Left Turn Intersection

Dual left turn lanes are typically operated with protected left turn signals, which means extra delay during non-peak hours compared to permissive operation. To reduce this delay, the authors designed, installed, and tested a “dynamic left turn intersection” (DLTi), which is a new way to operate dual left turn lanes. With DLTi, the both lanes are operated with protected phasing during the peak hours when higher capacity is needed, and only the leftmost left turn lane remains open for protected-permissive operation during off-peak hours. The test showed substantial delay savings, the crash experience has been minimal, and the public comments received have been predominantly negative but not overwhelming. Around 85 percent of left-turning motorists complied when the rightmost left turn lane was closed. The team believes that the DLTi test has been a success, and that agencies should begin searching for other suitable locations for DLTi installation.

Simulation optimisation of displaced left-turn intersection layout with multi-objectives

Displaced left-turn (DLT) intersections, which effectively solve the conflict between left-turn and opposing-through traffic, are currently the most efficient innovative intersection design. However, the special layout of DLT will inevitably cause high difficulty in channelisation design. For full use of the potential traffic capacity of DLT intersection, a multi-objective optimisation model for intersection with DLT layout (MOOM-DLTL) is built based on integrated simulation and mathematical programming (ISMP) framework. In this model, the signal scheme is regarded as the accompanying strategy of DLT layout optimisation to describe the interaction between layout and signal control. In addition, the multi-objective particle swarm optimisation based on shift-based density estimation (MOPSO+SDE) algorithm is developed to obtain the Pareto front of the proposed model. A series of experimental results show that the proposed optimisation method is successful in improving the traffic efficiency of DLT intersection.

Simulation optimisation of displaced left-turn intersection layout with multi-objectives

Simulation optimisation of displaced left-turn intersection layout with multi-objectives

Evaluation and Analysis Model of the Length of Added Displaced Left-Turn Lane Based on Entropy Evaluation Method

As the number of vehicles continues to grow in China, the problem of urban traffic congestion gets more serious, particularly at intersections. As a new type of unconventional intersection, the displaced left-turn (DLT) intersection has been widely recognized to improve the efficiency of intersections with heavy left-turn traffic flows. Converting an existing intersection into an intersection with additional DLT lanes is a valuable solution. However, the studies on DLT intersections mainly focus on performance, applicability, and safety. The guidelines on the specific engineering design process mostly come from experience, and the study on the considering multifactor design method is still insufficient. Therefore, this paper proposed an evaluation and analysis model of the lengths of added DLT lanes based on the entropy evaluation method, in which VISSIM and Surrogate Safety Assessment Model (SSAM) software were adopted for simulation. A design process for the length of the added DLT lanes was proposed with this model. An urban intersection in Xi’an was taken as a case study, and the application of the model and the design process was studied in detail. After selecting four evaluation indicators, the model was applied to calculate and analyze the optimal length of the added DLT lanes under 45 different traffic volume combinations. The recommended lengths of different situations were within the range recommended in the guidebook published by Federal Highway Administration. The results of the case study proved that the model proposed in this paper was advanced, reasonable, and practical.

Optimal Trajectory Control for Left-Turn Vehicles at Exit Lane for Left-Turn Intersections

The exit lane for left-turn (EFL) intersection is a newly proposed unconventional intersection that can alleviate left-turn traffic congestion at intersections. The EFL design characteristic lies in that a part of exit lanes can be provisionally used as left-turn lanes to provide additional capacity for left-turn traffic. The inappropriate lane selection of human drivers decreases the effectiveness of such design. This paper establishes an optimal trajectory planning model for left-turn vehicles at EFL intersections under the automated driving environment. The longitudinal acceleration and lane changing variables are optimized simultaneously. The optimization model is formulated as a mixed-integer linear model, which ensures the computational efficiency. The effectiveness of the proposed model is explored under various traffic, geometric, and signal control conditions. The results show that the model can provide a suitable control strategy for left-turn vehicles. On average, traffic delay can be reduced by 47.3%. The proposed model has a promising control effect under high volume conditions. Moreover, the proposed model performs stably under the various length of the mixed-usage area.

Signal timing optimization of shifted left-turn intersections

A signal timing optimization method based on shifted left turn lane intersections is proposed to increase the efficiency of shifted left turn lane junctions. In previous studies, vehicle delays were often the only concern but vehicle exhaust emissions were ignored, which could easily aggravate environmental pollution. A multi-objective optimization model was developed in this paper for intersection signal timing from a vehicle and environmental perspective, using vehicle delay, capacity and exhaust emissions as indicators. A modified particle swarm algorithm was used to resolve the impact of a shifted left turn lane on vehicles at a selected junction in Shanghai. The proposed scheme can reduce vehicle delay by 24.58%, increase traffic capacity by 17.09% and reduce tail gas emission by 34.68% in peak period compared with before improvement. In low peak period, the delay, exhaust emission and traffic capacity are reduced by 49.04%, 41.68% and 17.09% compared with those before improvement. Using this optimization scheme can improve vehicle delay to a certain extent, improve vehicle traffic capacity and reduce pollution caused by exhaust emission to the environment. It also verifies the validity of the model and provides some theoretical basis for setting the signal timing for shifted left-turn lane intersections.

Modeling the Operation of Left-Turn Vehicles at Exit Lanes for Left-Turn Intersections

AbstractThis study aimed to describe the operation of left-turn vehicles under the impact of exit lanes for left-turn (EFL) control. A microscopic traffic flow model was proposed, in which a multiv...

Evaluation of displaced left-turn intersections

Displaced left-turn intersections (DLTs) are designed to enhance the operational performance of conventional intersections that are congested due to heavy left-turn traffic volumes by excluding the left-turn movements at the main intersection. This results in reducing the number of potential conflict points and increasing the intersection capacity. However, since drivers are not familiar with DLTs’ operation, there is a need to assess the safety and operational efficiency of this type of intersections. This paper evaluates the safety performance of DLTs using two common methods, which are a before-and-after study with comparison group and cross-sectional analysis. Furthermore, it investigates the operational performance of DLTs using a general linear model describing the relationship between a selected measure of performance and other operational and geometric characteristics based on high-resolution traffic data. The safety analysis indicates that DLTs can increase crash frequency in comparison to conventional intersections. In addition, the operational analysis implies that DLTs have the potential to reduce the delay at intersections. Consequently, evaluation of the different aspects of costs and benefits were conducted to decide if this alternative design is appropriate for implementation. The study concludes that DLTs have negative safety impacts in comparison to conventional intersections for many crash types, but it might be more efficient for operational performance. It is recommended that appropriate safety countermeasures should be developed and implemented to enhance traffic safety at DLTs.

Signal control method and performance evaluation of an improved displaced left-turn intersection design in unsaturated traffic conditions

ABSTRACT This paper proposes an improved layout for the Displaced Left-turn (DLT) intersection by combining the conventional DLT intersection with protected left-turn phases, based on the safe-crossing requirements of pedestrians and non-motorized vehicles. The delay and stops are weighted to form an integrated performance index (PI) in a real-time vehicle-to-infrastructure communication environment. The PI models, pertaining to all vehicles in non-DLT lanes, DLT lanes and shared through-right lanes are established based on the improved DLT intersection in unsaturated traffic conditions. In addition, a dynamic optimized method of traffic signal timing parameters is constructed based on minimizing average PI per vehicle and considering the traffic signals’ coordination at the main intersection and left-turn crossovers. The operational performance of the optimized method is validated using data collected at an intersection in Harbin, China.

Operational Performance Comparison between Conventional Intersections and Two Unconventional Alternative Intersection Designs (UAIDs) Under Heterogeneous Traffic Conditions in Cairo, Egypt

Although the wave of valuable research works and the numerous efforts done by researchers focused on studying, analyzing and evaluating the different types of UAIDs relying on the homogenous traffic conditions, the heterogeneous traffic conditions still underestimated. Thus, the driving force of this study is to investigate the UAIDs applicability under the heterogeneous traffic complexities. These complexities are characterized by the diversity of some static and dynamic properties of vehicles, and the aggressive driving behavior which results in non-lane based traffic systems. Hence, the purpose of this article is to compare the operational efficiency of existing conventional signalized intersections with two proposed UAIDs schemes namely; the Displaced Left-Turn (DLT) intersection and Superstreet Median (SSM) intersection. As a realistic case study of such traffic conditions, three existing intersections in an arterial corridor in Cairo, Egypt were selected. The microsimulation software VISSIM, as a time-step, stochastic and behavior based model was utilized to accomplish this study objective. The simulation results emphasized the outperformance of the proposed UAIDs over the conventional counterparts. The results indicated to the obvious improvement of the level of service (LOS) of the studied intersections. It was found that the proposed UAIDs schemes reduced the overall delay and the total travel time while the average speed was increased. On the other hand, it was concluded that the heterogeneous traffic influenced the proposed UAIDs efficiency. The main findings of this research may provide a guidance on presenting UAIDs in the developing cities.

Robust Signal Control of Exit Lanes for Left-Turn Intersections With the Consideration of Traffic Fluctuation

Traffic throughput at intersections can be improved by using exit lanes for left-turning (EFL), tidal flow lanes near an intersection, which has been recently introduced. This paper considers the operational robustness of the EFL intersection in relation to the control scheme applied to the traffic light setting. For safety and efficiency, it is important that the tidal lanes are emptied before traffic in the opposing direction uses these lanes. Hence, the signal control should not only be optimized for the mean value but be robust for all kinds of fluctuations. This paper formulates a traffic control scheme using robust optimization, i.e. an optimization scheme which explicitly accounts for extreme events. The fluctuation of traffic is considered from three aspects: the distribution of traffic demand, the distribution of base saturation flow rate, and the distribution of actual travel speed. Via a case study and extensive numerical analysis, we find that the established robust optimization method produces an efficient design of signal control and design speed at the EFL intersection under traffic demand and supply fluctuations. Though the optimization method is now applied to intersections with an EFL, it is considered useful for all intersections with high fluctuation of traffic demand and saturation flow rate.

Saturation Flow Models of Exit Lanes for Left-Turn Intersections

AbstractA newly proposed unconventional intersection design, exit lanes for left-turn (EFL) intersections, has been demonstrated to be very promising for capacity improvement. However, the differen...

Challenges in Hazard Detection for Commercial Motor Vehicle Drivers: A Driving Simulator Training Study

There are few research studies that have assessed the hazard detection (HD) challenges of experienced, skilled drivers. This paper presents the pilot study results of an HD training program, Commercial Driver Assessment and Training System (CDATS), developed for commercial motor vehicle (CMV) drivers. The training involved simulation-based videos that highlight potential vehicle, pedestrian, and visually hidden hazards during unprotected intersection maneuvers: left-turn, right-turn, and straight-thru. Low-fidelity driving simulations were designed to reinforce video lessons and increase the expectation and detection of potential hazards. Training efficacy was assessed using a driving simulator HD task presented to short-haul CMV drivers ( N = 16) at pre-/post-assignment to CDATS training or a control condition. Results suggested that CMV drivers had highest HD task accuracy (% correct) for vehicle hazards and lowest accuracy for visually hidden hazards. Performance for pedestrian hazards was dependent on the intersection maneuver, with performance decreases for left-turn, right-turn and straight-thru intersections, respectively. Post-test results suggested overall HD improvement in the CDATS training group with no change in the control group; however, there was no significant change in relative hazard type by intersection maneuver pattern. Similar to prior research, experienced CMV drivers may also exhibit challenges in HD, particularly for visually hidden and visible pedestrian hazards, and may benefit from HD training.

Development of Gap Acceptance Models for Permitted Left Turn Intersections during Rainfall

Development of Gap Acceptance Models for Permitted Left Turn Intersections during Rainfall

Aggressive Driving Behavior in the Protected/Permissive Left Turn(PPLT) Intersections

Aggressive Driving Behavior in the Protected/Permissive Left Turn(PPLT) Intersections

Safety evaluation of intersections with dynamic use of exit-lanes for left-turn using field data

As a newly proposed unconventional intersection design, the exit-lanes for left-turn (EFL) intersection is found to be effective in increasing the intersection capacity with high level of application flexibility, especially under heavy left-turn traffic conditions. However, the operational safety of EFL is of most concern to the authority prior to its implementation. This paper evaluates the safety of the EFL intersections by studying the behavior of left-turn maneuvers using field data collected at 7 locations in China. A total of 22830 left-turn vehicles were captured, in which 9793 vehicles turned left using the mixed-usage area. Four potential safety problems, including the red-light violations, head-on collision risks, trapped vehicles, and rear-end crash risks, were discussed. Statistical analyses were carried out to compare the safety risk between the EFL intersection and the conventional one. Results indicate that the safety problems of EFL intersections mainly lie in higher percentages in red-light violations at the pre-signal (1.83% higher), wrong-way violation problems during the peak hours (the violation rate reaches up to 11.07%), and the lower travel speeds in the mixed-usage area (18.75% lower). Such risks can be counteracted, however, by providing more guiding information, installing cameras to investigate and punish violation maneuvers, and adjusting design parameter values for layout design and signal timing, respectively.

Development of Gap Acceptance Models for Permitted Left Turn Intersections

Development of Gap Acceptance Models for Permitted Left Turn Intersections

The role of navigation instruction at intersections for older drivers and those with early Alzheimer’s disease

AimsOur purpose was to explore the effect of navigation instruction on older drivers’ driving performance at left turn intersections. Left turns at intersections are particularly complex because they require many perceptive and cognitive abilities under considerable time pressure. MethodsFifty-four participants were recruited: 18 drivers with early-stage Alzheimer’s disease (AD), 18 neurologically healthy older drivers and 18 younger individuals. Various cognitive processes were measured, and 9 left turn maneuvers with or without navigation instruction were evaluated during an in-traffic road test. The psychomotor, planning and decision-making components involved in left turn were also analyzed closely. ResultsOnly older drivers (both healthy drivers and those with AD) were negatively affected by navigation instruction during the maneuver. The planning and decision-making components were more likely to be affected by the navigation instruction. ConclusionThis finding highlights the importance of carefully considering the use of navigation instructions when developing navigation systems. Adapting this instruction is necessary to simplify our understanding of the real-world driving environment and to avoid increasing the cognitive load of older drivers.