Left-turn Waiting Area Research Articles

Revisiting Left-Turn Waiting Areas: Optimizing Left-Turn Signal Timing to Eliminate Twice Startup, Reduce Emissions, and Improve Traffic Efficiency

Revisiting Left-Turn Waiting Areas: Optimizing Left-Turn Signal Timing to Eliminate Twice Startup, Reduce Emissions, and Improve Traffic Efficiency

Arterial Signal Coordination Considering the Impacts of Left-Turn Waiting Areas

Arterial Signal Coordination Considering the Impacts of Left-Turn Waiting Areas

Evaluating the traffic safety performance of left-turn waiting areas at signalized intersections

Left-turn waiting area (LWA) is an innovative traffic design that is popularly applied to improve the traffic capacity of signalized intersections in China. The traffic safety impacts of the LWA, however, have not been fully discussed in previous studies. Thus, the study aims to evaluate the safety performance of the LWA by means of the traffic conflict technique. A field investigation was conducted to collect the post-encroachment time (PET) of conflicts and relevant variables at the signalized intersections in Jinhua, China. The Chi-square and two sample t-tests were adopted to examine the difference in conflict distribution between the intersections with and without LWA. The random parameter ordered logit model was employed to identify the factors contributing to the risks of vehicular collisions. Results indicate that (1) intersections with LWA are generally associated with more merging conflicts; (2) there are no significant discrepancies in the PET values between intersections with and without LWA; and (3) factors such as the number of left-turn lanes, number of receiving lanes, conflict type, vehicle type, driving direction, stopping outside LWA and overtaking behavior are identified to significantly impact the traffic conflicts. The findings serve to develop the countermeasures to ensure the safe operation of LWA.

Signal Control Method for Through and Left-Turn Shared Lane by Setting Left-Turn Waiting Area at Signalized Intersections

This paper proposes a signal control method for the through and left-turn shared lanes at signalized intersections to solve traffic conflicts between left-turn vehicles and opposing through vehicles by setting left-turn waiting area (LWA). Delays and stops are weighted to form an integrated performance index (PI) in a vehicle-to-infrastructure cooperation system. The PI models pertaining to all vehicles are established based on the LWA intersection. In addition, an optimized method of signal timing parameters is constructed by minimizing the average PI. VISSIM simulation shows that the average PI decreases by 6.51% compared with the original layout and signal timing plan of the intersection, since the increased delay of the side-road left-turn vehicles is insufficient to offset the reduced delay of the side-road through vehicles after the improvement. The sensitivity analysis shows that the greater the traffic volume of the phase including the through and left-turn shared lanes, the higher the operation efficiency of the LWA intersection compared with the typical permitted phase intersection. When the left-turn vehicles of the shared lanes in each cycle are less than the stop spaces, the LWA intersection can effectively reduce the average PI of the shared lanes. Furthermore, the more the stop spaces in the LWA, the lower the average PI in the same traffic conditions.

Using Micro-Simulation VISSIM to Study the Effectiveness of Left-Turn Waiting Area Implementation

Numerous attempts have been made to improve the existing intersection systems to maximize capacity and reduce the delay costs and queues. This paper introduces a simulation method to study the effectiveness of a new technique introduced recently in China – the left-turn waiting area. This has an extended left lane that allows the vehicles to wait before the signal turns green. It is reported that this system can significantly improve intersection performance. This paper introduces the different types of left-turn waiting areas which have been widely implemented in China. The method of using micro-simulation VISSIM to study the effectiveness of left-turn waiting area is proposed in this paper, along with some preliminary results of a case study.

Increasing the capacity of signalized intersections with left-turn waiting areas

One of the most complex issues for the design of at-grade signalized intersections is accommodating left-turn (LT) movements, especially when approaches have insufficient available spatial resources. In this study, we mitigated this problem by reorganizing left-turning traffic flows within intersections through the use of a left-turn waiting area (LTWA). We proposed a series of design pattern left-turn waiting areas for different combinations of spatial and temporal treatments of left-turn movements: exclusive left-turn lanes with protected left-turn phasing, exclusive left-turn lanes with permitted left-turn phasing, and shared left-turn lanes with permitted left-turn phasing. Based on probability theory, an analytical procedure is developed for estimating the capacity of shared and short lanes. Explicit VISSIM simulations are conducted to validate the accuracy of the proposed capacity models, and the impact of design parameters for the proposed system on the left-turn capacity are studied. On the basis of the analyses, benefits of the proposed system are identified, and the domain of application where these benefits are most significant is identified. In addition, optimal LTWA design scheme and critical LT volumes of exclusive LT lane and protected LT phase with different LTWA schemes are presented from the operation efficiency perspective.

Multiobjective Evaluation of Left-Turn Waiting Areas at Signalized Intersections in China

This study presents a procedure for evaluating the impacts of left-turn waiting areas at signalized intersections considering multiple performance measures, including traffic operations, safety, environmental impacts, and fuel consumption. Data were collected at 33 sites in Nanjing, China. Vissim simulation models were developed for both isolated intersections and a roadway segment to evaluate the operational and environmental impacts of left-turn waiting areas at signalized intersections. The frequency of traffic conflicts associated with the left-turning traffic was considered the safety performance measure. The life-cycle cost method was used to combine different components in the total benefit for an isolated intersection. It was found that first, for an isolated signalized intersection, the implementation of left-turn waiting areas is overall economically beneficial when the storage capacity of the left-turn waiting area is more than one vehicle. Second, when signal coordination at arterials is considered, a set of factors may determine the overall benefits of using left-turn waiting areas, including the distance between adjacent intersections, the signal timing strategy, the size of left-turn waiting areas, and other factors. The overall benefits of using left-turn waiting areas should be determined case by case. For more than 70% of the randomly generated network cases, the lead-lag phase yields greater maximized progression bandwidth than the dual lagging phase. In this situation, it is generally recommended to implement a left-turn waiting area on one approach with a lead-lag left-turn phase. For only a few network cases in which the maximized progression bandwidth of the lag-lag phase is larger than that of the lead-lag phase, the implementation of left-turn waiting areas on both approaches with a dual-lagging left-turn phase is recommended.

Safety evaluation of signalized intersections with left-turn waiting area in China

In recent years the metropolitans in China have seen the surging installations of the left-turn waiting area (LWA) at the signalized intersections. The design allows the left-turning vehicles to enter the intersection at the onset of the through green phase (of the same approach) and wait for the exclusive left-turn signal at the LWA. The LWA layout can effectively reduce the probability of stranded and queue overflow of the left-turn vehicles, but no study is conducted yet to assess the safety performance of the signalized intersections with LWA. The paper adopts the traffic conflict technique (represented by post-encroachment time), compares the discrepancy of conflict types between intersections with LWA and without, and develops the severity models to identify the contributing factors for the left-turn conflicts. Results demonstrate that the left-turn volume, driving outside the LWA, running red light, the presence of secondary conflicts, and the rear-end conflicts significantly increase the severities of traffic conflicts at the LWA. The findings serve to provide recommendations to revise the current design standard of the LWA (GB5768-2009) and consequently improve the safety operations of signalized intersections with LWA in China.

Effects of Left-Turn Waiting Areas on Capacity and Level of Service of Signalized Intersections

Transportation professionals in China have started using an unconventional left-turn waiting area design as an innovative approach to mitigate traffic congestion at signalized intersections. The waiting area is set up beyond the stop bar at single or dual left-turn lanes at signalized intersections with lagging protected left-turn phases. This paper evaluated the effects of left-turn waiting areas on capacity and level of service of exclusive left-turn lanes at signalized intersections using empirical data. Capacity and delay models were developed by analyzing the arrival and discharge patterns of left-turning vehicles at single and dual left-turn lanes with differently sized left-turn waiting areas. The saturation headway, start-up lost time, and clearance time for left-turning passenger cars were estimated with field data measured from 22 sites. The capacity and delay models were calibrated and validated against both field-measured and simulated data. The results of sensitivity analyses showed that left-turn waiting areas increase the capacity of left-turn lanes at signalized intersections, and the capacity gains will increase with an increase in the storage capacity of the left-turn waiting areas. A procedure was proposed to determine the level of service of left-turn lanes with left-turn waiting areas at signalized intersections.

Evaluating the Operational Impact of Left-Turn Waiting Areas at Signalized Intersections in China

Transportation professionals in China have started using left-turn waiting areas and lagging left-turn phasing to improve traffic efficiency at signalized intersections. Left-turn waiting areas are usually set up beyond the stop bar at an exclusive left-turn lane or dual left-turn lanes. This design allows left-turning vehicles to enter and wait at the left-turn waiting area after the initiation of the through phase. The operational impact of left-turn waiting areas at signalized intersections was evaluated, and the arrival and departure processes of left-turning vehicles at exclusive left-turn lanes with and without waiting areas were compared. A procedure for estimating the capacity of an exclusive left-turn lane with a waiting area was proposed. Cross-sectional analysis used data collected from 12 approaches at nine signalized intersections to compare the start-up lost time and saturation headways of left-turn passenger cars for four scenarios. The capacities of exclusive left-turn lanes with differently sized left-turn waiting areas were compared. The results indicate that left-turn waiting areas increase the capacity of exclusive left-turn lanes and that the capacity gains would increase with an increase in the storage capacity of the left-turn waiting area.

Can Left-turn Waiting Areas Improve the Capacity of Left-turn Lanes at Signalized Intersections?

This study estimated the operational impacts of left-turn waiting areas at signalized intersections using the VISSIM simulation technique. A procedure was proposed to model capacity of single left-turn lanes with waiting areas in VISSIM. Using data collected from 7 different sites, the VISSIM simulation model was calibrated and validated. The simulation results of the calibrated VISSIM model were compared to field measured capacity, as well as the capacity estimated using the analytical model developed in our previous studies. The calibrated VISSIM simulation model yields a Mean Absolute Percent Error (MAPE) of 8.28% for the exclusive left-turn lanes, indicating that VISSIM provides reasonable capacity estimates for left-turn lanes with waiting areas at signalized intersections. Based on the calibrated VISSIM simulation model, the capacity for left-turn lanes with waiting areas with different storage capacity was compared with the scenario for which the left-turn waiting area is not installed. The results show that the use of left-turn waiting areas could increase the capacity for the left-turn movement, and the capacity gains would increase with the increase in the size of the left-turn waiting areas.

Traffic Performance in Signalized Intersection with Shared Lane and Left-Turn Waiting Area Established

This paper highlights the left-turn waiting area in an intersection and proposes a different perspective for measuring the capacity of the traffic flows, which permits the through vehicles to queue on the left lane in a protected signal operation. The effect of flow diverting from the through lanes on the left lane is quantitatively analyzed with random service system theory and probability theory. The utilization of the left-turn waiting area significantly improves the discharge rate of the through lane without compromising the efficiency of left-turning flows, thus reducing the average vehicle delay. A typical intersection with a different capacity of left-turn waiting area is presented to verify the advantage of shared-use operation in the average delay. Besides, effects of the length of the left-turn waiting area, green ratio, and left-turn proportion on the capacity in shared lane are constructed in different conditions. The relationships between these parameters and the actual capacity are presented to show the trade-off between shared use and the exclusive configuration. Theoretical analysis and simulation results show that the shared-use style still works even when the arrival rate of through flows reaches the road capacity, which may result in congestions.