Left-turning Vehicles Research Articles

Operational Performance at Two-Way Stop-Controlled Intersections

When two cars approach the stop-controlled legs of a two-way stop-controlled (TWSC) intersection at the crossing of a major and a minor roadway, driver perception concerning which vehicle should be granted the right-of-way is often unclear. This confusion can increase if one of the drivers intends to execute a left turn. The research described in this paper was performed primarily to identify any safety issues with driver perception or understanding in the case of one left-turning vehicle with an opposing right-turning or straight-through vehicle at the stop-controlled legs of a TWSC intersection. The data collection involved filming and observing vehicle interactions at seven TWSC intersections in the cities of Bryan and College Station, Texas. The way left-turning vehicles responded to the TWSC intersection when an opposing vehicle was present was specifically evaluated. This scenario occurred 113 times for the seven intersection locations during a total evaluation period of approximately 25 h. For these 113 observations, the researchers performed statistical analyses and determined that the minor roadway volume and the first vehicle to approach the intersection significantly influenced driver behavior. The overall study findings confirm the hypothesis that drivers do not fully understand the appropriate (legal) maneuver protocols when stopped at TWSC locations.

Exploring Factors Impacting Paths of Left-Turning Vehicles from Minor Road Approach at Unsignalized Intersections

At unsignalized intersections, left-turning vehicles from minor road approach are more likely to be involved in traffic conflicts and traffic crashes and are one of the most leading factors impacting traffic efficiency and capacity. The authors of the paper observed that some drivers behaved illegally and dangerously while performing left turns from minor road approach, resulting in abnormal trajectories at unsignalized intersections. By applying binary logistic analysis, a probability prediction model was developed to explore various factors affecting probability of normal path taken by drivers while turning left from minor road approach. Based upon the model, measures such as lowering running speeds of vehicles on major road or minor road and adding more lanes on minor road can be used to encourage more drivers to take normal vehicle paths, which is helpful for the improvement of traffic safety, efficiency, and capacity. Results of the paper can be used for the guidance of design and management of unsignalized intersections.

Data Delivery Delay Reduction for VANETs on Bi-Directional Roadway

In this paper, we investigate the data delivery delay from source to destination for VANETs on bi-directional roadways. The topology includes bi-directional roadways, left-turn lane, straight through lane, right-turn lane with traffic lights deployed at the intersections. Due to the multi-hop feature of data delivery and the limited range of radio transmission, the roadways’ topology and the switch operations of traffic lights will jointly affect the data delivery delay. By employing the queuing theory and analyzing the traffic lights operations, we propose the formulae of data delivery delay for different scenarios and extend the analysis to a more general scenario. We find that in the scenario of single intersection, the data delivery delay can be reduced by appropriately selecting the relay nodes. Specifically, in the case of green traffic light at the intersection, opposite lane vehicles can be used to reduce the delay, while for red traffic light, left-turn lane vehicles are used to reduce the delay in a similar approach, i.e., by using multi-hop transmission. The proposed algorithm is verified on single lane roadway, opposite-only, and left-turn-only lane for different simulation time slots, the number of mobile nodes and the value of $R/W$ ( $R$ is the wireless communication range and $W$ is the length of the road intersection) through VanetMobiSim and NS-2. Numerical results show that for single intersection, the data delivery delay can be reduced by choosing appropriate relay nodes. Besides, the successful packet delivery rate of bi-directional roadway is better than that of single line roadway scenario.

Visibility of Two-Wheelers Approaching Left-Turning Vehicles Compared with Other Hazards Under Nighttime Conditions at Urban Signalized Intersections

In the past, researchers have investigated ways to increase the conspicuity of two-wheelers (i.e., motorcycles, mopeds, scooters, and other motorized vehicles) under daytime conditions. However, only a few researchers have analyzed their conspicuity under nighttime conditions. The aim of this study was to evaluate the visibility of two-wheelers encountered by left-turning motorists at urban intersections under nighttime conditions, and compare them with other hazards. A low-fidelity simulator was used to collect data and perform evaluations. The simulator presented a series of videos from a motorist’s perspective, while a passenger vehicle was positioned in the permitted left-turn lane at a signalized intersection. During each video the study participants were instructed to determine whether a left-turn maneuver was safe under the given set of nighttime traffic conditions. The response times for 30 participants were recorded and totaled 627 responses. The observed response times to a two-wheeler were not different from the response times to a passenger vehicle with two headlights. However, the response times were significantly shorter than the times to recognize no hazard or a two-wheeler with no headlight. The conspicuity issues that pertain to two-wheelers in daytime and nighttime conditions were not observed to be the same. Further, the same treatments proposed for two-wheelers in daytime conditions may not be as beneficial or even needed during nighttime driving.

Modeling Left-Turn Driving Behavior at Signalized Intersections with Mixed Traffic Conditions

In many developing countries, mixed traffic is the most common type of urban transportation; traffic of this type faces many major problems in traffic engineering, such as conflicts, inefficiency, and security issues. This paper focuses on the traffic engineering concerns on the driving behavior of left-turning vehicles caused by different degrees of pedestrian violations. The traffic characteristics of left-turning vehicles and pedestrians in the affected region at a signalized intersection were analyzed and a cellular-automata-based “following-conflict” driving behavior model that mainly addresses four basic behavior modes was proposed to study the conflict and behavior mechanisms of left-turning vehicles by mathematic methodologies. Four basic driving behavior modes were reproduced in computer simulations, and a logit model of the behavior mode choice was also developed to analyze the relative share of each behavior mode. Finally, the microscopic characteristics of driving behaviors and the macroscopic parameters of traffic flow in the affected region were all determined. These data are important reference for geometry and capacity design for signalized intersections. The simulation results show that the proposed models are valid and can be used to represent the behavior of left-turning vehicles in the case of conflicts with illegally crossing pedestrians. These results will have potential applications on improving traffic safety and traffic capacity at signalized intersections with mixed traffic conditions.

Reliability Analysis of Left-Turn Sight Distance at Signalized Intersections

The current method for the analysis of sight distance for left-turn vehicles at signalized intersections assumes that all component variables are deterministic. This paper presents a probabilistic approach based on such random variables as major-road speed, time gap required for left-turn vehicle, vehicle width, lateral position of left-turn vehicle, distance between driver eye of left-turn vehicle and its front, and lateral and longitudinal positions of positioned opposing left-turn vehicle. A safety margin is defined as the difference between available and required sight distances. Relationships for the mean and standard deviation of the safety margin were developed using the first-order second-moment (FOSM) method. This method identifies the offset (distance between left edge of the left-turn lane and right edge of the opposing left-turn lane) at signalized intersections for a desired probability of noncompliance based on intersection and traffic characteristics. The proposed reliability method was validated using Monte Carlo simulation, and design graphs were established. The results show that the deterministic method provides very conservative offsets and that the offset is most sensitive to vehicle width and lateral distance-related variables and less sensitive to longitudinal distance-related variables.

Safety Effects of Protected Left-Turn Phasing at Signalized Intersections: An Empirical Analysis

Left-turn crashes occur frequently at signalized intersections and often lead to severe injuries. This problem can be addressed through the implementation of protected left-turn signals. This gives left-turning vehicles the right to enter the intersection free from conflict with opposing drivers and pedestrians. The present study analyses the effect of this measure on crash occurrence. The study included 103 signalized intersections with left-turn signals in highways in Flanders, Belgium, of which 33 received only changes in the signal control and 70 also received additional changes. The effect on traffic safety is analyzed through an Empirical Bayesian before-and-after study on crashes, in which general trend effects and regression-to-the-mean are controlled. On the 33 intersections that received only changes in the signal control, the number of injury crashes decreased significantly (−46%, 95% CI (−36%; −55%)) during the after-period. This was mainly attributable to a decrease in left-turn crashes: −60%, 95% CI (−39%; −74%). The number of rear-end injury crashes did not change significantly after the implementation of a protected left-turn signal. A larger effect was identified for more severe crashes (involving serious injuries and fatalities) as compared with crashes resulting in lighter injuries: −66%, 95% CI (43%; −80%). Furthermore, the effect of left-turn phasing on the number of injured car occupants, cyclists, moped riders and motor cyclists was examined, and favorable effects were found for each of these groups.

Start-Up and Acceleration Profile for Protected Left-Turn Vehicles at Signalized Intersections

AbstractThe law of start-up, acceleration profile and leave-out for queuing vehicles at signal intersections is a fundamental question for the queuing theory, traffic simulation and etc in traffic engineering. This paper investigates the vehicular flow at two protected left-turns by video cameras installed at signal intersections, and checks the accuracy of speed processing software. Based on the statistical analysis and the method of curve fitting, the research team establishes the model of start-up and speed-time profile for the queuing vehicles in the protected left-turns at signal intersections. Then the leave-out time of vehicles is calculated based on the established formulas in these models, which is consistent with the observed leave-out time of vehicles by the video. The developed models proved to be accurate. The paper concludes that the queuing vehicles follow by a linear start after the green light, and the speed-time profile indicates an “S” shape from vehicles starting to reach the stable saturation flow. The speed and the queue sequence of first vehicle of saturation flow are different at different intersections, but the law of start-up of vehicles is the same: The same reaction time for the first vehicle and the same linear start-time interval for the adjacent vehicle in the queue. The relationship of leave-out time and the queue sequence of vehicle is nonlinear before the saturation flow. According to the models developed in this paper, the queue sequence of first vehicle of saturation flow and the law of leave-out time of vehicles can be calculated accurately, which is the fundamental for the queuing theory and the traffic simulation.

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.

Study of Feasibility Analysis for the Protected-Permissive Left-Turn Signal Control in Three-Leg Signalized Intersections Using a Microscopic Traffic Simulation Model

PURPOSES : This study evaluated the feasibility of implementing protected-permissive left-turn (PPLT) signals at three-leg signalized intersections. METHODS: A three-leg signalized intersection with permissive left-turn was first selected. A VISSIM simulation model was constructed using data collected from the test site. The VISSIM network was calibrated by adjusting related parameter values in order to minimize the difference between the simulated and surveyed critical gap. The calibrated network was validated by the number of waiting left-turning vehicles per cycle. Finally, the mobility and safety measures were extracted from simulation runs in which permissive, protected left turns as well as PPLTs were realized based on diverse traffic volume scenarios. RESULTS : The mobility-related measures of effectiveness (MOEs) of the case with PPLT outperformed the other two left-turn treatment scenarios. In particular, the average waiting time per cycle for the left-turn vehicles in the case with PPLT was reduced by 30 s. The safety-related MOEs of the case with PPLT were somewhat higher than those in the case with protected left-turns and much higher than those in the case with permissive left-turns. CONCLUSIONS : Based on the mobility- and safety-related MOEs generated from the VISSIM simulation runs, the use of PPLT seems to be feasible at three-leg signalized intersections where the left-turn is permissive and a pedestrian signal exists at the conflicting approach. However, in order to use the PPLT in earnest, it is necessary to revise the road traffic act, traffic signs, and related manuals.

Evaluation of left-turn lane offset using the naturalistic driving study data

IntroductionThe Strategic Highway Research Program 2 (SHRP 2) Naturalistic Driving Study (NDS) data were used to evaluate gap acceptance behavior of drivers at left-turn lanes with negative, zero, or positive offsets ranging from −29ft to +6ft. The objectives of the study were to develop guidance for the design of offset left-turn lanes used as a safety countermeasure, and to provide insight regarding the use of the NDS data to future users. MethodThe study included 3350 gaps in opposing traffic evaluated by 145 NDS volunteer drivers and 275 non-NDS drivers at 14 two-way stop-controlled intersections and 44 signalized opposing left-turn pairs. Logistic regression was used to model the critical gap length for drivers as a function of offset, under conditions when their view was either blocked or not by an opposing left-turning driver. ResultsThe analysis found that the critical gap was longer at left-turn lanes with negative offsets than at those with zero or positive offsets, and was also longer when sight distance was blocked by an opposing left-turning vehicle. Sight distance was much more likely to be restricted by an opposing left-turning vehicle at negative-offset and drivers at those intersections were less likely to accept a gap when an opposing left-turn driver was present. ConclusionsLonger gap lengths could potentially result in decreased operational efficiency of an intersection. In addition, drivers making left-turns at negative-offset left-turn lanes are, on average, more likely to leave the shortest amount of time between their turn and the arrival of the next opposing through-vehicle, which may present a potential safety concern. Practical applicationsThe findings provide guidance for highway designers considering using offset left-turn lanes as a crash countermeasure. This research also highlights the benefits and limitations of using the SHRP 2 NDS data to answer similar research questions.

An Approach to an Intersection Traffic Delay Study Based on Shift-Share Analysis

Intersection traffic delay research has traditionally placed greater emphasis on the study of through and left-turning vehicles than right-turning ones, which often renders existing methods or models inapplicable to intersections with heavy pedestrian and non-motorized traffic. In the meantime, there is also a need for understanding the relations between different types of delay and how they each contribute to the total delay of the entire intersection. In order to address these issues, this paper first examines models that focus on through and left-turn traffic delays, taking into account the presence of heavy mixed traffic flows that are prevalent in developing countries, then establishes a model for calculating right-turn traffic delay and, last, proposes an approach to analyzing how much each of the three types of traffic delay contributes to the total delay of the intersection, based on the application of shift-share analysis (SSA), which has been applied extensively in the field of economics.

Study on Left-Turning Traffic Flow Characteristics under Different Pedestrian Violation Rates at Signalized Intersection

Conflicts between left-turning vehicles and pedestrians are common at signalized intersection in most developing countries. A new cellular automaton model is proposed to characterize left-turning traffic flow. New status update rules and driving behavior in affected areas and nonaffected areas are defined. Indexes of density, average speed and volume under different pedestrian violation rates are compared to quantify the impact of conflicts on left-turning traffic flow. Simulation results illustrate that pedestrian violations have a great impact on left-turning traffic flow and capacity of the intersection. Therefore, taking countermeasures will improve vehicle maneuvers, reduce the number of pedestrian accidents and increase the capacity of the intersection.

Comparison of hook-turn scheme with U-turn scheme based on actuated traffic control algorithm

This paper addresses an innovative traffic regulation scheme at signalised intersection, termed as the Hook-turn (HT) scheme, and contrasts its performance with the classic U-turn (UT) scheme. The HT relocates the right-turning vehicles (in the countries where driving is on the left) from the far-side lane to the curbside lane, requires them to dwell at the intersection, and eventually leave during the green time of the side road. This paper comprehensively compares the performance of these two schemes based on VISSIM simulations, in terms of three different performance measures (Average Delay, Average Travel Time, and Number of vehicles crossing the network per hour (NVPH)). An Actuated Control Algorithm is proposed to dynamically adjust the traffic signal plans under 48 different scenarios. The simulation results can be summarised as: (1) in all the scenarios, UT can outperform HT, in terms of the Average Travel Delay of through vehicles, left-turning vehicles and trams; (2) when the intersection is oversaturated, the Average Travel Delay of right-turning vehicles under UT is higher than that of HT; (3) The Average Travel Time of right-turning vehicles under the HT scheme is evidently shorter than that of UT; (4) the UT scheme yields higher NVPH to the right-turning vehicles; yet; the HT scheme gives rise to higher NVPH to the through vehicles.

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.

Left-turn phase: Permissive, protected, or both? A quasi-experimental design in New York City

The practice of left-turn phasing selection (permissive, protected-only, or both) varies from one locality to another. The literature evidence on this issue is equally mixed and insufficient. In this study, we evaluate the safety impacts of changing left-turn signal phasing from permissive to protected/permissive or protected-only at 68 intersections in New York City using a rigorous quasi-experimental design accompanied with regression modeling. Changes in police reported crashes including total crashes, multiple-vehicle crashes, left-turn crashes, pedestrian crashes and bicyclist crashes were compared between before period and after period for the treatment group and comparison group by means of negative binomial regression using a Generalized Estimating Equations (GEE) technique. Confounding factors such as the built environment characteristics that were not controlled in comparison group selection are accounted for by this approach. The results show that the change of permissive left-turn signal phasing to protected/permissive or protected-only signal phasing does not result in a significant reduction in intersection crashes. Though the protected-only signal phasing does reduce the left-turn crashes and pedestrian crashes, this reduction was offset by a possible increase in over-taking crashes. These results suggest that left-turn phasing should not be treated as a universal solution that is always better than the permissive control for left-turn vehicles. The selection and implementation of left-turn signal phasing needs to be done carefully, considering potential trade-offs between safety and delay, and many other factors such as geometry, traffic flows and operations.

Evaluating Pedestrian Level of Service at Signalized Intersections in China: Intercept Survey Method

Approximately 1.24 million people die annually in road traffic deaths around the world, and more than 90% of those deaths occur in low-income and middle-income countries, such as China. Pedestrians are the most vulnerable components of road traffic; therefore, it is important to develop more refined methods of improving their walking experience. With use of an intercept survey (IS) method, the influence of pedestrians' characteristics, traffic design, and operation factors on pedestrian level of service (LOS) was evaluated. Factors related to pedestrians' perception and traffic operation had significant impacts on pedestrian LOS. When possible effects of other variables were held constant, significant factors included age, travel purpose, single-step crossing, nearside crossing, and conflicts with left-turning vehicles. Perceived and actual waiting times were compared, and when actual waiting time exceeded 60 s, the perceived waiting time increased faster than the actual waiting time. At 120 s, perceived waiting time was 50% longer than was actual waiting time. An ordered logit model of pedestrian LOS was constructed to evaluate pedestrian LOS in China. This study found several factors more influential in and specific to China than did other international LOS studies. The IS approach was compared with other LOS methods that are part of a series of studies of pedestrian LOS in China. Suggestions are provided on the applicability of IS, contingent field survey, and pedestrian crossing video simulation methods. IS was found to be more suitable for crosswalks of moderate to high levels of pedestrian LOS. Pedestrian crossing video simulation is not recommended for crosswalks with a high possibility of red light crossing.

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.

Risk-Taking Behavior of Left-Turners in Gap Acceptance and Its Effects on Capacity Estimation at Signalized Intersections

The capacity of signalized intersections with a permissive left-turn phase is influenced significantly by the gap acceptance of left-turners. Left-turners' perception of risk when they are deciding whether to accept a gap is of great importance for understanding such driver behavior and for developing countermeasures to improve intersections. This study's objective was thus to model the tradeoff relationship between the perceived risk and the time-saving benefit in gap acceptance for left-turners in China. In the proposed model, the perceived risk was measured by the postencroachment time of the left-turning vehicle and of the gap-ending through vehicle at the conflict; the time-saving benefit was indicated by the potential time to wait for the next acceptable gap. A gap acceptance model that incorporated both variables was then developed and validated by using data collected at two intersections in Shanghai. The acceptable risk level of left-turners could then be defined as the ratio of the estimated model coefficients of those two variables. Results indicated that the wait time significantly affected the gap acceptance and the critical gap decreased as the acceptable risk level rose. In addition, the acceptable risk level was found to be approximately 60 at the observed intersections. With the results, impacts of the acceptable risk level on the capacity of permissive left-turn traffic were investigated through a numerical study. The findings revealed that the capacity of permissive left-turn traffic could be stochastic in nature rather than constant because of random traffic flow characteristics as well as different risk perceptions of drivers.

Assessing Safety Improvements to Pedestrian Crossings Using Automated Conflict Analysis

Surrogate safety measures, such as the traffic conflict technique, have been promoted as an alternative or complementary approach to evaluate road safety from a broader perspective than collision statistics alone. The before-and-after evaluation of safety treatments is one application that can significantly benefit from the use of surrogate safety measures. This study demonstrated the use of automated traffic conflict analysis to conduct before-and-after safety evaluations. The objective was to conduct a time-series (before-to-after) safety evaluation for an intersection in Surrey, British Columbia, Canada, where several pedestrian-related countermeasures were implemented. Treatments included one or more of the following: use of protected-only turns for left-turning vehicles, installation of pedestrian countdown timers, crosswalk realignment, and use of drop-down sidewalks. Results indicated a significant decrease in both pedestrian conflict frequency and severity at the intersection following the treatments. A greater reduction of conflicts was exhibited on the western portion of the intersection where several countermeasures were implemented, including a protected left-turn phase, dual drop-down ramps, and a shift in the crosswalk further west. This variation in conflict reduction along different segments of the same intersection gives a particularized view of the impact of the adopted countermeasures. The outcome of this research provides evidence that surrogate safety indicators can be used effectively to diagnose safety problems and evaluate countermeasures at intersections.