Merging Zones Research Articles

Multi-Vehicle Cooperative Decision-Making in Merging Area Based on Deep Multi-Agent Reinforcement Learning

In recent years, reinforcement learning (RL) methods have shown powerful learning capabilities in single-vehicle autonomous driving. However, few studies have focused on multi-vehicle cooperative driving based on RL, particularly in the dynamically changing traffic environments of highway ramp merge zones. In this paper, a multi-agent deep reinforcement learning (MARL) framework for multi-vehicle cooperative decision-making is proposed based on actor–critic, which categorizes vehicles into two groups according to their origins in the merging area. At the same time, the complexity of the network is reduced and the training process of the model is accelerated by utilizing mechanisms such as partial parameter sharing and experience playback. Additionally, a combination of global and individual rewards is adopted to promote cooperation in connected autonomous vehicles (CAVs) and balance individual and group interests. The training performance of the model is compared under three traffic densities, and our method is also compared with state-of-the-art benchmark methods. The simulation results show that the proposed MARL framework can have stronger policy learning capability and stability under various traffic flow conditions. Moreover, it can also effectively improve the speed of vehicles in the merging zone and reduce traffic conflicts.

Variable speed limit control strategy considering traffic flow lane assignment in mixed-vehicle driving environment

To accurately predict traffic flow and optimize the operations of freeway bottleneck areas in a mixed-vehicle driving environment, this paper proposes a traffic prediction model and a variable speed limit (VSL) cooperative control strategy. Firstly, a lane-level short-term traffic prediction model, physics informed Transformer and cell transmission model (PIT-CTM), is constructed by combining the Transformer neural network and lane-level cell transmission model (CTM) based on the physics-informed deep learning framework. On this basis, the accuracy and transferability of PIT-CTM are analysed. Secondly, a lane assignment decision model is presented, which enables the dynamic planning of the optimal traffic distribution across lanes. Furthermore, a lane-level VSL control model is constructed based on the model predictive control (MPC) framework. The model induces vehicles to change lanes earlier by setting the speed limit difference between lanes. By regulating the input flow in the bottleneck area of the freeway, it reduces conflicts between mainline vehicles and ramp vehicles. Finally, the feedback regulation between the lane assignment decision model and the lane-level VSL control model promotes the cooperative optimisation of the lateral and longitudinal flows and adapts the control strategy to the dynamic traffic characteristics. A three-lane freeway merging zone is selected, the numerical experiment is conducted and compared with differential lane-level VSL. The results show that the strategy can effectively optimise the mixed-vehicle traffic state and maintain better control performance under any connected and autonomous vehicle (CAV) penetration rates.

Traffic conflict analysis in continuous confluence area of cross-river bridge driven by vehicle trajectory data

Objectives To conduct an in-depth study on the spatial distribution of traffic conflicts in the continuous merging areas of cross-river bridges and ensure public transportation safety. Methods First, we utilized drone aerial photography to collect videos of vehicle movements. Using the YOLOv7 object detection algorithm and the Strong SORT multi-object tracking algorithm, we extracted high-precision vehicle trajectory time-series data. Next, based on the motion characteristics of traffic entities, we proposed using Deceleration Rate (DR) to describe rear-end conflicts and Lane Change Speed (LCS) to describe lane-changing conflicts. Additionally, we employed the K-means clustering method to determine the threshold values for minor, moderate, and severe levels of rear-end and lane-changing conflicts. Finally, based on the obtained trajectory data, the values of traffic conflicts are calculated and their severity is classified. A heat map of the spatial distribution of vehicle conflicts in continuous merging zones is then created to study the spatial distribution patterns of traffic conflicts. Results The threshold values for minor, moderate, and severe levels of rear-end conflicts are determined to be 3.06 m/s2, 5.36 m/s2, and 8.04 m/s2, respectively. For lane-changing conflicts, the thresholds are 1.13 m/s, 2.07 m/s, and 3.45 m/s. The spatial distribution of traffic conflicts exhibits a “first increase, then decrease, and then increase again” trend. Conclusions The study identifies the critical areas of traffic conflicts in the continuous merging zones of cross-river bridges. The research results provide a novel approach for acquiring traffic data in these areas and offer a reliable quantitative method for assessing safety risks on these road segments. This provides a theoretical basis for proposing targeted traffic safety management strategies.

Diagnosis of unsteady disturbance characteristics induced by the tip leakage vortex in a compressor based on data-driven modal decomposition methods

The structural information about the tip leakage vortex at the design point remains largely unknown. Here, the dynamic mode decomposition method is utilized to visualize the main coherent structures corresponding to unsteady disturbance frequencies induced by the tip leakage vortex of an isolated rotor at the design point. The results show that the tip clearance size has a significant impact on unsteady disturbance characteristics at the blade tip region. The flow field within the blade tip region can be categorized into four distinct regions: the formation region of the main tip leakage vortex (MTLV), the formation region of the secondary tip leakage vortex (STLV), the merging zone where the MLTV and the STLV interact, and the vortex shedding zone induced by the leakage vortex breakdown. The disturbance peak in the frequency domain decreases from 121.3 RF to 70.96 RF as the tip clearance size increases from 1.5% blade height to 2%, resulting in a reduction of 41.36%. The increase in the tip clearance size amplifies unsteady disturbances caused by the MTLV and STLV. The STLV exhibits more pronounced oscillatory characteristics than the MTLV. The unsteady disturbance induced by the MLTV mainly occurs at around 0.5 blade passing frequency (BPF). In contrast, high-frequency unsteady disturbances (>1 BPF) in the flow field are caused by vortex shedding resulting from the interaction and collision between the STLV and the MTLV. A better understanding of the unsteady disturbance characteristics induced by leakage vortex benefits the study of stall warning technology.

Study on Driver Behavior Pattern in Merging Area under Naturalistic Driving Conditions

To reduce the risk of traffic conflicts in merging area, driver’s behavior pattern was analyzed to provide a theoretical basis for traffic control and conflict risk warning. The unmanned aerial vehicle (UAV) was used to collect the videos in two different types of merging zones: freeway interchange and service area. A vehicle tracking detection model based on YOLOv5 (the fifth version of You Only Look Once) and Deep SORT was constructed to extract traffic flow, speed, vehicle type, and driving trajectory. Acceleration/deceleration distribution and vehicle lane-changing behavior were analyzed. The influence of different vehicle models on vehicle speed and lane-changing behavior was summarized. Based on this data, the mean and standard deviation of velocity, acceleration, and variable acceleration were selected as the characteristic variables for driving style clustering. To avoid redundant information between features, principal component dimensionality reduction was performed, and the dimensionality reduction data was used for K-means and K-means++ clustering to obtain three driving styles. The results show that there are obvious differences in the driving behaviors of vehicles in different types of merging areas, and the characteristics of different areas should be fully considered when conducting traffic conflict warnings.

Collision-Free Merging Control Via Trajectory Optimization for Connected and Autonomous Vehicles

On-ramp merging zones have long been accident-prone spots as well as major triggers of traffic congestion in freeway networks. This paper proposes a collision-free merging control for connected and autonomous vehicles based on trajectory optimization to facilitate traffic safety and efficiency. The optimization is embedded in a model predictive control algorithm with the aim of maximizing the average travel speeds of all vehicles in the planning horizon. To guarantee collision-free merging, the merging control allows only one vehicle to pass the merging zone at a time. Safety constraints, including minimum time gaps and minimum distances between vehicles, are also considered. A rolling horizon control framework is established to enable dynamic traffic control; specifically, generating optimal acceleration decisions for each time step. The optimization problem is formulated as mixed-integer linear programming to enable efficient computation. Numerical studies and sensitivity analysis were conducted to validate the effectiveness and applicability of the proposed method. The results show that the introduced safety constraints can guarantee collision-free merging. Compared to the traditional method, Ih is built on the intelligent driver model and the minimizing overall braking induced by lane-change model, the proposed optimization-based approach results in 5.0%–22.2% improvements with respect to average travel speeds during the merging process. The safety and efficiency improvements are more significant when dealing with higher demand levels. Notably, compared to the difference in initial speeds between the mainline and on-ramp vehicles, the length of the acceleration lane has a greater impact on the control performance.

A Cooperative Control Methodology Considering Dynamic Interaction for Multiple Connected and Automated Vehicles in the Merging Zone

A Cooperative Control Methodology Considering Dynamic Interaction for Multiple Connected and Automated Vehicles in the Merging Zone

Purpose of acceleration and deceleration lanes. Comparison of the regulatory framework for the design acceleration and deceleration lanes in Bulgaria, Austria, Germany and the USA (California).

The report examines and analyzes the purpose of acceleration and deceleration lanes at two-level road interchanges. For the preparation of the current report are used the regulatory framework for the design of acceleration and deceleration lanes from Bulgaria, Austria, Germany and USA – California. The design elements of the acceleration and deceleration lanes are compared in detail. Widths and lengths of lanes, merging zones, angles and slopes. The conclusions of the report are given as guidelines for good practice in the design of road interchanges at one and two levels.

Numerical Study of Mixed Convection of Buoyant Twin Jet

Abstract The effect of mixed convection of twin vertical jets is investigated numerically in this paper. The results are presented specifically for flows affected by buoyancy for two parallel jets of same velocities ranging between 0.25 m/s and 5.0 m/s and temperatures between 295 K and 320 K. Both jets generate a slow flow with a temperature difference (with the ambient flow) less or equal to 32 °C (305 K). Predictions of dynamical and thermal parameters are obtained for the merging and combining regions. This study reveals that the trajectory of the two jets is strongly influenced by the ratio of buoyancy to inertial forces. Results indicate that, relative to isotherm jets, the location along the vertical symmetry plane at which the two jets merge (merging point) decreases with increasing jet inlet temperature. It was also found that the location of the merging point is shifted toward the confining wall as the velocity of the jets increases. The behavior law (linear regression), relating to the expansion of the jet, is not verified in the developed region for each value of the inlet velocity and temperature. This is explained by the fact that natural convection is more predominant than forced convection. The results show that the self-similarity of the cross profiles of the mean velocity and the behavior law relating to the expansion of the jet are obtained throughout the developed region.

Driving safety field modeling focused on heterogeneous traffic flows and cooperative control strategy in highway merging zone

Connected and Automated Vehicles (CAVs) will coexist with Human-Driven Vehicles (HDVs) in the foreseeable future. Proactive safe controls indeed play a vital role in thus a complex heterogeneous traffic environment. This paper mainly constructed the safety field models for vehicles and environments respectively to address the problems of unclear rules of heterogeneous traffic flow and unclear safety mechanisms in the complex scenes of merging areas. Firstly, the action range of CAV vehicle field was constrained with the differential approximation algorithm to fill in the weakness of the infinite influence range of the existed vehicle field. Then the safety field model of HDV was also reconstructed by taking into account the driver’s environmental psychological tolerance with three indicators from driver experience, environmental visibility and trust. Meanwhile, the environmental field model was innovatively set up with the longitudinal distance variable to overcome the drawbacks of sudden changes in field strength as the number of lanes changes. Based on above mechanism models, this study further reconstructed the early lane-changing model that cored with the minimum distance model and the mandatory lane-changing model in the merging zone that cored with the driving safety index (DSI). Those models provided explicit judgment for the selection of vehicle lane-changing model and CAV behavior control in the merging zone. Finally, the simulation experiments show that the cooperative control strategy with a higher of 45% CAV penetration rate in low-density traffic (1200 veh/h) scenario outperforms than those strategies of SUMO or without early lane-changing in adapting the features of highway merge zone. While in a high-density traffic (1600 veh/h) scenario that with a fixed 30% CAV penetration rate, the time-average speed and space-average speed of the cooperative control strategy improved 15.56% and 25.15%, respectively.

An Acceleration Denoising Method Based on an Adaptive Kalman Filter for Trajectory in Merging Zones

Vehicle trajectory data can reveal naturalistic driving behaviour trends. However, owing to measurement and processing errors, the trajectory data extracted from videos often contain obvious noise. In merging zones, vehicles tend to accelerate and decelerate frequently, leading to poor denoising performance of the linear Kalman filter (KF). To address this issue, this study proposes a new denoising method based on the adaptive Kalman filter, which automatically switches between KF and Unscented KF to accommodate car-following and merging behaviours, respectively. A merging behaviour detection method was designed based on the PELT method and normalized innovation squared (NIS). The F1 score of 92.9% shows the accuracy of behaviour detection. According to our results, the proposed method minimizes the range of jerk compared with other methods, reducing it from −4927.78 to 4960.72 of raw data to −44.92 to 47.14, indicating a significant improvement in denoising and trajectory smoothing. The goal of this study is to achieve high-precision trajectory data under complex real traffic scenarios.

Coordination of Mixed Platoons and Eco-Driving Strategy for a Signal-Free Intersection

This paper investigates the collaborative control of vehicular traffic for a signal-free intersection. The traffic under consideration is mixed with connected autonomous vehicles (CAVs) and human-piloted vehicles with advanced driver assistance systems (ADAS). The proposed collaborative control is of two levels. At the upper level, the objective is to minimize total delay via platoon control and dynamic priority control of conflicting movements. We formulate the platoon coordination of mixed traffic as a mixed-integer linear programming problem (MILP). This MILP determines whether adjacent vehicles will form a platoon and prioritize any two conflicting movements subject to lateral safety and rear-end safety constraints. At the lower level, we propose an eco-driving strategy to minimize the energy consumption by optimizing the speed profile of the platoon leading vehicles subject to the dynamic priority control from the upper level, i.e., the entry time to the merging zone. We deduce an analytical solution to the eco-driving problem using optimal control theory. Compared with existing benchmarks, such as the first-come-first-served policy, the proposed method outperforms the state-of-the-art controllers in reducing the total delay. Sensitivity analysis regarding the penetration rate of CAVs shows that substantial improvements can be achieved even at low to medium penetration rates of CAVs.

Integrated Control for Mixed CAV and CV Traffic Flow in Expressway Merge Zones Combined with Variable Speed Limit, Ramp Metering, and Lane Changing

In the conventional human driving environment, due to poor traffic information transmission and the inability to actively control vehicles, variable speed limits (VSLs) and ramp metering (RM) strategies often fail to achieve the desired results when dealing with the merging zone of an expressway under high traffic demand. To improve traffic efficiency, an integrated control method for traffic flow in the merging area of expressways is proposed by combining connected and autonomous vehicle (CAV) active lane change (LC) technology with traditional VSL and entrance RM strategies. This method uses an upgraded cell transmission model (CTM) to estimate the state of the mainline and ramp input traffic volume and then uses the genetic algorithm (GA) to solve for the optimal combination of the mainline speed limit, number of mainline vehicles changing lanes, and ramp regulation under maximized flow in the merging zone. This integrated control strategy incorporating VSL, LC, and RM (VSL-LC-RM) enables synergistic control of the mainline and ramp traffic entering the merging zone in time-space. Finally, simulation experiments are conducted with the mainline two-lane and on-ramp single-lane expressway merging zone scenarios. The results show that compared with the VSL strategy and the strategy incorporating only VSL and RM (VSL-RM), the proposed VSL-LC-RM strategy can enhance the regulation of traffic flow, improve the flow of merging bottlenecks, and make full use of the road space-time resources.

Hybrid Microfluidic-Flow Injection System for Determining Copper(II) in Aqueous Solution by Homemade Microfluidic-Chip

Background: A new technique was designed for determining copper in an aqueous solution. Copper was determined by a hybrid system microfluidic coupled with flow injection. The homemade microfluidic chip (MFC) is used for injecting copper and 2,9-Dimethyl-1,10-phenanthroline (2,9DMP) reagent as a merging zone technique, whereas uric acid is used as a reducing agent and carrier. Methods: A microfluidic chip was made by a Computer Numerical Control (CNC) laser machine using the AutoCAD application for the study of copper by the hybrid system. The chip contains two microchannels with a volume of 60 μL for copper(II) and 2,9DMP reagent. As a carrier solution and reducing agent, 40 mg/L of uric acid was pumped at a flow rate of 5.2 mL/min. Conditions of the coupled technique and analyses were measured at 454 nm. Results: This system's approach has a linear range, a detection limit (S/N=3), and a quantitation limit (S/N=10) at 0.1-25 mg/L (r2 0.9979), 0.03 and 0.09 mg/L, respectively. Also, repeatability of analyses (n=7) with an average RSD of 0.97 % for concentrations of 5, 10, and 20 mg/L. The dispersion coefficients were 1.977, 1.789, and 1.555 for the three concentrations 5,10, and 20 mg/L, respectively. The recovery of copper in the aqueous solution was estimated to be 103.5%. Dead volume and throughput were zero and 62 per hour, respectively. Sandell’s sensitivity and molar absorptivity were 2.467×10-3 µg/cm2 and 1.947×105 L/mol cm, respectively. Conclusion: The analysis in the novel hybrid microfluidic-flow injection system is efficient, simple, and fast, and it can be used to determine the concentration of copper in an aqueous solution. The homemade microfluidic chip is a low-cost component that uses only an small volume of copper and reagent during analysis.

Evaluating the Effectiveness of Countermeasures in Improving the Safety of Highway Merging Zones

The merging process from an acceleration lane to the through lane of a motorway is an important aspect at interchanges, both in terms of safety and operating conditions. Several studies have demonstrated that the merging zones of interchanges are the main sources of interference between through and entering vehicles. In this context, incorrectly assessed gaps and headways can lead to severe crashes and traffic delays at interchanges. This study investigates the effectiveness of different countermeasures to improve the safety of merging zones and the ability of through drivers to adopt safe headways to vehicles entering from the motorway on-ramp. Four different countermeasures were tested in a driving simulator study: i) a gap metering signalization, consisting of a Variable Message Sign (VMS) and new pavement markings; ii) a static symbol projected on the vehicle's windshield by means of a Head-Up Display (HUD) that informed the driver to maintain safe headways to the entering vehicle; iii) a dynamic symbol based on Augmented Reality (AR) technology, built into connected vehicle technology, that provided additional visual information to the driver about his current headway to the entering vehicle; iv) the AR system was also tested with an additional audio warning. The driving behavior of forty-four drivers under the four different configurations based on the tested countermeasures was then compared to the driving behavior recorded under a configuration without any countermeasures (baseline condition). The results revealed significant positive effects of all the countermeasures, especially of the AR systems that helped through drivers to adjust their headway to the entering vehicle and thus the most effective solution for improving the safety of the merging zone. This study confirmed the great potential of AR and connected vehicle technologies to improve general safety conditions on the road network, especially in risky situations and difficult maneuvers.

A Cooperative Trajectory Optimization Algorithm for Connected Vehicles in Merging Zones

Traffic flow optimization and trajectory guidance in merging zones have significant implications for improving capacity and reducing time consumption. The development of V2X communication provides new insights to solve this problem by tackling the information and releasing trajectories schemes. Therefore, this paper aims to discuss the trajectory management in the merging zone for ACC vehicles. A vehicle dispatching and car-following model is proposed to generate steady traffic flow first. An algorithm framework for consecutive traffic flow is presented with the idea of FIFO rules. Then, a two-step method for an individual vehicle is discussed in detail to compute a trajectory. The first step is to select and determine the priority of the optional gaps. The next step is to verify the options’ feasibility, decide on the target gap, and output the trajectories to merge successfully. Numerical experiments validate that the proposed method guarantees safe driving and provides relatively smooth trajectories to the vehicles. Furthermore, increased capacity and higher velocity are observed in a comparative experiment. The cooperative optimization algorithm could be applied efficiently in practice and benefit from its rapid response and low computation complexity.

How stair configurations in buildings affect pedestrian dynamics on stairs? A simulation study via an extended three-dimensional force-based model

Pedestrian movement on stairs is a complex three-dimensional dynamic process. However, previous models are inherently limited in that they ignored the significant effect of stair configurations. This paper presents an extended three-dimensional force-based model to describe pedestrian movement and evacuation dynamics on stairs. By calibrating with previous real-human experiments, this unique model is able to accurately reproduce the velocity/density relation under a wide range of inclination stairways. Then, we explored the basic questions about pedestrian dynamics on complex stair configurations. The results demonstrated that: (1) this unique model shows good universality for simulating pedestrian dynamics on stairs; (2) under the combined effect of narrow exit and stairway, the stair part is the primary factor that affects the specific flow; (3) the optimal stair dimension is a set of tread depth and riser height; (4) pedestrian density and the geometric layout of the stairwell significantly influence pedestrian merging ratio at the merging zone.

Metropolitan spatial structure analysis based on the identification of commuting zones with Nanjing City as an example

Commuting zone research is critical to the understanding of the operational rules of the metropolitan spatial structure and improving spatial performance. This study aims to identify the main commuting centers and zones by using cellular data with Nanjing City as the example. This study analyzes the operational features of the internal spatial structures of the city from two dimensions by merging multi-source data, namely, commuting centers and zones, thus achieving an understanding of the existing problems with the urban spatial structures and their internal causes. Results showed that the commuting zones of Nanjing are distributed in a pattern of “multiple commuting centers”, with Xinjiekou–Hunan Road and Hongwu Road–Chaotiangong–Shuangtang as the core, Mochou Lake as the main commuting area, and Dongshan and Jiangpu as the secondary commuting zones. Significant differences and similarities are discovered in our comparisons along the two dimensions of commuting zones and centers in terms of spatial structural factors, such as land use, transportation, and commuting in the city. The similarity is shown as a common declining trend in the values of all our indicators with the increase in the distance of commuting zones from the city center. However, the differences are significant in terms of the clustering features of the various parameters concerning commuting centers and zones. Specifically, four clustering patterns are discovered, namely, “monocentric clustering”, “circular monocentric clustering”, “polycentric clustering”, and “sparsely dotted distribution”. This study sheds light on the existing problems with the city's spatial structure and proposes some overall suggestions toward urban spatial structure improvement on the basis of these findings.

A Platoon-Based Hierarchical Merging Control for On-Ramp Vehicles Under Connected Environment

Connected autonomous vehicle technology is conductive to promoting the transition from traditional merging control (e.g., ramp metering) to automated merging control. This paper proposes a platoon-based hierarchical merging control algorithm for on-ramp vehicles to achieve automated merging control under connected traffic environment. The proposed algorithm optimizes merging maneuvers of on-ramp vehicles to smooth their merging trajectories without frequent decelerations or stops at the end of the ramp, and to minimize disruption to the mainline traffic in the merging zone. A tactical layer controller is designed to select pre-target merging gaps for on-ramp vehicles, in which the future motion (i.e., acceleration and deceleration) of mainline vehicles is considered through the grey prediction model. An operational layer controller is constructed based on model predictive control to adjust the speed of on-ramp vehicles in advance, and controls on-ramp vehicles to merge into the pre-target merging gaps under state constraints (i.e., safe headway, maximum speed and so on). Through numerical simulation, the effectiveness of the proposed algorithm is validated under different merging scenarios. It is shown that on-ramp vehicles smoothly merge into the mainline within the pre-target merging gap at the same speed as adjacent mainline vehicles. Compared with the baseline merging control algorithm, the proposed algorithm significantly reduces both fuel consumption and travel time of on-ramp vehicles, and improves passenger comfort.

Model and Approach of Solid Line Setting Based on Merge Safety and Merge Probability

To improve the safety of merging vehicles and reduce the possibility of accidents, the easiest and most effective way is to adjust the existing traffic facilities. This study examines the requirements and approach of setting a new merge marking. First, a marking calculation model for the acceleration lane was constructed by taking the vehicle-merging probability as the limiting condition and combining the acceptable gap theory. Second, considering the limitation of ramp speed and acceleration lane length, the length of the solid merge line under different volumes and speeds was determined, and the value under different cases was given. Third, the safe change clearance and the length of the solid merge line under different scenarios were analyzed with numerical simulations using MATLAB. Finally, VISSIM was used for the simulation verification of the actual merging zone. The calculation results are that at the same probability, the increase of the volume outside the mainline, the longer the length of the solid merge line. When the volume of the outer lane is 100 pcu/h and 500 pcu/h, the actual gap value is greater than the minimum gap value, and vehicles can safely merge into the mainline. When the volume is 1000 pcu/h, the gap value is less than the minimum safe gap and cannot meet the safe merging, and control measures need to be taken for the lane. The results of the TTC conflict analysis show that it is recommended to set the solid merge line at service level two and above and that the service level three can be set in some cases. The setting of the solid merge line can further increase the vehicle acceleration space, improve the merge speed, and enhance the safety of the merge.