Utilizing Simulated Vehicle Trajectory Data from Connected Vehicles to Characterize Performance Measures on an Arterial After an Impactful Incident


Book Description

Traffic incidents are unforeseen events known to affect traffic flow because they reduce the capacity of an arterial corridor segment and normally generate a temporary bottleneck. Identification of retiming requirements to enhance traffic signal operations when an incident occurs depends on operations-oriented traffic signal performance measurements when effective and real-time traffic signal performance metrics are employed at traffic control centers, delays, fuel use, and air pollution may all be decreased. The majority of currently available traffic signal performance evaluations are based on high-resolution traffic signal controller event data, which gives data on an intersection-by-intersection basis but requires a substantial upfront expenditure. The necessary detecting and communication equipment also involves costly and periodic maintenance. Additionally, the full manifestation of connected vehicles (CVs) is fast approaching with efforts in place to accelerate the adaptation of CVs and their infrastructures. CV technologies have enormous potential to improve traffic mobility and safety. CVs can provide abundant traffic data that is not otherwise captured by roadway detectors or other methods of traffic data collection. Since the observation is independent of any space restrictions and not impacted by queue discharge and buildup, CV data offers more comprehensive and reliable data that can be used to estimate various traffic signal performance measures. This thesis proposes a conceptual CV simulation framework intended to ascertain the effectiveness of CV trajectory-based measures in characterizing an arterial corridor incident, such as a vehicle crash. Using a four-intersection corridor with vii different signal timing plans, a microscopic simulation model was created in Simulation of Urban Mobility (SUMO), Vehicles in Network Simulation (Veins) and Objective Modular Network Testbed in C++ (OMNeT++) platforms. Furthermore, an algorithm for CVs that defines, detects and disseminates a vehicle crash incident to other vehicles and a roadside unit (RSU) was developed. In the thesis, it is demonstrated how visual performance metrics with CV data may be used to identify an incident. This thesis proposes that traffic signals performance metrics, such as progression quality, split failure, platoon ratios, and safety surrogate measures (SSMs), may be generated using CV trajectory data. The results show that the recommended approaches with access to CV trajectory data would help both performance assessment and operation of traffic control systems. Unlike the current state of the practice (fixed detection technology), the developed conceptual framework can detect incidents that intersection-vicinity-limited does not capture detectors while requiring immediate attention.




Real-time Traffic Safety Evaluation in the Context of Connected Vehicles and Mobile Sensing


Book Description

Recently, with the development of connected vehicles and mobile sensing technologies, vehicle-based data become much easier to obtain. However, only few studies have investigated the application of this kind of novel data to real-time traffic safety evaluation. This dissertation aims to conduct a series of real-time traffic safety studies by integrating all kinds of available vehicle-based data sources. First, this dissertation developed a deep learning model for identifying vehicle maneuvers using data from smartphone sensors (i.e., accelerometer and gyroscope). The proposed model was robust and suitable for real-time application as it required less processing of smartphone sensor data compared with the existing studies. Besides, a semi-supervised learning algorithm was proposed to make use of the massive unlabeled sensor data. The proposed algorithm could alleviate the cost of data preparation and improve model transferability. Second, trajectory data from 300 buses were used to develop a real-time crash likelihood prediction model for urban arterials. Results from extensive experiments illustrated the feasibility of using novel vehicle trajectory data to predict real-time crash likelihood. Moreover, to improve the model’s performance, data fusion techniques were proposed to integrated trajectory data from various vehicle types. The proposed data fusion techniques significantly improved the accuracy of crash likelihood prediction in terms of sensitivity and false alarm rate. Third, to improve pedestrian and bicycle safety, different vehicle-based surrogate safety measures, such as hard acceleration, hard deceleration, and long stop, were proposed for evaluating pedestrian and bicycle safety using vehicle trajectory data. In summary, the results from this dissertation can be further applied to real-time safety applications (e.g., real-time crash likelihood prediction and visualization system) in the context of proactive traffic management.




Path Planning and Tracking for Vehicle Collision Avoidance in Lateral and Longitudinal Motion Directions


Book Description

In recent years, the control of Connected and Automated Vehicles (CAVs) has attracted strong attention for various automotive applications. One of the important features demanded of CAVs is collision avoidance, whether it is a stationary or a moving obstacle. Due to complex traffic conditions and various vehicle dynamics, the collision avoidance system should ensure that the vehicle can avoid collision with other vehicles or obstacles in longitudinal and lateral directions simultaneously. The longitudinal collision avoidance controller can avoid or mitigate vehicle collision accidents effectively via Forward Collision Warning (FCW), Brake Assist System (BAS), and Autonomous Emergency Braking (AEB), which has been commercially applied in many new vehicles launched by automobile enterprises. But in lateral motion direction, it is necessary to determine a flexible collision avoidance path in real time in case of detecting any obstacle. Then, a path-tracking algorithm is designed to assure that the vehicle will follow the predetermined path precisely, while guaranteeing certain comfort and vehicle stability over a wide range of velocities. In recent years, the rapid development of sensor, control, and communication technology has brought both possibilities and challenges to the improvement of vehicle collision avoidance capability, so collision avoidance system still needs to be further studied based on the emerging technologies. In this book, we provide a comprehensive overview of the current collision avoidance strategies for traditional vehicles and CAVs. First, the book introduces some emergency path planning methods that can be applied in global route design and local path generation situations which are the most common scenarios in driving. A comparison is made in the path-planning problem in both timing and performance between the conventional algorithms and emergency methods. In addition, this book introduces and designs an up-to-date path-planning method based on artificial potential field methods for collision avoidance, and verifies the effectiveness of this method in complex road environment. Next, in order to accurately track the predetermined path for collision avoidance, traditional control methods, humanlike control strategies, and intelligent approaches are discussed to solve the path-tracking problem and ensure the vehicle successfully avoids the collisions. In addition, this book designs and applies robust control to solve the path-tracking problem and verify its tracking effect in different scenarios. Finally, this book introduces the basic principles and test methods of AEB system for collision avoidance of a single vehicle. Meanwhile, by taking advantage of data sharing between vehicles based on V2X (vehicle-to-vehicle or vehicle-to-infrastructure) communication, pile-up accidents in longitudinal direction are effectively avoided through cooperative motion control of multiple vehicles.




Predicting Vehicle Trajectory


Book Description

This book concentrates on improving the prediction of a vehicle’s future trajectory, particularly on non-straight paths. Having an accurate prediction of where a vehicle is heading is crucial for the system to reliably determine possible path intersections of more than one vehicle at the same time. The US DOT will be mandating that all vehicle manufacturers begin implementing V2V and V2I systems, so very soon collision avoidance systems will no longer rely on line of sight sensors, but instead will be able to take into account another vehicle’s spatial movements to determine if the future trajectories of the vehicles will intersect at the same time. Furthermore, the book introduces the reader to some improvements when predicting the future trajectory of a vehicle and presents a novel temporary solution on how to speed up the implementation of such V2V collision avoidance systems. Additionally, it evaluates whether smartphones can be used for trajectory predictions, in an attempt to populate a V2V collision avoidance system faster than a vehicle manufacturer can.




Simulation and Characterization of Complex Mixed Traffic Behavior


Book Description

Recent years, automated vehicle (AV) technology, which is expected to solve critical issues, such as traffic efficiency, capacity, and safety, has been put a lot of efforts and making considerable progress. There is another technology called connected vehicle (CV) which connect vehicles through dedicated short-range communication devices. Combining the AV technology and CV technology leads to the more comprehensive connected and automated vehicle (CAV) technology. Although some of the car industry companies, such as Tesla, Waymo, has made great progress in developing CAV, it is still hard to realize commercial use due to the safety issue and cost issue. It seems CAV is not the solution for autonomous in near future. Thus, another innovating technology has been brought into the public's view which is connected automated vehicle highway systems (CAVH). CAVH provides a safer, more reliable, and more cost-effective solution by redistributing vehicle driving tasks to the hierarchical traffic control network and roadside unit (RSU) network. But the cost of a full CAVH system is still too high for commercial use. As a result, a new system has been brought into discuss which is the Partially Instrumented CAVH (PI CAVH). The PI CAVH network facilitates sensing, prediction, decision making for low automated level vehicles (Level 2 CAV) in the areas which involving heavy weaving activities, on/off ramp, work zones, etc. The PI CAVH is considered as a feasible solution for the commercial use of autonomous driving. However, even with the implementation of PI CAVH, human driving vehicles (HDV) will still dominate the road in the near future. Therefore, to find a proper platoon level car following strategy for CAVs under PI CAVH will be a challenging problem. Due to the lack of empirical data, we have to simulate the scenarios under PI CAVH. The current simulation platform cannot reproduce realistic HDV trajectories (especially of different driving styles). The deep learning techniques have demonstrated promising capability in traffic trajectory generation. Neural Networks are widely applied in the research of the car-following model. Among those networks, long short-term memory neural networks (LSTM) is the most used and has great potential for car following behavior modeling. This research focuses on establishing a car following model that can represent various driving styles and generate large numbers of realistic HDV trajectories with the help of deep learning techniques. The proposed model will help us to determine the performance of different car following strategy for CAVs under PI CAVH. This dissertation first reviews on car-following models and CAV control algorithms. Then a unidirectional interconnected LSTM car following model with heterogeneous driving style is established to generate numerous trajectories to simulate scenarios under PI CAVH. Several experiments are carried out to analyze the performance of different car following strategies.




Real-time Estimation of Arterial Performance Measures Using a Data-driven Microscopic Traffic Simulation Technique


Book Description

Traffic congestion is a one hundred billion dollar problem in the US. The cost of congestion has been trending upward over the last few decades, but has experienced slight decreases in recent years partly due to the impact of congestion reduction strategies. The impact of these strategies is however largely experienced on freeways and not arterials. This discrepancy in impact is partially linked to the lack of real-time, arterial traffic information. Toward this end, this research effort seeks to address the lack of arterial traffic information. :To address this dearth of information, this effort developed a methodology to provide accurate estimates of arterial performance measures to transportation facility managers and travelers in real-time. This methodology employs transmitted point sensor data to drive an online, microscopic traffic simulation model. The feasibility of this methodology was examined through a series of experiments that were built upon the successes of the previous, while addressing the necessary limitations. The results from each experiment were encouraging. They successfully demonstrated the method's likely feasibility, and the accuracy with which field estimates of performance measures may be obtained. In addition, the method's results support the viability of a "real-world" implementation of the method. An advanced calibration process was also developed as a means of improving the method's accuracy. This process will in turn serve to inform future calibration efforts as the need for more robust and accurate traffic simulation models are needed. :The success of this method provides a template for real-time traffic simulation modeling which is capable of adequately addressing the lack of available arterial traffic information. In providing such information, it is hoped that transportation facility managers and travelers will make more informed decisions regarding more efficient management and usage of the nation's transportation network.




Real-time Prediction of Vehicle Locations in a Connected Vehicle Environment


Book Description

The wireless communication between vehicles and the transportation infrastructure, referred to as the connected vehicle environment, has the potential to improve driver safety and mobility drastically for drivers. However, the rollout of connected vehicle technologies in passenger vehicles is expected to last 30 years or more, during which time traffic will be a mix of vehicles equipped with the technology and vehicles that are not equipped with the technology. Most mobility applications tested in simulation, such as traffic signal control and performance measurement, show greater benefits as a larger percentage of vehicles are equipped with connected vehicle technologies.The purpose of this study was to develop and investigate techniques to estimate the positions of unequipped vehicles based on the behaviors of equipped vehicles. Two algorithms were developed for this purpose one for use with arterials and one for use with freeways. Both algorithms were able to estimate the positions of a portion of unequipped vehicles in the same lane within a longitudinal distance. Further, two connected vehicle mobility applications were able to use these estimates to produce small performance improvements in simulation at low penetration rates of connected vehicle technologies when compared to using connected vehicle data alone, with up to an 8 percent reduction in delay for a ramp metering application and a 4.4 percent reduction in delay for a traffic signal control application.The study recommends that the Virginia Center for Transportation Innovation and Research (VCTIR) continue to assess the data quality of connected vehicle field deployments to determine if the developed algorithms can be deployed. If data quality is deemed acceptable and if a connected vehicle application is tested in a field deployment, VCTIR should evaluate the use of the location estimation algorithms to improve the applications performance at low penetration rates.This is expected to result in reduced delays and improved flow for connected vehicle mobility applications during times when few vehicles are able to communicate wirelessly.




Database-Mediated Preview of Roadway Friction and Model Predictive Path Tracking Control for Connected Vehicles


Book Description

The primary focus of this dissertation is to preview roadway friction via database-mediated connected and autonomous vehicles (CAVs) and develop a method to incorporate this previewed information into vehicle path tracking control for improved performance. Tracking a target-planned path -- a lane centerline of a highway, a lane-changing maneuver, or a trajectory for obstacle avoidance -- is one of the most challenging tasks of vehicle driving. Due to the lack of information, current vehicle control systems generally assume that the road friction conditions ahead of a vehicle are unchanged relative to the conditions at the vehicle's current position. This can result in dangerous situations if the friction is suddenly decreasing from the current situation or overly conservative driving styles if the friction of the current situation is worse than the roadway ahead. Future driving systems must go further so that they are capable of maneuvering even on unfavorable road conditions, for example, tracking sharp turning paths on the road with a sudden decrease in friction. This may be enabled by using new technologies, for example, the connectivity of CAVs, that can provide information about the environment, particularly the friction between vehicle tires and the road surface. Therefore, the challenge is to find a way to aggregate the data from CAVs for roadway friction preview and incorporate previewed friction information to improve vehicle path tracking performance. Specifically, the challenge in the creation of road friction preview maps is the very large quantity of data involved, and the measurements populating the map are generated by vehicle trajectories that do not uniformly cover the grid in situations of varying road surface friction. Furthermore, even if road conditions are known, incorporating the information into the path tracking control system is a challenge on its own. To incorporate previewed roadway friction information into the vehicle path tracking control, a systematic approach to the analysis and development of controllers is needed. The key contributions of this dissertation are: (1) a micro-simulation framework for studying the CAVs control and road friction preview based on a database-mediated data sharing system; (2) a road friction map generation strategy that aggregates the measured road-tire friction coefficients along the individual trajectories of CAVs into a road surface grid; (3) a vehicle longitudinal speed planning algorithm according to the previewed roadway friction and path geometry constraints; (4) a model predictive path tracking control structure that utilizes preview friction to achieve tracking accuracy and stability near the vehicle dynamic limits.







Modelling Realistic Intersection Vehicle Trajectories Utilizing Real-world Traffic Datasets


Book Description

The automation of motor vehicles has been one of the major front lines of transportation advancement in the 21st century. With the expansion of public-road testing of Automated Driving Systems (ADS) these days and the deployment of ADS vehicles in the future, the coexistence of vehicles driven by human drivers as well as ADS will be normal. Consequently, it is important to ensure that the ADS can robustly react to the varying behaviors of human drivers and the challenging scenarios on the public roads. To verify the ability of ADS in such circumstances, some scenarios that reflect real-world traffic conditions should be established and tested on the ADS. This dissertation proposes a data-based comprehensive effort to enrich intersection confliction scenarios for ADS testing. First, the intersection-related safety-critical events (SCEs) from a naturalistic driving study (NDS) dataset is categorized and summarized. The frequencies of vehicle crash modes as well as contributing factors to the SCEs are discussed. The results will be compared with crash data from General Estimates System (GES) to reveal the common patterns of vehicle conflictions in intersections, which could serve as a basis for the organization of conflict scenarios. Then, the longitudinal speed profiles of non-conflicting real-world vehicle trajectories are adjusted to create potential two-vehicle conflictions in intersections. Last, a longitudinal and lateral turning trajectory model is presented. This model takes intersection geometry and approaching speed as input and predicts the possible path and speed profile that a human driver may take. Based on a large number of recorded vehicle trajectories, this model has the potential of replacing the constant speed or acceleration models widely used in current testing scenarios and greatly increase the fidelity of such scenarios. The contribution of this dissertation include 1) the distribution of real-world intersection-related crash and near-crash events based on the vehicle maneuvers based on the SHRP 2 NDS dataset, 2) a data extraction and map-based filtering approach on the nuScenes ADS dataset which delivers a extracted trajectory library of potential conflicting trajectory sets, 3) a vehicle turning trajectory model in the intersection that takes into account the longitudinal and lateral behaviors of human drivers observed from existing data, 4) an empirical model that estimates trajectory based on the initial driver behaviors and intersection layout, the model is built based on the extracted data from the nuScenes dataset.