Properly designed roundabouts may lead to safety improvements based on both reducing approaching speeds and controlling traffic. Measurements of deflection of vehicle trajectories are commonly used to estimate roundab...Properly designed roundabouts may lead to safety improvements based on both reducing approaching speeds and controlling traffic. Measurements of deflection of vehicle trajectories are commonly used to estimate roundabout speed control. One of these measurements is the deviation angle, which is mentioned in both the Italian and Swiss road standards and, in specific conditions, can be more effective than other methods.This article presents a general mathematical formulation for linking several geometric parameters with the deviation angle in different rural and urban one-lane roundabout configurations, which is currently missing in the literature. For urban roundabouts, refuge islands for pedestrians and cyclists were considered. Based on the proposed formulation, a sensitivity analysis of the influential geometric parameters was conducted. Results suggest that an insufficient deflection of trajectories(deviation angle less than 45°) is always present for roundabouts with inscribed circle diameter less than 25 m;for urban roundabouts with refuge islands for pedestrians and cyclists having inscribed circle diameter less than34 m and orthogonal legs;and for roundabouts with angles between opposite legs smaller than 140°. The main parameters which are responsible for a decrease in the deviation angle are: a decrease in the inscribed circle diameter;a decrease in the angle between opposite legs;and an increase in the width of the circulatory lane. Some optimized procedures for roundabout design, the generalized application of the deviation angle method and alternative speed control measures in cases of small deviation angles are discussed.展开更多
针对目前车道线识别系统因处理对象为离线图像或视频文件而难以实现车道线在线识别的问题,大多数车道线识别算法为了减少图像处理运行量,通常选取固定的兴趣区域(region of interest,ROI)进行处理,导致难以适应环境的动态变化且存在不...针对目前车道线识别系统因处理对象为离线图像或视频文件而难以实现车道线在线识别的问题,大多数车道线识别算法为了减少图像处理运行量,通常选取固定的兴趣区域(region of interest,ROI)进行处理,导致难以适应环境的动态变化且存在不同程度的识别误差。为此,提出了一种基于机器视觉的不设定兴趣区域的车道线在线识别系统。首先,利用VBAI(Vision Builder for Automation Inspection)平台对实时采集的彩色道路图像进行预处理,完成彩色图像的灰度化、滤波及二值化处理。然后,建立图像坐标系,并构建多条向外发散的灰度值采集线,灰度值采集线与车道线相交处的灰度值会发生较大改变,当某点的灰度值高于设定的灰度阈值时,记该点为边缘突变点。接着,借助直线拟合算法对所有车道边缘突变点进行拟合以完成车道线识别,并求解两侧内车道线的远方消失交点坐标和车辆行驶偏离车道中心线的相对航偏角,当相对航偏角超过不同等级的安全阈值时,系统人机交互界面的提示框呈现不同的颜色以进行提醒或预警。最后,借助LabVIEW进行API(application programming interface,应用程序接口)脚本调用,实现图像处理程序的连续运行与车道线在线识别。试验结果表明,所提出的车道线在线识别系统的识别准确率达98.41%以上,相对航偏角的测量误差小于0.056°,图像处理速度达42帧/s以上,兼具识别的准确性与实时性。综上可知,基于机器视觉的车道线在线识别系统可有效识别出不同环境路面的车道线,并实现行驶偏离预警,可将其应用于基于自动驾驶技术的车道保持辅助(lane keeping assist,LKA)系统。展开更多
文摘Properly designed roundabouts may lead to safety improvements based on both reducing approaching speeds and controlling traffic. Measurements of deflection of vehicle trajectories are commonly used to estimate roundabout speed control. One of these measurements is the deviation angle, which is mentioned in both the Italian and Swiss road standards and, in specific conditions, can be more effective than other methods.This article presents a general mathematical formulation for linking several geometric parameters with the deviation angle in different rural and urban one-lane roundabout configurations, which is currently missing in the literature. For urban roundabouts, refuge islands for pedestrians and cyclists were considered. Based on the proposed formulation, a sensitivity analysis of the influential geometric parameters was conducted. Results suggest that an insufficient deflection of trajectories(deviation angle less than 45°) is always present for roundabouts with inscribed circle diameter less than 25 m;for urban roundabouts with refuge islands for pedestrians and cyclists having inscribed circle diameter less than34 m and orthogonal legs;and for roundabouts with angles between opposite legs smaller than 140°. The main parameters which are responsible for a decrease in the deviation angle are: a decrease in the inscribed circle diameter;a decrease in the angle between opposite legs;and an increase in the width of the circulatory lane. Some optimized procedures for roundabout design, the generalized application of the deviation angle method and alternative speed control measures in cases of small deviation angles are discussed.
