Naturalistic driving study of rear seat child occupants: Quantification of head position using a Kinect™ sensor

Objective: Restraint performance is evaluated using anthropomorphic test devices (ATDs) positioned in prescribed, optimal seating positions. Anecdotally, humans—children in particular—assume a variety of positions that may affect restraint performance. Naturalistic driving studies (NDSs), where cameras and other data acquisition systems are placed in a vehicle used by participants during their regular transportation, offer means to collect these data. To date, these studies have used conventional video and analysis methods and, thus, analyses have largely been qualitative. This article describes a recently completed NDS of child occupants in which their position was monitored using a Kinect sensor to quantify their head position throughout normal, everyday driving trips. Methods: A study vehicle was instrumented with a data acquisition system to measure vehicle dynamics, a set of video cameras, and a Kinect sensor providing 3D motion capture at 1 Hz of the rear seat occupants. Participant families used the vehicle for all driving trips over 2 weeks. The child occupants' head position was manually identified via custom software from each Kinect color image. The 3D head position was then extracted and its distribution summarized by seat position (left, rear, center) and restraint type (forward-facing child restraint system [FFCRS], booster seat, seat belt). Results: Data from 18 families (37 child occupants) resulted in 582 trips (with children) for analysis. The average age of the child occupants was 45.6 months and 51% were male. Twenty-five child occupants were restrained in FFCRS, 9 in booster seats, and 3 in seat belts. As restraint type moved from more to less restraint (FFCRS to booster seat to seat belt), the range of fore–aft head position increased: 218, 244, and 340 mm on average, respectively. This observation was also true for left–right movement for every seat position. In general, those in the center seat position demonstrated a smaller range of head positions. Conclusions: For the first time in a naturalistic setting, the range of head positions for child occupants was quantified. More variability was observed for those restrained in booster seats and seat belts than for those in FFCRS. The role of activities, in particular interactions with electronic devices, on head position was notable; this will be the subject of further analysis in other components of the broader study. These data can lead to solutions for optimal protection for occupants who assume positions that differ from prescribed, optimal testing positions.研究目标：现有约束系统性能评估均采用置于规定最佳坐姿位置的人体模型测试装置（anthropomorphic test devices, ATDs）开展。但据观察，人类——尤其是儿童——会呈现多种不同坐姿，这可能对约束系统性能产生影响。自然驾驶研究（naturalistic driving studies, NDSs）通过在参与者日常代步车辆中部署摄像头及其他数据采集系统，可采集此类坐姿数据。截至目前，此类研究多采用传统视频与分析方法，因此分析结果大多为定性描述。本文介绍一项新近完成的儿童乘员自然驾驶研究，该研究借助Kinect传感器监测乘员姿态，以量化日常驾驶行程中儿童的头部位置变化。 研究方法：本研究在试验车辆上加装了用于采集车辆动力学数据的系统、多台摄像头，以及一套可对后排乘员以1赫兹频率开展三维运动捕捉的Kinect传感器。参与研究的家庭需在为期2周的时间内，将该车辆用于所有日常驾驶行程。研究人员通过定制软件从每帧Kinect彩色图像中手动标记儿童乘员的头部位置，进而提取其三维头部坐标，并按座椅位置（左侧后排、右侧后排、中部后排）与约束类型（面向前的儿童约束系统[forward-facing child restraint system, FFCRS]、增高座椅、安全带）对头部位置分布进行汇总统计。 研究结果：本次研究共收集到18个家庭（涉及37名儿童乘员）的582次带儿童乘车的行程数据用于分析。儿童乘员的平均年龄为45.6个月，其中51%为男性。25名儿童使用面向前的儿童约束系统，9名使用增高座椅，3名直接使用安全带。随着约束系统的约束强度从高到低依次为面向前的儿童约束系统、增高座椅、安全带时，儿童头部的前后位置范围逐渐增大，平均范围分别为218 mm、244 mm与340 mm。这一趋势在各座椅位置的头部左右移动范围中同样成立。总体而言，中部后排座椅上的儿童头部位置范围更小。 研究结论：本研究首次在自然驾驶场景中量化了儿童乘员的头部位置分布范围。相较于使用面向前的儿童约束系统的儿童，使用增高座椅与安全带的儿童头部位置变异程度更高。研究还发现，儿童的活动——尤其是与电子设备的互动——对其头部位置存在显著影响，这将作为本大型研究后续其他子课题的分析主题。本次采集的数据可为针对未处于规定最佳测试坐姿的乘员提供最优防护解决方案提供参考依据。