Effect of automated versus manual emergency braking on rear seat adult and pediatric occupant precrash motion

<b>Objective:</b> Emergency braking can potentially generate precrash occupant motion that may influence the effectiveness of restraints in the subsequent crash, particularly for rear-seated occupants who may be less aware of the impending crash. With the advent of automated emergency braking (AEB), the mechanism by which braking is achieved is changing, potentially altering precrash occupant motion. Further, due to anatomical and biomechanical differences across ages, kinematic differences between AEB and manual emergency braking (MEB) may vary between child and adult occupants. Therefore, the objective of this study was to quantify differences in rear-seated adult and pediatric kinematics and muscle activity during AEB and MEB scenarios. <b>Methods:</b> Vehicle maneuvers were performed in a recent model year sedan traveling at 50 km/h. MEB (acceleration ∼1 <i>g</i>) was achieved by the driver pressing the brake pedal with maximum effort. AEB (acceleration ∼0.8 <i>g</i>) was triggered by the vehicle system. Inertial and Global Positioning System data were collected. Seventeen male participants aged 10–33 were restrained in the rear right passenger seat and experienced each maneuver twice. The subjects’ kinematics were recorded with an 8-camera 3D motion capture system. Electromyography (EMG) recorded muscle activity. Head and trunk displacements, raw and normalized by seated height, and peak head and trunk velocity were compared across age and between maneuvers. Mean EMG was calculated to interpret kinematic findings. <b>Results:</b> Head and trunk displacement and peak velocity were greater in MEB than in AEB in both raw and normalized data (<i>P</i> ≤ .01). No effect of age was observed (<i>P</i> ≥ .21). Peak head and trunk velocities were greater in repetition 1 than in repetition 2 (<i>P</i> ≤ .006) in MEB but not in AEB. Sternocleidomastoid (SCM) mean EMG was greater in MEB compared to AEB, and muscle activity increased in repetition 2 in MEB. <b>Conclusions:</b> Across all ages, head and trunk excursions were greater in MEB than AEB, despite increased muscle activity in MEB. This observation may suggest an ineffective attempt to brace the head or a startle reflex. The increased excursion in MEB compared to AEB may be attributed to differences in the acceleration pulses between the 2 scenarios. These results suggest that AEB systems can use specific deceleration profiles that have potential to reduce occupant motion across diverse age groups compared to sudden maximum emergency braking applied manually.

**研究目的：** 紧急制动可能会产生碰撞前乘员运动，进而影响后续碰撞中约束系统的防护效果，对于对即将发生的碰撞感知较弱的后排乘员而言尤为如此。随着自动紧急制动（Automated Emergency Braking, AEB）的出现，制动实现机制发生了变化，可能会改变碰撞前乘员的运动状态。此外，由于不同年龄段人群在解剖学和生物力学上存在差异，自动紧急制动与手动紧急制动（Manual Emergency Braking, MEB）之间的运动学差异可能在儿童与成人乘员之间有所不同。因此，本研究旨在量化自动紧急制动与手动紧急制动场景下，后排成年与儿童乘员的运动学参数及肌肉活动差异。
**研究方法：** 本研究采用一款近年款轿车开展车辆操纵试验，初始行驶速度设定为50 km/h。手动紧急制动（加速度约1g）由驾驶员全力踩下制动踏板实现；自动紧急制动（加速度约0.8g）由车辆系统自动触发。采集惯性及全球定位系统（Global Positioning System, GPS）数据。招募17名年龄在10至33岁之间的男性受试者，将其固定于后排右侧乘客座椅，每名受试者均完成两次相同操纵试验。采用8镜头三维运动捕捉系统记录受试者的运动学数据，采用肌电图（Electromyography, EMG）技术采集肌肉活动信号。对头部与躯干的原始位移、按坐姿身高归一化后的位移，以及头部与躯干的峰值速度，按年龄组别及制动类型开展对比分析；计算平均肌电信号以辅助解释运动学试验结果。
**研究结果：** 原始数据与归一化数据均显示，手动紧急制动场景下的头部与躯干位移及峰值速度均高于自动紧急制动场景（P ≤ 0.01）。未观察到年龄因素带来的显著影响（P ≥ 0.21）。手动紧急制动场景下，首次试验的头部与躯干峰值速度高于第二次试验（P ≤ 0.006），而自动紧急制动场景未出现该差异。胸锁乳突肌（Sternocleidomastoid, SCM）的平均肌电信号在手动紧急制动场景下高于自动紧急制动场景，且手动紧急制动场景下第二次试验的肌肉活动较首次试验有所提升。
**研究结论：** 无论受试者年龄如何，手动紧急制动场景下的头部与躯干偏移量均高于自动紧急制动场景，尽管前者的肌肉活动更强。该现象或提示乘员试图抬头支撑的动作未生效，或是存在惊吓反射。手动紧急制动场景下偏移量更大的现象，或可归因于两种制动场景下的加速度脉冲存在差异。本研究结果表明，相较于驾驶员手动施加的突发全力紧急制动，自动紧急制动系统可通过定制化减速曲线，在不同年龄段乘员中均实现乘员运动幅度的降低。