Kinematic analysis of an unrestrained passenger in an autonomous vehicle during emergency braking

Silvia Santos-Cuadros; Álvaro Page Del Pozo; Carolina Álvarez-Caldas; José Luis San Román García

doi:10.3389/fbioe.2024.1270181

Kinematic analysis of an unrestrained passenger in an autonomous vehicle during emergency braking

Front Bioeng Biotechnol. 2024 Mar 12:12:1270181. doi: 10.3389/fbioe.2024.1270181. eCollection 2024.

Authors

Silvia Santos-Cuadros¹, Álvaro Page Del Pozo², Carolina Álvarez-Caldas¹, José Luis San Román García¹

Affiliations

¹ Mechanical Engineering Department, Instituto de Seguridad de los Vehículos Automóviles (ISVA, Institute for Vehicle Safety Assurance), Carlos III University of Madrid, Leganés, Spain.
² Instituto Universitario de Ingeniería Mecánica y Biomecánica, University Institute of Mechanical and Biomechanical Engineering, Universitat Politècnica de València, Leganés, Spain.

Abstract

Analyzing human body movement is a critical aspect of biomechanical studies in road safety. While most studies have traditionally focused on assessing the head-neck system due to the restraint provided by seat belts, it is essential to examine the entire pelvis-thorax-head kinematic chain when these body regions are free to move. The absence of restraint systems is prevalent in public transport and is also being considered for future integration into autonomous vehicles operating at low speeds. This article presents an experimental study examining the movement of the pelvis, thorax and head of 18 passengers seated without seat belts during emergency braking in an autonomous bus. The movement was recorded using a video analysis system capturing 100 frames per second. Reflective markers were placed on the knee, pelvis, lumbar region, thorax, neck and head, enabling precise measurement of the movement of each body segment and the joints of the lumbar and cervical spine. Various kinematic variables, including angles, displacements, angular velocities and accelerations, were measured. The results delineate distinct phases of body movement during braking and elucidate the coordination and sequentiality of pelvis, thorax and head rotation. Additionally, the study reveals correlations between pelvic rotation, lumbar flexion, and vertical trunk movement, shedding light on their potential impact on neck compression. Notably, it is observed that the elevation of the C7 vertebra is more closely linked to pelvic tilt than lumbar flexion. Furthermore, the study identifies that the maximum angular acceleration of the head and the maximum tangential force occur during the trunk's rebound against the seatback once the vehicle comes to a complete stop. However, these forces are found to be insufficient to cause neck injury. While this study serves as a preliminary investigation, its findings underscore the need to incorporate complete trunk kinematics, particularly of the pelvis, into braking and impact studies, rather than solely focusing on the head-neck system, as is common in most research endeavors.

Keywords: Biomechanics; autonomous braking; cervical injury; human movement analysis; joint kinematics; road safety; unrestrained passenger.

Grants and funding

The author(s) declare that financial support was received for the research, authorship, and/or publication of this article. This work has been supported by the Government of the Community of Madrid, Spain, under the Multiannual Agreement with UC3M in the line of Excellence of University Professors (EPUC3M20), and in the context of the V PRICIT (V Regional Plan of Research and Technological Innovation).