Low-speed Rear-end Collisions Research Articles

Passive stiffness changes in the lumbar spine following simulated automotive low speed rear-end collisions

BackgroundHistorically, there has been a lack of focus on the lumbar spine during rear impacts because of the perception that the automotive seat back should protect the lumbar spine from injury. As a result, there have been no studies involving human volunteers to address the risk of low back injury in low velocity rear impact collisions. MethodsA custom-built crash sled was used to simulate rear impact collisions. Randomized collisions were completed with and without lumbar support. Measures of passive stiffness were obtained prior to impact (Pre), immediately post impact (Post) and 24 h post impact (Post-24). Low back pain reporting was monitored for 24 h following impact exposure. FindingsNone of the participants developed clinically significant levels of low back pain after impact. Changes in the passive responses persisted after impact for the length of the low stiffness flexion and extension zone. The length of the low stiffness zone was longer in the Post and Post-24 trial for low stiffness flexion and longer in the Post-24 for low stiffness extension. InterpretationFindings from this investigation demonstrate that during a laboratory-simulation of an 8 km/h rear-impact collision, young healthy adults did not develop low back pain. Changes in the low stiffness zone of the passive flexion/extension curves were observed following impact and persisted for 24 h. Changes in passive stiffness may lead to changes in the loads and load distributions during movement within the passive structures such as the ligaments and intervertebral discs following impacts.

Prediction of neck injury using multiple linear regression and bumper damage: Case study for low-speed rear-end collisions

The most frequent type of traffic accident is a low-speed rear-end collision, which can damage parts of the vehicle, including the bumper, and cause neck injury to the occupants. Even in minor damage accidents, such as scratches on bumper covers, 26.3% of occupants received treatment for bodily injuries whose main symptom was neck injuries through auto insurance. This study was conducted to evaluate the potential for neck injuries in low-speed accidents. Fifty-nine low-speed rear-end impact tests were conducted, and the motion of the struck vehicle and the neck injury criterion (NIC) of the occupant according to the test conditions were predicted using multiple linear regression derived via supervised machine learning. It was confirmed that the NIC can be predicted using vehicle motion values that can be obtained through an event data recorder. The coefficients of determination of the regression equations were 0.67–0.83. Lastly, we investigated whether neck injuries can be predicted through bumper cover damage that can be checked immediately after a vehicle accident. In the case of the vehicle damage type 1/2/3 category applied to auto insurance by the Korean government, an occupant would have a very low possibility of neck injury or symptoms. No symptoms or injuries were reported in the volunteer tests conducted for this study.

Combined with finite element analysis of car seat safety performance improvement

Neck injuries caused by low-speed rear-end collisions are a worldwide problem. The reasonable design of car seat can effectively prevent or reduce the passenger neck injuries. In this paper, the finite element analysis (FEA) and whiplash test are combined to optimize the seat structure parameters to enhance the safety. The whiplash test results of the existing car seats according to C-NCAP (2015) were matched with FEA, and the optimization scheme was developed by computer simulation. For the improvement of seat safety, the optimizations are applied to determine backrest stiffness, backrest rotational stiffness, headrest rotational stiffness and headrest stiffness. The retest results of optimized seat show that its safety performance is greatly improved. Furthermore, it shows that the combination of finite element analysis and whiplash test can optimize seat structure to improve safety performance.

Low Speed Rear End Automobile Collisions and Whiplash Injury, the Biomechanical Approach

The extent of injury in low speed rear end collisions is controversial. In many cases, the impact speed of the striking vehicle is low, neither car shows much if any post collision damage, and at the scene, the occupant of the struck vehicle appears uninjured. Yet many of these incidents progress to lawsuits with sometimes very significant damage and injury claims. In testimony, Plaintiff argues that the collision was significant while Defendant describes the collision as minor. A Biomechanical approach which addresses the forces in the collision and the resulting forces and kinematics of the occupant can help to resolve some of these issues. In the following, the process of a biomechanical analysis is described, using a specific example. A discussion of how courts have viewed this type of testimony is then presented.

Design for Headrest Including Guides Slot to Reduce the Neck Force in Rear End Impact

Whiplash injuries are one of the most common injuries reported in automotive rear end collisions. Automobile seat back and head restraints play a role in reducing neck injuries during low speed rear end collisions. Currently, many studies are being conducted on ways to reduce neck injuries. These deal with the design parameters that cause neck injuries and do not address the design of the head restraint connection structure. In this paper, we analyze the various trajectories of the headrest and propose a new design for a connection structure that can move along the corresponding trajectory. We model the headrest connection mechanism as a virtual link using kinematic modeling and perform trajectory analysis. Using the trajectory of motion, we select an oblong shape for the guide slot by fitting it with the equation of an ellipse and propose a new headrest connection mechanism. To evaluate the design of the proposed mechanism, we model the shape of the mechanism and test it using dynamic simulation under collision conditions. In addition, we design a prototype for the proposed guide, conduct a sled test, and confirm that the neck force is reduced by the proposed connection structure. In the proposed structure, the values of maximum upper neck shear and tension decreased by more than 20 % compared to existing headrest.

Scenario establishment and simulation analysis for multiple-car rear-end collision accidents

Multiple-car rear-end collision accidents can be divided into three categories: sequential collision from the rear; sequential collision from the front; mixed-order collision. In this study, a total of five scenarios were constructed by using a statistical analysis based on the National Automotive Sampling System Crashworthiness Data System and by setting the gap between the cars based on the travel distance calculated from the reaction time of the driver and the speed and/or the deceleration of the car. Two simulation analysis methods were proposed for each scenario. The first method used a three-dimensionally scanned car model in the simulation program. This enabled more realistic simulations to be utilized for tuned cars. The second method involved simulating high-speed multiple rear-end collisions by using a program originally made for low-speed single rear-end collisions. This paper proposed appropriate tests and analysis methods for multiple collisions which will help to improve safety devices for cars.

Parametric analysis of an anti-whiplash system composed of a seat suspension arrangement

Neck injuries frequently seen in low-speed rear-end collisions are referred to as whiplash injuries. Most of the proposed anti-whiplash systems in the literature rely on reducing the backset. A relatively new and promising alternative concept is a slideable seat. This study aimed to parametrically analyze an anti-whiplash vehicle seat that can slide backward against a horizontal suspension arrangement composed of a spring and a damper in response to a rear-end collision, and to investigate the effects of the suspension parameters on the injury risk. A simplified model of a slideable vehicle seat is developed, and simulations are conducted in LS-DYNA® environment using this slideable seat model and the commercially available finite element model of the BioRID II dummy. The maximum value of the Neck Injury Criterion (NICmax) is used as the measure of the injury risk. As a result, a strong linear inverse correlation is observed between NICmax and the maximum seat sliding distance, while the stiffness and damping coefficients of the suspension are varied. This result is also verified by obtaining the same NICmax value for the same maximum seat sliding distance (although the stiffness and damping coefficients are different). It is also shown that, for a given backset value as large as 60 mm, a slideable seat with the suspension parameters selected to yield a reasonable maximum seat sliding distance such as 100 mm significantly improves NICmax compared to a standard seat. As the maximum seat sliding distance is increased, the injury risk becomes smaller.

Determining Impact Speed and Occupant Injury Propensity in Low-Speed Rear End Collisions

Determining Impact Speed and Occupant Injury Propensity in Low-Speed Rear End Collisions

Common Errors in Determining Impact Speed and Occupant Injury Propensity in Low Speed Rear-End Collisions

Common Errors in Determining Impact Speed and Occupant Injury Propensity in Low Speed Rear-End Collisions

Determining Impact Speed and Occupant Injury Propensity in Low-Speed Rear End Collisions

AbstractIntroduction. Vehicle impact severity has been used to infer whiplash injury to asymptomatic healthy occupants in low-speed rear-end collisions. However, this depends greatly upon closing speed, which is difficult to estimate a posteriori, as well as the weights of the vehicles involved. The proposed paper explains how closing speed can be accurately estimated based upon each vehicle's damage cost estimate, make, model, and occupant weights.Methods. Low-speed bumper damage cost data for staged collisions are available from various sources. By comparing damage from a particular accident to damage reported from available test data, we show how to use available analysis techniques to determine whether an actual two vehicle impact was more or less severe than published data for low-speed impacts.Results. Using available cost data from staged bumper tests on a variety of individual vehicles and a published analysis procedure, this work demonstrates how to approximate the closing speed of actual collisi...

Common Errors in Determining Impact Speed and Occupant Injury Propensity in Low Speed Rear-End Collisions

When evaluating what is commonly called “low speed” rear-end collisions it is important to understand the limitation and assumptions inherent in the data and approaches used. Many errors exist in determining impact speed and occupant injury potential in these types of impacts. These errors range from the inappropriate use of damage to misapplication of the laws of physics to the promulgation of non-existent thresholds. This paper addresses eleven of the common errors that can lead to erroneous conclusions.

Examining bumper cars as a surrogate for low-speed rear-end and frontal collisions

Examining bumper cars as a surrogate for low-speed rear-end and frontal collisions

Variability in Vehicle and Dummy Responses in Rear-End Collisions

Objective. The objective of this study was to quantify the occupant response variability due to differences in vehicle and seat design in low-speed rear-end collisions. Methods. Occupant response variability was quantified using a BioRID dummy exposed to rear-end collisions in 20 different vehicles. Vehicles were rolled rearward into a rigid barrier at 8 km/h and the dynamic responses of the vehicle and dummy were measured with the head restraint adjusted to the upmost position. In vehicles not damaged by this collision, additional tests were conducted with the head restraint down and at different impact speeds. Results. Despite a coefficient of variation (COV) of less than 2% for the impact speed of the initial 8 km/h tests, the vehicle response parameters (speed change, acceleration, restitution, bumper force) had COVs of 7 to 23% and the dummy response parameters (head and T1 kinematics, neck loads, NIC, N ij and N km ) had COVs of 14 to 52%. In five vehicles tested multiple times, a head restraint in the down position significantly increased the peak magnitude of many dummy kinematic and kinetic response parameters. Peak head kinematics and neck kinetics generally varied linearly with head restraint backset and height, although the neck reaction moment reversed and increased considerably if the dummy's head wrapped onto the top of the head restraint. Conclusions. The results of this study support the proposition that the vehicle, seat, and head restraint are a safety system and that the design of vehicle bumpers and seats/head restraint should be considered together to maximize the potential reduction in whiplash injuries.

Influence of braking force in low-speed vehicle collisions

The aim of this research is to find out the influence of braking force on the impact dynamics in low-speed rear-end collisions. The method used to simulate the crash is a step-by-step impulsive model including tyre friction and the rolling resistance effect. The simulation allows a separate analysis of the compression and restitution phases. The first is based upon experimental data of the crash test between the vehicles, the latter leads to two different choices of reconstruction, considering the bumper rebound or neglecting it. The coefficient of restitution is calculated by the force reached at compression ending, thus including the influence of external forces (as friction). The results show a great accuracy and matching with experimental data. The main changes in the impact dynamics due to the rise in braking force are the enlargement of the crush with a delay of the restitution start and a lowering of the coefficient of restitution, the increase of the impact duration and the decrease of the velocities at the collision end. These effects depend on the closing velocity and are more marked at low speed. This study therefore demonstrates that the braking force is not negligible in a good reconstruction of impact dynamics at low speed.

The Biomechanics of Gender Difference and Whiplash Injury: Designing Safer Car Seats for Women

Female car users are reported to have a higher incidence of soft tissue neck injuries in low speed rear-end collisions than males, and they apparently take longer to recover. This paper addresses the whiplash problem by developing a biomechanical FEM (Finite Element Method) model of the 50th and the 5th percentile female cervical spines, based on the earlier published male model created at the Nottingham Trent University. This model relies on grafting a detailed biomechanical model of the neck and head onto a standard HYBRID III dummy model. The overall philosophy of the investigation was to see if females responded essentially as scaled down males from the perspective of rear end collisions. It was found that detailed responses varied significantly with gender and it became clear that females cannot be modelled as scaled-down males, thus confirming the need for separate male and female biomechanical models and a revision of car test programmes and regulations which are currently based on the average male. Further investigation is needed to quantify the gender differences and then recommendations can be made for changes to the design of car seats and head restraints in order to reduce the risk of soft tissue injury to women.

Reconstruction of low speed rear-end collisions - technical means of assessing cervical spine injuries.

In recent years, an increasing number of cervical spine injuries sustained by vehicle occupants in collisions at comparatively low speeds have been reported to insurance companies and in civil litigation. The reported injuries occur in both rear‐end and side impact collisions. The paper describes how a detailed assessment of such cases requires interdisciplinary teamwork involving technical, biomechanical and medical experts.

N km --A Proposal for a Neck Protection Criterion for Low-Speed Rear-End Impacts

Soft tissue neck injuries sustained in low speed rear-end collisions are of continued concern in road traffic. To assess the risk of sustaining such injuries, various neck injury criteria have been proposed. In this study a new candidate for such an injury predictor called N km was developed. It is based on a linear combination of shear forces acting in the sagittal direction and extension/flexion bending moments, both measured at the occipital condyles. Results from a total of 40 sled tests, all performed using the same test procedure, with various car front seat models, and using a Hybrid III/TRID as well as a BioRID dummy, were evaluated in order to validate the new criterion. Additionally, a mathematical model was set up to determine the behavior of the N km at a higher crash pulse than the one used in the sled tests. It was shown that the new criterion offers the additional possibility to assess the kinematic phase of forward motion. Furthermore, the influence of the seat design on its protective potential could be related to the N km values obtained and thus, the new criterion is eligible to be part of a standard seat test procedure.

Fluid-Structure Interaction in the Biomechanics of Soft Tissue Neck Injuries: A Finite Element Study to Analyze Blood Vessel Pressure Effects in the Venous Plexus

Soft tissue neck injuries, which are sustained particularly in low-speed rear-end collisions, are of continued concern in road traffic. As a possible cause for this injury, it has been hypothesized that pressure pulses induced in cervical fluid compartments during the impact could damage the membrane of spinal nerve cells. A theoretical analysis has been undertaken in order to investigate the pressure and flow pulse emerging in a cervical fluid compartment under conditions representing rear-end impacts with a j v of 15 km/h. Using the finite element (FE) method, a model of the cervical spine was developed that included a typical venous blood vessel. To be able to determine the pressure behavior inside the blood vessel, fluid-structure interaction was taken into account by using combined structural mechanics/fluid dynamics simulation. The calculated pressure pulses are in qualitative agreement with the reported measurements. From the associated flow pulses, the shear stresses acting on the vessel wall can be determined. An extrapolation of the results into the interstitial space where nerve cells are located does at this stage not allow assessment as to whether a damage threshold may be reached.

Experimental analysis of a new flexible neck model for low–speed rear–end collisions

Whiplash injuries occur frequently in rear-end automobile accidents even at low-speed. The hybrid III dummy has been used for various tests in order to investigate the mechanism of whiplash injuries. However, since this dummy neck is too rigid for low-speed collisions, we developed a new flexible neck model for low-speed rear-end collisions. Each component of this new flexible neck model is made of polymers with material properties close to those of the human body. Sled tests were conducted to measure the displacements of cervical vertebrae of the new flexible neck model at 11 km/h. The figures of s-shape and shear displacement in the plane of the intervertebral disks were observed, and it was recognized that shear displacement resulted from the inconsistency of motion between the head and neck. The regions of shear displacement agreed well with the statistics of the critical regions where whiplash injuries have frequently occurred. It is assumed that shear displacement is one of the causes of the mechanism of whiplash injuries.

1A31 頚部鞭打ち損傷に関する研究(1A3 損傷のバイオメカニクス)

1A31 頚部鞭打ち損傷に関する研究(1A3 損傷のバイオメカニクス)