Ola Boström

How crash severity in rear impacts influences short- and long-term consequences to the neck

The main public-health problem concerning WAD are injuries leading to long-term consequences. Yet epidemiological studies mostly concentrate on data based on the injury outcome occurring shortly after the crash. The purpose of this article is to study the influence of crash severity in rear impacts leading to short and long-term consequences to the neck (WAD 1-3), lasting less than or more than 1 year. The influence of change of velocity as well as the car acceleration were investigated by using data from crash pulse recorders (CPR) installed in vehicles, involved in rear impacts. The influence of the car acceleration were also investigated by studying the frequency of occurrence of a tow-bar (hinge) on the struck car. Apart from real-life data, full-scale car-to-car crashes were performed to evaluate the influence of a tow-bar on the struck car. The crash tests showed that a tow-bar may significantly affect the acceleration of the car as well as that of the occupant. According to real-life crashes, a tow-bar on the struck car increased the risk of long-term consequences by 22% but did not affect the risk of short-term consequences. Out of the 28 crash recorder-equipped struck cars involving 38 occupants, 15 sustained no injury where the peak acceleration was 6g or less, 20 sustained short-term consequences where the peak acceleration was 10g or less. Three occupants from two different crashes sustained long-term consequences. The two crashes which resulted in long-term disabling neck injuries had the highest peak acceleration (15 and 13 x g), but not the highest change of velocity.

Neck injuries in car collisions — a review covering a possible injury mechanism and the development of a new rear-impact dummy

A review of a few Swedish research projects on soft tissue neck injuries in car collisions is presented together with some new results. Efforts to determine neck injury mechanisms was based on a hypothesis stating that injuries to the nerve root region in the cervical spine are a result of transient pressure gradients in the spinal canal during rapid neck bending. In experimental neck trauma research on animals, pressure gradients were observed and indications of nerve cell membrane dysfunction were found in the cervical spinal ganglia. The experiments covered neck extension, flexion and lateral bending. A theoretical model in which fluid flow was predicted to cause the transient pressure gradients was developed and a neck injury criterion based on Navier-Stokes Equations was applied on the flow model. The theory behind the Neck Injury Criterion indicates that the neck injury occurs early on in the rearward motion of the head relative to the torso in a rear-end collision. Thus the relative horizontal acceleration and velocity between the head and the torso should be restricted during the early head-neck motion to avoid neck injury. A Bio-fidelic Rear Impact Dummy (BioRID) was developed in several steps and validated against volunteer test results. The new dummy was partly based on the Hybrid III dummy. It had a new articulated spine with curvature and range of motion resembling that of a human being. A new crash dummy and a neck injury criterion will be very important components in a future rear-impact crash test procedure.

Pressure measurements in the spinal canal of post-mortem human subjects during rear-end impact and correlation of results to the neck injury criterion.

The aim of this study is to validate the pressure effect theory on human beings during a realistic rear-end impact and to correlate the neck injury criterion to pressure in the spinal canal. Sled experiments were performed using a test setup similar to real rear-end collisions. Test conditions were chosen based on accident statistics and recordings of real accidents. In particular, velocity change and acceleration level were reproduced similar to actual collisions. The head restraint as well as the seat back were adjusted to different positions. Two small pressure transducer were implemented to the spinal canal of postmortem human subjects and pressure measurement similar to the pig experiments (using exactly the same equipment) were performed. A total set of 21 experiments with four different subjects were performed. The subjects were additionally instrumented with triaxial accelerometers that allowed for calculation of the NIC criterion. Results showed that NIC and pressure amplitudes of the CSF correlate well and therefore NIC seems to be able to predict these amplitudes also for human beings. Conclusions whether these pressure effects induce soft tissue neck injuries or not could not be drawn and should be investigated in further research.

Head Injury Causation Scenarios for Belted, Rear-Seated Children in Frontal Impacts

Objectives: Head injuries are the most common serious injuries sustained by children in motor vehicle crashes and are of critical importance with regard to long-term disability. There is a lack of understanding of how seat belt–restrained children sustain head injuries in frontal impacts. The aim of the study was to identify the AIS2+ head injury causation scenarios for rear-seated, belt-restrained children in frontal impacts, including the set of parameters contributing to the injury. Method: In-depth crash investigations from two National Highway Traffic Safety Administration (NHTSA) databases, the National Automotive Sampling System–Crashworthiness Data System (NASS-CDS; 1997–2008) and the Crash Injury Research and Engineering Network (CIREN; 1996–2009), were collected and analyzed in detail. Selection criteria were all frontal impacts with principal direction of force (PDOF) of 11, 12, and 1 o’clock involving rear-seated, three-point belt-restrained, with or without booster cushion, children from 3 to 13 years with an AIS2+ head injury. Cases were analyzed using the BioTab method of injury causation assessment in order to systematically analyze the injury causation scenario for each case. Results: There were 27 cases meeting the inclusion criteria, 19 cases with MAIS2 head injuries and 8 cases with MAIS3+ head injuries, including 2 fatalities. Three major injury causation scenarios were identified, including head contact with seatback (10 cases), head contact with side interior (7 cases,) and no evidence of head contact (9 cases). Conclusions: Head injuries with seatback or side interior contact typically included a PDOF greater than 10 degree (similar to the Insurance Institute for Highway Safety [IIHS] and EuroNCAP offset frontal testing) and vehicle maneuvers. For seatback contact, the vehicles movements contributed to occupant kinematics inboard the vehicle, causing a less than optimal restraint of the torso and/or torso roll out of the shoulder belt. For side interior contact, the PDOF and/or maneuvers forced the occupant toward the side interior. The cases without evidence of head/face contact were characterized by high crash severity and accompanied by severe injuries to the thorax and spine. These data lead to increased understanding of the injury patterns and causation in this crash restraint scenario so that interventions to mitigate the burden of injury can be advanced.

Transient pressure gradients in the pig spinal canal during experimental whiplash motion causing membrane dysfunction in spinal ganglion nerve cells

SummaryMechanical loading of the cervical spine during car accidents often lead to a number of neck injury symptoms with the common term Whiplash Associated Disorders (WAD). Several of these symptoms could possibly be explained by injuries to the cervical spinal nerve root region.It was hypothesised that the changes in the inner volume of the cervical spinal canal during neck extension-flexion motion would cause transient pressure changes in the CNS as a result of hydro-dynamic effects, and thereby mechanically load the nerve roots and cause tissue damage.To test the hypothesis, anaesthetised pigs were exposed to experimental neck trauma in the extension, flexion and lateral flexion modes. The severity of the trauma was kept below the level where cervical fractures occur. Transient pressure pulses in the cervical spinal canal were duly recorded. Signs of cell membrane dysfunction were found in the nerve cell bodies of the cervical spinal ganglia. Ganglion injuries may explain some of the symptoms associated with soft-tissue neck injuries in car accidents. When the pigs head was pulled rearward relative to its torso to resemble a rear-end collision situation, it was found that ganglion injuries occurred very early on in the neck motion, at the stage where the motion changes from retraction to extension motion. Ganglion injuries did not occur when pigs were exposed to similar static loading of the neck. This indicates that these injuries are a result of dynamic phenomena and thereby further supports the pressure hypothesis. A Neck Injury Criterion (NIC) based on a theoretical model of the pressure effects was developed. It indicated that it was the differential horizontal acceleration and velocity between the head and the upper torso at the point of maximum neck retraction that determined the risk of ganglion injuries.ZusammenfassungDie mechanische Belastung der Halswirbelsäule (HWS) bei Autounfällen verursacht oft eine Reihe von Halsverletzungen, die unter dem Begriff Schleudertrauma zusammengefaßt werden. Mehrere dieser Symptome können möglicherweise durch Verletzungen im Bereich der Nervenwurzeln der HWS erklärt werden. Die Hypothese wurde aufgestellt, daß während der Extensions- und Flexionsbewegungen des Halses, aufgrund von hämodynamischen Auswirkungen, Änderungen des inneren Volumens des Halswirbelkanals kurzzeitige Druckveränderungen im ZNS verursachen und daß dadurch Gewebeschäden durch die mechanische Belastung der Nervenwurzel entstehen. Um die Hypothese zu überprüfen, wurden anästhesierte Schweine einem experimentellen Schleudertrauma mit Extensions-, Flexions- und Seitneigungsbewegungen ausgesetzt. Die traumatische Belastung wurde unterhalb einer Stufe gehalten, bei der eine Halswirbelfraktur stattfinden könnte. Während der Belastung wurde der Pulsdruck im Halswirbelkanal gemessen. In diesem Zusammenhang ergaben sich Hinweise einer Dysfunktion der Zellmembran bei Nervenzellkörpern der Spinalganglien. Die ganglionären Verletzungen können möglicherweise einige der mit Weichteilverletzungen des Halses nach Autounfällen einhergehenden Symptome erklären. Um die Situation bei einem Auffahrunfall zu simulieren, wurde der Kopf des Schweines rückwärts vom Torso weggezogen. Dabei wurde festgestellt, daß die ganglionären Verletzungen zu einem sehr frühen Zeitpunkt während der Halsbewegungen stattfinden und zwar in der Phase, in der die Bewegung von der Retraktion zur Extension wechselt. Bei einer ähnlichen, jedoch statischen Belastung des Halses wurden keine ganglionären Verletzungen bei den Schweinen festgestellt. Dies ist ein Hinweis darauf, daß diese Verletzungen durch dynamische Faktoren verursacht werden und bietet somit weitere Unterstützung für die Druckhypothese. Auf der Basis eines theoretischen Modells wurden Kriterien für Halsverletzungen (neck injury criterion = NIC) entwickelt. Es weist darauf hin, daß das Risiko von ganglionären Verletzungen am Punkt der maximalen Halsretraktion durch die unterschiedliche horizontale Beschleunigung und Geschwindigkeit zwischen Kopf und oberem Torso bestimmt wird.

Real-Life Fatal Outcome in Car-to-Car Near-Side Impacts—Implications for Improved Protection Considering Age and Crash Severity

Objective: Recent studies have shown that current side airbags, protecting head and chest, are saving lives in near-side impacts (Kahane 2007; McCartt and Kyrychenko 2007). The aim of this study was to analyze NASS/CDS real-life data on fatal trauma in near-side car-to-car crashes, stratified by age into non-senior and senior occupants. Furthermore, a hypothetical model explaining side airbag effectiveness as a function of lateral delta-v was presented. The model together with the field data was then used to demonstrate further enhancement of side airbag restraint performance. Method: Weighted NASS/CDS data from 1994 to 2006 for front seat occupants in near-side car-to-car impacts was used to calculate the exposure, incidence, and risk of fatal trauma with respect to lateral delta-v. The dataset was also divided into non-senior (10–59 years) and senior (age ≥ 60 years) occupants. The hypothetical model was created to adjust the NASS/CDS data to represent a car fleet fully equipped with current side airbag protection. The model was then used to evaluate the increase in effectiveness of improved side airbag protection achieved by increasing the lateral delta-v in the range where the airbag have most mitigating effect, increasing the airbag protection level within the delta-v range currently tested, and a combination of the two approaches. Results: From the NASS/CDS data, the median delta-v for fatal injury was 37 km/h for the total sample. When stratified with respect to age, the median delta-v for fatal injury was 41 km/h for non-seniors and 28 km/h for senior occupants. The exposures for both age groups were similar. However, the fatal incidence showed a difference in delta-v range between non-senior and senior occupants. Applying the airbag model increased the median delta-v to 40 km/h for the total sample and 47 and 30 km/h for non-seniors and seniors, respectively. Conclusions: Current side airbag systems offer very good protection for non-senior occupants up to delta-v 40 km/h. Though still high, the protection for senior occupants is lower. To enhance side airbag protection, the side airbag performance should be maximized where the fatal incidence is high. Therefore, to further reduce non-senior fatalities, the test speed should be increased. To further reduce senior fatalities, the protection level within severities currently tested should be increased. A combination of the two approaches would result in about a 40 percent increase of the side airbag effectiveness.

Benefits of a 3+2-point belt system and an inboard torso side support in frontal, far-side and rollover crashes

3-point belted occupants are still being injured in numerous crashes. In frontal collisions this is partly explained by the range of hard tissue tolerance amongst car occupants. In side collisions occupants on the far side of the intrusion are mainly restrained by the lap part of the 3-point belt, with an associated high risk of sustaining a severe head injury. During a rollover crash the 3-point belt cannot fully prevent harmful head impacts. In this study an additional 2-point belt (single handed optional operation) is combined with an inboard torso side support. The idea is simply to distribute the belt load on more anatomical structures (bones) as well as constituting a non-injurious inboard and upward restraint. The inboard side support prevents a direct loading by the 2-point belt to the cervical spine in far-side collisions. It also supports the torso when the 2-point belt is not buckled. To prove if this design measure is advantageous, frontal, far side and rollover tests were performed. Current standard crash test dummies lack appropriate biofidelity when assessing sophisticated enhancements of standard safety restraints. Therefore the Thor dummy with a set of modifications from the BioSID were used in the tests. The results showed a considerable reduction of chest deflection in the frontal crash tests, head horizontal motion in the far side tests and head upward motion in the rollover tests. To conclude, an additional 2-point belt, in conjunction with, a 3-point belt and inboard torso side support offer a considerably increased protection in various crash situations without any negative consequences. For the covering abstract see ITRD E825082.

Development and validation of pedestrian sedan bucks using finite-element simulations: a numerical investigation of the influence of vehicle automatic braking on the kinematics of the pedestrian involved in vehicle collisions

Previous vehicle-to-pedestrian impact simulations and experiments using pedestrian dummies and cadavers have shown that factors such as vehicle shape, pedestrian anthropometry and pre-impact conditions influence pedestrian kinematics and injury mechanisms. Generic pedestrian bucks, which approximate the geometrical and stiffness properties of current vehicles, would be useful in studying the influence of vehicle front-end structures on pedestrian kinematics and loading. This study explores the design of pedestrian bucks, intended to represent the basic vehicle front-end structures, consisting of five components: lower stiffener, bumper, hood leading edge and grille, hood and windshield. The deformable parts of the bucks were designed using types of currently manufactured materials, which allow fabricating the bucks in the future. The geometry of pedestrian bucks was approximated according to the contour cross-sections of two sedan vehicles used in previous pedestrian dummy and cadaver impact tests. Other cross-sectional dimensions and the stiffness of the buck components were determined by parameter identification using finite-element (FE) simulations of each sedan model. In the absence of a validated FE model of human, the FE model of the POLAR II pedestrian dummy was used to validate a mid-size sedan (MS) pedestrian buck. A good correlation of the pedestrian dummy kinematics and contact forces obtained in dummy–MS pedestrian buck with the corresponding data from dummy–MS vehicle simulation was achieved. A parametric study using the POLAR II FE model and different buck models – an MS buck and a large-size sedan (LS) buck – were run to study the influence of an automatic braking system for reducing the pedestrian injuries. The vehicle braking conditions showed reductions in the relative velocity of the head to the vehicle and increases in the time of head impact and in the wrap-around-distances (WAD) to primary head contact. The head impact velocity showed a greater sensitivity to the different buck shapes (e.g. LS buck versus MS buck) than to the braking deceleration. The buck FE models developed in this study are expected to be used in sensitivity and optimisation studies for the development of new pedestrian protection systems.

The Frontal-Impact Response of a Booster-Seated Child-Size PMHS

Objectives: This article presents the response of a child-size postmortem human subject using a booster seat in a series of three frontal impact sled tests. Methods: A 54-year-old female cadaver was seated in a booster seat in the rear seat of a buck representing a mid-sized American sedan. Two different restraint systems (conventional belt and pretensioning, force-limiting belt) were used to run three simulated frontal impacts (one at 29 km/h, two at 48 km/h). Instrumentation included accelerometers rigidly mounted on relevant body landmarks as well as chest bands. Trajectories were assessed through high-speed video cameras. Results: Specific focus was on the whole-body kinematics and resulting head trajectories under two different restraint conditions (booster seat and standard belt, booster seat and force-limiting pretensioning belt) in a rear seat environment. At 48 km/h, the pretensioning, force-limiting seat belt reduced the forward excursion of both the head (353 mm vs. 424 mm) and the h-point (120 mm vs. 152 mm) compared to the standard system. Maximum torso pitch was similar for both seat belts. Conclusions: A complete description of the outcome of the tests is presented in the article. These results suggest that the introduction of a pretensioning force limiting belt in the rear seat can be beneficial for small size occupants like children using booster seats.

Census Study of Fatal Car-to-Car Intersection Crashes in Sweden Involving Modern Vehicles

Objective: Intersections are challenging for many road users. According to US, European, and global statistics, intersection-related crashes with fatal outcome represent approximately 20 percent of all traffic fatalities. The aim of this study was to use Swedish data to investigate and characterize fatal car-to-car intersection crashes for modern cars equipped with frontal and side air bags. Method: The Swedish Transport Administration (STA) national database on fatal crashes was searched to find vehicle-to-vehicle intersection crashes involving modern cars that occurred between 2003 and 2009 that resulted in fatal injuries for at least one of the involved passengers. From all intersection crashes, the car-to-car crashes from the sample were analyzed at an occupant level. Occupant location in the target vehicle with respect to impact direction as well as AIS3+ injuries to body regions was examined for the total car-to-car sample. Crashes involving a target vehicle equipped with front and side air bags were then selected for an in-depth study. Results: In the STA database, 39 vehicle-to-vehicle crashes matched the search criteria. Of 39 crashes, 17 involved a heavy goods vehicle (HGV) as the striking vehicle, and 17 were car-to-car crashes. All car-to-car crashes were side impacts, occurring at rural intersections, involving 20 (12 female and 8 male) fatally injured occupants, 15 of whom were 61 years or older and classified as senior occupants. A majority of fatally injured occupants sustained combined AIS3+ injuries to more than one body region. Conclusions: All modern car-to-car crashes with a fatal outcome occurring at Swedish intersections from 2003 to 2009 were side impacts. The crashes were characterized by a senior front seat driver, traveling with a front seat passenger, hit on the left side at approximately 70 km/h. In this study all fatal crashes occurred at severities beyond those currently evaluated in side impact rating procedures but were within survivable limits for a non-senior occupant in a majority of cases.