The influence of confounding factors on the relationship between muscle contraction level and MF and MPF values of EMG signal: a review

The purpose of this article is to gather results of studies on the relationship between median frequency (MF) and mean power frequency (MPF) and the level of muscle contraction, and to use those results to discuss the differences in the trends according to factors related to measurement technique and subject. Twenty-one studies with 63 cases for upper limb muscles and nine studies with 31 cases for lower limb muscles were analysed. Most results showed an increase in parameters with an increased level of muscle contraction, only some studies showed a decrease. The influence on parameters of the level of muscle contraction and factors such as subjects, type of contraction, muscle length and electrodes was analysed for each muscle. It was concluded that when analysing the influence of different factors on MF and MPF, because those factors interact they should be considered together, not separately.     

The effect of muscle activation on neck response

Prevention of neck injuries due to complex loading, such as occurs in traffic accidents, requires knowledge of neck injury mechanisms and tolerances. The influence of muscle activation on outcome of the injuries is not clearly understood. Numerical simulations of neck injury accidents can contribute to increase the understanding of injury tolerances. The finite element (FE) method is suitable because it gives data on stress and strain of individual tissues that can be used to predict injuries based on tissue level criteria.The aim of this study was to improve and validate an anatomically detailed FE model of the human cervical spine by implement neck musculature with passive and active material properties. Further, the effect of activation time and force on the stresses and strains in the cervical tissues were studied for dynamic loading due to frontal and lateral impacts.The FE model used includes the seven cervical vertebrae, the spinal ligaments, the facet joints with cartilage, the intervertebral disc, the skull base connected to a rigid head, and a spring element representation of the neck musculature. The passive muscle properties were defined with bilinear force-deformation curves and the active properties were defined using a material model based on the Hill equation. The FE model's responses were compared to volunteer experiments for frontal and lateral impacts of 15 and 7 g. Then, the active muscle properties where varied to study their effect on the motion of the skull, the stress level of the cortical and trabecular bone, and the strain of the ligaments.The FE model had a good correlation to the experimental motion corridors when the muscles activation was implemented. For the frontal impact a suitable peak muscle force was 40 N/cm2 whereas 20 N/cm2 was appropriate for the side impact. The stress levels in the cortical and trabecular bone were influenced by the point forces introduced by the muscle spring elements; therefore a more detailed model of muscle insertion would be preferable. The deformation of each spinal ligament was normalized with an appropriate failure deformation to predict soft tissue injury. For the frontal impact, the muscle activation turned out to mainly protect the upper cervical spine ligaments, while the musculature shielded all the ligaments disregarding spinal level for lateral impacts. It is concluded that the neck musculature does not have the same protective properties during different impacts loadings.     

Development and Validation of the Total HUman Model for Safety (THUMS) Toward Further Understanding of Occupant Injury Mechanisms in Precrash and During Crash

Objective: Active safety devices such as automatic emergency brake (AEB) and precrash seat belt have the potential to accomplish further reduction in the number of the fatalities due to automotive accidents. However, their effectiveness should be investigated by more accurate estimations of their interaction with human bodies. Computational human body models are suitable for investigation, especially considering muscular tone effects on occupant motions and injury outcomes. However, the conventional modeling approaches such as multibody models and detailed finite element (FE) models have advantages and disadvantages in computational costs and injury predictions considering muscular tone effects. The objective of this study is to develop and validate a human body FE model with whole body muscles, which can be used for the detailed investigation of interaction between human bodies and vehicular structures including some safety devices precrash and during a crash with relatively low computational costs.

Methods: In this study, we developed a human body FE model called THUMS (Total HUman Model for Safety) with a body size of 50th percentile adult male (AM50) and a sitting posture. The model has anatomical structures of bones, ligaments, muscles, brain, and internal organs. The total number of elements is 281,260, which would realize relatively low computational costs. Deformable material models were assigned to all body parts. The muscle–tendon complexes were modeled by truss elements with Hill-type muscle material and seat belt elements with tension-only material. The THUMS was validated against 35 series of cadaver or volunteer test data on frontal, lateral, and rear impacts. Model validations for 15 series of cadaver test data associated with frontal impacts are presented in this article. The THUMS with a vehicle sled model was applied to investigate effects of muscle activations on occupant kinematics and injury outcomes in specific frontal impact situations with AEB.

Results and Conclusions: In the validations using 5 series of cadaver test data, force–time curves predicted by the THUMS were quantitatively evaluated using correlation and analysis (CORA), which showed good or acceptable agreement with cadaver test data in most cases. The investigation of muscular effects showed that muscle activation levels and timing had significant effects on occupant kinematics and injury outcomes. Although further studies on accident injury reconstruction are needed, the THUMS has the potential for predictions of occupant kinematics and injury outcomes considering muscular tone effects with relatively low computational costs.     

A study on chest injury mechanism and the effectiveness of a headform impact test for pedestrian chest protection from vehicle collisions

This study was aimed at investigating the injury mechanism of pedestrian chests in collisions with passenger vehicles of various frontal shapes and examining the influence of the local structural stiffness on the chest injury risk by using the headform impact test at the chest contact area of the vehicle. Three simulations of vehicle to pedestrian collisions were conducted using three validated pedestrian finite element (FE) models of three pedestrian heights of 177 (AM50th), 165 and 150 cm and three FE vehicles models representing a one-box vehicle, a minicar and a medium car. The validity of the vehicle models was evaluated by comparing the headform acceleration against the measured responses from headform impact tests. The chest impact kinematics and the injury mechanisms were analyzed in terms of the distribution of the von Mises stress of the ribcage and in terms of the chest deflections. The chest contact locations on the front panel and the bonnet top were identified in connection to the causation of rib fractures. The risk of rib fractures was predicted by using the von Mises stress distribution. The headform impact tests were carried out at the chest contact area on the front panel and bonnet to examine the safety performance with respect to pedestrian chest protection. In simulations of the one-box vehicle to pedestrian collisions, the chest was struck directly by the frontal structure at a high velocity and deformed substantially, since a shear force was generated by the stiff windshield frame. The acceleration of the headform was related to the rib deflections. The injury threshold of the ribcage deflection (42 mm) corresponded to the headform average acceleration of 68 G. In the minicar collision, the chest was struck with the bonnet top and cowl area at a low velocity, and the deformation was small due to the distributed contact force between the chest and the bonnet top. Besides, the ribcage deformation was too small for bridging a relation between the headform accelerations and rib deflections. In the medium car collision, the deformation mode of the chest was similar to that in the minicar collision. The chest collided with the bonnet top at a low velocity and deformed uniformly. The deflection of the ribs had an observable correlation with the headform accelerations measured in the headform impact tests. The frontal shape of a vehicle has a large influence on a pedestrian’s chest loadings, and the chest deformation depends on the size of the pedestrian and the stiffness of the vehicle. The one-box passenger vehicle causes a high chest injury risk. The headform impactor test can be utilized for the evaluation of the local stiffness of a vehicle’s frontal structure. The reduction of the headform acceleration is an effective measure for pedestrian chest protection for specific shapes of vehicles by efficacy in modifying the local structural stiffness.     

The effects of hand force variation on shoulder muscle activation during submaximal exertions

Upper limb injuries are highly prevalent in the workplace and new tools are needed to proactively design workstations to reduce injury risk. The objective was to characterize spatial, load and direction dependency of muscle activity for hand exertions in the upper limb workspace. Electromyographic signals were collected from 14 upper limb muscles during exertions for all combinations of 4 submaximal hand forces (20/30/50/60?N) in 6 cardinal (up/down/left/right/forward/backward) directions at 5 hand locations. Linear muscle activity increases accompanied increased hand forces. Total muscle activity increases between 20 and 60?N hand forces ranged by direction from 92% (downward) to 189% (right). Prediction equations for all muscles depended on hand force, and linear, quadratic and interaction permutations of hand location. Muscle activity associated with manual tasks is load, direction and spatially dependent. Equations developed to describe these complex relationships can be used to better design future and evaluate current occupational activities.     

基于复杂网络的内河船舶碰撞事故致因分析

为了探明内河船舶碰撞事故致因内在联系,基于船舶碰撞事故调查报告,从人-机-环-管视角构建事故致因复杂网络模型。运用“2-4”模型从人-机-环-管视角识别和提取事故致因,采用事故树方法分析调查报告中碰撞事故过程,提取内河船舶碰撞事故致因链,利用复杂网络理论融合多事故致因链,构建包括36个节点、123条边在内的事故致因网络,计算致因网络拓扑特征参数,定量分析内河船舶碰撞事故致因之间相互作用。研究结果表明：疏忽瞭望、错误估计碰撞危险、安全管理不到位、船员不适任、船与船通信信息不足、未及时行动是内河船舶碰撞事故的关键致因。同时,内河船舶碰撞致因网络是1个无标度网络,且具有小世界特性,表明事故致因之间连锁效应明显,管控上述关键致因可有效预防碰撞事故。研究结果可为预防内河船舶碰撞事故、提高内河航运管理水平提供参考。     

Simulating the relative influence of tire,vehicle and driver factors on forward collision accident rates

Introduction: There is currently a strong focus within the automotive industry centered on traffic safety, with topics such as distracted driving, accident avoidance technologies, and autonomous vehicles. These papers tend to focus on the possible improvements from a single factor. However, there are many factors that are present in each accident, and it is important to understand the influence of each factor on the relative accident risk in order to identify the most effective approaches for improving driver safety. Rear-end accidents tend to be the most common accident type with approximately 1.8 M cases, or 31% of all accidents, in 2012, according to NHTSA. Of the rear-end accident scenarios, approximately 18–23% occur on wet surfaces. Method: A Monte Carlo Forward Collision Simulation models the conditions of a wet rear-end accident and estimates the relative impact of various vehicle collision parameters. The model takes distributions of these parameters as inputs, and outputs a risk of collision relative to a known reference case. The parameters that can be studied include: tire grip level, road grip level, vehicle velocity, following distances, and the presence of vehicle technologies (ABS, FCW & AEB). Distributions of some of these parameters have been improved thanks to Naturalistic Driving Study data from SHRP2. Results: This study shows that these vehicle systems have a large impact on safety and can change the amount of influence attributed to other parameters such as tire grip levels. As the use of automated vehicle systems expands, so will the influence of tire grip performance levels on collision risks. Practical Applications: It is more important than ever for consumers and auto manufacturers to consider tire performance levels. Therefore, the tire industry should continue to focus on wet grip as a key performance related to safety and should strive to continue to improve tire performance.     

Simulator study of young driver's instinctive response of lower extremity to a collision

Objective: A driver's instinctive response of the lower extremity in braking movement consists of two parts, including reaction time and braking reaction behavior. It is critical to consider these two components when conducting studies concerning driver's brake movement intention and injury analysis. The purposes of this study were to investigate the driver reaction time to an oncoming collision and muscle activation of lower extremity muscles at the collision moment. The ultimate goal is to provide data that aid in both the optimization of intervention time of an active safety system and the improvement of precise protection performance of a passive safety system.

Method: A simulated collision scene was constructed in a driving simulator, and 40 young volunteers (20 male and 20 female) were recruited for tests. Vehicle control parameters and electromyography characteristics of eight muscles of the lower extremity were recorded. The driver reaction time was divided into pre-motor time (PMT) and muscle activation time (MAT). Muscle activation level (A_COL) at the collision moment was calculated and analysed.

Results: PMT was shortest for the tibialis anterior (TA) muscle (243～317 ms for male and 278～438 ms for female). Average MAT of the TA ranged from 28-55 ms. A_COL was large (5～31% for male and 5～23% for female) at 50 km/h, but small (<12%) at 100 km/h. A_COL of the gluteus maximus was smallest (<3%) in the 25 and 100 km/h tests. A_COL of RF of men was significantly smaller than that of women at different speeds.

Conclusions: Ankle dorsiflexion is firstly activated at the beginning of the emergency brake motion. Males showed stronger reaction ability than females, as suggested by male's shorter PMT. The detection of driver's brake intention is upwards of 55ms sooner after introducing the electromyography. Muscle activation of the lower extremity is an important factor for 50 km/h collision injury analysis. For higher speed collisions, this might not be a major factor. The activations of certain muscles may be ignored for crash injury analysis at certain speeds, such as gluteus maximus at 25 or 100 km/h. Furthermore, the activation of certain muscles should be differentiated between males and females during injury analysis.     

Force-Velocity Characteristics of Individual Human Skeletal Muscles: TBCIat and TBCIong. Outline of the Method

The aim of the work is to outline a procedure of finding force-velocity (F–V) characteristics (F = f(V)) of individual skeletal muscles of the human locomotor system. The presentation is based on an example concerning extensors of the elbow joint: the lateral and long heads of triceps brachii (TBCIat and TBCIong). The experimental part of the procedure involves a natural movement of using the upper extremity to push an external object of variable, adjustable load, engaging both the elbow and shoulder joint.

Five men aged 23 took part in the experiment. Their task was to push the handle of a physical pendulum whose moment of inertia could be adjusted within the range of 58 kg m²-450 kg m², so as to give it maximum angular velocity. During each trial the movement of the trunk, of the upper extremity and of the pendulum was video recorded and the force applied with the hand to the handle of the pendulum was measured.

In order to find the F–V characteristics a simulation model SHOULDER was used, which is capable of solving the synergy problem for muscles of the arm and the shoulder girdle.

It was found that despite considerable dispersion of experimental points the respective regression lines revealed a clear tendency of decreasing muscle force for increased shortening velocity of the monoarticular head (TBCIat) and of increasing muscle force for increased lengthening velocity of the biarticular head (TBCIong) of the triceps brachii muscle.     

Myoelectric manifestation of muscle fatigue in repetitive work detected by means of miniaturized sEMG sensors

Upper limb work-related musculoskeletal disorders have a 12-month prevalence ranging from 12 to 41% worldwide and can be partly caused by handling low loads at high frequency. The association between the myoelectric manifestation of elbow flexor muscle fatigue and occupational physical demand has never been investigated. It was hypothesized that an elbow flexor muscle fatigue index could be a valid risk indicator in handling low loads at high frequency. This study aims to measure the myoelectric manifestation of muscle fatigue of the three elbow flexor muscles during the execution of the work tasks in different risk conditions. Fifteen right-handed healthy adults were screened using a movement analysis laboratory consisting of optoelectronic, dynamometer and surface electromyographic systems. The main result indicates that the fatigue index calculated from the brachioradialis is sensitive to the interaction among risk classes, session and gender, and above all it is sensitive to the risk classes.     

井下支护作业人员颈部肌肉疲劳特性研究*

为探究井下支护作业人员颈部肌肉疲劳受伸张和屈曲角度变化的影响,采用表面肌电法（sEMG）实验模拟测量7种点位角度下,颈部夹肌、斜方肌以及胸锁乳突肌在不同作业频率时的疲劳情况,以积分肌电值(iEMG)及中值频率（MF）评价各肌肉疲劳程度。研究结果表明:低频实验中随点位角度的增大,颈部屈曲活动时,胸锁乳突肌疲劳变化明显,iEMG疲劳前后差值最大为1.55,MF下降率最大为0.60;颈部伸展活动时,夹肌疲劳变化明显,iEMG疲劳前后差值最大为1.59,MF下降率最大为0.59;斜方肌未表现出明显疲劳变化规律。高频实验相较低频实验疲劳发生速度加快,疲劳积累程度显著提升,颈部活动主要肌肉疲劳发生时间由16~19 min提前至13~17 min,各肌肉MF下降速度为低频实验的1~1.55倍。     

Experimental Verification of the Computerized Method for Work Space Optimization in Conditions of Static Work

The aim of this study was to verify a theoretical model for upper extremity work space optimization. In order to do that, experimental studies were conducted in which two parameters of the electromyography (EMG) signal were analyzed: AMP (amplitude calculated as Root Mean Square) and SZC (coefficient of the slope of the regression line between time and Zero Crossing values). Values of forces in muscles (parameter MOD) were calculated from theoretical studies. A comparison of experimental (AMP, SZC) and theoretical (MOD) parameters was performed by analyzing the coefficient of correlation between those parameters and differentiation of muscular load according to external load value. Analysis showed that the theoretical and experimental results are in step, which means that the developed model can be used for upper extremity work space optimization.     

Review: The Dynamics of Near Vertex Head Impact and its Role in Injury Prevention and the Complex Clinical Presentation of Basicranial and Cervical Spine Injury

The clinical presentation of cervical and basilar skull fractures following bead impact is often complex, particularly when multiple noncontiguous fractures are present. Based on the results of 22 human cadaver head-neck impact experiments, a biomechanical framework of spinal injury is developed in which these complex cases may be better understood. This includes the significance of head rebound, head and neck decoupling, cervical spine buckling, cervical injury mechanisms, basilar skull fractures, and cervical spine tolerance. These data also demonstrate that compliant pads significantly increase the risk for spinal injury though they also significantly reduce peak head force and the head injury criteria (p < 0.04). On the basis of these observations, we hypothesize that impact injury should be modeled as the dynamic response of two large masses, coupled by a segmented curved beam-column composed of seven small masses with interposed nonlinear viscoelastic flexibility elements.     

The Relation Between Upper Limb Muscle and Brain Activity in Two Precision Levels of Repetitive Light Tasks

A study was conducted to investigate the effects of repetitive light tasks of low and high precision on upper limb muscles and brain activities. Surface electromyography (EMG) and electroencephalography (EEG) were used to measure the muscle and brain activity of 10 subjects. The results show that the root-meansquare (RMS) and mean power frquency (MPF) of the muscle activity and the mean power of the EEG alpha bands were higher on the high-precision task than on the low-precision one. There was also a high and significant correlation between upper limb muscle and brain activity during the tasks. The longer the time and the more precise the task, the more the subjects become fatigued both physically and mentally. Thus, these results could be potentially useful in managing fatigue, especially fatique related to muscle and mental workload.     

A new THOR shoulder design: a comparison with volunteers, the Hybrid III, and THOR NT

OBJECTIVE: Since the shoulders are rarely seriously injured in frontal or oblique collisions, they have been given low priority in the development of frontal impact crash test dummies. The shoulder complex geometry and its kinematics are of vital importance for the overall dummy kinematics. The shoulder complex also influences the risk of the safety belt slipping off the shoulder in oblique forward collisions. The first aim of this study was to develop a new 50th percentile male THOR shoulder design, while the second was to compare the new shoulder, mounted on a THOR NT dummy, with volunteer, THOR NT, and Hybrid III range of motion and stiffness data. The third aim was to test the repeatability of the new shoulder during dynamic testing and to see how the design behaves with respect to belt slippage in a 45 degrees far-side collision. METHODS: The new 50th percentile THOR shoulder design was developed with the aid of a shell model of the seated University of Michigan Transportation Research Institute (UMTRI) 50th percentile male with coordinates for joints and bony landmarks (Schneider et al., 1983). The new shoulder design has human-like bony landmarks for the acromion and coracoid processes. The clavicle curvature and length are also made similar to that of a male human, as is the range of motion in the anterior-posterior, superior-inferior, and medial-lateral directions. The new shoulder design was manufactured and tested under the same conditions that T?rnvall et al. (2005b) used to compare the shoulder range of motion for the volunteers, Hybrid III, and THOR Alpha. The new design was also tested in two dynamic test configurations: the first was a 0 degrees full-frontal test and the second was a 45 degrees far-side test. The dummy tests were conducted with an R-16 seat with a three-point belt, the Delta V was 27.0+/-0.5 km/h and the maximum peak acceleration was approximately 14.6+/-0.5 g for each test. RESULTS: A new shoulder design with geometry close to that of humans was developed to be retrofitted to the THOR NT dummy. The results showed that the range of motion for the new shoulder complex during static loading was larger by at least a factor of three, for the maximum load (200 N/arm), than that of either the Hybrid III or the THOR NT; this means it was more similar to the volunteers' range of motion. It was observed that the THOR NT with the new shoulder did not slide out of the shoulder belt during a far-side collision. The performance of the new shoulder was reasonably repeatable and stable during both the static tests and the sled tests. CONCLUSION: A new shoulder for the THOR NT has been designed and developed, and data from static range of motion tests and sled tests indicate that the new shoulder complex has the potential to function in a more human-like manner on the THOR dummy.     

Effects of vehicle impact velocity, vehicle front-end shapes on pedestrian injury risk

Objective: This study aimed at investigating the effects of vehicle impact velocity, vehicle front-end shape, and pedestrian size on injury risk to pedestrians in collisions with passenger vehicles with various frontal shapes. Method: A series of parametric studies was carried out using 2 total human model for safety (THUMS) pedestrian models (177 and 165?cm) and 4 vehicle finite element (FE) models with different front-end shapes (medium-size sedan, minicar, one-box vehicle, and sport utility vehicle [SUV]). The effects of the impact velocity on pedestrian injury risk were analyzed at velocities of 20, 30, 40, and 50?km/h. The dynamic response of the pedestrian was investigated, and the injury risk to the head, chest, pelvis, and lower extremities was compared in terms of the injury parameters head injury criteria (HIC), chest deflection, and von Mises stress distribution of the rib cage, pelvis force, and bending moment diagram of the lower extremities. Result: Vehicle impact velocity has the most significant influence on injury severity for adult pedestrians. All injury parameters can be reduced in severity by decreasing vehicle impact velocities. The head and lower extremities are at greater risk of injury in medium-size sedan and SUV collisions. The chest injury risk was particularly high in one-box vehicle impacts. The fracture risk of the pelvis was also high in one-box vehicle and SUV collisions. In minicar collisions, the injury risk was the smallest if the head did not make contact with the A-pillar. Conclusion: The vehicle impact velocity and vehicle front-end shape are 2 dominant factors that influence the pedestrian kinematics and injury severity. A significant reduction of all injuries can be achieved for all vehicle types when the vehicle impact velocity is less than 30?km/h. Vehicle designs consisting of a short front-end and a wide windshield area can protect pedestrians from fatalities. The results also could be valuable in the design of a pedestrian-friendly vehicle front-end shape. [Supplementary materials are available for this article. Go to the publisher's online edition of Traffic Injury Prevention for the following free supplemental resource: Head impact conditions and injury parameters in four-type vehicle collisions and validation result of the finite element model of one-box vehicle and minicar. ].     

改善热轧降尘效率的雾化参数分析*

为提高热轧工作区的雾化降尘效率,研究尘雾颗粒碰撞相关理论,以热轧产生的氧化铁皮粉尘为研究对象,建立基于雾滴粒径、雾滴速度和液体流量多个雾化参数的降尘效率计算模型;分析单一雾化参数对降尘效率的影响;通过实验,测得不同气液压力组合下的雾化参数,运用响应曲面法,分析多个雾化参数耦合对降尘效率的影响。结果表明:降尘效率随着雾滴粒径的减小、液体流量增大而提高,雾滴速度对其影响不明显;多因素耦合时,通过调节气液压力组合来控制降尘效率,结合高温环境对雾滴存活时间的影响分析,当气压0.3 MPa、液压0.5 MPa时,粒径为21～27 μm的粉尘沉降效果最佳,降尘效率达到90%以上,可有效解决热轧车间粉尘污染问题。     

Cervical vertebral motions and biomechanical responses to direct loading of human head

There is little known data characterizing the biomechanical responses of the human head and neck under direct head loading conditions. However, the evaluation of the appropriateness of current crash test dummy head-neck systems is easily accomplished. Such an effort, using experimental means, generates and provides characterizations of human head-neck response to several direct head loading conditions. Low-level impact loads were applied to the head and face of volunteers and dummies. The resultant forces and moments at the occipital condyle were calculated. For the volunteers, activation of the neck musculature was determined using electromyography (EMG). In addition, cervical vertebral motions of the volunteers have been taken by means of X-ray cineradiography. The Ethics Committee of Tsukuba University approved the protocol of the experiments in advance. External force of about 210 N was applied to the head and face of five volunteers with an average age of 25 for the duration of 100 msec or so, via a strap at one of four locations in various directions: (1) an upward load applied to the chin, (2) a rearward load applied to the chin without facial mask, (3) a rearward load applied to the chin with the facial mask, and (4) a rearward load applied to the forehead. The same impact force as those for the human volunteers was also applied to HY-III, THOR, and BioRID. We found that cervical vertebral motions differ markedly according to the difference in impact loading condition. Some particular characteristics are also found, such as the flexion or extension of the upper cervical vertebrae (C0, C1, and C2) or middle cervical vertebrae (C3-C4), showing that the modes of cervical vertebral motions are markedly different among the different loading conditions. We also found that the biofidelity of dummies to neck response characteristics of the volunteers at the low-level impact loads is in the order of BioRID, THOR, and HY-III. It is relevant in this regard that the BioRID dummy was designed for a low-severity impact environment, whereas THOR and HY-III were optimized for higher-severity impacts.     

Occupant Risk,Partner Risk and Fatality Rate in Frontal Crashes: Estimated Effects of Changing Vehicle Fleet Mass in 15 Years

The effect of vehicle fleet mass on car crash fatalities was estimated, using a new mathematical model to isolate vehicle mass from related factors like size, stiffness and inherent protection. The model was based on fatality risk data, impact speed, fleet mass distribution, and collision probabilities. The fleet mass distribution was changed over 15 years to (a) a homogeneous fleet of 1300 kg cars, (b) a bimodal fleet of 600 and 1600 kg cars, and (c) a 300 kg lighter fleet.

Occupant and collision partner fatality risks were estimated for the new fleets. The new fleets were achieved by various strategies, and the average fatality rate was calculated after and during the transition to the new fleet.Occupant fatality risk decreased and partner risk increased as occupants changed to a heavier car. The average fatality rate was 59% higher after the transition to a bimodal fleet mass, and 11 % lower for a homogeneous fleet. A 300 kg lighter fleet had a 8% higher fatality rale, but the strategy influenced the number of fatalities accumulated during the transition. The safest strategy to attain the lighter fleet was to reduce the mass of the heaviest cars first.

It was concluded that vehicle fleet mass significantly affects traffic safety. Downsizing consequences can be compensated for by improving inherent vehicle protection or reducing impact speed. The fatalities during downsizing can be limited by choosing an appropriate strategy.     

Crash-Pulse Recorders in Real-Life Accidents: Influence of Change of Velocity and Mean and Peak Acceleration on Injury Risk in Frontal Impacts

Several parameters based on acceleration levels, such as mean or peak acceleration, may correlate with injury risk, or may together with change of velocity, explain the risk of injury, and thus may form the risk function for different kind of injuries. The aim was to study the influence on injury risk for mean and peak acceleration and change of velocity as well as how these correlate with each other. The results from 144 crash-pulse recorders and the diagnoses from driver injuries in real-life frontal impacts were analysed. Change of velocity and mean and peak acceleration were calculated from each recorded crash-pulse. The results and conclusions were that Δv, mean and peak accelerations influence the injury risk, where either high Δv, high mean or high peak acceleration may lead to severe injuries. Mean and peak accelerations together may explain the risk of injury in the studied impacts. When these parameters were combined, a limit could be drawn, above which there was an 89% risk of receiving a moderate or severe injury, while the risk was only 5.5% below that line. The different combinations of impact severity parameters shown in this study are helpful when crash pulses are created for crash tests and computer simulations.