Theoretical Head Impact Velocity Research Articles

Dynamic tests of the protective and security barrier system probar

The purpose of this paper is to present a series of dynamic tests for testing the protective and security barrier of the PROBAR system, developed by STRIX Chomutov, a.s., according to the PAS 68:2013 standard. The goal of the tests was to assess how the obstacle resist impacts and whether it can absorb the energy exerted on it. Verification of the mechanical properties of the device was performed in two types of impact configurations. Emphasis was placed on the behaviour of both the obstacle and the vehicle during the impact and in the short time interval after the collision. In terms of criteria for evaluating the impact tests, it can be stated that Test 2 exceeded the Theoretical Head Impact Velocity (THIV) criterion by 20 km h−1, while Test 1 did not exceed the limit value. However, all values for other criteria (ASI, PHD, HIC, 3ms) were within the specified limits, and the safety barrier met the required criteria which allows to be certificated.

Finite Element Analysis and Investigation of Critical Impact Point of Steel Guardrails Affecting Safety and Structural Performance

After the guardrails are designed, the structural adequacy and safety criteria are determined by the relevant standards and full-scale crash tests. One of the widely used standards is European Norm 1317 (EN1317). Guardrail systems generally consist of rails and posts. The guardrails are more rigid around the posts, which are mounted on the ground or embedded in soil at certain intervals. Therefore, it is important for driver/passenger and roadside safety to determine the most critical point in terms of structural and safety performance and design according to the most unfavourable situation. With this motivation, in this study, the effect of different impact points on the structural and safety performance of the H1W4 guardrail was investigated by finite element (FE) analysis. For this purpose, first of all, the finite element models of the H1W4-A system were calibrated and validated with real crash test data. Then, with the help of the validated models, analyses were completed for different impact points as 0.5, 1.0, 1.5 and 2.0 meters with a half-meter difference for the standard 2-meter post spacing. In the light of the measured safety parameters such as Acceleration Severity Index (ASI), Theoretical Head Impact Velocity (THIV) and structural performance criteria such as working width (W) and exit angle (α), the critical impact point for the guardrail was determined. Contrary to what is generally known, crashing vehicles into flexible points (0.5 and 1.0 m) rather than impacting rigid points (1.5 and 2.0 m) creates a more negative situation in crash tests.

Experimental and Numerical Assessment of Supporting Road Signs Masts Family for Compliance with the Standard EN 12767.

The analysis aimed to assess the passive safety of supporting masts for road signs in accordance with EN 12767. Experimental tests were carried out based on the requirements of the standard for the smallest and the largest constructions within the product family. Numerical models of crash tests were prepared for whole product family using the Finite Element Method in the LS-Dyna environment. Based on the comparison of the experimental tests and the numerical calculations, the usefulness of the numerical model for estimating the actual value of the Acceleration Severity Index (ASI) and the Theoretical Head Impact Velocity (THIV) was assessed. With the use of these relationships the values of ASI and THIV for masts not tested experimentally were estimated. It was confirmed that the analyzed masts met the requirements for the passive safety of structures set out in the standard EN 12767. It was possible since as a result of the impact, the mast column detached from the base, allowing the vehicle to continue moving. The behavior of the masts was primarily influenced by the destruction of the safety connectors. The paper presents the most important elements from the point of view of designing such solutions.

Assessment of the Effectiveness of Different Safety Measures at Tunnel Lay-Bys and Portals to Protect Occupants in Passenger Cars

Tunnel portals and tunnel lay-bys are hazardous spots for road users. Different infrastructure safety measures are in use, but the protection level is not known. In this study the following safety measures for reducing the injury risk are investigated: angular positioned 4 m and 8 m concrete barrier, crash cushion Alpina F1-50 and Alpina <prototype> crash cushion. A passenger car equipped with a data acquisition unit is accelerated to 100 km/h and impacts the safety measure. The assessment of the latter is based on the EN 1317 criteria, specifically the Acceleration Severity Index (ASI), Theoretical Head Impact Velocity (THIV). Further assessment criteria are related to intrusions into the passenger compartment and post-crash motion. The best result in terms of ASI and THIV was achieved by the 8 m (ASI: 1.6, THIV: 30 km/h) concrete barrier. The crash cushion Alpina <prototype> showed good results for the ASI (1.8) but the THIV (57 km/h) was less satisfactory, while the angular positioned 4 m concrete barrier (ASI: 2.9, THIV: 53 km/h) and the crash cushion Alpina F1-50 (ASI: 3.3, THIV: 74 km/h) performed worst. Even though some of the measures showed good results, no protection measure tested currently complies with all the assessment criteria used.

Numerical Simulation of Vehicle-Lighting Pole Crash Tests: Parametric Study of Factors Influencing Predicted Occupant Safety Levels.

In this paper, numerical simulations of the EN 12767 test procedure for a vehicle–lighting pole crash are presented. A representative soil–vehicle–lighting pole model is first developed. The Geo Metro vehicle model is used, and significant attention is given to representing the soil and its interaction with the traffic pole. Soil is represented using smoothed particle hydrodynamics (SPH) coupled with finite elements (FEs). A parametric study is carried out to investigate the key factors influencing the outcomes and consequently the estimation of the occupant safety levels during crash scenario described in EN 12767. First, a sensitivity study of lighting pole mesh is conducted As a result, the optimal mesh size is used for further studies regarding physical parameters such as soil properties and friction coefficient in vehicle–pole interfaces. Friction and mesh size are found to have a considerable influence on the acceleration severity index (ASI), theoretical head impact velocity (THIV), post-impact velocity and vehicle behavior during the lighting pole crash scenario.

Determination of ASI and THIV parameters based on the results of experimental and numerical research in relation to EU standards

Determining the values of ASI (Acceleration Severity Index) and THIV (Theoretical Head Impact Velocity) parameters during tests allows you to assign an appropriate class for a given type of object to determine the safety level and to give the CE marking. The paper presents the methodology for determining these parameters based on the EN 1317-1 and EN 12767 standards. The paper also presents a tool created with the use of the Python programming language, which, based on the results of experimental tests or the results of numerical calculations, allows to determine the ASI and THIV values. The values of key parameters from the point of view of normative tests were calculated based on the results of experimental tests of the road sign supporting mast and numerical analysis carried out for the same case using the Finite Element Method and LS-Dyna software, following the EN 12767 standard.

Numerical investigation of occupant injury risks in car-to-end terminal crashes using dummy-based injury criteria and vehicle-based crash severity metrics

Guardrails were designed to deter vehicle access to off-road areas and consequently prevent hitting rigid fixed objects alongside the road (e.g. trees, utility poles, traffic barriers, etc.). However, guardrails cause 10 % of deaths in vehicle-to-fixed-object crashes, which recently attracted attention in the highway safety community on the vehicle-based injury criteria used in regulations. The objectives of this study were to investigate both full-body and body-region driver injury probabilities using finite element (FE) simulations, to quantify the influence of pre-impact conditions on injury probabilities, and to analyze the relationship between the vehicle-based crash severity metrics currently used in regulations and the injury probabilities assessed using dummy-based injury criteria.A total of 20 FE impact simulations between a car (Toyota Yaris) with a Hybrid III M50 dummy model in the driver seat and an end terminal model (ET-Plus) were performed in various configurations (e.g. pre-impact velocities, offsets, and angles). The driver’s risk of serious injuries (AIS 3+) was estimated based on kinematic and kinetic responses of the dummy during the crashes. A non-linear regression approach was used to compare the injury probabilities assessed in this study to the vehicle-based crash severity metrics used in the testing regulations. In particular, the US Manual for Assessing Safety Hardware (MASH) guideline and European procedures (EN1317) were used for the study.All the recorded dummy-based injury criteria values pass the Federal Motor Vehicle Safety Standard (FMVSS) 208 limits which indicated a low driver risk of serious injury. Overall, the pre-impact vehicle velocity showed to have the highest influence in almost all injury probabilities (59 %, 79 %, 62 %, and 44 % in full-body, head, neck, and chest injuries, respectively). The offset between vehicle midline and the guardrail barrier was the most important variable for thigh injuries (56 %). The assessed injury probabilities were compared to vehicle-based severity metrics. The full-body and chest injuries showed the highest correlation with Occupant Impact Velocity (OIV), Acceleration Severity Index (ASI), and Theoretical Head Impact Velocity (THIV) (R2 > 0.6). Lower correlations of thigh injuries were recorded to OIV (R2 = 0.59) and THIV (R2 = 0.46). Meanwhile, weak correlations were observed between all the other regressions which indicated that no vehicle-based criteria could be used to predict head and neck injuries.Car-to-end terminal crash FE simulations involving a dummy model were performed for the first time in this study. The results pointed out the limitations of the standard vehicle-based injury methods in terms of head and neck injury prediction. The dummy-based injury assessment methodology presented in this study could supplement the crash tests for various impact conditions. In addition, the models could be used to design new advanced guardrail end terminals.

Limitations of the European barrier crash testing regulation relating to occupant safety

The safety of roadside restraint systems in Europe is ensured by the EN 1317 regulation. The ability of the barrier to mitigate injury to the occupants of vehicles is tested according to two occupant injury metrics: Acceleration Severity Index (ASI) and Theoretical Head Impact Velocity (THIV). Both metrics aim to predict occupant head injury from vehicle kinematics, despite the potential to easily measure actual head kinematics from instrumented Anthropomorphic Test Dummies, a non-instrumented version of which is already required according to the regulation. Retrospective data provided by AISICO S.r.l. for 33 certificated barrier tests, where acceleration of the dummy’s head had also been recorded, were re-analysed. ASI and THIV were compared with Head Injury Criterion (HIC15) and Neck injury Criterion (Nij), as well as corresponding Real Head Impact Velocity (RHIV) values. Three barriers presented HIC15 values above the threshold used in crashworthiness testing, two of which corresponded to fatal injury according to the Abbreviated Injury Scale. One barrier presented an Nij value corresponding to a 30% risk of neck injury. RHIV values were above the regulation threshold in 15% of tests, but were not significantly different from the corresponding THIV values. It was concluded that vehicle kinematics do not accurately predict head kinematics during barrier testing. The presented data indicate the current EN 1317 regulation was not capable of detecting all potential dangerous outcomes, with the potential to underestimate occupant risk. Further investigation is necessary to devise suitable indices based on actual head and neck data. These data would be obtained from a dummy instrumented with both a head accelerometer and neck load cell and, possibly, a gyroscope. To consistently test the true worst-case scenario, the tested side window should be closed and non-reinforced.

Correlation of Occupant Evaluation Index on Vehicle-occupant-guardrail Impact System

Aiming at the occupant safety risk assessment of vehicle guardrail impact, a finite element model of vehicle-occupant-guardrail impact system was established and the validation of the model was verified based on the test result. Different impact speed such as 60 km/h, 80 km/h, 100 km/h, 120 km/h and different impact angle such as 25°, 30°, 35°were selected and combined to conduct 12 groups of vehicle guardrail impact simulation test by Hyper Mesh and LS-DYNA. The Acceleration Severity Index (ASI), Theoretical Head Impact Velocity (THIV), Post-impact Head Deceleration (PHD) and Head Injury Criterion (HIC) were analyzed by obtaining the longitudinal, transverse and vertical acceleration data of vehicle centroid and occupant head in the impact process. Quantitative corresponding relations between other occupant risk assessment index and Head Injury Criterion (HIC) was analyzed by SPSS, and the results showed that ASI and HIC had good correlation. Fitting degree between ASI and HIC is 0.93 with the exponential function. The study results of occupant would have guiding significance for related standards’ development and revision of related standard, experimental study and product development.

A risk-based methodology to assess run-off-road crashes on austrian motorways – The Riskant Project

Run-off-road (ROR) crashes are extremely severe road accidents that often result in serious injuries or fatalities. On Austrian motorways, about 40% of all injury accidents are ROR crashes, which account for more than 60% of the fatalities on the primary road network. This is one of the reasons why the Austrian highway operator (ASFINAG) postulates in its road safety program till 2020 that new safety strategies and new road safety measures have to be developed to prevent vehicles from running off the road and (in a worst case scenario) collide with stationary obstacles on the roadside. RISKANT is a research project funded within the 2011 Call “Transportation Infrastructure Research (VIF)” of the Austrian Research Promotion Agency (FFG) in conjunction with ASFINAG. The main objective of RISKANT was to develop a risk model for crashes with stationary obstacles along the roadside. In order to achieve this goal, a so-called accident prediction model was used to estimate the probabilities of ROR crashes due to the characteristics of the road and the road environment. Furthermore, Finite element simulation studies were conducted to incorporate the severity of injuries due to collisions with different stationary obstacles. Two indices, the Acceleration Severity Index (ASI) and Theoretical Head Impact Velocity (THIV) were used to evaluate the injury risk level for vehicle occupants.

LS-DYNA 프로그램을 이용한 차량과 가드레일의 충돌해석에 관한 연구

A study is to research crash barriers for vehicles that prevent road breakaway of vehicles and protect car passengers and pedestrians as absorbing impulse. Protection performance tests on vehicle passengers were simulated by using a LS-DYNA program. Through repetitive simulation on various speed and angles, passenger protection performance according to different impact condition was contemplated. Variable setting for the simulation was calculated as the mean weight of domestic car sales. By analyzing NASS (National Automotive Sampling System) of NHTSA (National Highway Traffic Safety Administration) of the U.S., the actual speed and collision angle section of accidents were computed. As a result, we confirmed that THIV (Theoretical Head Impact Velocity) and PHD (Post-impact Head Deceleration) are increased according to the impact speed and angle. Also, when the vehicle hit the guardrail post, we could be confirmed that the passenger protection performance greatly decreased.

Strategy to increase the speed of a small car impact to a semi-rigid barrier designed for high impact severity

ABSTRACTFor a safety barrier to accommodate both small and large vehicle impacts, it should be designed structurally strong to contain large vehicles and flexible to ensure small vehicles’ occupant safety. A semi-rigid barrier was first designed to resist a high impact severity of 272 kJ (13-ton bus – 90 km/h – 15°) and then was modified to ensure the occupant safety of a small car impact of 0.9 tons – 120 km/h – 20° by performing extensive finite element analyses (FEAs). The vehicle relative velocity–time history gradients should have a bi-linear pattern to meet the occupant safety requirements of a strength-designed semi-rigid barrier, other than geometric considerations used to avoid possible snagging. The lateral velocity gradient should increase steeply at the initial stage of impact and decrease moderately around the time when a flying occupant's head is supposed to hit the imaginary frontal or side wall (time of theoretical head impact velocity). The final design was verified through full-scale vehicle crash tests. Furthermore, FEA and a full-scale vehicle crash test revealed that the designed semi-rigid barrier should ensure the occupant's safety at a 0.9 tons – 130 km/h – 20° impact.

How to Protect the Tunnel SOS Niche Wall in the Event of Vehicle Impact

An increase in the number of traffic accidents in tunnel emergency stop areas has been recored in the last two years in many countries with long road tunnels. In most cases, the collisions of passenger cars into the emergency stop area walls were fatal, which presents an even bigger obligation for the road management authorities to find a solution to the problem. Even though the tunnel emergency stop areas tunnels are designed and built according to the valid legislation, it has turned out that the current implementation of the emergency stop area wall in the driving direction presents a serious potential traffic safety risk.With the purpose of determining the most suitable method of protecting the SOS tunnel niche wall in the event of vehicle impacts, comparative numerical analysis of vehicle impacts has been performed in accordance with the SIS – EN 1317 standard. For the emergency-stop-area wall-impact protection, two different designs were considered: the H2 safety railing and the crash cushion composed of eight cylindrical steel sheet tubes. The tube diameter is 500mm and the sheet thickness is 3mm. Both designs were subject to collision simulations in accordance with EN 1317 parts 1 and 2 (EN 1317-1 – -4). As the safety of passenger cars was being studied, the tests TB 11 (vehicle mass 900kg and vehicle velocity 100km/h) and TB 21 (vehicle mass 1300kg and vehicle velocity 80km/h were simulated with a finite-element-model-based explicit dynamic analysis. The kinematic values of the vehicles just prior to the collision were determined by simulating the driving dynamics several seconds before the collision in PC-Crash. Based on the FEM analysis results in LS-Dyna for each crash scenario, a comparative analysis of the two protection systems was performed in order to determine their efficiency and suitability for installation in the existing tunnel emergency stop areas.Based on comparative analyses of the values of the Acceleration Severity Index (ASI), Theoretical Head Impact Velocity (THIV) and values of the Post-Impact Head Deceleration (PHD), the crash cushion provides the best results for the events of impacts of TB 11 vehicles and TB 21 vehicles into an SOS tunnel niche.

Estimation of THIV for Car Crash against Attachable Roadside Barriers Made of the High Strength Steel

A finite element simulation study was performed to gain the theoretical head impact velocity about the crash test details. Accuracy of the simulation was verified using qualitative and quantitative comparisons. Based on in-depth examination of crash simulation recordings, energy distributions occurred in the barrier against the car are determined. In this paper, the existing finite element crash analysis of barriers using the LS-DYNA program is further extended to study the dynamic response of the barrier with module structures connected by anchor bolt inserted through concrete bridge decks. The numerical results for various parameters are verified by comparing different models with or without the high strength steel such as HS800.

Comparative study of European tunnel emergency-stop-area-wall protection measures

Due to the increasing number of traffic accidents involving the collisions of vehicles with the emergency-stop-area head walls in tunnels, a comparative numerical analysis in accordance with the EN 1317 standard has been performed in order to assess the quality of the available protective safety barriers. Based on the simulation results, the values of the relevant injury criteria – the acceleration severity index (ASI), the theoretical head impact velocity (THIV) and the post-impact head deceleration (PHD) – were computed for several collision scenarios involving two different passenger vehicles colliding with two different safety barriers in various ways. The results show that due to the geometrical restrictions in the tunnel's emergency stop area none of the barriers can provide total protection for the occupants of the vehicle in the event of a collision. The installation of a steel-sheet-tube crash cushion was, however, found to provide the best possible protection within the given limitations. The results of the analysis were the basis for selecting a safety-barrier design for existing tunnel installations and for the proposed changes in regulations governing the geometry of the tunnel's emergency stop area.

Multibody modelling of a TB31 and a TB32 crash test with vertical portable concrete barriers: Model verification and sensitivity analysis

In this article the multibody simulation software package MADYMO for analysing and optimizing occupant safety design was used to model crash tests for Normal Containment barriers in accordance with EN 1317. The verification process was carried out by simulating a TB31 and a TB32 crash test performed on vertical portable concrete barriers and by comparing the numerical results to those obtained experimentally. The same modelling approach was applied to both tests to evaluate the predictive capacity of the modelling at two different impact speeds. A sensitivity analysis of the vehicle stiffness was also carried out. The capacity to predict all of the principal EN1317 criteria was assessed for the first time: the acceleration severity index, the theoretical head impact velocity, the barrier working width and the vehicle exit box. Results showed a maximum error of 6% for the acceleration severity index and 21% for theoretical head impact velocity for the numerical simulation in comparison to the recorded data. The exit box position was predicted with a maximum error of 4°. For the working width, a large percentage difference was observed for test TB31 due to the small absolute value of the barrier deflection but the results were well within the limit value from the standard for both tests. The sensitivity analysis showed the robustness of the modelling with respect to contact stiffness increase of ±20% and ±40%. This is the first multibody model of portable concrete barriers that can reproduce not only the acceleration severity index but all the test criteria of EN 1317 and is therefore a valuable tool for new product development and for injury biomechanics research.

Investigation of Occupant Fatalities and Injuries During the Impact of Vehicle and Road Safety Barrier

The main purpose of any road restraint system is saving human life and minimizing injuries. The efficiency of road restraint system is its capability to hold vehicle on the road, to decrease occupant injuries and damage to the impacted objects. The road restraint systems currently used in Lithuania meet the European Standard EN 1317. Acceleration Severity Index (ASI) and Theoretical Head Impact Velocity (THIV) are derivative values used in this standard mainly to describe simulation of vehicle and safety barrier impact situations and to study vehicle crash dynamics. This paper presents simulation of different situations of vehicle and road restraint system crash. Computer impact simulation analysis was performed as well as comparable investigation of conventional injury criterions Head Impact Criteria (HIC) and those used in the European Standard EN 1317.

The relationship of injury risk to accident severity in impacts with roadside barriers

Roadside barriers are homologated in Europe to EN1317, which includes tests for containment (resistance to penetration by an impacting vehicle), and accident severity, measured by acceleration severity index (ASI) and theoretical head impact velocity (THIV). Barriers are classed according to ASI measurement. There has been debate as to whether class C barriers (ASI 1.5 to 1.9) should be considered acceptable from an injury risk point of view, but the debate has been hampered by lack of quantitative correlation between accident severity level and injury risk. This study presents data from three physical crash tests and 50 computer simulations. A small car equipped with crash dummy was impacted into a barrier at a range of speeds and angles, and with variations to the vehicle conditions and occupant positions. Measurements from the crash dummy in the tests and simulations were compared with published injury limits derived from volunteer and cadaver tests and plotted against ASI and THIV. Results showed that, although ASI did show a correlation with injury risk, the level chosen for the boundary between class B and C barriers in EN1317 does not provide significant discrimination between higher and lower risk of injury. However, the EN1317 limit for THIV, which applies to all barrier classes, was found to be a reliable discriminator between acceptable and unacceptable injury risk.