Pedestrian Fatality Risk And Prediction Of Specific Head Injuries In Traffic Accidents

Road traffic accident is gradually developing into a major cause of injury or death with the rapid development of automobile industry.Pedestrians,as the most vulnerable road users,have high casualty rates in accidents,and traumatic brain injury is the main cause of pedestrian deaths.Researchs for injury risk of pedestrians contribute to develop pedestrian safety regulations and design automobile.Foreign studies for pedestrian injury risk is comprehensive,but the results cannot be directly applied to pedestrian safety protection in our country due to differences in race,vehicle type,road conditions,and the relatively backward medical level.Meanwhile,Researchs for pedestrian injury risk is less in China.China is a large country lead to large differences of pedestrian accident data between different regions.Researchs in single area cannot meet the needs of assessment for pedestrian injury risk.On the other hand,due to the limitation of various experimental conditions and the complexity of human head,the mechanics analysis model combined with real cases is a better approache for study of head injuries.However,most researchers abroad focus on the head injuries sustaind by football players,which usually is slight and concussion injury due to protection of the helmet.pedestrians who suffered head injuries type is more and more serious.Given lacks of assessment data for pedestrian injury risk,and shortages of the prediction methods of head injuries at present.The team of author carried on an in-depth investigation on pedestrian accidents in Chongqing.Weight procedures were applied to the sample regarding the distribution of pedestrian injury severity in Chongqing and national police data,and analyzing the main factors affecting pedestrian injury,and evaluate the pedestrian injury risk;Screening with video data and the typical cases of head injury results in detail,using multi-rigid-body dynamics software for precise accident reconstruction,obtaining the pedestrian head moments before contact with the vehicle windshield in center of mass of each direction linear velocity and angular velocity and the head rotation Angle position,to obtain the initial conditions of loading as THUMS head finite element model for the reconstruction of the process of head injuries,the use of regression analysis it is concluded that the head of different damage types,the optimal prediction parameters and the risk of injury.For pedestrian injury protection,vehicle safety design,and to provide theoretical basis for the diagnosis and treatment of head injuries.The main studying methods and results are as follows:(1)The in-depth investigation and analysis for pedestrian accidentsVehicle-pedestrian accident data is important to the study,comprehensive and accurate collection are helpful to the next step studies.We conducted in-depth investigation for pedestrian traffic accidents by using the traditional method combining with several new accident data collection technologies developed by our team in early.The collected data included vehiculary,personal and environmental factors.A total of 518 pedestrian crashes were collected between 2010 and 2016.Descriptive statistics analyses were performed for 443 pedestrian crashes with relative complete information: the accident involving car and pedestrian has the highest proportion,reached 48.5%.Car is still the most common vehicle type in pedestrian traffic accidents;The production date of accident vehicles mainly concentrated in the year 2009 to 2015.Combined with the the timing of the accident,it showed new vehicles has a higher proportion;56.9% of crashes were happened in the velocity section between 41-80 km/h,and it showed higher travel speeds were easier to cause the pedestrian traffic accidents;the proporetions of pedestrians whose head hit the engine cover and front windshield were 43.8% and 41.5%,respectively.It shows that engine cover and front windshield were the main collison parts of pedestrian head,and improve the structure and the stiffness of the parts help reduce pedestrian head injuries;Pedestrians in the accident in the running state of the proportion accounted for 53.7%,that pedestrians running conditions are more likely to happen traffic accident;The pedestrian crossing a road accident proportion is as high as 90.7%,but in the pedestrian accident rate is only 7%,explains not the crosswalk when pedestrians crossing the road is one of the main causes of accidents;The highest percentage of pedestrian head injuries,69.3%;Compared with other vehicle types,cars and suvs hit when pedestrians are more likely to result in head injuries.(2)The analysis of factors influencing injury severity of pedestriansVehicle and pedestrian accident,there are many factors may affect the severity of the pedestrian injury,to understand what factors are more significant effect on pedestrian injuries,helps the pedestrian injury protection.From the early stage of the acquisition of pedestrian traffic accident cases,choose a video data of 111 cases of typical cases and the accident,this paper analyzes the factors which may affect the damage result.Results show that the collision speed,pedestrians,age,and the head in the vehicle collision parts are the main factors affecting pedestrian head injury severity and death;And pedestrian skull fracture in addition to under the influence of impact velocity and the head impact point,the vehicle type is also the main influence factors of SUV hit a pedestrian causes the highest percentage of skull fracture,van lead to lowest skull fracture,accounted for 68% of the group and 34%,respectively,the pedestrian age although no statistical differences with the skull fracture,but we found that the proportion of young skull fracture(28%)was lower than that in group of middle-aged(52%)and elderly group(56%).(3)Evaluation of pedestrian fatality risk based on weighting dataDue to collect the data sample is not representative,as a result,according to the pedestrian accident mortality and incidence light injuries of chongqing region pedestrian accidents of selection of weighted samples,and compared two kinds of weighting methods of analysis results,a total of 161 cases with video data of pedestrian traffic accident was used to carry out logistic regression analysis.Based on the weighted samples acquired from national pedestrian accident data analysis,the risk of pedestrian deaths reached 10%,50% and 90%,of the vehicle collision speed of 42 km/h,respectively 64 km/h and 86 km/h.Based on weighted samples acquired from chongqing region pedestrian accident data analysis,the risk of pedestrian deaths reached 10%,50% and 90%,the impact velocity of the vehicle respectively 48 km/h and 67 km/h and 86 km/h.Results showed that the risk of pedestrian deaths with increased with increasing impact velocity,at the same time,when the impact velocity more than 40 km/h,risk of pedestrian deaths began rising sharply;By comparing with foreign research results,based on the pedestrian light incidence of injuries to hierarchical weighted samples can get more accurate risk of pedestrian deaths.(4)Pedestrian accident reconstruction based on multiple rigid body mechanicsPedestrian accident reconstruction is the foundation of subsequent head injuries reconstruction,thus improve the accuracy of accident reconstruction is helpful to subsequent head injuries prediction research,this article is based on multi-rigid-body dynamics method for pedestrian accident reconstruction were studied,and according to the typical pedestrian accident cases of accident reconstruction method is introduced in detail.Accident reconstruction,the collision of the vehicle speed,speed,pedestrian movement speed reduction are calculated accurately through the video,pedestrians before the collision posture according to vehicles and pedestrians in the video contact the previous frame adjustment,accident reconstruction of dynamic response process compared with the process of real accident,one more matches on several key moments,show the pedestrian accident reconstruction method in this paper has a certain accuracy.In addition,through experiment and comparison,the pedestrian height has a large influence on dynamic response;Pedestrians weight,speed and vehicle deceleration impact head angular velocity,have less effect on the linear acceleration,speed;Pedestrians before the collision posture affects deflection direction after the pedestrian was hit,resulting in differences between pedestrian head and contact parts of the vehicle.Tip in pedestrian accident reconstruction,the above several factors should be considered as a reconstruction of the initial conditions.(5)Prediction of different head injury typesLaminated glass is set up the finite element model of vehicle windscreen response characteristics,and based on real cases rupture range of the windshield and model to validate the model,the results show that the established model can better simulate the real circumstances forced deformation of the windshield.Screening have video data and detailed head injuries at the same time the diagnosis of 29 cases,and the selected case of accident reconstruction,accident reconstruction for the boundary conditions loading to as THUMS head head injuries reconstruction based on the finite element model,and the damage reconstruction results are binomial logistic regression analysis,finally it is concluded that the head and mechanical parameters of different damage types.Results show that the maximum negative pressure cerebrospinal fluid can better predict a subdural hematoma,when the biggest pressure is 271 kpa cerebrospinal fluid,head 50% of a subdural hematoma may occur;The most dazheng cerebrospinal fluid pressure prediction of subarachnoid hemorrhage effect is good,when the most dazheng cerebrospinal fluid pressure is 208 kpa,head 50% of subarachnoid hemorrhage may occur;The maximum shear strain of 0.38 in the brain,the head of diffuse axonal injury risk of about 50%;Equivalent stress is forecasting brain contusion better indicators,when the equivalent stress of the brain is 29 kpa,50% of the brain contusion may occur;The effect of the skull fracture of skull internal energy was good,when the skull internal energy reaches 1096 mJ,skull 50% of fracture may occur.