| In China, pedestrians and bicyclists, as vulnerable road users, represent apopulation with high risk of fatal and severe injuries in mixed traffic environment. In2010, traffic accidents in China included16,281reported fatalities for pedestrians and4,616for cyclists based on police data. The total number of killed pedestrians andcyclists accounted for32%of all traffic fatalities. Thus, to reduce the fatality risk andinjury severity of pedestrians and bicyclists, it has great significance to quantitativelycompare the casualty risk between them and understand the injury mechanisms basedon the detailed accident data collected by in-depth accident investigation. Head injuryis one of the most popular injuries in pedestrian and bicyclist accidents, whichaccount28.1%and37.1%of total injuries, respectively. Therefore, it is crucial toconduct research on head injury pattern, injury mechanisms, and protectivetechnology for pedestrians and bicyclists in our country.The current study documented the pedestrian accident cases that happened from2007to2010and bicycle accident cases that happened from2001to2010inChangsha. Based on these accident data, the study of traffic injury epidemiology forpedestrian and bicyclist was conducted using descriptive statistics method. The studyshows that pedestrian and bicyclist accidents appear uneven distribution in space andtime, urban general road and fast road is the main road type and straight ordinaryintersection is the main location on the road for of pedestrian and bicyclist accidents.Traffic control services are inadequate in Changsha, and more than half of pedestrianand bicyclist accidents occur in the absence of traffic control measures. Most ofpedestrian and bicyclist accidents occurred in sunny day and little of them happenedin snow or drowny day. The number of pedestrian and bicyclist accidents happened inday time is more than that occurred in night. Passenger car is the main type of vehicleto cause pedestrian and bicyclist accidents, accounting for61%and54%of thevehicle, respectively. Fatality risk of bicyclists in traffic accidents is lower than thatof pedestrians. Head and leg of are the main injury bodies in accidents. Theprobability of male to female in traffic accidents is increased with injury severity,which reaches1.5:1in pedestrian fatal accidents and3:1in bicyclist fatal accidents.The elders over the age of60are easier to get fatal injuries than other age group, andthe age group of31-50years has a higher incidence of bicyclist accidents. Then, the relationship between vehicle speed and casualty risk of pedestrians andbicyclists was analyzed using371pedestrian accident cases and67bicyclist accidentcases that collected by in-depth accident investigation. The casualty risk models ofpedestrians and bicyclists were devised in terms of vehicle impact speed with logisticregression analysis method. The influence of urban road speed limit on casualties ofpedestrian and bicyclists under the urban road traffic environment in China wasstudied according to the above casualty risk models. The results shows that thefatality risk of both pedestrians and bicyclists has a significant relationship withvehicle impact speed. The fatality risk of bicyclists is little lower than that ofpedestrian. It has great significance of reducing pedestrians and bicyclists fatality riskto set a reasonable value for urban road speed limit. When urban road speed limitdecreased from60km/hto50km/h, AIS3+injury risk of pedestrians and bicyclistscan be reduce by2.9%and9.1%, respectively; while fatality risk of pedestrians andbicyclists can be reduce by25.5%and37.5%, respectivelyAfter that,21pedestrian accident cases and24bicyclist accident cases wereselected and reconstructed in MADYMO environment. Non-linear regression methodwas used to analyze the correlation between vehicle impact speed and dynamicparameters of pedestrians and bicyclists. The kinematics of pedestrians and bicyclistswas compared, and whether the adult pedestrian headform impactor test can be usedto evaluate the bicyclists’ head protective performance of vehicle was also discussed.Using nonlinear regression analysis to establish the vehicle collision speed andpedestrians and bicycle riders the relationship between the dynamic responseparameters, compared the pedestrians and bicycle riders with the dynamic response ofvehicle collision, discusses the pedestrian hammer impact test used to assess thefeasibility of the vehicle on the bicycle cyclist head protection performance.30reconstructed cases that head impact points were located on windscreen were selectedfor head injury reconstruction in order to investigate the head-brain injury mechanismof pedestrians and bicyclists in traffic accidents. The relationship of head-brain AIS2+and AIS3+injuries with injury parameters including coup pressure, contrecouppressure, von Mises stress and shear stress were analyzed and head-brain injury riskmodels were also derived. The results indicate that dynamic response and head impactconditions differ between pedestrians and cyclists in collisions with passenger cars.The area with a WAD of2000cm should be the main area for testing vehicleperformance for bicyclists’ head protection. Meanwhile, head impact velocity of34km/h and impact angle of46°is more reasonable for representing the biycclists’ head impact conditions in real-world accidents that involve collisions with passenger cars.80%of coup intracranial pressure peaks and70%of contrecoup intracranial pressurepeaks occurred in cerebral,83%of von Mises and shear stress occurred in brain stem.When coup/contrecooup pressure, von Mises and shear stress exceeds185kPa,-129kPa,19kPa and9kPa respectively, AIS2+head-brain injuries are likely tohappen with50%probability. When coup/contrecooup pressure, von Mises and shearstress exceeds239kPa,-167kPa,24kPa and12kPa respectively, AIS3+head-braininjuries are likely to happen with50%probability.At last, based on528passenger car-pedestrian accident cases collected throughin-depth accident investigation, the sample cars were classified according to theprofiles of longitudinal vertical plane. Pedestrian injury distribution, injury risk andhead impact condition were compared among different types of passenger cars. It isfound that pedestrian AIS3+injury risk in the collision with SUV and minivan ishigher than that impact with sedan. SUV caused a highest fatality risk to pedestrian,followed by minivan and sedan. For SUV-pedestrian collisions, pedestrian headimpact points located in the rear part of bonnet. The average value of head impactspeed and impact angle are34km/h and77°, respectively. For minivan-pedestriancollisions, windscreen and A pillar are the main parts for pedestrian head impact. Theaverage value of head impact speed and impact angle are34km/h and45°.In summary, based on real-world accident cases collected by in-depth accidentinvestigation, this paper quantitatively analyzed pedestrians and bicyclists casualtyrisk. The dynamic response of pedestrians and bicyclists in the collision withpassenger cars was compared. The head protection technology of head-brain injuryrisk was also investigated. The results can provide valuable background knowledgefor the improvement of the vehicle safety for vulnerable road users. |
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