According to the traffic accident data in Japan , the third largest number of fatalities is due to collision between car and cyclist. Head injuries are the most frequent cause of cyclist fatalities. Head injury risk depends on the stiffness of the head collision location of the vehicles. The collision location of a child’s head is different from that of an adult’s head in a traffic accident. Therefore, there is benefit of examining the injury mechanism of child cyclists for safety equipment.
In this study, a total of 400 cases of car-to-cyclist collision were simulated by varying car speed, bicycle speed and initial position of collision using child and adult human Finite Element (FE) models and the head injury mechanisms were analyzed by investigating the kinematics and the kinetics of child and adult cyclists. The THUMS Version 4 Ten Years Old (10YO) model was used for the child cyclist and the THUMS Version 4 American Mail 50%tile (AM50) model for the adult cyclist. The bicycle FE model of a city cycle was established bicycle. The occurrence risk of skull fracture and Diffuse Axonal Injury (DAI) was investigated in 10YO and AM50 cyclists. In 10YO, approximately 90 % of the head contact points were distributed on the car body and 10 % was distributed on the ground. In AM50, the head contact points on the ground accounted for approximately 30 %, 70 % were distributed on the car body.
It was found that the skull fracture and DAI occurrence were predicted in the 10YO when the head contacted the car hood in the car speed of 30 km/h or more. The impact velocity of the upper body was increased by contacting between the pelvis and the front edge of the car hood. As a result, head impact velocity and rotational velocity became high after the shoulder contacted the hood. In the AM50 whose pelvis rode on the hood, the upper body fell down toward the hood gradually. As a result, the skull fracture occurred when the head contacted the A-pillar in the car speed of 40 km/h or more, which was lower than that in the 10YO. In the case which bicyclists head contacted a ground after car collision, the skull fracture was predicted even in the car speed of 10km/h. The DAI occurrence was not predicted.