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Accident data show that the head and the chest are the most frequently injured body regions in side impact fatal accidents. Curtain side air bag (CSA) and thorax side air bag (SAB) have been installed by manufacturers for the protection devices for these injuries. In this research, first we studied the recent side impact accident data in Japan and verified that the head and chest continued to be the most frequently injured body regions in fatal accidents. Second, we studied the occupant seating postures in vehicles on the roads, and found from the vehicle's side view that the head location of 56% of the drivers was in line or overlapped with the vehicle's B-pillar. This observation suggests that in side collisions head injuries may occur frequently due to contacts with the B-pillar. Third, we conducted a side impact test series for struck vehicles with and without CSA and SAB.

Accident data show that the injury risks to children seated in child restraint systems (CRSs) are higher in side collisions than any other type of collision. To investigate child injury in the CRS in a side impact, it is necessary to understand the occupant responses in car-to-car crash tests. In this research, a series of full car side impact tests based on the ECE R95 test procedure was conducted. In the vehicle's struck-side rear seat location, a Q3s three-year-old child dummy was seated in a forward facing (FF) CRS, and a CRABI six-month-old (6MO) infant dummy was seated in a rear facing (RF) CRS and also was placed in car-bed restraint. In the non-struck side rear seat location, the RF CRSs also were installed. In addition to testing the CRSs installed by a seatbelt, an ISOFIX FF CRS and an ISOFIX RF CRS were tested. For the evaluations, occupant kinematic behavior and injury measures were compared.

In the current Japanese and European side impact regulation, occupant protection is evaluated based on anthropomorphic test device (hereafter referred to as the more commonly used term “dummy”) measurements recorded in a stationary car impacted by a moving deformable barrier (MDB). In order to validate and improve the side impact test procedures of the regulation and the associated new car assessment program, it is necessary to compare the side impact test procedure with car-to-car side impact tests conducted in various conditions. In this research, a series of car-to-car side impact tests using a small sedan as the target vehicle was conducted as follows: (1) A striking car impacted against the stationary car at 50 km/h at an impact angle of 90 degrees. (2) A 1BOX vehicle impacted the stationary car at 50 km/h at an impact angle of 90 degrees. (3) Both cars were moving, and the striking car impacted the struck car at an impact angle of 90 degrees.

This paper summarizes a future side impact test procedure based on the Japanese presentation at the recent IHRA Side Impact WG meeting. Under current Japanese regulations, the MDB specifications and test procedures were determined based on a market study more than ten years ago. Thus, they may not reflect current automobile characteristics, the actual accident situation, and crash test results. In this study (1) the vehicle types, velocity of striking and struck vehicles, body injury regions, causes of injuries, etc., are reviewed with reference to the latest Japanese side impact accident data. The occupant percentages for the non-struck-side, rear seat and for female occupants as well as the injury levels were analyzed. (2) To determine the MDB specifications, based on data from passenger car models registered in 1998, the curb mass, geometry and stiffness were examined. (3) For factorial analysis, side impact tests were performed as for real accidents.

Current accident analysis shows that the head of the pedestrian impacts most frequently into or around the windscreen since cars in recent have a short hood. Therefore, the injury risks to the head in contact with various locations of the car including the windscreen and its frame were examined on the basis of headform impact tests. The HIC is high from contact with the cowl, lower windscreen frame or A pillar, and it is low with increasing distance from these structural elements. In the windscreen center, the HIC is less than 500. The headform impact test results were compared between earlier and current car models. The HICs in the bonnet top area are similar in either type car except for the car built especially for pedestrian safety. However, on the A pillar, the HICs are much greater for current cars. From child headform impact tests for the WAD of 1000 mm, the HIC of SUV is higher than cars, and the SUV with steel bull bar leads to high injury risk.

The relationship between car size and occupant injury is examined using traffic accident data from all over Japan. For head-on collisions, the occupant injury rate is formulated based on the approximation of occupant injury by delta-V. The effects on occupant injury of the sizes of the striking and struck vehicles, as well as the effects of seat belt use and vehicle velocity, are examined in head-on, side-impact and single-car collisions. As occupant injuries are also influenced by the other car or cars involved in a collision, the number and size distribution of vehicles is important. Sensitivity analysis shows that the effect of the number of lighter cars is greater in head-on collisions and that the effect of the number of heavier cars is greater in side-impact collisions, relative to the total number of fatalities.

In car-to-car collisions, vehicle properties such as mass, stiffness and structure have a large effect on the extent of injuries to the occupants These properties, especially vehicle mass, are examined using accident investigation data of the Ministry of Transport (MOT) in Japan.

The strength of the passenger compartment is crucial for occupant safety in severe car-to-car frontal offset collisions. Car-to-car crash tests including minicars were carried out, and a low end of crash force was observed in a final stage of impact for cars with large intrusion into the passenger compartment. From overload tests, the strength could be evaluated from collapsing the passenger compartment. Based on the test, the end of crash force as well as the maximum forces might be important criteria to determine the passenger compartment strength, which in turn could predict the large intrusion into the passenger compartment in car-to-car crashes. A 64 km/h ODB test was insufficient to evaluate the potential strength of the passenger compartment because the maximum forces could not be determined in this test.