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. The tests were conducted based on the specifications of Regulation ECE/R95 except for the dummy seating position. The dummy seat positions were adjusted such that the dummy head overlapped the B-pillar. The test vehicles were small passenger vehicles and K-cars which are popular in Japan. The K-car is categorized in Japan as a very small size vehicle. It was demonstrated that the CSA and SAB were effective for reducing the number of head and chest injuries in car-to-car crashes. But it was also demonstrated that the effectiveness of CSA and SAB were dependent on the designs.