In depth studies of vehicles and injuries were made following hospitalization of 142 persons who wore seat belts during crashes in or about the city of Sydney. Most of the studied crashes involved car to car collisions. Main hazards were found to be narrow unyielding parts of car interiors which could be reached by heads, chest, pelvises or limbs of seat belt wearers. Seat belts were often adjusted loosely, in a few cases they broke and in some cases they transmitted forces to chest or abdomen which resulted in severe to serious injuries. Several of these cases involved unrestrained rear seat occupants pushing seat backs on to front seat belt wearers to substantially increase the forces in the seat belts. Reduction of injuries would be expected from redesigning occupant compartments to reduce the presentation of narrow unyielding surfaces or edges to occupants. Application of thick, stiff padding is needed on surfaces within reach of occupants, and more distant or yielding window glass might be beneficial. Some occupants would be helped by more strongly attached seats, others by more reliably attached engine bonnets. Further study of the effects of recent measures dealing with seat belt adjustment and strength is recommended. (A) this report is the project report on impact 2, the title of the study.