Studies of the effectiveness of safety belts were carried out under various directions of crashes, including dynamic sled investigations, destructive barrier tests, and impact tests. The studies showed that three-point belts were effective in frontal impact from 0-30 deg, but that their effectiveness diminished after 45 deg because the belt slips off the chest. The three-point belt did not provide protection for the knees. The studies also pointed out that the anchorage system of the belt is a very important factor in its effectiveness.