1.What happens in a vehicle accident if you are not wearing a seat belt?

Fig.1 Speed and Above-Ground Height
  Let's say a car runs into a wall at 50 km/h. A collision at 50 km/h would be the same as a fall from approximately 10 m (the top of a 3-storey building) onto a concrete surface.
  Although the human body can only absorb a slight amount of energy, the vehicle body is large enough to deform and absorb energy; compared with the sudden impact of the human body against concrete, the vehicle would come to a gradual stop as its body cushions the impact. And, the seat belt stops as much movement of the occupant as possible by moving in sync with the vehicle. Even so, the impact will be huge and the human body can expect to receive at least a 1-ton force. You can imagine what would happen if we did not have seat belts.
2.How does the use or non-use of seat belts affect the number of casualties?
  First, let's look at the changes in the number of casualties (fatalities + serious injuries + slight injuries) of vehicle occupants during the 20-year period from 1981 to 2001.

Fig.2 Changes in Number of Vehicle Occupant Casualties by Seat Belt Use Fig.3 Changes in Number of Vehicle Occupant Fatalities by Seat Belt Use
  Figure 2 shows the total number of casualties by seat belt use. The rise in the number of casualties is significant and a large percentage of them are occupants who used seat belts. The number of casualties shows a dramatic rise from 1986 to 1987, following the proliferation of mandatory use of seat belts on public roads.
  Figure 3 shows the changes in the number of fatalities. Overall, the number of fatalities has been declining since 1993. While the use of seat belts increased during the same period, the number of fatalities of occupants who did not use seat belts conversely shows a sharp decline.
  This can be attributed to the increase in the percentage of occupants who used seat belts--proof of which is offered by Figure 2. Tragedy can strike even when seat belts are used. However, more and more people are wearing seat belts and the total number of fatalities is significantly dropping.
  Figure 4 shows changes in the fatality rate of vehicle occupants by seat belt use, with the fatality rate expressed as the component ratio of fatalities contained in the number of casualties.

  The fatality rate varies from year to year, but since 1993 it has been practically constant for both the number of occupants wearing seat belts and that of occupants not wearing seat belts. The period since 1993 shows that, among occupants wearing seat belts, there are 2 - 3 fatalities for every 1,000 people injured. Nevertheless, tragic results occurred in collisions that were large enough to severely deform the vehicle body, even though the occupants were wearing seat belts. On the other hand, among occupants not wearing seat belts, there are 21 - 24 fatalities for every 1,000 people injured. Since this is almost 10 times the fatality rate of occupants wearing seat belts, it is evident that the non-use of seat belts is very dangerous. From this we can conclude that if the vehicle occupants not wearing seat belts were to use them, the number of fatalities would drop significantly, even if these people would still incur some degree of injury.

Fig.4 Changes in Fatality Rates by Seat Belt Use of Vehicle Occupants
4.What kind of person does not use seat belts?
  Figure 5 shows, by seating position, the component ratio of vehicle occupants who wear seat belts. The percentage of drivers who wear seat belts, including uninjured drivers, is 94.3%. Even in cases resulting in casualties, 90.4% of drivers use seat belts. However, 79.8% of front seat passengers and only 26.5% of rear seat passengers wear seat belts; in other words, only one in four rear seat passengers uses a seat belt. If we look at occupants who die in accidents, we see that less than 50% use seat belts, regardless of their seating positions, which underscores the likelihood of a fatal accident occurring to occupants who do not wear seat belts.
  It is therefore important that we put our voices together and encourage the use of seat belts not only among drivers but among front seat and rear seat passengers also.

Fig.5 Seat Belt Use Rate of Four-Wheeler Occupants by Seating Position (3-Year Total from 1999 to 2001)
  Figure 6 shows, by time of day, the seat belt use rate of vehicle occupants including uninjured occupants. Seat belt use is ten points lower during the night than during the day, especially late at night. Use seat belts to protect yourselves.

Fig.6 Seat Belt Use Rate of Four-Wheeler Drivers (Including Uninjured Drivers) by Time of Day (3-Year Total from 1999 to 2001)
  The seat belt use rate among young people is low (Figure 7), particularly among the 24-and-under group. Let's hope that this group of young people, who have only recently received driver's licenses, remember what they learned at driver training school and always wear their seat belts.

Fig.7 Seat Belt Use Rate of Four-Wheeler Drivers (Including Uninjured Drivers) by Age Group (3-Year Total from 1999 to 2001)
UP
Institute for Traffic Accident Research and Data Analysis (ITARDA)