How would increasing seat belt use affect the number of killed or seriously injured light vehicle occupants?

The expected effects of increasing seat belt use on the number of killed or seriously injured (KSI) light vehicle occupants have been estimated for three scenarios of increased seat belt use in Norway, taking into account current seat belt use, the effects of seat belts and differences in crash risk between belted and unbelted drivers. The effects of seat belts on fatality and injury risk were investigated in a meta-analysis that is based on 24 studies from 2000 or later. The results indicate that seat belts reduce both fatal and non-fatal injuries by 60% among front seat occupants and by 44% among rear seat occupants. Both results are statistically significant. Seat belt use among rear seat occupants was additionally found to about halve fatality risk among belted front seat occupants in a meta-analysis that is based on six studies. Based on an analysis of seat belt wearing rates among crash involved and non-crash involved drivers in Norway it is estimated that unbelted drivers have 8.3 times the fatal crash risk and 5.2 times the serious injury crash risk of belted drivers. The large differences in crash risk are likely to be due to other risk factors that are common among unbelted drivers such as drunk driving and speeding. Without taking into account differences in crash risk between belted and unbelted drivers, the estimated effects of increasing seat belt use are likely to be biased. When differences in crash risk are taken into account, it is estimated that the annual numbers of KSI front seat occupants in light vehicles in Norway could be reduced by 11.3% if all vehicles had seat belt reminders (assumed seat belt wearing rate 98.9%), by 17.5% if all light vehicles had seat belt interlocks (assumed seat belt wearing rate 99.7%) and by 19.9% if all front seat occupants of light vehicles were belted. Currently 96.6% of all (non-crash involved) front seat occupants are belted. The effect on KSI per percentage increase of seat belt use increases with increasing initial levels of seat belt use. Had all rear seat occupants been belted, the number of KSI front seat occupants could additionally be reduced by about 0.6%. The reduction of the number of KSI rear seat occupants would be about the same in terms of numbers of prevented KSI.