Official crash data from North Carolina is examined for benefits of rear seat lap/shoulder belts and front seat lap/shoulder belts. Both appreciably reduce serious and fatal injury. However, rear seat lap belts reach their limit of benefit in crashes of the most severe 2-3% that occur on the highway. For lap/shoulder belts the limit appears to be higher. Lap belts reduce fatalities about 25% among wearers.
This report also comments on the report of the National Transportation Safety Board (NTSB), mainly in reference to NTSB's case selection procedure resulting in crash cases of such severe outcome that neither lap belts nor lap/shoulder belts can be very effective. Indeed, in the NTSB cases neither restraint system appeared very beneficial compared to no restraint.