Availability of the seat belt defense: Implications for auto liability insurance

A “seat belt defense” allows a defendant in a third-party auto liability event to present evidence of seat belt nonuse to reduce a plaintiff's recovery. When successfully applied, the defense has a direct effect on reducing liability payouts by insurers for accidents. Our analysis reveals that seat belt defense laws are associated with a 10% reduction in auto claims costs, which equates to a reduction in loss costs of approximately $14 per insured vehicle. We find little evidence that the defense reduces accident frequency and no evidence that the defense affects seat belt usage. The lack of a deterrent effect on driving behavior suggests that the availability of the defense is not salient to drivers. The reduction in loss costs supports the notion that defense lawyers are aware of the defense and make use of it. The resulting effect of lowering insurance payouts may alleviate increasing auto insurance costs.