The report found a rapid transition from seatbelts-only vehicles to front and side airbag systems as model years advanced within the sample of vehicles involved in 2007 personal injury protection (PIP) claims.

Among vehicles from model year 1990, 80 percent had seatbelts but no airbags, and 20 percent had front airbags. Among 1998 model year vehicles, all vehicles were equipped with airbags--89 percent had front airbags only and 11 percent also included side airbags. Among vehicles from model year 2007, 82 percent had front and side airbags.

The presence of front and side airbag systems was associated with less significant injuries and lower claim costs, the study found.

Claimants injured in vehicles with front and side airbags were less likely than those in vehicles with seatbelts only or seatbelts and front airbags only to have serious injuries, to receive hospital treatment, or to experience a period of disability or fatality, the report said.

As a result, airbag systems were associated with markedly lower injury claim costs. The average PIP payment for claims from vehicles with seatbelts but without airbags was $6,994, 32 percent higher than the $5,308 average for vehicles with front airbags and 57 percent higher than the $4,457 average for vehicle with both front and side airbags, IRC found.

Elizabeth Sprinkel, IRC senior vice president, said, "Motor vehicles are becoming safer, and these improvements are having a noticeable impact on the seriousness of injuries and the ultimate cost of auto injury claims.

"These favorable trends have helped offset some of the pressure caused by the accelerating cost of medical treatment for auto injuries," she concluded.

The report, "Vehicle Characteristics and Auto Injury Claims," is based on vehicles with valid vehicle identification numbers. VIN analysis was provided by the Insurance Institute for Highway Safety (IIHS).