Despite the widespread availability of airbags and a belt use rate of over 85%, U.S. drivers involved in crashes continue to be at risk of serious thoracic injury. One hypothesis is that this risk may be due to the lack of airbag deployment or the airbag ‘bottoming-out’ in some cases. The objective of this study is to determine the incidence and thoracic injury risk of direct steering wheel contact due to airbag “bottoming-out”.

The analysis is based upon cases extracted from the National Automotive Sampling System Crashworthiness Data System (NASS/CDS) database for case years 1997-2011. The NASS/CDS data set was restricted to vehicles of model year 1998 and later. The approach was to compare the frontal crash performance of sled-certified airbags, sometimes called depowered airbags, with advanced airbags involved in frontal crashes. NASS/CDS steering wheel deformation measurements were used to identify cases in which thoracic injuries may have been caused due to steering wheel impact and deformation. The distributions of injuries for all cases were determined by body region and injury severity. These distributions were used to compare and contrast injury outcomes for cases with frontal airbag deployment for both belted and unbelted drivers.

Among frontal crash cases with belted drivers, observable steering wheel deformation occurred in less than 4% of all cases, but accounted for 29% of all MAIS3+ belted drivers and 28% of belted drivers with serious thoracic injuries (AIS3+). Similarly, observable steering wheel deformation occurred in approximately 13% of all cases with unbelted drivers involved in frontal crashes, but accounted for 58% of MAIS3+ unbelted drivers and 66% of unbelted drivers with serious (AIS3+) thoracic injuries.