A new study of the APR data for lateral impact tests using human subjects was undertaken to determine the quality of the possible correlations between the TTI and thorax-abdomen injuries.
The TTI (Thoracic Trauma lndex) was proposed by the NHTSA(1) in 1984; it takes into account the age and weight of the subjects tested as well as the maximum of transverse accelerations measured at the 4th and 8th ribs and the acceleration of the dorsal column, to determine injury probability. The TTI values were recalculated using the new formula described by the NHTSA at the last STAPP Conference(2). The conclusion reached was that thorax-abdomen protection cannot be based on this criterion; it does not enable to predict the level of injury resulting from a side impact, nor to correctly classify the results of tests carried out under different conditions.
Accidentological data coming from the LPB survey show that, in many cases severe abdominal injuries were observed without the victim sustaining thoracic injury; these were either abdominal injurics in isolation or abdominal injuries associated with pelvic fractures. It is difficult to see how in such cases a scale of injury severity based solely on thoracic acceleration could account for the severity of abdominal injuries. These arguments also go against the utilization of a criterion such as the TTI and also clearly s ow the need for separate criteria for abdominal protection and thoracic protection.