Update on Second-Row Children Responses in Rear and Frontal Crashes with a Focus on the Potential Effect of Stiffening Front Seat Structures 2020-01-1215

NHTSA has recently been petitioned to address the protection of second-row children in rear crashes due front seatback performance. The protection of children is important. However, it is more complex than assessing front seat performance in rear impacts. Viano, Parenteau (2008 [1]) analyzed cases of serious-to-fatally injured (MAIS 3+F) children up to 7 years old in the second row in rear impacts involving 1990+ model year vehicles using 1997-2005 NASS-CDS. They observed that intrusion was an important factor pushing the child forward into the back of the front seat, B-pillar or other front structure.

To help assess whether stiffening the front seats would be beneficial for second-row child safety, the 2008 study was updated using more recent data and model year vehicles. In the present study, 1997-2015 NASS-CDS data were analyzed for serious-to-fatally (MAIS 3+F) injured 0- to 7-year old children in the second row with 1994+ model year vehicles. First, the data were analyzed to estimate the distribution and risk of serious-to-fatally (MAIS 3+F) injured children by crash types. The results showed that the greatest numbers of second-row children were injured in frontal (39.3%) and in side (27.2%) crashes. Compared to other crash types, the highest relative injury risk for second-row children was found in rollovers (1.72% ± 0.36%) followed by rear crashes (0.75% ± 0.56%).

Individual rear and frontal impact cases were also reviewed to better understand injury mechanisms of children in the second row. The cases were downloaded and reviewed. The unweighted data indicated that there were 15 injured children involved in 14 rear impact crashes. Seven of the cases were new and not previously included in the 2008 study. The analysis of the 15 children indicated that half were associated with significant intrusion (30+ cm) into their seating area, pushing the child forward. The case review indicated that the front seat remained in its pre-crash position or was pushed forward in 7 out of 11 cases. The front seatback rotated rearward in 4 of 11 cases; two involved a severe-to-fatal injury (AIS 4+). In both cases, the child was pushed forward due to significant intrusion.

There were 34 unweighted cases involving children with serious (AIS 3+) head and spine injury in frontal crashes. Eleven of the cases were new and not previously included in the 2008 study. The data indicated that contact with the seatback was a frequent injury source (12 out of 34 cases).

A 54 km/h sled test previously conducted with an unbelted 6-year-old Hybrid III anthropomorphic test device (ATD) seated behind a stiff all-belts-to-seat (ABTS) seat was also analyzed. The head and chest acceleration and upper neck compression and flexion recorded in the test were all above injury assessment reference values (IARVs).

The field accident data and results from the sled test performed in this study suggest that stiffening the front seatback could increase impact forces and risk of injury due to increased resistance of the seatback to yielding forward during second-row occupant loading.