Occupant restraint in the rear seat:​ ATD responses to standard and pre-tensioning, force-limiting belt restraints

Forman, Jason<sup>1</sup>; Michaelson, Jarett<sup>1</sup>; Kent, Richard<sup>1</sup>; Kuppa, Shashi<sup>2</sup>; Bostrom, Ola<sup>3</sup>

Recent studies have shown that restrained occupants over the age of 50 in frontal crashes have a higher risk of injury in the rear seat than in the front, and have hypothesized that the incorporation of technology such as belt pre-tensioning and force limiting preferentially in the front seat is at least partially responsible for this trend. This study investigates the potential benefits and trade-offs of seat belt pretensioners and force-limiters in the rear seat using a series of frontal impact sled tests at two speeds (48 km/h and 29 km/h ΔV) with a buck representing the interior of the reat seat occupant compartment of a contemporary mid-sized sedan. Four different dummies were tested: the Hybrid III six year old (in a booster seat, H3 6YO), the Hybrid III 5th percentile female (H3 AF05), the Hybrid III 50th percentile male (H3 AM50), and the THOR-NT. The restraints consisted of either a standard three point belt, or a 3-point belt with a retractor pretensioner and a progressive force-limiter (FL+PT). Each test condition was repeated in triplicate. The FL+PT restraints (compared to the standard restraints) resulted in a significant (p≤0.05) decrease in peak internal chest deflection for each of the Hybrid III dummies at both test speeds (48 km/h: 29% decrease for H3 6YO, 38% decrease for H3 AF05, 30% decrease for H3 AM50), and for the THOR-NT at a ΔV of 29 km/h. At 48 km/h, the FL+PT restraint qualitatively decreased the average peak internal chest deflection of the THOR-NT, however this decrease was not statistically significant (p=0.06). Furthermore, the FL+PT system allowed little or no increase in forward head excursion, and improved whole-body kinematics for all dummies by restricting pelvic excursion and slightly increasing torso pitch. The results suggest that the FL+PT system studied here may provide injury-reducing benefit to rear seat occupants in moderate to high severity frontal crashes, although more study is needed to evaluate these restraints in other crash scenarios.

Year

Entry

2003

Parenteau C, Viano DC. Field data analysis of rear occupant injuries, I: adults and teenagers. In: Proceedings of the SAE World Congress & Exhibition. March 3-6, 2003; Detroit, MI. Warrendale, PA: Society of Automotive Engineers. SAE 2003-01-0153.

2006

Smith KM, Cummings P. Passenger seating position and the risk of passenger death in traffic crashes: a matched cohort study. Inj Prev. 2006;12(2):83-86.

1997

Crandall JR, Bass CR, Pilkey WD, Miller HJ, Sikorski J, Wilkins M. Thoracic response and injury with belt, driver side airbag, and force limited belt restraint systems. Int J Crashworthiness. 1997;2(1):119-132.

2005

Forman J, Kent R, Ali T, Crandall J, Bostrom O, Haland Y. Biomechanical considerations for the optimization of an advanced restraint system: assessing the benefit of a second shoulder belt. In: Proceedings of the 2005 International IRCOBI Conference on the Biomechanics of Impact. September 21-23, 2005; Prague, Czech Republic.337-353.

2003

Swanson J, Rockwell T, Beuse N, Summers L, Summers S, Park B. Evaluation of stiffness measures from the U.S. new car assessment program. In: Proceedings of the 18th International Technical Conference on the Enhanced Safety of Vehicles (ESV). May 19-22, 2003; Nagoya, Japan.