Relationship of Dynamic Seat/Head Restraint Ratings to Real-world Neck Injury Rates

Transcription

1 Relationship of Dynamic Seat/Head Restraint Ratings to Real-world Neck Injury Rates Charles M. Farmer, Laurie A. Hellinga, Jo Ann K. Wells, David S. Zuby

2 Basic method Collect insurance claims for late model vehicles with rear-crash damage Check for indication of neck injury to driver of struck vehicle Calculate rate of neck injury claim per rear-crash by seat/head restraint rating group Similar method used to establish efficacy of better rated static head restraint geometry, active head restraints, and Volvo Whiplash Protection System

3 Geometric seat and head restraint evaluations 4 distance above/below top of average-size man s head (cm) good acceptable marginal poor backset (cm)

4 Rear-struck drivers with neck injury claims By geometric seat rating, 1999 study 30% 25% 20% 15% 10% 5% 0% good acceptable marginal poor

5 Advanced seat designs Include features that respond to crash forces

6 Rear-struck drivers with neck injury claims Comparing advanced features with predecessor seat designs, 2003 study predecessor seats without feature seats with advanced feature active head restraint Volvo WHIPS

7 Dynamic seat and head restraint evaluations Measure head restraint geometry Conduct simulated rear crash test of seats with acceptable or good geometry seat design parameters (pass/fail) early restraint-to-head restraint contact ( 70 ms) low forward acceleration of torso ( 9.5 g at T1 vertebra) low neck forces

8 Dynamic seat and head restraint evaluations

9 Dynamic seat and head restraint evaluations chart 1: dynamic ratings derived from seat parameter and neck force results chart 2: overall ratings derived from both geometric and dynamic ratings seat parameters neck forces dynamic rating ratings geometric dynamic overall rating G G G A A A M M M G P P A M G A A M P A M P A M P =pass =fail =low =moderate =high

10 2007 study of neck injury and seat ratings, State Farm, and Nationwide 10,000 claims of rear-end damage to rated late model cars and SUVs random sample of 3,000 examined in detail Exclude no-fault states except Michigan information on both vehicles/drivers in single file Neck injury to driver of struck vehicle either stated explicitly or inferred from diagnostic (ICD-9) codes Account for driver gender, vehicle type, price, and damage severity

11 Injury rates showed expected trends Percent of rear-struck drivers with neck injury claims by various factors state group driver gender struck vehicle damage struck vehicle type striking vehicle mass 18.8% Tort states 21.7% female 33.3% with severe damage 19.7% car 21.0% heavier 16.0% Michigan 13.9% male 13.1% with minor damage 17.0% SUV 16.4% lighter

12 Percent of rear-struck drivers with neck injury claims By dynamic seat rating, 2007 study 25% 20% 15% 10% 5% 0% good acceptable marginal poor

13 Percent difference in neck injury rates By dynamic seat rating compared to vehicles rated poor, based on logistic regression 10% 0% 0-10% -20% -30% -40% good acceptable marginal

14 Percent of rear-struck drivers with neck injuries lasting 3 or more months By dynamic seat rating 6% 4% 2% 0% good acceptable marginal poor

15 Percent difference in rates of long-term neck injury (lasting 3 or more months) By dynamic seat rating compared to vehicles rated poor, based on logistic regression 10% 0% -10% -20% -30% -40% good acceptable marginal

16 Other dynamic test measurements A possible alternate rating method? Head fore/rearward acceleration Head rebound velocity Upper neck loads transverse force (Fx) axial force (Fz) bending torque (My) Nij (transverse & axial) Nkm (transverse & bending) Torso fore/rearward acceleration Time to head-to-restraint contact Neck distortion measures - head rotation neck retraction neck stretch/straightening Lower neck transverse force axial force bending torque LNL (lower neck loads) index

17 Dynamic test measurements Used in /IIWPG rating Head fore/rearward acceleration Head rebound velocity Upper neck loads transverse force (Fx) axial force (Fz) bending torque (My) Nij (transverse & axial) Nkm (transverse & bending) Torso fore/rearward acceleration Time to head-to-restraint contact Neck distortion measures - head rotation neck retraction neck stretch/straightening Lower neck transverse force axial force bending torque LNL (lower neck loads) index

18 Folksam/Swedish Road Authority ratings Different performance measures than /IIWPG Three different tests for each seat design Low severity: 16 km/h, low acceleration Medium severity: 16 km/h, same as /IIWPG High severity: 24 km/h

19 Dynamic test measurements Used in Folksam/Swedish Road Authority rating Head fore/rearward acceleration Head rebound velocity Upper neck loads transverse force (Fx) axial force (Fz) bending torque (My) Nij (transverse & axial) Nkm (transverse & bending) Torso fore/rearward acceleration Time to head-to-restraint contact NIC neck injury criterion Neck distortion measures - head rotation neck retraction neck stretch/straightening Lower neck transverse force axial force bending torque LNL (lower neck loads) index

20 Ratings with Folksam/SRA performance criteria Results from a single 16 km/h test 25 percent of rear-struck drivers with neck injury any injury injury lasting 3 or more months

21 Conclusions regarding IIWPG dynamic rating procedure Vehicles with seats/head restraints rated good have lower neck injury rates than those rated poor Good rated seats appear especially effective at reducing injuries resulting in long-term complaints Vehicles with acceptable or marginal rated seats/head restraints also appear to provide better protection than poor rated ones, at least for long term injuries Future work examine whether other dynamic test measures can better predict neck injury rates

22 Insurance Institute for Highway Safety Vehicle Research Center, Ruckersville, Virginia

23 For more information: