title: Evaluation of NASS-CDS side crash delta-V estimates using event data recorders.
abstract: OBJECTIVE
  Planar crash severity is most commonly defined by delta-V (ΔV), which is the change in a vehicle's velocity vector during a crash. All ΔV estimates contained in the NASS-CDS are generated using a damage-based program called WinSMASH. WinSMASH ΔV accuracy in side crashes has not previously been validated against real-world crash data. This study will investigate the accuracy of WinSMASH ΔV estimates in real-world side crashes.
  
  
  METHODS
  This study uses biaxial ΔV data from event data recorders (EDRs) to assess the accuracy of side crash ΔV estimates in NASS-CDS crash cases. Single-event side crashes were identified in the NASS-CDS for which (a) WinSMASH ΔV had been coded and (b) biaxial EDR data were available. For these crashes, the WinSMASH-estimated resultant ΔV was compared with the EDR-recorded resultant ΔV to assess the accuracy of the former. EDR ΔV values were adjusted for an assumed average restitution value of 10 percent, based on values reported in the literature. Principal direction of force (PDOF) is the orientation of the net crash impulse relative to the vehicle and is a key parameter in WinSMASH reconstructions. NASS-CDS PDOF estimates were compared to the PDOF computed from the EDR data to assess their accuracy as well.
  
  
  RESULTS
  WinSMASH systematically overestimates EDR ΔV by about 12.9 percent for cars struck by cars and by about 2.4 percent for cars struck by light trucks and vans (LTVs). ΔV error was significantly different (at 95% confidence) for crashes to different areas of the vehicle side. The mean discrepancy in NASS-CDS PDOF was -0.9° with a standard deviation of 12.6°.
  
  
  CONCLUSIONS
  WinSMASH systematically overestimates ΔV at common velocity by about 13 percent for cars struck by cars and about 2 percent for cars struck by LTVs. Since WinSMASH's assumption of zero restitution is accounted for in this analysis, this suggests that WinSMASH stiffness parameters represent LTV impacts better than car impacts in side crashes. ΔV error differs by impacted area, suggesting that side impact stiffness parameters used in damage-based ΔV reconstruction must closely represent the crash mode being reconstructed for best results. NASS-CDS estimates of PDOF do not appear to exhibit any systematic discrepancy. The amount of random PDOF discrepancy observed here is consistent with prior studies.
authors.affiliation: a Virginia Tech Center for Injury Biomechanics , Blacksburg , Virginia.
authors.forename: Nicholas S
authors.initials: NS
authors.lastname: Johnson
authors.forename: Hampton C
authors.initials: HC
authors.lastname: Gabler
mesh_terms: D000054:Acceleration; D000063:Accidents, Traffic / Q000706:statistics & numerical data*; D003625:Data Collection / Q000379:methods*; D016208:Databases, Factual; D006801:Humans; D015203:Reproducibility of Results; D012984:Software
keywords: NASS-CDS; crash reconstruction; delta-V; event data recorder