Over the years, vehicle manufacturers may have implemented structural changes to light vehicles to comply with upgraded Federal Motor Vehicle Safety Standards (FMVSS) such as advanced air bags (FMVSS No. 208), side impact protection (FMVSS No. 214), and roof crush (FMVSS No. 216), as well as to improve performance in tests conducted by consumer information programs such as NHTSA’s New Car Assessment Program (NCAP) and the Insurance Institute for Highway Safety (IIHS). Both programs have undergone changes in recent years. The NCAP was updated in 2010 to include advanced test dummies, new injury criteria, and a side pole test, and the IIHS adopted side impact, small overlap, and roof crush test protocols. Furthermore, as fuel economy requirements become more stringent, vehicle manufacturers may choose to light-weight vehicles and incorporate materials such as advanced high-strength steel and aluminum. This paper will investigate what effect, if any, these changes have had on vehicle crash pulses, as measured under NCAP. Although more stiffness metrics and crash pulse characteristics have been examined, this study mainly updates the analysis from the 2003 ESV paper, Evaluation of Stiffness Measures from the U.S. NCAP. [Swanson, 2003]

This paper utilizes data from model year (MY) 2002 to MY 2014 frontal NCAP crash tests to compute vehicle stiffness using four different methods:​ linear “initial” stiffness, energy equivalent stiffness, dynamic stiffness and static stiffness. The data are averaged and examined historically for three light duty vehicle classes (light duty pickup trucks (PUs), multi-purpose vehicles (MPVs), and passenger cars (PCs)) to provide a fleet perspective on changes to frontal crash characteristics. In addition, various crash pulse characteristics such as duration and peak acceleration are investigated. Collectively, these metrics have been traditionally used to characterize a vehicle’s crash behavior and can subsequently influence restraint design.

The Swanson study found that not only were the average stiffnesses of PCs increasing from MY 1982 to 2001, but there was also a large disparity between the average stiffnesses of PCs and those of MPVs and PUs. The current study identified different trends. The average stiffnesses of PCs and MPVs appear to be converging, indicating that these two vehicle classes may have become more structurally homogenous in this respect. This is also evidenced by the changes observed for the crash pulse characteristics. In recent years, the crash pulse durations for both PCs and MPVs have decreased (though MPVs slightly more than PCs) such that the pulse duration is now essentially equal, on average, for both vehicle classes. The average peak accelerations for PCs and MPVs also increased during the years in this study. PU data is presented for completeness, but no extensive conclusions were made on this vehicle class because no statistically significant trends could be identified.