An Assessment of Door Openings in NASS-CDS Resulting From Combined Longitudinal Compressive and Lateral Tensile Latch Loading

The April 1st, 2005 Global Technical Regulation (GTR) [ECE/TRANS/180/Add.1] Working Party for door locks and door retention components reviewed a combination loading static bench test for latch systems (combination test) that is capable of evaluating the strength of the latching systems and is designed to detect fork bolt detent bypass failures. In the combination test, the latch is mounted on a flat steel plate that moves horizontally. The striker is mounted on a vertically moving ram device. During the test, lateral tension of 6,650 N is applied and maintained on the coupled latch-striker system by moving the flat steel plate and then applying a longitudinal compressive force of 16,000 N by moving the striker at a constant rate. A study of field data from the National Automotive Sampling System - Crashworthiness Data System (NASS-CDS) data files for the years 2003 to 2007 was conducted to determine the prevalence of real world crashes with latch/ striker separation due to a loading environment similar to that in the combination loading test. The study also assessed whether requiring door latches to pass this combination test would translate into a significant safety benefit by reducing deaths and injuries that result when a vehicle occupant is ejected from a vehicle during a crash. Data was limited to later model year vehicles (1995+) and to cases that comprised the necessary information needed to determine impact location, direction, and severity. A total of 330 NASS-CDS cases from 2003 to 2007 were coded with at least one door latch/ striker separation. Photographic evidence and crash parameters were utilized to determine whether each door latch/ striker separation was due to loading environments represented by the combination loading test. Of the 330 cases of latch/ striker separations, 290 cases occurred in very severe crash conditions with significant vehicle damage. The latch/ striker separation in these cases was deemed to have resulted from excessive loads and vehicle deformation. Of the remaining 40 latch/ striker separation cases, only 14 had loading conditions similar to that simulated in the combination loading test for latch systems. This study also found that in recent years there has been a trend that clearly reflects a significant reduction in both the number of door latch/ striker separations and the deaths and injuries that are traceable to these failures. As a result of the small number of cases identified and the trend toward reduced numbers of door latch/ striker separations, this study found that imposing a requirement that door latches pass the combination test would prevent 1.38 to 5.37 fatalities and 0.98 to 27.20 serious injuries per year.