Although semitrailer underride collisions have a relatively high risk of injury, the significant body of data developed through crash testing has not been previously analyzed in a single study to be readily used by the accident reconstructionist. This study examined the publicly available IIHS semitrailer rear underride tests (N = 35). The crash data were classified as full-width (n = 9), 50% overlap (n = 11), and 30% overlap (n = 15). A 2010 Chevrolet Malibu impacted the rear underride guard of a stationary semitrailer at 35 mph. Several collision parameters, that is, vehicle longitudinal, lateral, and vertical delta-Vs, guard deformations, and occupant compartment intrusions were characterized and compared between different overlap groups. The coefficient of restitution and impact duration were also quantified and their relationship with different underride parameters was explored. The accuracy of the “black box” data for different overlap groups was evaluated. For N = 16 tests (n = 9 full-width; n = 1, 50% overlap; n = 6, 30% overlap), the vehicle delta-Vs captured independently by the Malibu’s event data recorders (EDRs) were validated against the instrumentation data. Finally, underride collision parameters were combined to estimate total crush energy and vehicle closing speed.
Full-width overlap crashes showed higher longitudinal delta-Vs but lower lateral and vertical delta-Vs than the 30% overlap collisions. The 30% overlap group had significantly higher intrusions. No intrusion was observed at (1) vehicle accelerations over 20 g; (2) guard deformations below 28 cm; and (3) vehicle excursions below 120 cm. The 30% overlap crashes also demonstrated lower restitution and higher impact durations than the full-width overlap group. The coefficient of restitution and impact duration indicated strong correlations with vehicle forward excursion. Analysis of EDR data suggested that in full-width overlap crashes, the vehicle delta-Vs were recorded with high accuracy (RMS error: 0.5 mph); whereas, in 30% overlap crashes they were consistently overestimated (RMS error: 3.9 mph). The accident reconstructionist should consider these accuracy issues when relying upon EDR data to analyze underride collisions.
This study provided baseline data for several collision parameters during offset underride. Such data leads to a more accurate reconstruction of underride, and therefore a better understanding of occupant biomechanics. This is also helpful to improve underride protection devices and enhance passenger vehicle safety.