Rear-end impacts are the most common crash scenario in the United States. Although automated vehicle (AV) technologies, such as frontal crash warning (FCW) and automatic emergency braking (AEB), are mitigating and preventing rear-end impacts, the technology is only gradually being introduced and currently has only limited effectiveness. Accordingly, there is a need to evaluate the current state of passive safety technologies, including the performance of seatbacks and head restraints. The objective of this study was to examine trends in head and neck loading during rear impact testing in new vehicle models over the prior decade. Data from 601 simulated rear impact sled tests (model years 2004 to 2018) conducted as a part of the Insurance Institute for Highway Safety (IIHS) Vehicle Seat/Head Restraint Evaluation Protocol were obtained. This dynamic evaluation involves a simulated rear-end crash using a Biofidelic Rear Impact (BioRID IIg) ATD positioned in the seat attached to a crash simulation sled and accelerated to represent a rear crash with a delta-V of approximately 15.6 kph (15.6 ± 0.26 kph). Head and neck injury metrics were calculated for all tests to evaluate trends in the test ATD responses across model years. Reductions in HIC 15, Nij, and upper neck tensile forces were observed across all model years. Nkm, upper neck flexion moments, extension moments, and shear forces were found to show little or no change by model year. Reductions in time to initial contact with the head restraint were observed and likely contributed to reduced head accelerations and neck tensile forces. Given the anticipated persistence of rear-end impacts and potential changes to the vehicle interior layout with improving AV technology, the data should be considered by designers, researchers, and evaluators looking to project future crash and injury rates in rear-end impacts.