This paper updates the findings of prior research addressing the relationship between seatback strength and likelihood of serious injury/fatality to belted drivers and rear seat occupants in rear-impact crashes. Statistical analyses were performed using 1995-2014 CY police-reported crash data from seventeen states. Seatback strength for over 100 vehicle model groupings (model years 1996-2013) was included in the analysis. Seatback strength is measured in terms of the maximum moment that results in 10 inches of seat displacement. These measurements range from 5,989 in-lbs to 39,918 in-lbs, resulting in a wide range of seatback strengths. Additional analysis was done to see whether Seat Integrated Restraint Systems (SIRS) perform better than conventional belts in reducing driver and rear seat occupant injury in rear impacts. Field data shows the severe injury rate for belted drivers in rear-impact crashes is less than 1%. Results also indicate there is no statistically significant relationship between seatback strength and the risk of serious/fatal injury to belted drivers or rear seat occupants in rear-impact crashes. Factors that have a statistically significant effect on the likelihood of serious/fatal injury include: occupant age, gender, roadway speed limit and a vehicle mass term representing vehicle incompatibility (striking vehicle mass / total mass in the collision). Additionally, there is no difference between vehicles with SIRS and vehicles with conventional belts in reducing serious/fatal injury to belted drivers in rear-impact crashes.