Frontal Impact Response for Pole Crash Scenarios

Abstract

Objective: Vehicle impacts with fixed roadside structures, such as poles, constitute a significant portion of road fatalities in North America. The purpose of this study was to evaluate occupant response in pole crash scenarios and compare the current vehicle kinematic–based injury metrics to occupant-based metrics to determine whether the vehicle metrics are representative of the injury levels sustained by an occupant. Methods: To better understand vehicle and occupant response during impact with a pole, frontal crash scenarios with 3 common pole types (a rigid pole, a rigid pole with a frangible base, and a deforming or energy-absorbing pole) were investigated at various impact velocities. A numerical model of a Hybrid III human surrogate was integrated with a numerical model of a mid-size sedan, including improvements to the vehicle and seat models, and implementation of an air bag and restraint system. The vehicle model was validated using the National Highway Traffic Safety Administration's (NHTSA) frontal crash data for varying impact velocities into a rigid wall. A numerical model of a high-energy-absorbing pole was developed and validated, along with a rigid pole and a previously developed breakaway pole, to examine the effects of pole compliance on the vehicle and occupant response. Occupant response was investigated at varying impact velocities with the poles aligned with the vehicle centerline. Offset impacts were then investigated with the energy-absorbing pole aligned with the driver-side crush structure. Results: The vehicle kinematic response metrics currently used to evaluate poles were compared to the currently accepted occupant injury response metrics and it was found, in general, that the occupant-based injury criteria predicted lesser injury than the vehicle kinematic response metrics for the same impact scenario. Specifically, the occupant impact velocity provided trends that differed from all other metrics. This can be attributed in part to the improvement in vehicle safety systems not accounted for by the vehicle-based metrics. Conclusions: For the same impact scenario, the breakaway pole resulted in the lowest predicted injury metrics for the vehicle occupant but was noted to be a potential threat to pedestrians and other nearby road users. The rigid pole resulted in the highest occupant injury predictions, whereas the energy-absorbing steel pole resulted in injury metrics below the threshold values, controlled the vehicle deceleration, and detached from the base only at higher velocity impacts. Appropriate evaluation of energy-absorbing poles requires consideration of the occupant response in addition to the current kinematic criteria.