Civil and Environmental Engineering



Ronald K. Faller

Date of this Version



Published in Journal of Transportation Engineering 138:1 (January 1, 2012), pp. 1–11; doi: 10.1061/(ASCE)TE.1943-5436.0000308


Copyright © 2012 American Society of Civil Engineers. Used by permission.


During oblique vehicular impacts with longitudinal barriers, an occupant’s head is often ejected out of a side window. When this occurs, the occupant’s head can contact the barrier or an object attached thereto. This impact event, often termed head slap, normally produces a serious injury or fatality. Roadside barriers and any attached hardware should be designed with sufficient offset at the top to preclude head slap for most impact conditions. The goal of this study was to identify the extent of head ejection that can be expected during high-speed crashes with longitudinal barriers. High-speed videos of full-scale vehicle crash tests were analyzed to determine the occupant head trajectories. Videos of 11 full-scale crash tests with both small cars and pickup trucks were analyzed to produce a head ejection envelope to encompass all head trajectories observed in the tests. Adjustments were made to the envelope to account for varying vehicle heights, seated passenger heights, and vehicle movements during impact. Two head ejection envelopes were created; one to encompass ejections from occupants at or below the 50th percentile male seated height and the other to encompass ejections from occupants at or below the 95th percentile male seated height. The final head ejection envelopes were constructed as a template for designing future barrier systems and for determining the safe placement of fixed objects on top of or behind rigid parapets.