Design Concepts for a Collapsing Turned-Down Guardrail

For many years, turned-down guardrail terminals have been constructed as a safety treatment for W-beam guardrails. This terminal is designed to drop down and allow vehicles impacting the end of the barrier to slowly ride up onto the guardrail and come to a controlled stop. However, testing has indicated that the rail element does not always release properly, thereby causing mini-size vehicles to rollover. This research study involved the development of several retrofit concepts for the turned-down guardrail terminal. The primary focus of this effort involved the development of a mechanism that allows the W-beam rail element to release at a lower force and thereby improve its performance during small car impacts. The major focus of this paper is to share the complicated modeling effort required for successful simulation of the vehicle-guardrail impact and its' redesign.