An end treatment for a thrie-beam type guardrail and a safety device specifically oriented toward trucks, vans and other utility vehicles having high profiles and centers of gravity. A slotted thrie-beam terminal is featured for use with highway guardrail systems. At least one reinforced slotted section is provided within the thrie-beam terminal to reduce the ability of the thrie beam to resist buckling in response to an axial type loading from end-on impacts. The terminal also provides for gating of laterally impacting vehicles. The terminal incorporates a breakaway support post cable release mechanism which lessens risk to impacting vehicles which impact the lead post.