Breakaway support post for highway guardrail end treatments

A breakaway support post (130) is provided for a highway guardrail system (120) to enhance the safety of a vehicle impacting with either the rail face of the associated guardrail or one end of the guardrail facing oncoming traffic. For some applications, the breakaway support post (130) may be formed from a steel I-beam with one or more elongated slots formed intermediate the ends of the steel I-beam. The slots are preferably formed in the flanges of the I-beam which are in turn aligned generally parallel with the associated guardrail. For other applications, a breakaway support post may have an upper (142) and a lower (144) portion with a rotatable coupling (140) assembly disposed therebetween. A shear pin (156) or other releasing mechanism is preferably provided to maintain the upper and lower portions generally aligned with each other prior to the impact of a vehicle with one end of the associated guardrail.