An end treatment of a guardrail safety system comprising: a terminal portion of a guardrail W-beam comprising a downstream end and an upstream end; a flattening portion having an outlet portion with an outlet at an upstream end and forming a channel, a vertical dimension of the channel being greater at a downstream end of the flattening portion than at an upstream end of the flattening portion; and an impact plate for engaging an impacting vehicle at an end of said guardrail W-beam, said impact plate being coupled to the flattening portion; wherein said impact plate and the flattening portion are advanced longitudinally along the guardrail W-beam in a downstream direction by a vehicle during an end-on impact, the advancement of the impact plate and flattening portion dissipating energy to decelerate the impacting vehicle and flattening the guardrail W-beam vertically as downstream portions of the guardrail W-beam are forced into the flattening portion; characterized in that: the terminal portion of the guardrail W-beam slopes from a first vertical height appropriate for redirecting an errant vehicle to a second vertical height proximate the surface of the ground at the upstream end of the terminal portion of the guardrail W-beam; the guardrail W-beam being installed throughout the channel of the flattening portion, such that a portion of the guardrail W-beam exits said outlet and is flattened vertically so as to resemble a stack of plates; the end treatment comprises a terminal post and the portion of the guardrail W-beam exiting the flattening portion is secured in tension to said terminal post at ground level such that the guardrail W-beam remains connected to the terminal post after an impact in the downstream direction. a terminal portion of a guardrail W-beam comprising a downstream end and an upstream end; a flattening portion having an outlet portion with an outlet at an upstream end and forming a channel, a vertical dimension of the channel being greater at a downstream end of the flattening portion than at an upstream end of the flattening portion; and an impact plate for engaging an impacting vehicle at an end of said guardrail W-beam, said impact plate being coupled to the flattening portion; wherein said impact plate and the flattening portion are advanced longitudinally along the guardrail W-beam in a downstream direction by a vehicle during an end-on impact, the advancement of the impact plate and flattening portion dissipating energy to decelerate the impacting vehicle and flattening the guardrail W-beam vertically as downstream portions of the guardrail W-beam are forced into the flattening portion; characterized in that: the terminal portion of the guardrail W-beam slopes from a first vertical height appropriate for redirecting an errant vehicle to a second vertical height proximate the surface of the ground at the upstream end of the terminal portion of the guardrail W-beam; the guardrail W-beam being installed throughout the channel of the flattening portion, such that a portion of the guardrail W-beam exits said outlet and is flattened vertically so as to resemble a stack of plates; the end treatment comprises a terminal post and the portion of the guardrail W-beam exiting the flattening portion is secured in tension to said terminal post at ground level such that the guardrail W-beam remains connected to the terminal post after an impact in the downstream direction. the terminal portion of the guardrail W-beam slopes from a first vertical height appropriate for redirecting an errant vehicle to a second vertical height proximate the surface of the ground at the upstream end of the terminal portion of the guardrail W-beam; the guardrail W-beam being installed throughout the channel of the flattening portion, such that a portion of the guardrail W-beam exits said outlet and is flattened vertically so as to resemble a stack of plates; the end treatment comprises a terminal post and the portion of the guardrail W-beam exiting the flattening portion is secured in tension to said terminal post at ground level such that the guardrail W-beam remains connected to the terminal post after an impact in the downstream direction.