The armco seems to be good if it doesnt separate granted if you hit it at the right angle!!
The Armco design could be greatly improved if enough effort goes into it. The steel rails will plastically deform at yield granting energy absorbtion, but at the unfortunate consequence of creating a a gulliotine of death for whatever gets between them. The improvement would be based somewhat on retaining toughness, and energy absoption without deflecting and slicing things in two.