Apparatus for absorbing energy when impacted by a vehicle, said apparatus comprising, in combination: a backstop structure affixed to the ground and extending upwardly therefrom; an elongated track (22, 22) extending along the ground toward said backstop structure; said track comprises two parallel rails spaced from one another; a plurality of supports mounted for independent movement along said track (22, 22) and extending upwardly from said track (22, 22), said supports being spaced from one another and spaced from said backstop structure; a plurality of elongated, collapsible, hollow metal tubes supported by and extending between adjacent supports with opposed ends of said tubes abutting said adjacent supports, said tubes having longitudinal axes extending parallel to one another and parallel to said track (22, 22); and stabilizer structure; said apparatus for absorbing energy when impacted by a vehicle characterized by said stabilizer structure being operatively associated with said track and with said supports stabilizing said supports in three planes to prevent tilting of said supports backward or forward, sideways or about a vertical pivot axis whereby said support is held stable relative to X, Y and Z axes when said supports move along the track (22, 22) toward said backstop structure due to impact between the apparatus and a vehicle, whereby each of the collapsing tubes between adjacent supports will collapse substantially uniformly about the longitudinal axis thereof when compressed between said adjacent supports; said stabilizer structure including channel defining structure (28, 30) of said rails defining longitudinal channels, said channel defining structure (28, 30) includes spaced upper and lower elongated guides (28, 30), said supports include rigid frameworks, said stabilizer structure including rotatable elements attached to said frameworks and supporting said frameworks positioned in said longitudinal channels between said upper and lower elongated guides (28, 30), said rotatable elements are wheels positioned on and supported by said lower elongated guides, said stabilizer structure additionally includes low friction plates attached to said frameworks and engageable with said upper elongated guides and said supports additionally include support brackets on said frameworks receiving and supporting the ends of said tubes. a backstop structure affixed to the ground and extending upwardly therefrom; an elongated track (22, 22) extending along the ground toward said backstop structure; said track comprises two parallel rails spaced from one another; a plurality of supports mounted for independent movement along said track (22, 22) and extending upwardly from said track (22, 22), said supports being spaced from one another and spaced from said backstop structure; a plurality of elongated, collapsible, hollow metal tubes supported by and extending between adjacent supports with opposed ends of said tubes abutting said adjacent supports, said tubes having longitudinal axes extending parallel to one another and parallel to said track (22, 22); and stabilizer structure; said apparatus for absorbing energy when impacted by a vehicle characterized by said stabilizer structure being operatively associated with said track and with said supports stabilizing said supports in three planes to prevent tilting of said supports backward or forward, sideways or about a vertical pivot axis whereby said support is held stable relative to X, Y and Z axes when said supports move along the track (22, 22) toward said backstop structure due to impact between the apparatus and a vehicle, whereby each of the collapsing tubes between adjacent supports will collapse substantially uniformly about the longitudinal axis thereof when compressed between said adjacent supports; said stabilizer structure including channel defining structure (28, 30) of said rails defining longitudinal channels, said channel defining structure (28, 30) includes spaced upper and lower elongated guides (28, 30), said supports include rigid frameworks, said stabilizer structure including rotatable elements attached to said frameworks and supporting said frameworks positioned in said longitudinal channels between said upper and lower elongated guides (28, 30), said rotatable elements are wheels positioned on and supported by said lower elongated guides, said stabilizer structure additionally includes low friction plates attached to said frameworks and engageable with said upper elongated guides and said supports additionally include support brackets on said frameworks receiving and supporting the ends of said tubes.