What is required is a solid barrier that has freedom to move away from the track. A steel sheet mounted on deformable supports, for example, or concrete blocks on a granular surface that allows it to move when pushed. In both cases, the chances of rebound are reduced because the surface moves in the direction of the impact and is non-elastic.
The SAFER system does this, in effect.
Both systems are effectively self regulating depending on the impact speed as they both move with the impact proportionally to the impact. Short of an active system, there is no way to increase movement with the square of the impact velocity (and thus match the various kinetic energy involved with speed (a square relationship).