During a collision, the shafts compress the energy absorbing material which absorbs collision energy.
This reduces the G forces on the passengers.
The energy absorbing material is shared between side and rear bumpers. The invention is called a "Shared Crumple Zone".
The newer Adaptive Bumper System invention will improve the performance
of the Share Crumple Zone invention by adjusting the amount of
energy absorbing material. This will minimize the g forces on passengers during low and high speed collisions.