I see this poem a little differently than the previous answerer, but that is part of what is so wonderful about poetry! It can be interpreted in many different ways.

I see the poem's imagery as representative of how humankind can go through horrible and tragic circumstances, but still rise up and continue on in their lives.  I see the poem as one that points out the resilience of humankind; not how humankind is "crushed" and cannot recover. 

In the 1930's William Carlos Williams used the expression The Term to describe a literary movement in poetry where poems could be analyzed as objects in and of themselves to reveal truth. It is still questioned whether he named the poem after the movement or the movement was named after the poem. So, what is the truth revealed in this poem? The truth lies in the weakness of man; that is, "a rumpled sheet of brown paper" has more resiliency that we do as we are "crushed" when cars (life)run(s) over us in the harshness and brevity of this world. However, the brown paper can rise again unlike man. A truth to ponder!