Wow!  This is beautiful.  I love the description of the feeling as a worm and how the whole poem is the study of one moment.  Great repetition of "and stopped / and leaned / and tied."  My only suggestion is to eliminate a couple of the present participles in the second and third lines.  The opening was a bit confusing as they were distracting. 

I think you could have used more punctuation, or alternately gotten rid of it completely.  Some of the sentences seemed to run on and on with totally new thoughts popping up.  I like the imagery, though a worm doesn't seem like the right metaphor for a shoelace.  Also, it seemed awkward to me that if two people were hurrying by each other, one of them stopping to tie the other person's shoe would have caused a mild collision and wouldn't have saved person A with the untied shoe more time than if she had tied her own shoe. 

You chose an interesting topic for your poem, but I think it needs more work. In certain places, it's just too rambling and repetitious and takes away the pleasure of reading it.