impediment (noun) : an impairment (as a stutter or a lisp) that interferes with the proper articulation of speech

source: http://www.merriam-webster.com/dictionary/impediments

“It saw you steeling yourself for the job interview, slowly and walking home after the late date, tripping over nonexistent impediments on the sidewalk.” City Limits by Colson Whitehead

This sentence means that New York City saw him when he was very confident after a job interview or when he was walking home after a late date and tripping over nonexistent things that will stop him from walking smoothly on the sidewalk.