There is another vehicle in the street, truck. They are shipping something to somewhere, and stop on the street. In this case, people think trucks and cars parking on the street as a part of environment of the street, like a tree.
Compared to where cars driving on the road and where cars parking on the road, cars driving make an impenetrable area (image upper left side), but this stream line (area) suddenly disappears while cars parking.
At this point, people are acrossing 13th street freely becasue they only care the center area of the road rather than the side of the road. (image blue area) This situation can be said in whole traffic of NYC; pedestrian does not care where they across a street, they just care if there is car passing.