Why are NYC streets always under construction?

Streets are both New York City’s circulatory system and its skin. Commerce and commuters crisscross more than 6,300 miles of roadway in the five boroughs. Heavy traffic and the passage of time take their toll. But roads are also uniquely vulnerable to the elements. Water, especially during the freeze-and-thaw cycle between fall and spring, is another major irritant. And just below the surface, there is another complication to their well-being: a labyrinth of aging infrastructure.
Read more: http://www.nytimes.com/interactive/2016/08/18/nyregion/new-york-101-streets-repair-and-maintenance.html?source=Snapzu