Ave. crossers

STS

["Think of what you often see at the end of street names on maps or signs, especially in cities. These two letters usually follow a saint's name."]

"Ave." is short for "avenue," so "Ave. crossers" refers to the streets that intersect avenues in a city grid. In many places, those cross streets are often labeled with the abbreviation "St." for "street," and since the clue is plural, the answer is simply "STS." It’s a shorthand way to represent multiple streets crossing avenues.