From the December 2014 Smithsonian "Ask Smithsonian."
Seth R. Digel of Smethport, Pennsylvania, asked the question.
ANSWER; A street is a basic paved traffic link within an urban area; an avenue was originally grander, wider and often lined with trees or other flora.
But the distinction has eroded over time, as when, for example, real estate developers indiscriminately call new roads "avenues" to make a more grandiose impression.
Nancy Post, curator of the National Postal Museum.
Now You Know. --AvenueDog (So Much More Grandiose, Don't You Know.)