An avenue is a wide roadway located within a city that has trees on both sides, and a street is primarily a residential roadway with buildings on one or both sides. Avenues do not have to have buildings on either or both sides, but streets do.
Streets are primarily residential, smaller than avenues and line on both sides with houses. They have a lower volume of traffic, and traffic itself is slower. Avenues are usually lined on both sides with trees and allow for heavy traffic flow. Avenues are often commercial in nature and have more business establishments than streets do. Although residential homes do find their way onto avenues and commercial enterprises also appear on streets, the major differences between the two are the volume of traffic that flows through them and their size.
A street is a standalone roadway with a few approaches, while an avenue allows for much heavier traffic flow, with traffic coming from many directions. Size also distinguishes differences between streets and avenues. Avenues are as much as three to four times wider than streets, and they are also longer than streets. Avenues are typically urban roadways and usually do not extend beyond the limits of the city.