Why was Route 66 called 'America's Main Street' and which different cities did it pass through?

Over the years, US 66 received numerous nicknames. Right after US 66 was commissioned, it was known as "The Great Diagonal Way" because the Chicago-to-Oklahoma City stretch ran northeast to southwest. Later, US 66 was advertised by the U.S. Highway 66 Association as "The Main Street of America".

Explanation:

Route 66 is probably the most famous road in the world. No other stretch of asphalt has been the subject matter of so many novels, movies, songs, and television shows. Route 66 is America’s Main Street. And to Europeans like us, it is a symbol of America.

Explanation:

what are the others?

i confess that there are several parts of this constitution which i do not at present approve, but i am not sure i shall never approve them: for having lived long, i have experienced many instances of being obliged by better information or fuller consideration, to change opinions even on important subjects, which i once thought right, but found to be otherwise. it is therefore that the older i grow, the more apt i am to doubt my own judgment, and to pay more respect to the judgment of others.