Re: in the street, in an street?
Quick note - it would be "a street" not "an street" because "street" does not start with a vowel sound.
This is another example of phrases that are used that aren't always logical. When we say "in the street" (or "on the street" in the US), we don't usually mean a specific street. We are just referring to "somewhere outside where people travel."
The average man in the street = any regular person you are likely to meet
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.